Fixed my "no heat" problem.

[old guy]

Now that it is getting colder I noticed that my heater wasn't working very well. The problem was being caused by a large air bubble somewhere in the heater circuit. I know when the bubble was created. Back in September the clip holding the rear CTS cracked and consequently the sensor blew out of the motor. At that time I had a difficult time getting all the air out. Apparently I never got it all out.

Here's any easy way to tell if you have air trapped somewhere. Get your motor up to temperature. Then SLOWLY crack open the reservoir cap. If you have an air entrapment you should be able to hear the coolant gurgling and the coolant level in the reservoir will noticeably increase as the entrapped air is allowed to expand. The bigger the bubble the more the tank level will increase. If the bubble is big enough it will push coolant out of the overflow port on the bottom of the reservoir so be careful that you don't burn yourself. Even if you don't have any entrapped air the level will rise just a little as the coolant hoses contract back from the pressure release. However, you probably won't hear the gurgling noise that accompanies the bubble as it expands.

Now that you have the cap off you can release some of the air by cracking opening the bleeder valve in the center of the upper coolant hard pipe. Open it just enough for the air to escape. As soon as you get a solid stream of coolant close it off. You may have to repeat this process numerous times before you manage to work all the air out. The reservoir cap needs to be off when you perform this procedure so the static pressure in the reservoir will act on the hard pipe and push out the air. I just kept a 5mm Allen wrench in the car and a wad of paper towels stuck under the hood. whenever I took a short trip I just popped open the hood, shoved the wad of paper towels underneath the hard pipe and used this procedure to bleed the air off.

Unfortunately in my case this didn't release all the air so I had to take more extreme measures. Apparently I had a large bubble located in the heater core that wasn't bubbling out. After releasing all the system pressure I reinstalled the reservoir cap and then separated the quick connect on the out-feed side of the heater core. If you unscrew the coolant reservoir you can move it out of the way for easy access to the quick connect. I had a plug ready to block off the lower coolant line when I opened the quick connect. I used a long necked funnel to pour coolant directly into the heater core via the out-feed line. I then reattached the quick connect. After I did this I had to repeat the bleeding procedure outlined above three or four more times to get the rest of the air out.

I now have heat!

[ruphianh]

Can you take a picture pointing to the bleeder valve. I did a reverse flush of my core and the heat didn't work for the first month but now it definitely is. I figured it was an escaped bubble, but I would like to make sure its all bled before snowboard season.

Now that it is getting colder I noticed that my heater wasn't working very well. The problem was being caused by a large air bubble somewhere in the heater circuit. I know when the bubble was created. Back in September the clip holding the rear CTS cracked and consequently the sensor blew out of the motor. At that time I had a difficult time getting all the air out. Apparently I never got it all out.

Here's any easy way to tell if you have air trapped somewhere. Get your motor up to temperature. Then SLOWLY crack open the reservoir cap. If you have an air entrapment you should be able to hear the coolant gurgling and the coolant level in the reservoir will noticeably increase as the entrapped air is allowed to expand. The bigger the bubble the more the tank level will increase. If the bubble is big enough it will push coolant out of the overflow port on the bottom of the reservoir so be careful that you don't burn yourself. Even if you don't have any entrapped air the level will rise just a little as the coolant hoses contract back from the pressure release. However, you probably won't hear the gurgling noise that accompanies the bubble as it expands.

Now that you have the cap off you can release some of the air by cracking opening the bleeder valve in the center of the upper coolant hard pipe. Open it just enough fore the air to escape. As soon as you get a solid stream of coolant close it off. You may have to repeat this process numerous times before you manage to work all the air out. The reservoir cap needs to be off when you perform this procedure so the static pressure in the reservoir will act on the hard pipe and push out the air.

