Randomly Overheating coolant levels are fine

[OneSlowA4]

Okay so today I noticed my car randomly jumped to the 3rd mark on the temp gauge and the coolant low light flashed. I still had heat and so I stopped to check my coolant (I have a miniscule leak from the upper radiator hose where it mounts to the plastic on the radiator). Coolant level was on min line but not low, I added some to the max line and continued on. Was driving fine when it got hot again and the coolant light came on, I stopped thinking I had a bigger leak but looked and hadn't lost any coolant. Still had perfectly good heat and the needle would go to the third mark then back down to the second where it's supposed to be. Then all of the sudden my car lost heat and overheated again, but coolant levels are still fine. There's a lot of pressure in the system tho as I took the resivour cap off it pushed a bunch of coolant out.

I ordered a resivour cap thinking maybe it's not relieving the pressure because every time I stop and take it off then start the car again temps are normal.

However I'm not 100% positive this is my answer. Anyone have any ideas?

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[OneSlowA4]

I should also add that I replaced both coolant temp sensors and the thermostat in the last 7,000 miles.

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[OneSlowA4]

Things got progressively worse as I got the car home. Took the cap off and lost a gallon of coolant on the road.

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[diagnosticator]

Check the coolant pump for a broken impeller. If the pump has a plastic impeller, they are known to crack across the center hole where it is pressed on to the pump shaft.

[OneSlowA4]

I'll check that tomorrow but if the impeller was broken would it build up so much pressure like that?

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[customa4]

Stop driving the car until you get the problem fixed. It will become much more expensive when you warp the head from overheating if you haven't warped it already.

[crazyquik22023]

Even a very small leak can let air get into the system. Also I recently purchased a thermostat for my b6 a few months ago, I won't name the vendor, and it failed within 500 miles. It does sound to me though like there is air getting into the system causing the thermostat to not operate correctly.

[OneSlowA4]

Stop driving the car until you get the problem fixed. It will become much more expensive when you warp the head from overheating if you haven't warped it already.

Once I got the car home I left it there and haven't been driving it. I know overheating issues can cause serious damage. I stopped before I let it get past the 3rd mark.

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[OneSlowA4]

Even a very small leak can let air get into the system. Also I recently purchased a thermostat for my b6 a few months ago, I won't name the vendor, and it failed within 500 miles. It does sound to me though like there is air getting into the system causing the thermostat to not operate correctly.

Well I'll tell you I bought the thermostat kit with the j-plug from ECS. Is that where you got yours? Doesn't seem to me like an issue with the thermostat as it is too much pressure in the system causing random air pockets that make my temps jump up and down.

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[OneSlowA4]

I'm putting on the new resivour cap and if that doesn't work I'm going to test for exhaust gasses in the coolant. That would point me towards a head issue.

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[crazyquik22023]

Well I'll tell you I bought the thermostat kit with the j-plug from ECS. Is that where you got yours? Doesn't seem to me like an issue with the thermostat as it is too much pressure in the system causing random air pockets that make my temps jump up and down.

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I have the ECS kit with the Hamburg Techinc thermostat, which I believe is the OEM thermostat just not branded, and that one I've had in for months now with no problems. That is not the one that failed on me. And why are you saying you have too much pressure in the system? It is normal for coolant to come rushing out of the expansion tank if the cap is opened when the system is pressurized.

[OneSlowA4]

I have the ECS kit with the Hamburg Techinc thermostat, which I believe is the OEM thermostat just not branded, and that one I've had in for months now with no problems. That is not the one that failed on me. And why are you saying you have too much pressure in the system? It is normal for coolant to come rushing out of the expansion tank if the cap is opened when the system is pressurized.

Well I've taken the cap off before while it was pressurized to top off the coolant and have never witnessed this. If I take the cap off now a gallon or so of coolant shoots straight out the bottom. Before I would only hear the normal "pssst" from the little bit of air pressure.

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[CyberPMG]

Sounds like you have something blocking the flow of coolant. Check the radiator to see if it's flowing through that properly (if it's hot on one end and cold on the other end, that's likely the source). Did you check the water pump? Check the hoses going to and from the heater core to see if it may be blocked there.

If you're unsure, I would suggest taking it over to German Auto Pros (www.germanautopros.com) since you're also in Northeast Ohio. They can do a proper pressure and flow test to see what's going on. I would call them up to make an appointment first. Then, you may want to consider having it towed over there to avoid any damage or any additional damage.

