High coolant temp. Help please (sitting on the side of the road content)

I'm not sure whether you can completely rule out water pump. Granted the M water pump is much better than non-M, but it can also fail. There are reports on non-M pumps that the impeller is loose so it may fail intermittently. Best bet is to take it out and inspect it.

Originally Posted by DeclanM3

It was at speeds between 60-80 when it occurred. I could be wrong but don't think a fan failure would make that much of a difference at those speeds?

It all depends on what the coolant temp reached. A large variety of conditions can cause the coolant temp to rise and the fan should come on at a certain temperature to get the air flow up - it's the only option the system has left at that stage.

If the fan doesn't come on due to a faulty sensor, faulty fan motor or dodgy electrical connection or something, then the overheat condition will continue until one or more of the other variables is changed for the better.

I never rule out anything...but I have never (in many decades) seen intermittent mechanical water pump failure.

Originally Posted by Brissyjohn

It all depends on what the coolant temp reached. A large variety of conditions can cause the coolant temp to rise and the fan should come on at a certain temperature to get the air flow up - it's the only option the system has left at that stage.

If the fan doesn't come on due to a faulty sensor, faulty fan motor or dodgy electrical connection or something, then the overheat condition will continue until one or more of the other variables is changed for the better.

I never rule out anything...but I have never (in many decades) seen intermittent mechanical water pump failure.

Coolant temp got up to 114 from normal running temps (88-92) in less than 2 minutes. Do you think a fan kicking in at 60-80ks an hour would've prevented that? (serious question, I am only just learning about cooling systems).

Yes, because if those temps are an overheat condition, then it should have come on prior to that to control the temp. That fan can shift a hellava lot of air through the radiator.

Your car seems to be doing fine if the coolant level is OK and the temp has been OK ever since. I think you indicated the coolant was flushed in the last year(ish) anyway. Every 3-4 years on BMW coolant should be OK.

I don't know what would be a "trigger' temp for the fan, but it would normally be on before you noticed any abnormally high reading on the temp gauge.

114 is high but not excessive with aircon on under high load (low speed, high temp etc.) or stop/start conditions. Did the cluster temp gauge actually get into the red zone and light up the warning light?

Originally Posted by Brissyjohn

Yes, because if those temps are an overheat condition, then it should have come on prior to that to control the temp. That fan can shift a hellava lot of air through the radiator.

Your car seems to be doing fine if the coolant level is OK and the temp has been OK ever since. I think you indicated the coolant was flushed in the last year(ish) anyway. Every 3-4 years on BMW coolant should be OK.

I don't know what would be a "trigger' temp for the fan, but it would normally be on before you noticed any abnormally high reading on the temp gauge.

114 is high but not excessive with aircon on under high load (low speed, high temp etc.) or stop/start conditions. Did the cluster temp gauge actually get into the red zone and light up the warning light?

It got into the red as I turned the car off. The warning light didn't come on

I'm certainly not worried about any damage to the engine from the spike in temp as it was so quickly and not a huge spike. I'm just worried about it reoccurring as it ruined my drive with a bunch of super cars

^ reading the codes should help you rule out any electrical issues such as what Brissyjohn is saying. If the computer could not activate the fan or had some other such issue on a sensor or anything that sends data back to the computer, it will be there.

Be really careful guys, if you ever see your temp gauge move at all, stop immediately, especially on an E46 with that moronic buffered gauge. Don't let it go anywhere near red.
My old 535i overheated on me once, rapidly climbed to three quarters (in about thirty seconds) and I turned it off. Three weeks later we discovered blown head gasket :*( Now the old bitch is sitting in pieces in my yard. I'm morbidly afraid of that gauge now.


This is a good time to do a complete cooling overhaul (assuming it hasn't already been done?). Five hundred bucks to do everything except the radiator (which lasts ages). It should be done anytime from 80,000km/6yrs onwards anyway.
I did mine at 160,000km/8yrs and everything was leaking/failing/stuffed except the water pump which someone had already replaced.

