Is there a check valve in the coolant system?

[LakeTahoeQuattr]

Two years ago I replaced my thermostat with an audi OEM 078121113F 87DEG C thermostat because my car would take 30 minutes to warm up. After replacement, same symptoms, car never warms up sort of like a thermostat stuck open condition.

Knowing the thermostat is good, is there ANYTHING else on this engine that could replicate a thermostat stuck open symptom like some sort of check valve somewhere allowing cold coolant to flow where it shouldn't?

Yes I have a new OEM CTS

[blitz2190]

never warms up as in the temp gauge or as in no heat?

[LakeTahoeQuattr]

never warms up as in the temp gauge or as in no heat?

Both. Temp gauge gets first tick mark, heat is 7/10 "bearable" under normal driving

Going down a hill, coolant gauge goes all the way to the left bad heat

Let the car sit and idle for 20-30 minutes temp gets up to ~200DEG F and heat is great, temp drops as soon as I start driving.

I know all fingers point to tstat, but Im pretty certain it isnt.

[S4gasm aka LOTR]

You need to bleed the system, there are 2 ways to bleed it. Google will show you the way.

[LakeTahoeQuattr]

I have bled the system a bunch of times all to the bently. I even bought the schwaben vacuum bleeder, no difference. I believe the system is fully bled. I would assume air pockets in the system would create more heat than anything..

Internet pic:


It appears that there is a check valve that is on line with the after run coolant system. Possibly this could be a culprit?

part # 078122349A

[jturnbull]

First things first, either replace or delete that coolant after run pump ASAP

[blitz2190]

^ dont think that is his he said its an internet pick, to the OP it does sound like a thermostat being stuck open unfortunately for that drastic of a temp change. It just suck they are where they are to replace.

[rguil]

OP previously replaced his thermostat. His car is minty fresh, were trying OEM coolant temp sensor next.
Ive had 2.7s with a bad TSTAT and after driving his car i dont think it is that. The shift in coolant temp isnt as dramatic as it would be if the tstat was stuck open, ive seen it. it shifts from hot to cold just going up a 200 yard hill with a bad tstat.

[blitz2190]

I saw that but I've seen them doa, also the op said the cts was new oem so didn't mention that.

[LakeTahoeQuattr]

Yea CTS is new OEM, I am going to try ANOTHER new CTS for fun. I know its not the CTS because the heat is poor so my skin tells me that the coolant is cold...

I tested the old thermostat against the new oem thermostat two years ago in boiling water and confirmed that both the old and new thermostats both opened and closed at the correct temperatures.

I confirmed that the thermostat closes when cold. I put it in the car. Car did not get up to temp. Been that way for two years.

It appears that that check valve in the picture above only comes on the allroad? Has anyone else seen that check valve on their 2.7s?

[blitz2190]

Yea CTS is new OEM, I am going to try ANOTHER new CTS for fun. I know its not the CTS because the heat is poor so my skin tells me that the coolant is cold...

I tested the old thermostat against the new oem thermostat two years ago in boiling water and confirmed that both the old and new thermostats both opened and closed at the correct temperatures.

I confirmed that the thermostat closes when cold. I put it in the car. Car did not get up to temp. Been that way for two years.

It appears that that check valve in the picture above only comes on the allroad? Has anyone else seen that check valve on their 2.7s?

I did not have one on my old one, but I'll check the one I have torn down this weekend for you.

[LakeTahoeQuattr]

More googling says that only the BEL had the check valve...

[Tiluleshpingen]

why cant we answer what the man is asking for? IS there a check valve in the cooling system? My answer is .. there is a hose with 1 way check valve by the reservoir, cant remember where it runs after

[LakeTahoeQuattr]

why cant we answer what the man is asking for? IS there a check valve in the cooling system? My answer is .. there is a hose with 1 way check valve by the reservoir, cant remember where it runs after

Yup you are correct. The coolant bleed off hose that goes to the back of the coolant pipe to the reservoir has a small check valve in it. I have replaced this pipe with a new one from OEM. Thanks for reminding me of that hose, l forgot about that one.