[OneSlowA4]

Sounds like you have something blocking the flow of coolant. Check the radiator to see if it's flowing through that properly (if it's hot on one end and cold on the other end, that's likely the source). Did you check the water pump? Check the hoses going to and from the heater core to see if it may be blocked there.

If you're unsure, I would suggest taking it over to German Auto Pros (www.germanautopros.com) since you're also in Northeast Ohio. They can do a proper pressure and flow test to see what's going on. I would call them up to make an appointment first. Then, you may want to consider having it towed over there to avoid any damage or any additional damage.

That was another guess of mine but when I did the thermostat I flushed the coolant as well. And it was perfectly clear and rushed out of the lower coolant temp sensor very quickly and that was within the last 3000 miles. If I cannot figure this out I will definitely give them a call and set something up!! Thanks for the referral i was wondering about a good German auto shop around.

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[OneSlowA4]

There's definitely flow through the radiator as I can feel the coolant running through the hoses as I squeeze them a little. So no blockage. Also have heat again. Replaced the resivour cap and it has been idling for 20 minutes with no issues do you guys think it's safe to take for a spin and see if the problem occurs again? I'm going to stay close to home this time.

Checked oil again and its not milky and is at the right level as well. Coolant didnt drop any from sitting over night either.

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[OneSlowA4]

It has to be the water pump. As soon as the car got to temp and the thermostat opened I lost heat and felt little to no flow through the hoses. Seems as if I have a broken impeller.

As soon as the thermostat opens it doesn't have enough flow to push it through the heater core I'm presuming. Does this sound about right?

If I get other people to agree I'll go ahead and order the timing belt kit from ECS and get started. What's the estimated time of this job with moderate mechanical knowledge. 6-8 hours? I know the front clip needs to come off.

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[crazyquik22023]

It has to be the water pump. As soon as the car got to temp and the thermostat opened I lost heat and felt little to no flow through the hoses. Seems as if I have a broken impeller.

As soon as the thermostat opens it doesn't have enough flow to push it through the heater core I'm presuming. Does this sound about right?

If I get other people to agree I'll go ahead and order the timing belt kit from ECS and get started. What's the estimated time of this job with moderate mechanical knowledge. 6-8 hours? I know the front clip needs to come off.

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Quick way to check water pump flow: Open the expansion tank cap and remove the small hose that goes to the expansion tank, hold the small hose above the expansion tank or over a container. At idle there should be a "trickle" of coolant dripping out of the hose. Have someone rev engine to around 2500 rpms. There should be a steady flow at 2500. If there is not a steady flow, then the water pump probably needs replaced.

[OneSlowA4]

Okay I'll check that. The more I think about it the more it makes sense because some jackass in a 1 ton truck pulled out in front of me in a 55 and I downshifted while braking trying to slow down in time and redlined on the downshift and the problem started some point after that. That over rev probably broke the already weak impeller as I have 82000 miles. Dumb move to downshift so hard but I may have hit him if not.

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[CyberPMG]

If you haven't done a full timing belt service, I would recommend doing that. For the 1.8T engine, it should be done every 60-70k miles. The complete kit includes the timing belt, accessory belt, tensioner, water pump, gasket, and coolant to do a full flush).

[Furly]

If you haven't done a full timing belt service, I would recommend doing that. For the 1.8T engine, it should be done every 60-70k miles. The complete kit includes the timing belt, accessory belt, tensioner, water pump, gasket, and coolant to do a full flush).

Timing belt service every 60k? You're pushing it. More like 80k is playing it safe but most do it 90k-100k.

Also age plays a role. So if you only put like 5k miles a year on your car, the service interval would. Apply more toward age than mileage .

[OneSlowA4]

Yeah I'm ordering the water pump/ timing belt kit since I have to pull everything off anyways. Literally was going to do this next week since it's supposed to warm up and I'm almost at 90k I figured if I did it before 100k I would be okay. Of course this week and weekend it's in the 20s.

I did your test and had no flow on idle and barely a trickle at 2500ish rpms so it's gotta be water pump. The car is an 04 so that age probably played a part. That over rev is what had to of done it because it happened the other day, but yesterday was the first time since it happend that I drove more than 5-10 minutes.

Too bad ECS doesn't offer pickup services because I live 5 miles from them. Oh well I guess. Last time shipping took 5 days tho. Kind of a bummer.