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Reading the codes is an awesome idea, that might indicate some sort of electrical issue with the temperature sensor or fan issue, though I believe you have a mechanical fan on the M3? I've got a Peake Reader if you wanted to try that, though a proper laptop set-up is probably easier to decipher.

How long ago was the coolant changed? The suggestion that an air lock popped up in the wrong place is the most likely possibility so far. They'll cause sudden rapid overheating and then disappear leaving you wondering what happened.

Sorry for what happened -

I can't help but think
- revving it highish for a while
- climbing uphill mountains
- full full full blast aircon (with the windows open ?! You know opening the windows with aircon makes the Ac continuously work harder and puts more load)
- a very hot day

All contributed to your high engine temps.

The e46 manual even says temps between blue and red are normal.

BUT I still think something is off - perhaps water pump ? (don't thermostats usually get stuck in open position)?

Good luck with the diagnosis!

Maybe there is pocket of Air in the coolant system ..... not enough to effect normal driving but when going UP HILL (engine/car on angle), hot day, Aircon running .... all contribute to this?

When was the last time you had your Radiator Service/Flush? My old GTR did that once, i tried all sort of things including new thermal stat, fresh oil, coolant ..... at the end it was the TOP TANK of the radiator that clogged up.
......then again, it's only a shitbox gtr and not an M3.

Getting the codes read would be a very good starting point.

If no codes applicable, then start looking for mechanical problems (thermostat, water pump etc) or fixed things like radiator, expansion tank, hoses etc.

I'll try get the codes read. I've got all the equipment at home just haven't set up the laptop yet. Shall try do this on my time off for Christmas..

The pocket of air sounds logical but I think it would've presented itself before. I have an Intravee II that logs trips including max coolant temp and I keep a pretty close eye on this when I go on spirited drives. It's never gone above 95 before and that was at the track. Done plenty of up hill driving too. Granted, this was on a pretty steep hill when the coolant temp rose but I've driven in very similar scenarios before. I've driven up Nebo before and had to drive above 4,000rpm the whole time to prevent a driveshaft vibration I had. No issues with coolant then so I think it's something mechanical / electrical that has failed.

Originally Posted by KOpower

Sorry for what happened -

I can't help but think
- revving it highish for a while
- climbing uphill mountains
- full full full blast aircon (with the windows open ?! You know opening the windows with aircon makes the Ac continuously work harder and puts more load)
- a very hot day

All contributed to your high engine temps.

The e46 manual even says temps between blue and red are normal.

BUT I still think something is off - perhaps water pump ? (don't thermostats usually get stuck in open position)?

Good luck with the diagnosis!

I do realise this but how else am I suppose to stay cool when it's 37 degrees outside and hear the symphony that is a GT3 RS, 430, 360, E60 M5, E92 M3 and many more all at WOT!

Originally Posted by DeclanM3

It was at speeds between 160-180 when it occurred. I could be wrong but don't think a fan failure would make that much of a difference at those speeds?

^Lolz !!

Anyway Declan - I am sure it's something small and easily fixable -
Dont give up on that BMW yet!!

Originally Posted by KOpower

^Lolz !!

Anyway Declan - I am sure it's something small and easily fixable -
Dont give up on that BMW yet!!

I'm test driving an M135i on Friday. Will be keeping the M3 though!

The M135 got an amazing review from Jeremy Clarkson compared to the other cars in it's category. I do agree with him that the M badge should be reserved for proper ///M Cars though.. Pretty sure I read a 0-100 in 4.9? Some of the other details I read up on seemed pretty impressive too. Still trying to get my eyes used to seeing the 1series hatch though, it's slowly growing.

Give me a buzz and let me know what you think Dec

Originally Posted by DeclanM3

I'm test driving an M135i on Friday. Will be keeping the M3 though!

I'm getting one (M135i) on Monday...after the Lotto win on Saturday night.

Well my overheating was a bung fan clutch. It was semi locked but turn it a few times and it would spin without resistance and not pull any air thru.

How did your M135i test drive go?