1988 325i overheating after new HG

[3bimmersover25]

Have put a new HG on a FL 325i, head skimmed, new WP, TB, thermostat, drive belts.

Problem is car over heated quickly on first start up - 3/4 on the gauge with an inital fill, unbled and was boiling in the hoses.

Have refilled and bled it several times and temp rises slowly to just over halfway on the gauge. Water then starts leaking from the cap (not the overflow) have replaced the cap with another 2nd hand one (2 bar)but it still leaks from the neck. Neck of reservoir does not appear to be cracked.

When its hot the bottom hose is still cold and so is the overflow. (new water pump fitted and belt tension is good) Top hoses are not and very firm (pressurized)

With the cap off there are no bubbles but the coolant (water at this stage) gets forced out as it warms. I figured this is normal in a pressurized system.

Car idles with a slight miss.

I'm going to pull the thermostat tomorrow to check it. After that will do compression test.

Any suggestions appreciated.

[jlevie]

If there is no air in the system, there will only be a small rise in coolant level as the engine comes up to temperature. A large rise is a sign of a large air bubble or air being pumped into the cooling system. There are a couple of simple checks for air being pumped into the cooling system.

Bleed the system (procedure below), drive the car for a bit, and re-bleed. Release of a significant amount of air then or on a subsequent bleed is evidence of a head gasket leak. The other simple check is to remove the cap when the engine is completely cold to release any pressure (the hoses will be soft then) and drive the car for a bit. Then check to see if the hoses are hard when the engine gets completely cold. Hard hoses then are evidence of a head gasket leak.

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500rpm for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.