In my case this didn't work so I had to take more extreme measures. Apparently I had a large bubble located in the heater core. After releasing all the system pressure I reinstalled the reservoir cap and then separated the quick connect on the out-feed side of the heater core. If you unscrew the coolant reservoir you can move it out of the way for easy access to the quick connect. I had a plug ready to block off the lower coolant line when I opened the quick connect. I used a long necked funnel to pour coolant directly into the heater core via the out-feed line. I then reattached the quick connect. After I did this I had to repeat the bleeding procedure outlined above three or four more times to get the rest of the air out.

I now have heat!

[old guy]

Can you take a picture pointing to the bleeder valve.

Here is a pic of a leaking bleeder valve:

[O2VW1.8T]

I need to do this also as my heat sucks. I bought a special tool that pulls a vacuum on the whole system and refills it. I haven't done it yet cause im lazy and it just started to get cold so i need to do it.

[JimmyBones]

I would check your coolant block plug on the back of the thermostat housing. They will shrink overnight and allow air into the coolant system. It will not leak when the engine is hot but if you pressure test the system after a night you will be able to see a leak. It is a cheap part but requires a lot of work to replace because it is very tight under the intake manifold.

[b4a41point8t]

To bleed I fill my tank, let it get to operating temp and open the reservoir. Accompanying the hiss of air will be gurgles that u can actually hear and see. My hoses move around as the air comes rushing out. It's always worked for me

[SEATONE]

hey Old Guy Ive had this issue for quite some time. Do you think this would cause damage to the CTS on the back of the motor? I have replaced it but havent been able to get all the air out and my car has been going into limp mode. My temp gauge is staying cold and only goes up to the first line at idle... Thanks for any help you can give me. Glad you got yours strieghtend out I will try this method as well.

[doublezero30]

glad to hear you fixed it fletcher! another way to bleed the system is to just fill the resivoir with coolant, leave the cap off, and let the car run and get up to opporating temp. when it gets up there, the fans will start and thermastat allows the coolant to flow. keep the resivior at the full mark while its cycling through. youll also want to monitor your temp gauge to be positive you dont overheat. you can hold the rpms at about 2000 to help it get up to temp faster. do this for about 20-30 minutes and you should be golden. thats how a tech at my work did it for me when my turbo burnt through a coolant hose that was installed incorrectly.

[old guy]

glad to hear you fixed it Fletcher! another way to bleed the system is to just fill the reservoir with coolant, leave the cap off, and let the car run and get up to operating temp. when it gets up there, the fans will start and thermostat allows the coolant to flow. keep the reservoir at the full mark while its cycling through. You'll also want to monitor your temp gauge to be positive you don't overheat. you can hold the rpm at about 2000 to help it get up to temp faster. do this for about 20-30 minutes and you should be golden. that's how a tech at my work did it for me when my turbo burnt through a coolant hose that was installed incorrectly.

^ That is a very effective method for refilling the system and I have used it successfully in the past. Apparently this time the air pocket in the heater core was just too big to move. It wasn't until I physically topped off the heater core that I could get the air out.

[old guy]

hey Old Guy Ive had this issue for quite some time. Do you think this would cause damage to the CTS on the back of the motor? I have replaced it but havent been able to get all the air out and my car has been going into limp mode. My temp gauge is staying cold and only goes up to the first line at idle... Thanks for any help you can give me. Glad you got yours strieghtend out I will try this method as well.

Do you have heat? Does your motor appear to be getting up to temperature and the problem is only with the gauge or is the motor actually running cold?

If you have an air pocket around the rear CTS you would most likely show an overheat condition instead of an under heat condition. An air pocket causes pressurized superheated steam to occur and usually spikes your temperature gauge. You may have a faulty thermostat.

Here’s something you can try to determine if the thermostat is working properly. Unplug the electrical connection to the thermostat. This eliminates the ECM’s ability to force the t-stat open and the t-stat will function as a normal mechanical unit. If this improves the output from your heater then you have a control issue. If the heater output stays the same I would recommend replacing the thermostat. This procedure will give you a code and possibly a CEL, but just reset everything after you run the test.

Before you do these procedures make every effort to get all the air out of your coolant system.

