A3 1.6tdi (2010) overheating coolant warning light

**Jblakes84** · 22-01-2020,10:26 AM

Cheers. Will have think about getting it done.

**jonathanfenton** · 22-01-2020,10:41 AM

Running heater on full technically cools your engine a little as some of the coolant goes through the heater matrix. So turning it off is why your car suddenly overheats. Keep it on. Let us know how you get on.

**Fexo** · 22-01-2020,12:29 PM

Originally Posted by jonathanfenton

Running heater on full technically cools your engine a little as some of the coolant goes through the heater matrix. So turning it off is why your car suddenly overheats. Keep it on. Let us know how you get on.

Yes, I had a similar problem with my old A3 and managed to get home by opening the windows and putting the fans and temperature up to maximum; I didn't really want to stop on the Heathrow perimeter road having done it once when the clutch went (police are there very fast!).

**Jblakes84** · 22-01-2020,12:41 PM

No, it's the other way round, the car overheats when heater is on full, the car cools when I turned it off and open the window.

**Crasher** · 22-01-2020,10:18 PM

That doesn’t make sense, does it lose any water by blowing it out of the expansion tank?

**VAG-Abound** · 22-01-2020,11:58 PM

Originally Posted by Jblakes84

No, it's the other way round, the car overheats when heater is on full, the car cools when I turned it off and open the window.

Is there a fuel powered auxiliary heater that could be turning on when it mistakenly thinks coolant is cold but heat is needed in cabin?

My other thought is some form of changeover valve that is trying to take pumped water through heater matrix which is blocked. Turning heater off takes water through open path that bypasses heater. No idea if such valve is installed though.

**jonathanfenton** · 23-01-2020,12:09 AM

Originally Posted by VAG-Abound

Is there a fuel powered auxiliary heater that could be turning on when it mistakenly thinks coolant is cold but heat is needed in cabin?

My other thought is some form of changeover valve that is trying to take pumped water through heater matrix which is blocked. Turning heater off takes water through open path that bypasses heater. No idea if such valve is installed though.

Only “valve” would be the thermostat.

**Crasher** · 23-01-2020,12:31 PM

They have a supplementary electric water pump which is prone to failure, that could be influencing it but I would still like to know if it is losing coolant out of the tank cap.

**Jblakes84** · 24-01-2020,05:55 PM

Cheers all for replies, no the coolant level hasn't moved, so not a leak anywhere.

How do I tell if I have an auxiliary heater, as I've no clue what one is.

Regards James