Posted this in the M3 forums but figure i might get some local help too....


So my car has been getting hot lately at first the Auxiliary fan went out so I thought that maybe that’s whas causing it to creep up a bit. So I replaced the Auxiliary fan get the car back and everything seems to be fine till about 30min of driving it starts to creep up again. Difference in overheating and creeping up, if im at a light or in heavy traffic the car stays at about 1 tab over normal but if im driving the wind I guess would cool it back down. Cooling system is fine. Water pump was replaced not long ago, so I can’t figure out what this is....

So I decided to do a compression test to check and see if I may have a small leak or something and here is what is read...

Compression/Leakdown Test Readout:

1- 180
2- 180
3- 179
4- 183
5- 180
6- 184

I've been told that these are low numbers but from what my tech said this is good for an s50 with 153k on it.

So now im thinking maybe I should get my water pump checked/replaced? Sticky thermostat? I can’t figure out what this is....would really appreciate some input....

My bet would be a faulty waterpump. When is it overheating? at a stop? driving? maybe there is air in the cooling system I would make sure to bleed it again.

Your compression numbers seem fine, they are usually around 200s but it all depends on how warmed up your motor was. You just want to makes sure they are within range of each other, which they seem to be.

Classic case of an improperly bled cooling system. I don't know how people have trouble with it, but it seems to trip up many.

Crank the car up cold and open the bleeder screw by the coolant reservoir. If you see bubbles you've got air in your cooling system. Add water to the reservoir until you get it all out. A few revs while the bleeder is open helps. Now normally the system should bleed itself unless there is a lot of air in there.

The other issue is you've got a coolant leak - a pretty big one. How did the plugs look? Do you have to ever add coolant to keep the reservoir up to the fill level?

My bet would be a faulty waterpump. When is it overheating? at a stop? driving? maybe there is air in the cooling system I would make sure to bleed it again.

It creeps up usually when at stop or heavy traffic, starts to cool down when im rolling but never back to normal temps.

Monday a cooler thermostat which Chad already has for me and a waterpump will be be going in....

Classic case of an improperly bled cooling system. I don't know how people have trouble with it, but it seems to trip up many.

Crank the car up cold and open the bleeder screw by the coolant reservoir. If you see bubbles you've got air in your cooling system. Add water to the reservoir until you get it all out. A few revs while the bleeder is open helps. Now normally the system should bleed itself unless there is a lot of air in there.

The other issue is you've got a coolant leak - a pretty big one. How did the plugs look? Do you have to ever add coolant to keep the reservoir up to the fill level?

Im pretty sure Chad has pressure checked and topped off the fluids for me but i can give that a shot....

But there is def no leak. I drive around with coolant in my trunk just in case and its been full since Chad topped it off, so im not exactly sure what it is....

Compression numbers can be affected by so many variables, but overall I don't see anything to worry about. Those are top notch readings, but certainly nothing to be weary of.

Thermostat for sure should be replaced, along with the clutch fan if it does not test strong.

Hey man, now that I read this thread it does sound like it could possible be an improperly bled cooling system. It makes sense that when the engine is at lower RPM's it is creeping up. Def worth checking before changing things that you know were already replaced. I havent been in the car when its creeping up, but it sounds very possible.

BTW - I'm betting your low compression numbers are due to you not opening the throttle all the way when doing it. Common mistake, but it'll make all cylinders read low(and a little closer).

BTW - I'm betting your low compression numbers are due to you not opening the throttle all the way when doing it. Common mistake, but it'll make all cylinders read low(and a little closer).

Chad from Stett performed the check for me...my work sched is too busy to do anything my self anymore. I even drop the car off a day in advance usually just to save me time. Work sucks!!! Im actually working now :(

the time you spent taking it there, dropping off and picking up, you could have done it yourself. Quit making excuses.

no considering id still have to buy a compression tester. Besides Stett is litterally a few min from my house 7min drive. Which is about how long my car lasts till it starts to creep up so id rather keep it cool then do more damage to my head.

does your heater blow hot when the temp starts to creep up past the middle mark like that?

Faulty water pump? It may be the water pump, though I doubt it's faulty? Try "leaking" the air out.

I am sure the compression test was done properly. I made that mistake the first time I did a compression check and nearly shit myself until I realized the issue. Its not bad given the mileage and each cyl is in range of each other. At least its not a $2k head gasket job...

seriously,
I told you a week ago to change your water pump along with thermostat.
Eddy told you the same thing.

What would you rather do? spend $100 on pump and stat? or $1k+ on a head?

its the damn WP or AIR in system, just becuase you replaced it doesn't mean its good. think logically. if you had a leak, the faster you go, the more air/heat the enigne puts out and there get worst. if the faster you go and the cooler it gets, its because the WP is spinning faster and moving more water. If you don't believe, next time it happens. just rev it up in place and you will see the temp drop

^ been there done that....lol just replace the wp like everyones said. if it still persists atleast you've done something good :)

all that has already been sched to be put in on Monday since last week. I was just thinking if it may be anyting else that Chad and I may have over looked.

Seriously thanks for all the imput guys. You guys have been more help than the guys in the M3 forums...

yep, he's doing my flywheel/clutch tomorrow also :)

wow guys, these cars are so easy to work on. you should do all this stuff yourself. maybe you guys just make more than me :(

meh I have no real mechanical abilities I'm much to afraid to eff something up i'd rather have someone do it whos a "professional"
Because I'm sure i'll end up spending more money if I do it. :(
And that's that.

meh I have no real mechanical abilities I'm much to afraid to eff something up i'd rather have someone do it whos a "professional"
Because I'm sure i'll end up spending more money if I do it. :(
And that's that.

i hear ya, but not too long ago I was in the same shoes and got tired of getting ass ripped.

Yea.. $100 in tools goes a LONG way towards doing almost anything you'd likely want to tackle yourself.

Its wired but when i had my integra i did everything my self. Turbo, coilovers, clutch but for some reason with this car i just dont want to bother. Then again i never used to work more than 40hrs a week either so id be looking for something to do all the time...meh Chads a cool guy ill give him something to do haha as if hes not already busy enough...