Engine overheating when driving/idling - What to check?

[quattro-nick]

when i'm done with the filling i start the engine and let it come on temp
when engine is on normal temp ,normaly the thermostat is open and the 2 radiator hoses or warm
afterwords a check my water level
if there is some air stuck in the engine block or around the thermostat it wont go open.

[Jonas_R]

Is there anybody that can check what the G62 temp sensor is at normal driving and at idle when the fan kicks in?

Thanks

[bluequattro]

On kv engines I used to try to fill the block directly from the top. Then do from expansion tank.
Plenty s2s running without aux rad so I'd be surprised if that was an issue unless in traffic.

[Jonas_R]

So changed thermostat, but both opened up in boiling water.

Changed back to my old mfts.

Bleed using Rusty procedure.

All is fine now.

[220bhp]

I had a problem with my engine getting hot.
the fan was not cutting in quick enough on fast speed.

[steverrquattro]

thermostate should be in this way:

the reason i asked for a auxillary radiator is, because if it is a bad one, the hot water gets bypassed over the main radiator and therefore it overheats

Just noticed that on the VAG diagram the thermostat is shown fitted the other way. As my engine seems to be running a little hot, it will be interesting to see which way round I fitted it last time.

https://audi.7zap.com/en/rdw/audi+80.../1/121-121015/

[SteveH]

I fit mine as per the picture above. There are stats that are supposed to fit our motors that don't close the coolant channel to the head. Check you have the right stat which opens enough to close the head coolant channel sufficiently. I measured the opening requirements and I think it was approx 33mm. I didn't make a note of the dimension, so measure from the mounting face to the round opening behind and check your stat has the expansion to pretty much close the opening. There are stats which only open 25mm with the correct part number, which may lead to coolant preferring the route through the head and not through the radiator.

[steverrquattro]

Fitted new Mahle OEM thermostat yesterday and the previous one was as per the picture, so it was the correct way round. I even fitted it vertically! The one that came out was not OEM.

Ran the engine, lifting the expansion tank and bled through the main radiator as the car has no auxillary radiator. The thermostat opened up and the hose was hot at the thermostat housing and also at the bottom of the radiator. Radiator bottom and top temps are fairly consistent.

I took some readings as I'd read about the radiator being the problem in some cases. Here's what I got:

Thermostat housing 91 Celcius.
Bottom of radiator 93 Celcius.
Top of radiator 98.9 Celcius.

Fan kicks in for 40 seconds periodically.

What do you guys think to the above temps?

PS Can smell antifreeze in the car so think the heater matrix may be on its way which may be causing the system to loose pressure?

[AndyP]

I don't know what the normal temp drop from top to bottom of the rad is, but that doesn't seem like a lot? how old is the rad?

[steverrquattro]

I don't know what the normal temp drop from top to bottom of the rad is, but that doesn't seem like a lot? how old is the rad?

The radiator is an alloy large racing type and the flow is good at entry/exit points. I think the issue is that I have a small leak somewhere, so a loss of pressure as I can smell the antifreeze. Also bearing in mind that the heater matrix is 38 years old, it's probably due for changing.

[newsh]

I’ve had similar issues when the pressure release valve in the coolant header tank cap went bad, worth trying a new one.
Are your windows getting greasy inside? If so the matrix is definitely gone.

[newsh]

Also had a crack in the bottom of the header tank too, that was hard to find as the coolant ran down the hose from the bottom and dropped under the middle of the car.

[Error404]

I wonder if it’s a China POS radiator core that is half as efficient as an OEM - plenty of those about.