[Tiluleshpingen]

Yup you are correct. The coolant bleed off hose that goes to the back of the coolant pipe to the reservoir has a small check valve in it. I have replaced this pipe with a new one from OEM. Thanks for reminding me of that hose, l forgot about that one.

No prob. do you remember where that hose connects after? pic?

[LakeTahoeQuattr]

No prob. do you remember where that hose connects after? pic?

Yea it goes from the expansion tank to the rear coolant pipe bleed off nipple by the fan switch. The small check valve is located inside the hose in the area marked with the |X|. I remember trying to blow air into it to check.

[Mille Bornes]

Has it resolved your issue?

[MacDaddy]

Maybe someone re routed your coolant hoses on the front of the engine wrong, or there is an air bubble, is the engine physically cool to the touch when the gauge shows low temp?

Bad thermostat? Installed backwards? Thermostat temp too low, 87* sounds lower than what OEM specs.

Lots of unanswered questions. I dont have a check valve on my after run pump and i dont think it would cause an issue as dramatic as yours if it was broken.

[audinutt]

Maybe someone re routed your coolant hoses on the front of the engine wrong, or there is an air bubble, is the engine physically cool to the touch when the gauge shows low temp?

Bad thermostat? Installed backwards? Thermostat temp too low, 87* sounds lower than what OEM specs.

Lots of unanswered questions. I dont have a check valve on my after run pump and i dont think it would cause an issue as dramatic as yours if it was broken.

defective thermostat is my guess... seen it on brand new thermostats.
I buy mine at the dealer for this reason.

-Richard

[julex]

Has to be partially stuck open thermostat, my car is right now having the same exact issue. I just put a large sheet of plastic between rad and evaporator as a temporary fix for winter. I found that obscuring about 3/4 of radiator area this way allows my car to warm up reasonably well with a wiggle room for warmer days.

And when you say "audi OEM 078121113F 87DEG C " thermostat, did you actually buy this at the Audi dealership or places like Genuine Audi Parts or is that one of these "OEM AUdi 078121113F " listings on ebay which 99% of times means not an original OE Audi part buy inferior quality shit part? There is a big difference between "OEM" and "OE". Contrary to what you might thing, OE means Original Equipment (as equipped on the car when sold new) parts vs Original Equipment Manufacturer which means squat, e.g. anybody can slap "OEM" mark on their product so long even if all they ever made were wooden brake pads (not joking here) for yugo in 1990 and now decided to make thermostat for audi .

[QuinnsterKID]

OP I know you do not want to hear this, but I am going with T stat as well. I had the same issues on my B5 A4. Car would never get up to full operating temp (needle in the middle) while driving and would go up and down depending on speed, hills, outside temp, etc. At idle the needle would sit right in the middle like nothing was wrong. My heat was hot but not the type of heat you expect. I replaced the T stat and problem solved. Car warms up quick, the needle does not fluctuate and heat feels like you're going to melt. Luckily on the A4 they are insanely easy to swap out. I had this problem on my B6 before also right after doing the timing kit. T stat was brand new, but my car was overheating. T stat ending up getting stuck open. Worst case is you could have a faulty T stat.

[LakeTahoeQuattr]

Has it resolved your issue?

No it has not

Maybe someone re routed your coolant hoses on the front of the engine wrong, or there is an air bubble, is the engine physically cool to the touch when the gauge shows low temp?
Bad thermostat? Installed backwards? Thermostat temp too low, 87* sounds lower than what OEM specs.
Lots of unanswered questions. I dont have a check valve on my after run pump and i dont think it would cause an issue as dramatic as yours if it was broken.

I believe 87DegC is spec. No I did not install it backwards. There are not many hoses on the front of the engine to re-route. Im am certain all the hoses are connected correctly.

Has to be partially stuck open thermostat, my car is right now having the same exact issue. I just put a large sheet of plastic between rad and evaporator as a temporary fix for winter. I found that obscuring about 3/4 of radiator area this way allows my car to warm up reasonably well with a wiggle room for warmer days.

