View Full Version : Coolant boiling? A4 2000 2.8L Quattro (AT, CAN)

12-01-2014, 10:31 AM
Hi there, my coolant would hardly reach 70C on normal driving and noticed it is boiling when I stop the vehicule.
There is no coolant leak at all.
I just replaced my coolant reservoir cap but didn't solve it.
Also my engine oil temperature isn't moving at all (even with a OBD2 adapter, no reading available)
Both fans are working

Possible Causes
-Coolant condition?
-Bad reservoir?
-Water pump?

It is actually 0 C outside, gonna reach -15C tonight.
BTW: After driving long highway distance (I'd say 1hour), my coolant temperature was fine (near by 90C)
Unfortunally my coolant and pressure tester are 300km away from home, but im pretty sure it holds it well, just unsure about coolant condition yet.

Thanks you for your help! Much appreciated!

12-01-2014, 11:14 AM
To me sounds like bad thermostat or coolant temp sensor. Start with temp sensor since is easy to replace and cheapest.

12-01-2014, 05:30 PM
Did you replace coolant recently? Was it bled?

Are the bubbles small like coke bubbles? Does it overheat?

Oil temp - check the oil temp sensor plug could've just got disconnected.

12-02-2014, 10:50 AM
I just bought the car, the radiator doesn't look too old.
It never overheat, in fact it's hard to get some heat inside the car!
I doubt it is the CTS because it looks like to show the right temp.

Could it still be the thermostat? Like I said, after very long drive on highway, I managed to reach the 90C.


EDIT: I can't see many bubbles, but you can see and hear the coolant inside the reservoir moving.

12-02-2014, 12:56 PM

You can barely see it but you can hear it. Coolant temperature was at 70C, no heat inside the car (30 minutes drive at -13C outside temperature)
On the same video, on the right side of the engine (near by the thermostat?), you can hear some weird noise, anyone knows what is it?

12-02-2014, 12:59 PM
Im having a very similar issue on my 97 2.8. Takes a while for heat to work. Heat kinda stops if come to a stop for to long.

Avant Nate
12-02-2014, 07:05 PM
Maybe a little stress crack in the reservoir? Usually you'll lose coolant at the same time though. Bleed and/or Pressure test.

12-02-2014, 08:13 PM
Take the two heater core hoses off and then take a garden hose and spray water threw the heater core then back flush it. Put the hoses back on top up the coolant then slightly raise the front of the car with the coolant cap off start car and increase the rpm up and down to take the air out

12-30-2016, 05:49 AM
Just to reply back, replacing the coolant, thermostat with waterpump and full timing belt kit fixed the operating temperature problem (Thermostat was clearly the cause). Coolant is still "boiling", unsure if this is normal or not for these models lol.