Good luck!

[Trev]

Great stuff old guy You continue to amaze me with your knowledge. Iv had this problem for a long time but have yet to see a definitive "how to". It seams every time this topic comes up some one has a different procedure to try.

I think my problem has to do with air entering the system at night when the engine cools down. Iv bled the coolant system probably 20 times now... Do you know how and with what i can use to cold pressure test the system?

[old guy]

Damn! Are you still struggling with this issue? If I recall it was around March or April of last year when you were looking for a cooling system pressure tester. Your local Autozone will probably "rent" you a pressure tester but I doubt that they will have the correct adapter for the VW/Audi cap. Try Googling an adapter and you can probably find something for around $25-$35.

What are your current symptoms? No heat? reservoir boiling over? Low temperature reading on the temperature gauge?

[Tone-Dogg]

glad to hear you fixed it fletcher! another way to bleed the system is to just fill the resivoir with coolant, leave the cap off, and let the car run and get up to opporating temp. when it gets up there, the fans will start and thermastat allows the coolant to flow. keep the resivior at the full mark while its cycling through. youll also want to monitor your temp gauge to be positive you dont overheat. you can hold the rpms at about 2000 to help it get up to temp faster. do this for about 20-30 minutes and you should be golden. thats how a tech at my work did it for me when my turbo burnt through a coolant hose that was installed incorrectly.

X2 on this one, did the timing belt on the B7 Sunday and coolant flush etc., and had the same issue, NO Heat! I ended up with the bubble and wasn't pulling the coolant thru the engine. I stepped away and waited until, the coolant drained down and the engine cooled and readded coolant and now I have heat. Thanks for Sharing, I wish I had read this 2 days ago.

[dewey527]

Now that it is getting colder I noticed that my heater wasn't working very well. The problem was being caused by a large air bubble somewhere in the heater circuit. I know when the bubble was created. Back in September the clip holding the rear CTS cracked and consequently the sensor blew out of the motor. At that time I had a difficult time getting all the air out. Apparently I never got it all out.
Here's any easy way to tell if you have air trapped somewhere. Get your motor up to temperature. Then SLOWLY crack open the reservoir cap. If you have an air entrapment you should be able to hear the coolant gurgling and the coolant level in the reservoir will noticeably increase as the entrapped air is allowed to expand. The bigger the bubble the more the tank level will increase. If the bubble is big enough it will push coolant out of the overflow port on the bottom of the reservoir so be careful that you don't burn yourself. Even if you don't have any entrapped air the level will rise just a little as the coolant hoses contract back from the pressure release. However, you probably won't hear the gurgling noise that accompanies the bubble as it expands.

Now that you have the cap off you can release some of the air by cracking opening the bleeder valve in the center of the upper coolant hard pipe. Open it just enough for the air to escape. As soon as you get a solid stream of coolant close it off. You may have to repeat this process numerous times before you manage to work all the air out. The reservoir cap needs to be off when you perform this procedure so the static pressure in the reservoir will act on the hard pipe and push out the air. I just kept a 5mm Allen wrench in the car and a wad of paper towels stuck under the hood. whenever I took a short trip I just popped open the hood, shoved the wad of paper towels underneath the hard pipe and used this procedure to bleed the air off.

Unfortunately in my case this didn't release all the air so I had to take more extreme measures. Apparently I had a large bubble located in the heater core that wasn't bubbling out. After releasing all the system pressure I reinstalled the reservoir cap and then separated the quick connect on the out-feed side of the heater core. If you unscrew the coolant reservoir you can move it out of the way for easy access to the quick connect. I had a plug ready to block off the lower coolant line when I opened the quick connect. I used a long necked funnel to pour coolant directly into the heater core via the out-feed line. I then reattached the quick connect. After I did this I had to repeat the bleeding procedure outlined above three or four more times to get the rest of the air out.

I now have heat!

