7A engine overcooling Coupe Quattro 1990

[willmears]

Hi all,

I'm currently having an issue with my early 1990 Audi Coupe Quattro 20v 7A.

It seems to be overcooling. When driving at slow town speeds it will nearly temp however, at A road speeds (60mph) the temp gauge drops to about 1/3 (my gauge doesn't have numbers but i presume about 70deg).
It has an aftermarket 40mm ally rad with the additional rad removed.
The heater works and runs hot.

Checking the top hose it seems to agree with the gauge, never going above 80.
Tried a new thermostat to no avail.
Is this just a thing of owning an older car in UK winter? (0°C)
No error codes.

Any ideas would be helpful.

[Tractor Dave]

I wouldn't worry too much. Back in the day you used to see people covering the grill vents in cold weather. You could try covering half and see what difference it makes.

[willmears]

I have thought that.
I was just wondering if there was any other behaviour going on.
Upon probing the lower hose from cold, it seems to get quite warm (65ish deg) but never reaching the magical 87deg that the thermostat is supposed to start opening at.
This could be through me measuring with an IR thermometer on the pipe but seems a bit odd no?

[psiconauta911]

Hád the same problem with my 90 20V because the lateral radiator shroud was missing and the MFTS was getting cold with air flow, solved by puting a piece of rubber pipe around ir.

[willmears]

I see, so it was over cooling of the temperatures sensor not the overall cooling system?

[psiconauta911]

Yes

[K Simmonds]

If you've tried two 87c thermostats that you've checked in a pan of water with proper a thermometer not a heat gun then that's what the engine should running at and I really wouldn't worry. What does the oil temp gauge read once you've gotten the car fully warmed up? It should be in the 80-90c range unless you're really cutting on.

Heat gun readings on the outside of hose's do not accurately reflect the temp of the water inside due to radiated heat loss. I can just about hold onto the bottom hose of my RS2 or V6 C4 using my my bare hand for a few seconds with the temp gauge reading 90c which would burn me instantly if that what the exterior temp actually was.

You could have a duff MTFS or it could be getting over cooled by air flow, though the rubber boot on the sender connection should really be enough to protect it, but if psiconauta911 has found extra insulation helps then it's certainly worth trying.

To improve engine access I stripped every bit of plastic out of my 3B engine bay apart from the air box intake duct's which are really important and never experienced this problem under any driving conditions but perhaps that was due the car being turbocharged and having high under bonnet temp's.

Oh yeah, to the forum, it's nice to see new members.