And when you say "audi OEM 078121113F 87DEG C " thermostat, did you actually buy this at the Audi dealership or places like Genuine Audi Parts or is that one of these "OEM AUdi 078121113F " listings on ebay which 99% of times means not an original OE Audi part buy inferior quality shit part? There is a big difference between "OEM" and "OE". Contrary to what you might thing, OE means Original Equipment (as equipped on the car when sold new) parts vs Original Equipment Manufacturer which means squat, e.g. anybody can slap "OEM" mark on their product so long even if all they ever made were wooden brake pads (not joking here) for yugo in 1990 and now decided to make thermostat for audi .

Yea I am leaning towards DOA. Which 3/4 of the radiator did you cover?

Yes I got it from the audi Reno dealership. Im gonna do the plastic trick for now and I guess Ill put another thermostat in there again. 3rd time in 40k…

OP I know you do not want to hear this, but I am going with T stat as well. I had the same issues on my B5 A4. Car would never get up to full operating temp (needle in the middle) while driving and would go up and down depending on speed, hills, outside temp, etc. At idle the needle would sit right in the middle like nothing was wrong. My heat was hot but not the type of heat you expect. I replaced the T stat and problem solved. Car warms up quick, the needle does not fluctuate and heat feels like you're going to melt. Luckily on the A4 they are insanely easy to swap out. I had this problem on my B6 before also right after doing the timing kit. T stat was brand new, but my car was overheating. T stat ending up getting stuck open. Worst case is you could have a faulty T stat.

Yea I cant think of what else it will be either. I am going to ask the dealer for a new one. This just pisses me off, hope no damage has been done to the engine during this time. Ive maintained oil changes ever 3-4k during this issue...

[LakeTahoeQuattr]

Here is why I dont think it is a thermostat. I had a meyle thermostat in the car when I first built it in November, 2013. The car never got to temp with that thermostat. I then replaced it with the CURRENT thermostat and same results. That is why i am trying to rule out thermostat as a culprit because the odds of it happening twice in a row is so unlikely...

Furthermore here is the kicker. Since I am a horder I saved the chinese melye thermostat until two weeks ago when we put it into our $350 craigslist a6 2.7t and the the temperature works just fine and as it should. The symptoms that existed in my allroad with the old thermostat do not exist in the old "new" a6.

[julex]

Here is why I dont think it is a thermostat. I had a meyle thermostat in the car when I first built it in November, 2013. The car never got to temp with that thermostat. I then replaced it with the CURRENT thermostat and same results. That is why i am trying to rule out thermostat as a culprit because the odds of it happening twice in a row is so unlikely...

Furthermore here is the kicker. Since I am a horder I saved the chinese melye thermostat until two weeks ago when we put it into our $350 craigslist a6 2.7t and the the temperature works just fine and as it should. The symptoms that existed in my allroad with the old thermostat do not exist in the old "new" a6.

The heat must go somewhere and the only way it can go without engine ending in catastrophic overheat failure is the radiator. The only device that closes and opens the path to radiator is the thermostat. It is possible that it is not PER SE the thermostat's fault that the coolant circulates regardless of coolant temperature... it also might be something funky with the thermostat seat in the block or something causing the thermostat to mechanically open when you bolt down the housing. I am thinking something stuck in there (bolt, piece of plastic, you name it, fucked up machining of block, etc, etc) that pushes it open once the Tstat is pushed against the seat or the T-stat ending in skewed position - just brainstorming here.

[MacDaddy]

Meyle is china junk, i went with a behr thermostat

[spacecadet]

Did you install it the right way? Dot up at the top?

[alphaVR]

Im hesitant to blame the Thermostat her if only because OP tested it in boiling water, in addition to the report of no performance change before or after the replacement.

There shouldn't be any check valves that affect cooling performance outside of the thermostat itself. The afterrun coolant pump is only there to provide additional coolant to the turbos after shutting the car off. Thats it. Anything connected/associated with the pump shouldn't make any appreciable effect on your coolant issue.

I would likely start with a full empty/fill of the coolant system again using the vacuum tool to ensure it's full. Afterward you can also check for air by opening the relief port on the coolant line just to the right of the power steering pump, forward of the afterrun coolant pump. Its a 6mm hex nut with a copper washer. Crack it open and make sure coolant comes out as thats the highest point of your coolant system.