I have tried this procedure several times since installing my tb and I still don't have heat. I will admit this has been an on going problem for some time...I think my only option is to replace the heater core. When I did try your procedure and unscrew the coolant cap, I did have coolant escaping the overflow. How much should I let drain? We are now in the 40's and I get only a wee bit of heat by turning the system on/off repeatedly. Then when I sit at a light it turns cooler. Trust me I have read and and read and have numerous threads bookmarked...

[old guy]

It sounds like you still have a substantial amout of air somewhere and it's probably in the heater core like the condition I was dealing with. Try disconnecting the quick connect coming from the heater core outflow. That would be the one closest to the driver’s side of the car. Have something ready to block off the lower coolant hard pipe side of the connection and be sure to have the reservoir cap on. Use a long neck funnel and see if you can add coolant into the heater core side of the quick connect. Once it is full slowly loosen the reservoir cap. If the heater core isn’t clogged you should see coolant flowing out of the core hose. Immediately close the reservoir cap and attach the quick connect back to the lower coolant hard pipe.

[SEATONE]

Do you have heat? Does your motor appear to be getting up to temperature and the problem is only with the gauge or is the motor actually running cold?

If you have an air pocket around the rear CTS you would most likely show an overheat condition instead of an under heat condition. An air pocket causes pressurized superheated steam to occur and usually spikes your temperature gauge. You may have a faulty thermostat.

Here’s something you can try to determine if the thermostat is working properly. Unplug the electrical connection to the thermostat. This eliminates the ECM’s ability to force the t-stat open and the t-stat will function as a normal mechanical unit. If this improves the output from your heater then you have a control issue. If the heater output stays the same I would recommend replacing the thermostat. This procedure will give you a code and possibly a CEL, but just reset everything after you run the test.

Before you do these procedures make every effort to get all the air out of your coolant system.

Good luck!

Well I dont have any heat, and my guage stays cold. Im not sure if the engine is running cold. I will try that test. Im gonna try to fill the heater core tho I really think thats where the issue is. (one big air pocket).....

[seattlematt]

If your temp gauge doesn't move up then it's most likely thermostat related.

[O2VW1.8T]

So i finally fixed my heat, I flushd out my heater core for the 3rd time, used some dawn dish soap to try and clean it out. Kept flushing it for 20minutes until clear water only came out. Refilled the heater core first with coolant to avoid air bubbles. Started it up and now i have some crazy heat, I hope it stays like this if not im buying a new heater core.

[seattlematt]

Great, maybe I'll try that. I've been bleeding constantly and the air just keeps coming. It's just not getting past the HC for some reason. I'll keep bleeding a bit more then I'll try your method.

[rollerton]

My wife's had pretty bad heat in the Passat wagon lately. It had a new heater core and radiator 20k miles ago so I figured it has to be air in there. I already filled/flushed/bled the thing for 2 hours last week.
Did this today, some of those air bubble can be stubborn and simply won't be forced out easily, so I decided to SUCK the bubbles out.
1. 3/4" ID clear hose connected to heater core inlet/ outlet
2. ELEVATE the hose to the inlet side so no air can get in your hose and submerge in bucket of clean water, have garden hose near to fill bucket as needed.
3.seal outlet hose to shop vac inlet hose.
4. Fire up the shop vac and SUCK the water through the heater core.
I emptied my shop vac cannister 4 or 5 times before I figured that should do it, though I never did see much air go through. Thats 25-30 gallons.
Then hook it back up and bleed as usual. There's NO WAY there's any air in there now. No way. (... . right...? )
Blows hot as shit now, but it was all warmed up, real test will be if it ever gets cold here again.

[diagnosticator]

Another way to bleed trapped air from the heater core, on the end of the upper metal pipe from the heater core, there is a notch cut that is specifically used to allow air to escape the heater core. To do this, remove the hose clamp sliding it toward the fire wall, then twist the hose to loosen on the pipe. Next, carefully slide the hose almost all the way off the pipe, but as soon as the notch in the pipe is uncovered, stop moving the hose and allow any air to escape through the notch. The expansion tank must be kept full with the cap loose in order that there is enough head pressure to cause coolant to flow into the core, and push the air out of the uncovered notch in the metal pipe. As soon as coolant flows from the notch, push the hose back onto the metal pipe all the way and replace the hose clamp. Done.

