Coolant reservoir overflowing

[hkdolphins]

My coolant reservoir overflowing sometime, just repalced the reservoir and still overflowing. New OEM radiator & hose installed 10K miles ago(3 years), just repalce new reservior, cap and clamp. Didnt see any leak, only find white powder under the reservior.

What cause the overflow? thanks

[Zolli]

My coolant reservoir overflowing sometime, just repalced the reservoir and still overflowing. New OEM radiator & hose installed 10K miles ago(3 years), just repalce new reservior, cap and clamp. Didnt see any leak, only find white powder under the reservior.

What cause the overflow? thanks

My guess would be either a stuck-closed thermostat, clogged radiator (unlikely since you recently replaced it), or sadly, the head gasket. The coolant is probably boiling off, rather than simply leaking. Does your car overheat?

[VinnysS4]

I can second that. Either you have way too much coolant in the system, or the coolant level is rising due to overheating or air infiltration into the cooling system. I would buy a cheap noncontact laser temperature gage and when this happens, check the temperature of the upper and lower radiator hoses and see how far apart the readings are. Another possibility would be a failing water pump that the impeller is spinning on the shaft. Our water pumps are driven off the oil pump gear assembly so I am not sure how that would come into play with the impeller blade.


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[luvsspeed]

Check the cap. I had a new cap not hold pressure and it allowed the tank to boil over.

[hkdolphins]

My guess would be either a stuck-closed thermostat, clogged radiator (unlikely since you recently replaced it), or sadly, the head gasket. The coolant is probably boiling off, rather than simply leaking. Does your car overheat?

never overheat, the coolant is clean. its obviously coolant going out from the reservoir escape around the cap and went to the bottom.

[hkdolphins]

Check the cap. I had a new cap not hold pressure and it allowed the tank to boil over.

how can i know the cap is bad?

[hkdolphins]

I can second that. Either you have way too much coolant in the system, or the coolant level is rising due to overheating or air infiltration into the cooling system. I would buy a cheap noncontact laser temperature gage and when this happens, check the temperature of the upper and lower radiator hoses and see how far apart the readings are. Another possibility would be a failing water pump that the impeller is spinning on the shaft. Our water pumps are driven off the oil pump gear assembly so I am not sure how that would come into play with the impeller blade.


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Vinny, thanks for your suggestion. I really don't know when it happened. Replaced the reservoir 30 miles ago, shop fill 3/4 beween min and max (about 1/2 over the middle and high), cleaned the valve cover. Found coolant only at the center line. and white powder on top of valve cover. Really hate to keep checking and add coolant.

[ShootingBrakeS4]

Happens to mine too, done trying to figure out this engine. All of the problems are intermittent too which makes them even harder to diagnose. I’m driving it till it explodes, f%$k it

[hkdolphins]

Happens to mine too, done trying to figure out this engine. All of the problems are intermittent too which makes them even harder to diagnose. I’m driving it till it explodes

I totall agree its "intermittent", that's why the shop advise me keep driving until related issue came up to diagnose it.

[Zolli]

Vinny, thanks for your suggestion. I really don't know when it happened. Replaced the reservoir 30 miles ago, shop fill 3/4 beween min and max (about 1/2 over the middle and high), cleaned the valve cover. Found coolant only at the center line. and white powder on top of valve cover. Really hate to keep checking and add coolant.

Vinny is never wrong, I’m glad he chimed in. Definitely follow his suggestion.

If it’s pretty obvious that the coolant is coming out from the cap, being pushed out when it reaches boiling (but car isn’t over heating), then it probably IS the cap like luvsspeed said. Did you get a genuine Audi cap?

I got non-Audi PVC valve and vacuum pumps once. They were OEM suppliers, but they still failed after a couple of months. I paid extra for the genuine Audi ones, and I haven’t had a problem since. That was nearly two years ago, now.

[badger.]

Happens to mine too, done trying to figure out this engine. All of the problems are intermittent too which makes them even harder to diagnose. I’m driving it till it explodes, f%$k it

hahahaha I am getting closer and closer to this every day with my sedan. I've had it 6 years and its at 217k miles now. it is tired and moody

[luvsspeed]

how can i know the cap is bad?

The o-ring on it could be damaged. I had an aftermarket cap on for about a month and I got a boil over one day, once I changed back to a OEM cap it never happened again.

[VinnysS4]

Vinny is never wrong, I’m glad he chimed in. Definitely follow his suggestion.

If it’s pretty obvious that the coolant is coming out from the cap, being pushed out when it reaches boiling (but car isn’t over heating), then it probably IS the cap like luvsspeed said. Did you get a genuine Audi cap?

I got non-Audi PVC valve and vacuum pumps once. They were OEM suppliers, but they still failed after a couple of months. I paid extra for the genuine Audi ones, and I haven’t had a problem since. That was nearly two years ago, now.

Well thank you for the kind words. Wish the lady said the same thing. Haha

I can second the non OEM parts. Lots are crap and fail quickly.


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[hkdolphins]

Vinny is never wrong, I’m glad he chimed in. Definitely follow his suggestion.

If it’s pretty obvious that the coolant is coming out from the cap, being pushed out when it reaches boiling (but car isn’t over heating), then it probably IS the cap like luvsspeed said. Did you get a genuine Audi cap?

I got non-Audi PVC valve and vacuum pumps once. They were OEM suppliers, but they still failed after a couple of months. I paid extra for the genuine Audi ones, and I haven’t had a problem since. That was nearly two years ago, now.

I total agree Vinny is very knowledgeable and thanks all his input. nearly all my replacement parts are Audi one or OE (not OEM) one. Acutally i wasn't happy about this cap which i ordered from europaparts.com. It's an OE one (not Audi) one and i guess may be i just order a new Audi to see. thanks

[Jdsb6s4]

I received a coolant refresh package from ecs. I wanted to go OEM but my buddy said l save $100. Never again! The viaco cap doesn’t even screw onto the viaco reservoir so I threw that away and the coolant temp sensor wouldn’t even clip in cause it wouldn’t go in far enough. I forgot the name of the off brand piece. At least the thermostat and housing were OEM.

[hkdolphins]

The o-ring on it could be damaged. I had an aftermarket cap on for about a month and I got a boil over one day, once I changed back to a OEM cap it never happened again.

I replaced the o-ring with Audi one on the OE cap year ago and still the same.

[VinnysS4]

I replaced the o-ring with Audi one on the OE cap year ago and still the same.

Do you have access to a bulb style “block tester “? First things first. Let’s eliminate the possibility of combustion gasses making their way into the cylinders causing problems. Autozone around me loans them out. I think you need the fluid. It’s cheap . I can’t imagine the old cap/Reservoir and a new cap and reservoir all going bad.
Do you have a scanner or vcds? You should check the coolant temperature temps regularly when it’s hot and see you what you were actually running as opposed to what the gauge tells you. The gauge is basically a dummy gauge and will report the center of the cage between x and y temp. (i’m not quite sure on our car what the temperature is. ) I have seen the gauge stay in the center and watched the reading jump 20° through VCDS. They make a radiator cap tester that you should be able to screw your cap on and check to see if that is the culprit. I would also poke around engine to see if there are any possible leaks anywhere. Any type of depressurization of the cooling system while it is hot will cause the temperature to rise and can cause too much expansion, Which would put the system above the radiator caps pressure level and would cause it to dump some coolant. The coolant tank leaking may very well be in effect and not the cause of your problem.


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