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[CyberPMG]

Timing belt service every 60k? You're pushing it. More like 80k is playing it safe but most do it 90k-100k.

Also age plays a role. So if you only put like 5k miles a year on your car, the service interval would. Apply more toward age than mileage .

That used to be the standard recommendation that many in here have made for the 1.8T engine. For the 3.0, the interval has been 70-80k miles. I'm not making this up

[OneSlowA4]

That used to be the standard recommendation that many in here have made for the 1.8T engine. For the 3.0, the interval has been 70-80k miles. I'm not making this up

I probably should have done it earlier but I don't have a heated garage and winter in Ohio is brutal most of the time so I was waiting for the weather to break. Is it unusal for a water pump to go so soon? I don't really drive the car hard because it's not fast or anything. Checked my odo and I'm at 83,560 miles. Seems soon for a water pump to gernade. I guess the age is the real issue.

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[customa4]

That was roughly the milage mine went. You have to remember, regardless of mileage, the pump can be up to 14 years old. That's pretty good if it's the original water pump.

[diagnosticator]

I'll check that tomorrow but if the impeller was broken would it build up so much pressure like that?

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The coolant pump does not develop system pressure. The pump only creates a differential pressure to cause the coolant to flow. System pressure is the result of the temperature increase of the coolant and engine.

[OneSlowA4]

The coolant pump does not develop system pressure. The pump only creates a differential pressure to cause the coolant to flow. System pressure is the result of the temperature increase of the coolant and engine.

Yeah that's what I figured also.

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[OneSlowA4]

That was roughly the milage mine went. You have to remember, regardless of mileage, the pump can be up to 14 years old. That's pretty good if it's the original water pump.

Very true. I guess since it's plastic too, age plays an even bigger role. When the impeller breaks do pieces get into the entire cooling system or is it not something to worry about after you flush the coolant.

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[CyberPMG]

If pieces of the impeller break off, it can flow through the coolant system and potentially get lodged somewhere and possibly block coolant flow. If you find pieces when draining the coolant, then you're likely to have flushed out the pieces. Do the flush and the full timing belt service (excellent how-to written up here), check on coolant temp and flow. If it still seems to be getting hotter than normal (temp above half), then you may have pieces blocking the flow that need to be removed.

[OneSlowA4]

Just to close this I did the water pump and timing belt and were all good to go! Thanks for the help everyone!

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[quattro guy]

im having issues with mine as well. it started with interminent heat and loss of coolant through the reservoir. as time went by things progressively got worst and it came to a point that I was forced to put only water in the system because I was loosing so much. when this was going on I noticed that It would overflow only when I would rev the car after 3500rpm. so I drove it and kept the rpm under 3000k. up until recently I stated to overheat. its getting worse each day. I noticed a pattern like when I would loose coolant. I would overheat even if I would rev to like 4500rpm for a quick second. and like a min later I was overheating. well I kept driving the car like a grandpa and I would overheat slightly but it would go back down. so today I was in the store parking lot idiling while I was texting and I started to over heat out of no where. I had the coolant light in the display but I had coolant in the reservoir. here is where things get confusing. I have replaced the thermostat, water pump, and flushed the entire system and yet somehow I still don't have heat most of the time and now im starting to over heat more often. I did a leak down test but since im not experienced in diagnosing I cant really tell. but there was no bubbles coming out of the coolant reservoir when I did the test in all the cylinders. I have ordered a head gasket because that's what ive narrowed it down to but im still not sure that will fix the problem. I somehow feel like im getting air in the system or if im clogged somewhere. leakdown test should have confirmed my suspicions of exhaust fumes getting in the cooling system, reason I say this is because of how it was behaving when I would rev it. I didn't see any bubbles so I have to be clogged. well then everything was flowing freely when I flushed it. so im at a loss. any help before I tear apart half my engine would be really appreciate it.

[Let it snow]

Before tearing into the engine did you do a coolant pressure test? You can also test your coolant cap using this.

Audizine Forums
http://www.audizine.com/forum/showth...DIY-(low-tech)

[quattro guy]

I believe you comment on another thread i posted as well. I didnt see any leaks but perhaps i might have missed something. I can always do it again. How long did you leave yours pressureized for? That might also be a reason why i didnt find anything on mine i left it for like an hour or a bit shy of that.

[Let it snow]

Sorry I did not know you already tried this. I left mine on for 4 hours.

[quattro guy]

I will try it longer and see if anything creeps out or anything.