After bleeding any air from the bleeder screw in the black coolant pipe, tighten the tank cap and drive the car normally checking for normal heater output.

If air continues to accumulate and stop coolant flow in the heater core, then there is likely a coolant leak somewhere or the head gasket is leaking combustion gasses into the cooling system.

[B6_Dolphin]

I would check your coolant block plug on the back of the thermostat housing. They will shrink overnight and allow air into the coolant system. It will not leak when the engine is hot but if you pressure test the system after a night you will be able to see a leak. It is a cheap part but requires a lot of work to replace because it is very tight under the intake manifold.

Yes, the infamous "J-plug". $13 at the stealership. I noticed at my last oil change I had a tiny coolant leak, and traced it to the J-plug. I guess just like all the other plastic fittings under the hood, the plug actually degrades with age and starts to leak. Audi mechanic said the J-plug is a common leak point for 1.8's.

[SEATONE]

Old Guys method worked perfect for me today. I have a B6 A4 1.8tq. First I flushed the whole system. Then I removed the top line on the heater core pluged it and ran an extension from the core. I filled the cooling system thru the resevior and then continued to fill the core thru the extension that I ran. After filling the core I bled the system at the bleeder screw and it pushed out some air. Once that was done I then hurried and pluged the hose back into the core like it should be and started the car. Let it idle for a little with the cap off. after about 5 min I reved it to 2000rpm and the heat just got retarded hot (LOL) : ).... Its been over a year like that and finally its fixed. Lets see if it stays that way haha.

Good luck guys with your heat that air pocket in the core is really stubborn. Thanks Old Guy, Once again YOU THE MAN!!!!!

[dewey527]

I am so friggin done with this...so I finally get some time to try to bleed the system the way diagnosticator said and no heat. loosen up the cap pull the top line just far enough (mine has a hole in the hose) and nothing. tighten up the cap and I get some flow. think everything is good, go to the cabin and cool air-fml. go back and try it again and I only get flow after opening then closing the cap, then it's sporatic. then I realize my cap really isn't that tight when closed all the way (getting a new one tomorrow) I replaced the coolant resevoir when I did my timing belt a few weeks back to the nice white one and thought everything was good. would having a cap that is slightly loose cause this issue? The process is pretty straight forward and I could only get flow some of the time. I actually had the cap off, hose to the leaking point with no flow. How about a clogged core...signing out, early morning tomorrow.

[old guy]

I am so friggin done with this...

Sounds like you have a large amount of air in your heater core. Go back and read post #15. You can do that in 15 minutes and it should fix your problem. The quick connect is easily accessible if you move the coolant reservoir to the side.

Edit: The procedure you tried works if the air is trapped around the rear coolant flange. The hose you were working with connects to the rear coolant flange and a separate hose runs from the coolant flange to the inflow side of heater core. If the bubble is in the heater core it doesn't always make it all the way up to the flange and out through the hard pipe.

As to the radiator cap. It doesn't have to be tightened down real tight to seal. An "O" ring seals the cap to the sides of the reservoir neck rather than to the top of the neck. I checked mine out by hooking my compressor up to the small line running into the reservoir and slowly turned up the pressure. It should blow off pressure between 1.4 to 1.6 bar (20-24 psi). If it blows off below 20 or over 25 psi you should replace it. I wouldn't recommend going over 26-27 psi when performing the test or you may blow something out (hose, sensor etc).

[dewey527]

Sounds like you have a large amount of air in your heater core. Go back and read post #15. You can do that in 15 minutes and it should fix your problem. The quick connect is easily accessible if you move the coolant reservoir to the side.

