Are these spark plugs toast?

[shadze36]

Thank you zellamay and R Shaffner for the info. I will definitely check the expansion tank for any damage and order a new one if needed. Also, yes I was using a 50/50 coolant mix from Oriellys (not using BMW coolant for now because it’s too expensive for just troubleshooting). Before driving I had made sure the upper radiator hose was warm and tight. After the test drive both radiator hoses were hot and tight so I can confirm the t-stat is working as it should. I will update you guys once the new cap and screw come in the mail.

[blckstrm]

Thank you zellamay and R Shaffner for the info. I will definitely check the expansion tank for any damage and order a new one if needed. Also, yes I was using a 50/50 coolant mix from Oriellys (not using BMW coolant for now because it’s too expensive for just troubleshooting). Before driving I had made sure the upper radiator hose was warm and tight. After the test drive both radiator hoses were hot and tight so I can confirm the t-stat is working as it should. I will update you guys once the new cap and screw come in the mail.

When the car gets hot are your fans working?

You haven't mentioned that at all.

Boiling point of water and coolant is about 225 - about the same place where the needle starts to move up from the 12:00 position.

Your car should be able to idle all day with the expansion tank cap off. The either fan alone will keep it cooler than 225 forever if you're just sitting (well, as long as it's not too much above 100).

If it's getting hotter than that, your pump is bad or the fans - both fans - are bad.

Have you checked your fans?

[R Shaffner]

When the car gets hot are your fans working?

You haven't mentioned that at all.

Boiling point of water and coolant is about 225 - about the same place where the needle starts to move up from the 12:00 position.

Your car should be able to idle all day with the expansion tank cap off. The either fan alone will keep it cooler than 225 forever if you're just sitting (well, as long as it's not too much above 100).

If it's getting hotter than that, your pump is bad or the fans - both fans - are bad.

Have you checked your fans?

^^^ Roger all that. Except perhaps the omission of the original concern, which was whether there was a breach between the exhaust and cooling systems (head or head gasket) that was causing coolant loss and too much heat and pressure in the cooling system, which would also cause coolant loss.

I agree that it makes sense to try the cheap/easy solutions first. Your compression test came out OK and you said there were no obvious signs of oil in the coolant or coolant in the oil. So you're trying to see if the car will start and run normally without overheating. Makes sense.

But you've had a few curve balls. No cabin heat is one. That's often a sign that someone isn't filling/bleeding things properly, but it this case that's sounding like a different problem (like a bad valve).

And it sounds like the system isn't building/holding pressure. No hiss or rush of air coming out when you cracked open the cap or bleed screw with a warm engine, right? And after the last drive it started to overheat and coolant came out all over the cap/screw area. Getting a a new cap and screw makes sense. (Still cheap and easy.)

What seems odd to me is that you were able to drive around for 10 minutes or so in stop-and-go traffic before it got hot and you noticed problems. I'd expect these things to cause problems sooner than that.

If the water pump was bad, the top hose wouldn't get real hot at idle and it would overheat right away.

If the fans were bad it might get too hot at long idles but would cool back down and be fine while moving.

If the thermostat didn't open at all, then again the top hose wouldn't get hot and the engine would overheat quickly.

If the thermostat opened but not all the way...? Then it might get warm and idle OK, but overheat when driven. (Something like that happened to be with an old car years ago. The thermostat got stuck partially open. The engine took longer to warm up at idle, and would run hot as soon as I drove it. Rare but possible. A test for that is whether the top radiator hose gets a little warm pretty soon after the engine starts from cold, but takes a long time to get hot. But that wouldn't tell you whether a thermostat was closing and opening, but not all the way. Still I think that's rare.)

What if the coolant/exhaust system breach was still small, like a slightly blown gasket or warped head? That might explain it. At idle the pressure in the leaking cylinder would be low. That cylinder might not even be firing well/regularly at idle, which would mean little or no exhaust into the cooling system at idle. But when you raised the rpms and put the engine under load? That cylinder might start firing again and then send exhaust gasses into the cooling system, causing it to overheat and spew coolant.

So, if this were my car, I'd test for those things -- stuck/odd thermostat and gasket/head leak. I'd get the new cap and screw like you are and try it again, but with a much longer idle, and perhaps a few real short drives.

