Persistant overheating... already searched...

[alexxander.foster]

Hello!

I am a new owner of a severely neglected 318is and I'm dealing with a stubborn overheating situation.  I've searched and searched for similar symptoms on the various bmw forums but to no avail.  I'm hoping you guys can help.

It started after I replaced the engine coolant temp sensor and re-routed the throttle body heater hoses.  The car's cooling system was always rock solid prior to opening up the cooling system, now it wont operate in the correct range.  The car has a fairly predictable overheating pattern:
- the car comes up to operating temp normally
- sits at normal operating temp for between 5 and 15 minutes depending on ambient temp
- the car begins to climb past 1/2 in incremental "jumps"
- the engine temp stops climbing between 3/4 and red
- it takes another 5 minutes for the car to reach the point between 3/4 and red
- revving the engine speeds up overheating to about 3 minutes, but the temp does not climb any higher

I've been bleeding the cooling system via the following procedures:
- turn cabin heater to full hot and fan speed to "1"
- remove the expansion tank cap
- fill to cold line
- start the engine
- fill again
- open bleeder briefly
- rev motor briefly

This is my fourth day of trying to bleed the cooling system.  I've already replaced the radiator, checked for leaks, and replaced the water pump (not by choice -one of the tabs broke on re-installation after inspection).  I also pulled out the thermostat and tested its operation in a pot of boiling water.  It opened and closed about 5 times without drama (though I did not test the opening against a thermometer).  The thermostat looks to have been recently installed and is in very good shape with the 92 deg C stamped on it.  I've also been keeping a very close eye on the exhaust.  There doesn't appear to be anymore moisture coming from the tail pipe than usual.  It also doesn't have any unusual odors -it just smells like burnt premium gas.  Additionally, I'm running a new fan clutch.  The electric fan on the car was damaged beyond repair so I removed it until I could source another one.

I'd consider myself a fairly competent DIY mechanic, but this has got me majorly confused.  Can I get some advice on how to proceed?  Anything would be greatly appreciated.

[bigskyis]

First order of the day is to perform a compression check.

[ti_tony]

Make sure the car is nose up as high as you can get it, this seems to help a lot. Double check the stat, I've got a bad one more than once over the year's.

Edit
 Make sure the car is nose up as high as you can get it while bleeding the system, this seems to help a lot. Ha-Ha that's better.

[DesktopDave]

Considering that the system was good before you opened it up, I'd assume that everything is OK.  I'll bet you've double-checked your work a hundred times.

I've had trouble with bleeding the car as well.  I usually water the coolant way down (2/3rds distilled water) and add RedLine Water Wetter.  I also park the car facing up a hill to finish up the bleeding process.  I usually open the bleed screw 3-4 times for 20-30 seconds every time, sometimes there's a few stubborn pockets of air.

Is the bleed passage clear on the thermostat housing?  If that little passage is gunked up the car will never bleed correctly.  Also be sure that the pump isn't air-locked.

If all that fails, get a pressure tester on the system.  The cap should be a 2.0bar unit IIRC.

[bigskyis]

"I am a new owner of a severely neglected 318is and I'm dealing with a stubborn overheating situation."

I would not assume anything. Compression check/leakdown test is the first stop on this train. Once you have established that the head gasket is intact or the cylinder head is not cracked...