HELPPP 03 M3 overheating THE WEIRDEST THING

[saimon69]

Hey everyone and thank you for all of you that will take part in this mystery I'm having. so... let me get right to it!


so, I recently bought the M3 (a month ago and it's a 03, 6sp with 190k miles) and right away (among other things the car needed but not relevant here) did all fluids change (brakes, power steering, diff, tranny & coolant - all OEM BMW) and also replaced the thermostat with an original BMW one. I did it for good measure not because there was a problem.

everything was fine since until this one day, like a week ago, it was a hot day (so cal) and I was driving with AC on, in traffic - but not too bad - and I noticed the temp gauge passed the center towards the 3/4 mark. I started moving again and it went back down and did not go back up for the rest of that drive.

when I got home, sitting in my parking spot (covered), engine and ac on, revving to constant 3000 revs, car overheated again and passed just slightly the 3/4 mark. shut the engine and noticed expansion tank is throwing coolant from the excess hose but also had marks of coolant all over it.

ordered new fan clutch and temp sensor (all OEM) and went to my mechanics (SWR MOTORSPORT - highly recommended if you need one). when I got there (no overheating on the way there - no AC) we looked and realized that the expansion tank "exploded" so replaced that as well (OEM that comes with the new hoses and cap). all was installed but still overheated when AC on and revving it while stationary.

we checked with a temp heat gun the temp on the upper and lower radiator hoses and there was 10 - 15 degrees difference only so we went ahead and replaced the radiator with a full aluminum CSF that promises 25% more cooling and a second coolant flush (BMW 50/50 OEM fluid). at that point, the condenser was air pressure clean and the temp difference with the new radiator came to 20 - 30 degrees between inlet and outlet but still was overheating.

next, we tried to put the OEM DME map without the B-spec tune i have (because I opt for the enhanced cooling and we thought it might doing something it shouldn't). without the tune, it seems like it's taking longer for it to overheat but it eventually did. went back to the tune at that point.

in the meantime Shane (from SWR) replaced the water pump with an all aluminum one, don't remember the brand but it was something he said he's running on his racecar (e36 with S54 swap) and it's a more efficient and durable than OEM. he also replaced the lower hose where the AUX sensor sits along with the sensor (all OEM) and did another coolant flush and it was doing the same!

he then run a similar test on his friends stock e46 m3 with 150k miles (AC on full blast when sets to 59f and revving while stationary) and it overheated same as mine!!!!!!!!!

he then just gave up and said maybe they were designed that way(?). the next day (today - Saturday) he recommended to add water/water and added 2 bottles of redline (like he did on his car) and you probably guessed it by now...it was doing the exact same thing!

I took it home, frustrated like never before. AC was set to 69f, fan speed was in the middle and on the freeway, going 90 in 6th, it went hot on me to the 3/4 again and only cooled down when I let off the gas.
when I got home, same AC temp and fan speed, while waiting for my gate to open (20 sec) it went to the 3/4 again this time while idling. it only cooled down when I pressed the AC button to turn the compressor off and revved it to about 2000 reves to help the water pump to circulate more water and faster.

the only component that wasn't replaced as of now is the auxiliary fan, and that is because Shane run a test on the fan with his scan tool and checked the 3 different speeds he needs to work on and it was as should. also, we compared that test to his friends stock m3 and values were the same.

at this point, I am really lost for words. can't think on what's next to possibly be responsible for that overheating.

BTW, head gasket likelihood was check and denied and the system was bled professionally by Shane in the shop endless times!

so..let me know what you guy's think. could definitely use all the help I could get.

thank you ALL again.

[MIKYZZ4]

Proper bleeding is critical,
check coolant level in the morning, engine cold,
top off to proper level.
Maybe upgrading to a Stewart water pump would improve coolant flow.

[saimon69]

Proper bleeding is critical,
check coolant level in the morning, engine cold,
top off to proper level.
Maybe upgrading to a Stewart water pump would improve coolant flow.

Will check coolant level in the morning and will bleed the system once again.

Will report back.

[dworthy]

Also on the M3's the temp gauge isn't buffered as much as the stock E-46's. I think that the center is 160-200 degrees, and the 3/4 mark is 220 degrees. I would be conserned if you went past the 3/4 mark on the gauge. What is the oil temp looking like during all this?

So as a side note, what was the actual inlet and outlet temps? You can see this info in INPA, ISIT or other BMW diagnostic tools. What I normally will see is about a 50 degree differance between the 2.

[TerraPhantm]

Also on the M3's the temp gauge isn't buffered as much as the stock E-46's. I think that the center is 160-200 degrees, and the 3/4 mark is 220 degrees. I would be conserned if you went past the 3/4 mark on the gauge. What is the oil temp looking like during all this?

Center on the M3 is actually 85 - 95C (185F - 203F). And M3 generally often hangs out at more like 83C, so it's not unusual for the gauge to be slightly below center. It maxes out at 115C (239F). The start of the red zone is at 105C (221F), so the 3/4 mark should be somewhere roughly in the middle of 203 and 221

Proper bleeding is critical,
check coolant level in the morning, engine cold,
top off to proper level.
Maybe upgrading to a Stewart water pump would improve coolant flow.

M3 is self bleeding, and the Stewart pump isn't a thing for it. And in fact, the OE water pump on the M3 is better than pretty much all of the aftermarket options.

First time I've heard of an M3 expansion tank cracking.

[MIKYZZ4]

Sorry, assumed an m54,my mistake.
Yes, an electric self bleeding water pump.
This bit of information coupled with expansion tank cracking,
has me suspecting compression gases escaping into cooling system,
signs of a HG leak, so I would have a cylinder leakdown test performed.