How hot (Water temperature) is yours at highway speeds?

[Tony B]

(I know that there is no water temperature gauge on these cars so access to the hidden menu is required, if you do not have the steering wheel with shift lights/temp readouts in the rim, or the M Drive Analyser dongle/app)

Long story, medium short summary.

I noticed my M3 had started to run quite cool (water temp) at highway speeds, as well as taking a long time to warm up at urban speed.

I timed a warm-up from cold start - 16 minutes of urban driving, 12C ambient temperature, to reach 80C coolant temperature. Failing to get above 75C at highway speeds.

Fuel consumption (UK gallons) was down to 20.x mpg, from the more normal 23.x that I had been getting

After a lot of persuasion my dealer changed the water thermostat (under warranty).

First lengthy drive (60 miles) returned an average of 24.1mpg (yay...) but the coolant temperature is still only around 80C at constant highway speeds (with oil temps in the low 90s).

Surely this is a bit low?

I used to see high 80s in similar circumstances.

I thought that the water thermostat was supposed to open at 86C?

[RocketyMan]

If you were to replace the thermostat yourself, you'd notice that the activation range is stamped 79C on the stock thermostat--kinda neat.

At any rate, 80C would seem the correct temp for operating conditions give or take. As far as oil temps, 90C would seem correct for a cruising temp under low power conditions. The stock oil cooler thermostat opens at just above that.

I would wager you have nothing to worry about. The oil temp will take longer to get up to temp in comparison to coolant temp.

[Mr.Zisky]

Mine takes ages to get to the temp as well. Did you time it (or eyeball it at least) how long does it take to warm up after the thermostat change?

[Helmsman]

I measure temps and other bits regularly (due to various reasons). Also replaced Tstat earlier.
Water should go to 78C and stick there as long as air cooling is okay/high way driving. Goes up 80-85C in stop/go and then down quite quickly to 78C once up to speed again. I'd say oil at 90C is low, takes time to get up but should stick just under 100C after a while.

[Tony B]

Originally Posted by Mr.Zisky

Mine takes ages to get to the temp as well. Did you time it (or eyeball it at least) how long does it take to warm up after the thermostat change?

I have not had a chance to do that yet - but will in the next few days.

Ambient temperatures have jumped recently so that might make a difference, too.

[Tony B]

Originally Posted by RocketyMan

If you were to replace the thermostat yourself, you'd notice that the activation range is stamped 79C on the stock thermostat--kinda neat.

At any rate, 80C would seem the correct temp for operating conditions give or take. As far as oil temps, 90C would seem correct for a cruising temp under low power conditions. The stock oil cooler thermostat opens at just above that.

I would wager you have nothing to worry about. The oil temp will take longer to get up to temp in comparison to coolant temp.

Thanks for the feedback.

I have just checked again (lol) on Realoem, which identifies the thermostat as "79CEL" so I should have taken the hint...;-)

I had a lengthy drive yesterday (in 22C ambient) and the coolant temp was generally around high 70s/ low 80s when at speed.

The car felt absolutely great and the engine has such a strong surge at the top end it is a delight.

I do still have to sort out a throttle actuator issue, which is really bugging me, but as no fault codes are present, it will take some further investigation

[RocketyMan]

Originally Posted by Tony B

Thanks for the feedback.

I have just checked again (lol) on Realoem, which identifies the thermostat as "79CEL" so I should have taken the hint...;-)

I had a lengthy drive yesterday (in 22C ambient) and the coolant temp was generally around high 70s/ low 80s when at speed.

The car felt absolutely great and the engine has such a strong surge at the top end it is a delight.

I do still have to sort out a throttle actuator issue, which is really bugging me, but as no fault codes are present, it will take some further investigation

Sounds like it's all sorted.
Thanks for reporting back.