BrooksB9

Hope everyone is fine.

Car has been running amazing lately considering its peak summer (30 degree C weather)

So today for maybe the first time I heard the fan running without the AC as I drove home from work.
The fan kept running after I parked which I found very odd.

Let the car sit and cool down maybe 2 hours.
Just started it again and the fan ran from the get go and temp showed 90 which I found odd because the car does cool down fairly quickly.

Noted coolant below min so I topped it up close to Max.
Took it for a drive and when I stopped at the stop light I noticed the temp gauge was hitting close to max 180C but no warnings on Dash.

Panicked and started driving back home and temp gauge kept going up and down between 180C and 90C and fan kept going on and off.
Could it be a sensor or something? Because fan runs and temp drops back to 90C within seconds so it's not gradual. Makes me wonder if the car is actually overheating?

Note that car has done 140k kms and Water Pump has never been changed at least in my ownership and I have owned it since 60k kms.
Car does go through some coolant gradually (falls below min every 1000kms) so might be a slow leak in the plastic water pump but nothing else.

Experts please help. Hopefully I don't go nuts trying to diagnose this like last time when it was the starter!!

BrooksB9

Ok I scanned the car with OBDEleven. No fault codes. Brought the car up to temperature and it did overheat.
Here is the live data:

This is at initial start and idle:
Coolant temperature - 100 - 105 degree
Coolant circulation pump, activation - 10%
Coolant temperature at engine start - 81.7 degree
Coolant temp at radiator output, unconditioned voltage - 3.047 v - 3.531 v
Coolant temperature at engine outlet, unconditioned voltage - 0.701 v
Coolant temperature at radiator outlet, actual value - 20.1 degree
Coolant temperature at engine outlet, specified value - 105.7 - 108.7 degree
Coolant temperature at radiator output, specified value - -48 degree
Coolant difference between engine an radiator - 87.0 degree
Coolant fan 1, activation - 10.16%
Coolant fan 2, activation - 10.16%

This is after 2km drive and at idle:
Coolant temperature: 110 - 115 degree
Coolant circulation pump, activation - 10%
Coolant temperature at engine start - 81.7 degree
Coolant temp at radiator output, unconditioned voltage - 0.605 v to 1.599 v
Coolant temperature at radiator outlet, actual value - 69.4 degree
Coolant temperature at engine outlet, specified value - 112.5 degree
Coolant temperature at radiator output, specified value - -48 degree
Coolant difference between engine an radiator - 42.7 degree
Coolant fan 1, activation - 89.94%
Coolant fan 2, activation - 89.94%

@SMac770

SMac770

There's nothing wrong with 115°C. That's the design target to turn on the fans and for the Gen3 in the B9. 105°C was the fan kick on for Gen2 in the B8, while 105°C is the target coolant temp for Gen3 when at low speed/load. That you run up the temp and then come to a stop and idle (like a drive thru), yeah, the temp will heat soak and eventually the fans will kick on. But none of that is an overheat.

As for a "180°C" reading, that seems a bit odd. Maybe some issue with the coolant temp sensor? I wouldn't trust anything on the dash for a temperature reading; always use the measuring values via a scan tool.

BrooksB9

Thank you SMac for your message!
My apologies I meant to say 130C (the max temp stated on the heat guage on dash); not 180C

I guess I am concerned because I have never seen the car temp increase between 90C (the mid mark)

The numbers below are the ones that seem wierd to me:

• Coolant temperature at radiator, actual value - 22.3C (too less?)
• Coolant temperature at engine outlet, specified value - 114.7 (which I am guessing is read by engine block coolant sensor)
• Coolant temperature at radiator output, specified value - -48 degree (can’t seem the figure this out. Is rad hose sensor bad?)
• Coolant temperature difference between engine and radiator - 93 degree (seems like a lot? Did come down but not a lot. Lower rad hose seems cold)

A part of me is tempted to replace both sensors and water pump as preventative maintenance anyways but now I am thinking if the system needs to be bled properly because I did top up coolant as it was below min mark.

SMac770

The G62 coolant temp sensor is in the engine. The G83 coolant temp sensor is on the radiator outlet. So basically the G83 tells the ECM if the coolant is being sufficiently cooled by the current radiator fan setting. The G62 is the one determining how hot the engine is and if the managed thermostat needs to direct any to the radiator.

I'm not sure there's any point in a specified value for the G83. It's a computed target, not a measurement. So "as cold as it can get" is the logical interpretation of that value. Difference between G62 and G83, why bother with a value. Anyone can do G62 minus G83.

I'd still say never trust displays on the dash. Audi hasn't presented a legitimate presentation of the coolant temp on the dash in decades. But if the G62 (coolant temp engine) measuring value was over 115°C, then yeah, I'd be wondering why. The fans should kick in at ~115°C and the thermostat should route coolant to the radiator, and it should bring that temp back down to target or below without issue. But if you're also loading the air through the radiator with A/C cooling, maybe it's just too much in that hot ambient?