B5 a4 aeb overheating

[ert]

So long story short. Had "fun" and drove the car 130+ kmh/80mph on country roads and at some point noticed that the temp gauge is creeping up to 100C. Drove home slowly while keeping eyes on the gauge and when i got home turned off the car. It spit about 3-4 liters of coolant out through coolant reservoir overflow. I let it cool down and filled the reservoir and took a low rpm cruise around the block, the temp gauge stayed nicely below 90C like it is supposed to. Took it to a highway and did normal drive of about 10km, again everything was OK. Let the car run at idle for about 30min again ok, everything was fine and the temp stayed below 90.

So now my question is that can it be the water pump failing? Considering that the previous owner didn't take care of the car well it most likely has plastic impeller pump inside which should be about 4 years and 80 000km old. Or is it something worse? If it was the head the temp should have gone high at idle?

I'd just like to ask opinions from smarter/more experienced guys before throwing money at it. If it's a pump it's no biggie as i was planning to do the belt and the pump anyway.

[Marc]

could be damage to the water pump. could be a partially clogged radiator. the thermostats on these cars generally fail open so my money is on one of those two.

[ert]

Well finally got enough time to change the belt and the pump. The pump was completely fine. I was hoping that maybe it's thermostat partially opening and was about to change it and ran into an issue. As i understand the only way to get the flange off is to remove the power steering pump? Or does someone have a good and easy trick to bypass pulling the front off again?

I guess the car has to sit for another month as i just don't have enough time to deal with it's issues.

-edit-
Well it's probably too soon to party but i finally got the thermostat out (used 1/4 wobble extension) and threw the old motorad and the new gates one into a pot. The old one opened later, slower and much less than the new one. In a few days i'll put the car back together and see whether this is/was just part of the problem or the problem.

-edit2-
Drove the exact same route that i did the last time when the car overheated. Seems like thermostat was the bad guy, it opened (in the pot), but very slowly, then stopped and when the water boiled for some time opened some more, thats probably why the temp gauge never went visibly over 100.

[ert]

Well here i am again. It overheated again (was on the same small road again and drove a little bit over the speed limit/higher rpm's) and spit the coolant out, i refilled it immediately and it sat at 90'C after that. What i did notice is that the electric fan wasn't working at all, and to me it seemed that the viscous fan was also at "idling" speed.

Everything was ok til i got to town and slowed down, on highway the temp sat at 90.

I'm ordering a new fan switch and a new viscous coupling. I guess i have to be ready for the head gasket also, it has already overheated twice during my ownership.

-edit-
Well i looked at the temp gauge scale more precisely and technically it never overheated. It hit about 95C/203F. Why does it shoot the coolant out then?

[ChrisAudi80]

Make sure you replace all fan relays. It could just be that. Are you sure the overflow reservoir is tight? No cracks?

[ert]

Make sure you replace all fan relays. It could just be that. Are you sure the overflow reservoir is tight? No cracks?

Well i did do output test for the fan using the cable-vcds. The electrical fan did work but it looked like only at lower speed, does it have to cycle through both low and high speed with the output test?
I guess i have to check for cracks more thoroughly, when i changed the oil filter and pcv system i had the reservoir at all sorts of angles and it never leaked that way. The fuses are also fine.

[ChrisAudi80]

You should have high speed as well.

BTW, what temp does the coolant sensor show? If the sensor is worn out, it might not turn on the high speed.