temperature issues


Registered User
Hi All

Sorry for the long winded explanation.
Need some help diagnosing a temperature problem on my 2007 audi a3 tdi 170 (BMN eng code).

The issue started when sitting stationary in traffic the temp gauge started to drop down approx 75-80 deg but would increase back to normal 90 deg and then drop again when stationary.

I have changed the following items thermostat and two coolant temp sensors G83 and G62 (one on the thermostat housing and one below the tandem pump). All parts from audi dealer.
I let the car run up tp temp (90 deg) and bled it.

I now have the following issues:
1) Bottom hose cold even with car idling for 3 hrs and a 20 min drive even after many attemps of bleeding. The car does not over heat (eng temp 90 deg and oil temp 82 deg steady).
2) With the heating on high temp and medium fan both engine temp and oil temp start to drop gradually and so does the hot air from heater. With heating off both eng temp (90 deg) and oil temp (80 deg) rise and stay steady but bottom hose still cold even after many attempts of bleeding. The car was running for 2 hours.

I have tested both new and old thermostats in a pan and both open at approx 86 deg.
I have run the car for 2 hours without the thermostat and all is fine with temperatures engine at 90 deg and oil at 80 deg steady even with the heater on but have no heat from heater.
I have run the car for 3 hours with fuse 8 out and thermostat back in and can get the thermostat to open only when oil temp gets to 87 deg even though engine temp shows steady 90 deg. The engine temp did not go over 90 deg and did not overheat.
Looks like i only get heat with thermostat in place but have fluctuating eng and oil temp and closed thermostat.

I seem to have the only car not to overheat............

Am i missing something


Registered User
Just a daft question, does the temp light come on at all?

wondering if it could be the signs of a cracked cylinder head like on my a3


Registered User

Still not found a cure yet. I have been driving the around town with no issues with engine temp gauge sits at 90 and the car warms upto 90 with in 10mins of driving, the oil temp rises as normal and i have good heating.

There is no temp light coming on. The head was replaced by Audi 4yrs ago to a REV C and i have no signs of losing coolant. or overheating.

Could someone be so kind and check on their car once it has reached 90 deg let it idle and put the heater on full temp and full fan speed to see if the temp gauge and the oil temp on the DIS start to decrease.
Another thing to check is to see at what oil temp the bottom radiatior hose starts to warm up.

I will be going on a long test drive over the weekend and report.

Many thanks


Well-Known Member
VCDS Map User
My old golf bkd did cool down on idle. I remember I left all the windows down one night and it pished it down. Ran it round the block to get the engine hot then let it idle with the blower on to dry the inside out. Temp gauge dropped. Diesels are more heat efficient and as such take ages to warm up compared to a petrol so it makes sense the temp drops when idling.

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Registered User
I don't think you have a problem. As said before Derv's run at a cooler temperature anyway, especially in winter.


Audi A3 2010 Sportback 2.0 TDI 170 (CBBB engine)
I don't think you have a problem. As said before Derv's run at a cooler temperature anyway, especially in winter.
I agree with Sooty. When the general outside temperature dips below 10c, I notice my car struggles to get to 90C (according to the temperature gauge which I assume is not totally accurate) unless on a very long run or in stop/start traffic.


Registered User
My 2005 bkd Sport sportback does the same .Did a 7 mile journey this morning, outside temp 1.5c .Parked up with the engine still running for about 15 minutes .Temp drops back from 90 to about 80 degrees.


Registered User
Many thanks for the replies. I have just come back from round trip to stanstead and car is running with no issues.
It must be normal and was nothing ever wrong with it, just me being over concious.
Never mind at least it has a new thermostat and fresh coolant now as the original was a 2007 date code.
Many thanks again.