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Trying to track down an issue I am having but only seems to happen on the track. Car is a 1998 M3 and its basically a track only car. Engine is pretty stock other than a mishimoto rad, electric fan, Stewart water pump, and Mishimoto low temp thermostat. Street driving no issues at all, needle doesnt move from centerline. Track is where I have issue, couple of laps in coolant start coming out my hood vents and the temps go way up. The overflow bottle will blow coolant out the cap. Next track day switched the cap and really tightened it down, second session started getting the coolant all over and the rear coolant line from the back of the head to the heater valve ballooned and split open.
Initial thought was head gasket and I havent ruled that out yet. However the signs arent there, when I pull the cap no bubbling or oily residue. Compression and leak down for cylinders from what I recall was in the 185-195 range, but leakdown on cyl 4-6 was a bit higher but nothing alarming. Also checked the coolant with the exhaust gas test and that was negative.I have a yet to be installed Mishimoto metal expansion tank but my thought is if there is too much pressure in the cooling system the next weakest component will fail. Has anyone had any issues like this before?
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Is the electric fan wired correctly and verified to turn on at the desired coolant temperature? Is the fan just a cheap puller zip tied to the back of the core, pulling air from less than half the core area? Is the engine undertray in place? If it is a flat aftermarket plate, is there a baffle to the radiator core? Are the radiator baffles that duct air to it, so that air won’t simply pass around it, in place?
If there are no issues found based ln the questions above, I would suspect a cracked head.
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Its a spal 16 inch fan and I have it off a switch so basically running all the time. I do have the Turner undertray with the LTW front lip so that is all sealed off. Its doesnt have a flow through hole and it is a solid aluminum sheet.
I will have to double check about the side ducts, from what I recall they were there but its been a bit since I've had the bumper off.
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Replace all your hoses and do a thorough job bleeding it and see how it goes. Did you turn it off immediately when you saw something was wrong? If not and you tried to limp it in then the head will be damaged.
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Its happened at a few events and when it overheats I have to limp it over to the pits. Unfortunately there isnt really anywhere to pull over and let it cool down. Whatever damage, if any is already done. The thing I am thrown off is, I cant get it to overheat on the street.Originally Posted by Eric93se
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Some cracks will require more heat to allow exhaust gasses to push into the cooling system.
Just so you know these engines don't typically mix oil/coolant.
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I see, thats what I was preparing myself for. Time to start looking for a new head.
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Do a compression test. Also when all the plugs are out look at the piston tops to see if any are steam cleaned.
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replicating the oem radiator baffle might be in your best interest if there's a gap under your radiator. also running an AUX fan if you have it removed. the 16in spal dosnt really move alot of air. and the oem fan clutch would move alot of air at 5krpm+ might be able to sort your issues with junk parts before you tear into head gasket.
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I did a compression test and leak down, nothing alarming although I would like leakdown to be lower.
Cyl 1 190 psi leakdown 11-10%
Cyl 2 193 psi leakdown 4%
Cyl 3 195 psi leakdown 6%
Cyl 4 195 psi leakdown 15%
Cyl 5 187 psi leakdown 6%
Cyl 6 192 psi leakdown 12%
This weekend I’ll try and inspection camera to check top of my pistons.
I do still have the aux fan in place. Good point on the spal fan, looking at the specs it’s not the greatest amount of air. I’ll also look into those sheet metal ducts that direct airflow.
Looking at bimmerworld on their fans kits I do see a note about not for track use. Before this car I used to track my 97 m3 sedan with the same spal fan without any issues but it was more stockish form. This car I am running 275 square with ltw wing and front splitter. Probably a lot more load on the cooling system.
Last edited by kev70ss; 09-21-2022 at 12:49 AM.
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If you had to drive it after suffering coolant loss then the head is most likely damaged. If you aren't already using the 80C thermostat then you really should.
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I have the Mishimoto one which is super low 68C, didnt make a difference.
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Mishimoto regular radiator isn’t anything special. The x-line or Z3 S54M version, is decent. The best is probably the Zionsville Fat Boy.
You can try better ducting or a better fan or a better radiator but the cracked head is my guess. Good coolant exhaust gas sampling results and even compression and compression leak down tests don’t seem to consistently rule out cracked heads on these cars.
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Why did you replace the first cap?
The new cap apparently didn't work as intended, otherwise the pressure couldn't have gone up so far to blow hoses. If the coolant gets hotter and hotter and cooling is not sufficient, temps and with it pressure will go up and eventually blow hoses if the cap doesn't release the pressure.
Last edited by samy01; 09-21-2022 at 10:12 PM.
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Just more of a trouble shooting, I had an old cap just to try. When its overheating I get its going to find the weakest point to blow. I have a yet to be installed Mishimoto expansion tank but I dont think thats going to do a thing. The Z3M s54 radiator is what I am going to look into.
As far as cylinder head, anyone ever use this company before?
http://autoheadperformance.com/_mgxr...bmw_heads.html
Seems like a better idea to just get a rebuilt head.
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ive been very curious about these aftermarket head castings and the quality of the work preformed on the valve train.. unfortunately i haven't really seen any real world reviews. this leads me to believe people dont have issues....just maybe a performance oriented rebuild might be better but less cost effective. i dunno.
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I'm not seeing any actual temperatures.
Get a cheap OBD2 Bluetooth transmitter from Amazon and download Torque or whatever iPhone offers and get some actual data. I suspect you're getting hot on the street, too, just not enough to see the needle move.
Also, the order of observations seems... interesting. I'd expect to see temps going up and THEN coolant spewing after you overheat.
Why don't you acquire some data reading / acquisition capability and then come back with some actual data? Temp / activity / conditions, etc.
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I do have one of those and I can try street driving to pull some DME data. Just gotta figure out to to log it first.
I did try heating the car up on the dyno to see what temps got to and from what I remember 215-225 range. I believe factory cap is 16lbs? so would be pretty borderline on the boil over point.
The first cap I had must of had a weaker spring which coolant would blow out of the cap and onto my windshield and FR tire. I would get coolant droplets on my windshield first and then coolant temps would go red. The cap I replaced it with didnt seem to boil over but soon after coolant lines broke. Suspect with that not venting pressure the weakest hose failed first.
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Don't blame the source of your trouble on the cap. Once the engine goes into the red the head can and will be damaged.
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Definitely not, I'm pretty convinced the head or gasket is done. At this point seems like a good idea to find a set of cams while I take the head off.
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The source of the trouble is insufficient cooling, and second comes the cap situation that apparently didn't release the pressure. Put OEM cap. The rear cyl. head to heater hose bursting isn't too special, it's usually the first hose to burst. They sometimes also burst just like that from age. No special scenario needed for that to happen.
I find going straight to removing the head without diagnosing the head or gasket to have failed questionable.
Last edited by samy01; 09-29-2022 at 03:23 AM.
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Gonna replace the remaining heater hoses this weekend, install low temp fan switch, mishimoto aluminum expansion tank and do some testing. When I pressure tested the cooling system the only super minor leak was the port on the head where the water line goes to the throttle body, changing that too. I do still have the factory bumper air ducts in place for the radiator. I am going to remove that and fabricate something a little more sealed off to the radiator.
As far as radiators go Z3M S54 vs CSF any preference? Gonna change that out too.
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