Hello again! 1st car "issue" with heating

[Alais DJA]

Hope all is well with all the ASN members.

To the matter at hand -

The A3 has decided to start overheating recently and i cant figure why?

Drive normally 30 - 40mph it's fine sits at 90oC

Take it up to 40+ and the needle starts going up....to eventually engine temp warning display

I took it out yesterday for 10 minutes and took it up to 50mph and it registered at 120!

Popped the bonnet and it's barely hot

No coolant loss or leaks

Oil level honey colour, all levels fine, no leaks

Can see coolant being pumped around.

After it registers 120oc, i turn off, count to 10, and it goes straight back down to 90oC

Any ideas...im hoping its just oil temp sensor

 

[colicabcadam]

water pump, or your thermostat in stuck shut (which is rare), or possibly an air lock in the cooling system

let the car warm up with the coolant tank cap off and let the bubbles escape whilst squeezing the coolant hoses

 

[colicabcadam]

ps does the radiator feel warm at all ?

 

[Alais DJA]

Rad not warm

And strangely putting the heating on doesnt make any difference

I can see coolant being pumped through the system when its on, and it was low yesterday after i had to limp it home so water pump must be still working?

 

[aragorn]

My water pump failed the other day with very similar symptoms.

Leaving the garden centre after lunch, I noticed the guage move slightly past 90, probably 92-93 indicated, and instantly thaught "thats not right" so brought up the climate display and it was showing 105c (after having been parked for half an hour and only running for about 3 minutes...)

Seemed to be RPM related. 30mph in 5th with the heaters blowing full hot and it would hold at about 100c on the climate display and the gauge would remain pointing at 90.

Change to 3rd and continue driving steadily at 30, and the temp would instantly start climbing. Highest i saw was 105c, but thats because i was watching it and being careful. I can only imagine it got quite a bit higher than that, because before i stopped for lunch i'd given it a bit of welly overtaking people etc and noticed the oil temp was up to 100c when i parked up!

I guess at higher RPM's the impeller starts to slip on the shaft, whereas at lower RPM's theres less force on it so it grips fine.

Changed the pump yesterday morning and sure enough the impeller had split.

 

[colicabcadam]

if the rad is not warm, it'll be the thermostat or the water pump

 

[Alais DJA]

My water pump failed the other day with very similar symptoms.

Leaving the garden centre after lunch, I noticed the guage move slightly past 90, probably 92-93 indicated, and instantly thaught "thats not right" so brought up the climate display and it was showing 105c (after having been parked for half an hour and only running for about 3 minutes...)

Seemed to be RPM related. 30mph in 5th with the heaters blowing full hot and it would hold at about 100c on the climate display and the gauge would remain pointing at 90.

Change to 3rd and continue driving steadily at 30, and the temp would instantly start climbing. Highest i saw was 105c, but thats because i was watching it and being careful. I can only imagine it got quite a bit higher than that, because before i stopped for lunch i'd given it a bit of welly overtaking people etc and noticed the oil temp was up to 100c when i parked up!

I guess at higher RPM's the impeller starts to slip on the shaft, whereas at lower RPM's theres less force on it so it grips fine.

Changed the pump yesterday morning and sure enough the impeller had split.

Yeah sounds about the same scenario.

Is it difficult to change over the waterpump, what sort of timescale to do etc...

 

[aragorn]

Took me a morning. That was on an A4 though, completely different to an A3! No idea if the A3 is easier or harder, but i wouldnt think it'd take much longer than 3-4 hours.