740i overheating

[knilive2]

1997 740i bmw having overheating problems. i change thermo, and waterpump , but still overheating. allso i am experiencing heat problem inside the car . sometimes it blow hot then it stop blowing hot air in blow cool. overheat while driving. please help asap with this.

[Ishtfan]

Overheating is a big issue, check the cylinders compression to make shure that combustion is not entering in the water system, this will also show if there is an exess pressuere in the hosses (but when overheating you will always have pressure). Also how is the radiator, do you still have water in it or you have to add all the time. There are some hoses at the back of the angine, they are for the heater core but they often leak.

[Bear]

Does the over heat occur at both low and high speeds (in traffic and on the road). If the over heat is at idle or in traffic only then I would suspect the fan clutch.

[Chris V]

If you changed water pump and thermostat, it oculd be that you have an air bubble in the cooling system from refilling the coolant. This is fairly common after working on these cars' cooling systems (since it's common to have to replace a cracked radiator or expansion tank).

The proper procedure to do this can be found at E38.org.

[sarkar]

hello
I have 1999 BMW 740il, just bought it. As soon as I start the car
temp needle goes to red, I checked the coolant and filled coolant so far
one and half container, I tried to bleed the air ,coolant is coming out of the
bleeding screw and under the screw whole, no coolant going back to coolant tank, I have to heat on full but not getting any heat inside, also after running for almost 10 min light smoke coming out from the left side of the engine and making some hissing noise, I would appreciate any advise or help. thank you

[daddyo8]

Hi K,
the 4.4 has had some problems in general with water leaks. One of the most sinister is under the intake manifold where the valley pan gasket (oem) was inexpensively made and has a limited shelf life. This repair looks daunting but, when you get into it, it becomes a real challenge to your manhood and a true educational experience and the intricacies and "genius" of the German auto-makers' toys are made manifest. If the boys had used only the best gasket material, electronics, etc., what incredible cars these BMWs, Mercs et al would be. Or maybe they used the best available at the time.
Look up BMW valley pan on youtube. Also check under your car and see if there is rust at the bottom where the bell housing touches the engine block. there are some holes at the seam that permit radiator fluid to pass out of the housing caused by a leak at the valley pan. When you lose fluid, there are bubbles of air that stop flow to heater core etc.
Lots of parts to buy and things to learn but is was fun once I got into "Das Mindset".