And I'd do some of the tests mentioned on the 1st page of this thread for seeing if coolant is making it's way into a cylinder, or the leak-down test.

(Sorry for such a long post. Just trying to figure this out and wondering what I'd do.)

[blckstrm]

Thank you zellamay and R Shaffner for the info. I will definitely check the expansion tank for any damage and order a new one if needed. Also, yes I was using a 50/50 coolant mix from Oriellys (not using BMW coolant for now because it’s too expensive for just troubleshooting). Before driving I had made sure the upper radiator hose was warm and tight. After the test drive both radiator hoses were hot and tight so I can confirm the t-stat is working as it should. I will update you guys once the new cap and screw come in the mail.

People underestimate the importance of the fans, especially while moving. The race car crowd thinks they do nothing once you're moving, and this is false - and especially on a normal street car. I ran with only an aux fan for a while, and when the connection failed - with the AC on at 80mph on the highway - the car couldn't keep itself cool. There's a lot going on under hood, and the fans absolutely make a difference whether you're moving or not.

My guess is this played a role in both overheats, and the second also may have had air in the heater core given the heater valve seems suspect.

[R Shaffner]

People underestimate the importance of the fans, especially while moving. The race car crowd thinks they do nothing once you're moving, and this is false - and especially on a normal street car. I ran with only an aux fan for a while, and when the connection failed - with the AC on at 80mph on the highway - the car couldn't keep itself cool. There's a lot going on under hood, and the fans absolutely make a difference whether you're moving or not.

My guess is this played a role in both overheats, and the second also may have had air in the heater core given the heater valve seems suspect.

I have to agree that bad/broken fans can cause overheating in stop-and-go traffic. (My experience is different regarding cars in motion. For me even modest forward speed has been enough to keep a car at operating temp.)

That's why I suggested watching the car warm up all the way as part of the bleeding process. That is, I watch it get warm until I feel hot air being blown from the radiator by one or both fans. If the car can idle that way for a while, build pressure without leaking, and not overheat, then I've learned all I can in the driveway and it's time for a few short drives.

[blckstrm]

I have to agree that bad/broken fans can cause overheating in stop-and-go traffic. (My experience is different regarding cars in motion. For me even modest forward speed has been enough to keep a car at operating temp.)

That's why I suggested watching the car warm up all the way as part of the bleeding process. That is, I watch it get warm until I feel hot air being blown from the radiator by one or both fans. If the car can idle that way for a while, build pressure without leaking, and not overheat, then I've learned all I can in the driveway and it's time for a few short drives.

Modest forward speed is great. 80+mph forward speed generates a lot of heat, and especially at 110+ ambient temp plus AC running is more than just airflow can handle.

My aux fan connector was making intermittent contact in this situation (and a dead clutch in the mechanical fan) and I had to shut off the AC or the car would get hot. I finally pulled over, fixed the connections (the female receptacles inside the plug were to big and had to be bent to make contact with the male pins. Anyway...) and the car could keep itself cool enough (somewhere below 12 o'clock) on the drive back to Dallas.

[shadze36]

Sorry for the dead thread revival guys but I ended up taking the car to a bmw speciality shop a few months ago and they confirmed with a leak-down test that there was a blown headgasket in cylinder 3 with a possible cracked head/block. So I ended up taking the car to a friend of a friends shop, and he swapped in another M52 motor he got off an auction, and $1500 later I am back in action. He also confirmed that the head cracked on the old motor. He also swapped over my Stewart water pump and new t-stat, so I am good to go again. Thanks for all your input, it was a difficult problem to diagnose because of all the different variables but I am glad its all over with and I get to drive it again!

Edit: also, if anyone knows of a good digital temp gauge please send me a link! I never want to have to deal with overheating issues ever again :/

[Eric93se]

First page I told you the head was toast!

Glad you got it going again!

[jmo69]

I have a Prosport electric temp gauge that is tapped into the coolant line going to the throttle body. The gauge is mounted in the sunglasses cubby. If you want digital get the OBD Fusion app for your smart phone with the appropriate dongle and read all kinds of data. The pic only shows one screen.

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