Edit: The procedure you tried works if the air is trapped around the rear coolant flange. The hose you were working with connects to the rear coolant flange and a separate hose runs from the coolant flange to the inflow side of heater core. If the bubble is in the heater core it doesn't always make it all the way up to the flange and out through the hard pipe.

As to the radiator cap. It doesn't have to be tightened down real tight to seal. An "O" ring seals the cap to the sides of the reservoir neck rather than to the top of the neck. I checked mine out by hooking my compressor up to the small line running into the reservoir and slowly turned up the pressure. It should blow off pressure between 1.4 to 1.6 bar (20-24 psi). If it blows off below 20 or over 25 psi you should replace it. I wouldn't recommend going over 26-27 psi when performing the test or you may blow something out (hose, sensor etc).

I removed the top hose. Coulda sworn I was working with the heater core hoses:) I checked the coolant once I got to work and it was below the "low" mark. So I filled er up and will try it again tonight.

[rollerton]

i know what everyone else says, but do not remove the reservior cap when you're bleeding the system.
Just dont. It makes it harder. You WANT the system pressurized because the coolant EXPANDS when the cap is removed and when it expands and it is open to atmosphere this creates air bubble. It helps to have 2 people.
The pressure on the heater core outlet (bleeder) builds as the rpm's DROP. So get the thing nice and hot, then rev the engine from 2k to 4k several times, hold it at 3-4k for a few seconds too.
THEN slide the hose back to expose the hole in the bleeder- you WILL get coolant (and air if any is present) out of that hole. When the flow from the hole slows down, close bleeder and repeat until you've got SOLID stream of coolant out of the bleeder.
Or just hook up a shop vac and suck the air out in 2 minutes.

[Dan[FN]6262]

Fletcher, I'm just going to drive down to your house, and let you bleed my system. I've spent 4 hours and went through 4 gallons of antifreeze/water so far, and I was positive that I had it fixed last night. but, this morning, after I got in my car, I had heat for like..... 8 minutes, then suddenly COLD air was blowing out of the vents. I'm about to light this thing on fire.



and, just to be sure, I'm going to order a new headgasket, and replace that.

[old guy]

I removed the top hose. Coulda sworn I was working with the heater core hoses:) I checked the coolant once I got to work and it was below the "low" mark. So I filled er up and will try it again tonight.

OK. I see where the confusion is coming from. I always take the easiest method (for me) when I work on something. I didn’t bother to pull the rain guard off to access the hoses where you did because I didn’t want to mess with cleaning up the coolant and the hose clamps are a pain in the ass. I just used the quick disconnect on the engine bay side of the outflow line where all you have to do is pull out the wire clip. I plugged the hard pipe connection and used a long neck funnel to get the coolant level high enough to backfill the heater. Put it all back together and viola! Heat.

Doing it from where you are working should work even better. Just be sure to fill the outflow hose all the way as well as the heater core side.

[SEATONE]

damn guys just buy some heater hose, block the hose coming from the engine to the core ( top hose ) hook up that hose you bought to the core and pour coolent in the hose. once it stops taking coolant open the bleeder on the pipe. itll let out any air in there. close it again and put more coolant in the hose. bleed again once it dosnt take any more. also make sure the resevior is topped off. now quickly reconnect the top hose back like normal. Use your thumb to block the hose coming from the motor while you remove the hose you bought from the core. once thats done start the car with the res. cap off and rev to like 2000rpm. I massaged the top rad hose a little and wala. you also have to keep bleeding thru the top screw and at the bleeder hole on the hose a couple times but it should work. good luck.

[tommy782]

I search the quick connect for the hose and I don't find it. someone have a picture?

[SEATONE]

If you remove the resevoir and push-pull on the top hose of the core you will see where it connects to. hope that helps.