Also replacing the CTS to ensure proper readouts would be recommended. You should be able to feel your upper radiator hose to see if the heat of the coolant flowing through that hose is consistent with a car at running temp.

From there... should give you an idea of what youre dealing with. I would hold off on replacing the thermostat until you've run out of options.

[Tiluleshpingen]

how is you coolant diluted? 50-50 am hoping. are you using stealership pink g12

[LakeTahoeQuattr]

Did you install it the right way? Dot up at the top?

Yes I have done several 2.7t timing services, no problems.

I would likely start with a full empty/fill of the coolant system again using the vacuum tool to ensure it's full. Afterward you can also check for air by opening the relief port on the coolant line just to the right of the power steering pump, forward of the afterrun coolant pump. Its a 6mm hex nut with a copper washer. Crack it open and make sure coolant comes out as thats the highest point of your coolant system.

I am going to do this next, full drain and fill. Last time I tried to suck with the vacuum tool the coolant that was in there. I go thru coolant with these audis like it is free. I have never touched the 6mm bleed nut on the block, it is not however the highest point on the cooling system, the heater hose is. I don’t understand the benefit of bleeding from here but it is well worth the try…

how is you coolant diluted? 50-50 am hoping. are you using stealership pink g12

Oh yea, one gallon at a time from the dealer. They give us “forum member” discount so it comes out to like $17.50 which I think is hella cheap.

[alphaVR]

If its not THE highest point, its the highest on the engine for sure and thats why it's there. The upper radiator hose would bleed the air into the coolant reservoir. Heater core could have an air pocket but if you do a full drain, vacuum check, and vacuum fill using the tool, you all but guarantee there will be no air pockets. Checking the bleeder is just good practice to make sure the engine itself doesn't have any air left floating around in the system.

[blitz2190]

just be careful putting it back in they strip very easily.

[LakeTahoeQuattr]

Some updates but no guaranteed answers yet. I replaced the CTS again and bled off the coolant again with the Schwaben bleeder. Coolant rises quicker and heat comes on quicker. However this was tested on a 55DegF day, not 20. But, when driving down the grade from Tahoe to Carson (30 miles of braking) my coolant temp maintained. So maybe all this time it was a simple bleed. I hope to report with a true warm up time when I have another cold morning to know for sure. Thanks for everyone's input here...

[rguil]

It isnt the damn thermostat!

[LakeTahoeQuattr]

So just to close the book on this thread and report my solution.

I replaced the CTS with another CTS. Old one looked pretty used for 40k miles. I then sucked the bubbles out with the vacuum filler for about 3 minutes. I was surprised at how much air is left in the system after just a normal coolant fill from the top.

The problem has completely gone away, not only does the needle rise up to middle after the normal amount of driving time, but the heat comes with it. Much faster than before. I think the mixture of the new CTS with the vacuum bleeding solved the problem. T-stat is good...

[S4gasm aka LOTR]

So just to close the book on this thread and report my solution.

I replaced the CTS with another CTS. Old one looked pretty used for 40k miles. I then sucked the bubbles out with the vacuum filler for about 3 minutes. I was surprised at how much air is left in the system after just a normal coolant fill from the top.

The problem has completely gone away, not only does the needle rise up to middle after the normal amount of driving time, but the heat comes with it. Much faster than before. I think the mixture of the new CTS with the vacuum bleeding solved the problem. T-stat is good...

Like i said from the very beginning, you had air in the system. You're welcome ;)

[LakeTahoeQuattr]

Like i said from the very beginning, you had air in the system. You're welcome ;)

Correct. I was never able to fully bleed it with the gimmic heater hose bleeder.. That vacuum filler sucked bubbles out for 3 whole minutes. I was really impressed and so extremely pleased. Thanks

[ElementR]

I have bled my system several times and never had any problem with following the factory bleed procedure. Air will find the highest level which is the heater core in the B5. That little bleed hole on the heater hose is there for that reason and any entrained air from the engine/radiator will vent into the bottle so after some miles on the car, it will find its way into the bottle. Then you just top off the bottle and you should be fine unless there's a leak.