[JMRQuattro]

Yeah, this definitely takes some time. It took me a long time before I finally cleared out an air bubble I had the first winter I owned the car. It blew only cold air and the air bubble would sometimes pass at high rpm's, so my heat would be temporarily restored until the bubble recirculated back through. Turns out my head gasket was bad so coolant was leaking into cylinder 2 and burning out of my exhaust. But I just used the bleeder screw (only open partially because it has a notch), opened up the reservoir cap, and squeezed on the rubber hose that runs in front of the intake mani. I would just squeeze rapidly and collapse the hose and hold for a second and then release. This forced air out of both the bleeder screw and the reservoir and then sucked coolant back in. And I just repeated this process until coolant started to flow on it's own out of the bleeder screw and the hose felt firm.

[old guy]

I search the quick connect for the hose and I don't find it. someone have a picture?

Do you ever have one of those times when you wish you hadn't posted something? well this is one of those times. Sometimes I tend to get lazy and look for the easiest way to do things. If it works for me, great! But it may not always be the best for everyone else.

To answer your question, the quick connect for the return hose from the heater core can be seen by looking directly down from the back edge of the intake manifold. It's pretty much dead center in the pic. Just pull the wire clip to the right and you can disconnect the return hose from the lower hard pipe. Have something ready to plug the hard pipe side. Inset a long neck funnel into the return hose and pour in the coolant. You need to have the funnel high enough to get the coolant to run into the return hose to the height of the the heater core. Pull the funnel out and quickly reconnect the hose quick connect. This worked for me and took all of 5 minutes.
If it doesn't work for you then pull off the rain tray and disconnect the top heater hose and bleed the core from there as shown in dewey's pic. Or better yet, instead of trying to bleed out the air, add coolant instead. Use the method that SEATONE did and use a hose and funnel to fill the heater core from there. In fact, you will probably have more success just doing it from there to begin with. [IMG][/IMG]

[IMG][/IMG]

[tommy782]

first I try to bleed it with the bleeder valve. I unscrew it and nothing?!? no coolant in the hard pipe with the bleeder valve!! normal if I have a air bubble??

[old guy]

first I try to bleed it with the bleeder valve. I unscrew it and nothing?!? no coolant in the hard pipe with the bleeder valve!! normal if I have a air bubble??

Open the reservoir cap.

[seattlematt]

I suspect that my coolant leak is introducing air into the system. I had it bled out pretty well and now it's full of air again. Bleeding through the heater core return hose bleed hole is definitely helpful.

[diagnosticator]

i know what everyone else says, but do not remove the reservior cap when you're bleeding the system.
Just dont. It makes it harder. You WANT the system pressurized because the coolant EXPANDS when the cap is removed and when it expands and it is open to atmosphere this creates air bubble. It helps to have 2 people.
The pressure on the heater core outlet (bleeder) builds as the rpm's DROP. So get the thing nice and hot, then rev the engine from 2k to 4k several times, hold it at 3-4k for a few seconds too.
THEN slide the hose back to expose the hole in the bleeder- you WILL get coolant (and air if any is present) out of that hole. When the flow from the hole slows down, close bleeder and repeat until you've got SOLID stream of coolant out of the bleeder.
Or just hook up a shop vac and suck the air out in 2 minutes.

If the coolant is cold, the tank cap must be loosened to allow coolant to flow into the heater core when bleeding, your suggested method will only work if the cooling system is warmed up and there is pressure in the cooling system.

[dewey527]

Wow...so I spent an hour trying different methods and finally have heat <crosses fingers> This method was bleeding from the hose that comes from the firewall with the coolant cap off, coolant cap on, heat on, heat off, tried from the bleeder screw, shop vac and just about got the 5lb sledge...What finally worked for me was having the coolant cap closed, hvac completely off, hold rpm around 2-3k for 30-60 seconds, run to the hose and slightly pull back until bubbles then coolant. Did this 15 times before I coolant only came out!!!!!!!!!! Did not drive the car afterwards since I was scared of the results but will post tomorrow.

[tommy782]

so me too I have heat now with the doublezero30 method. now I think I have a double problem. I have very hot heat now but sometime when I drive, the car overheat 5-10 sec overflow a lot of coolant and return to 90..?? what can cause that?? thermostat fail?