Mechanics

MY 98 740I OVERHEATS...

1998 BMW 740 • 135,000 miles

Hi I have a 98 BMW 740i and it over heats, I recently changed the thermostat and the fan clutch and I still overheats, Im about to change the water pump and see if that fixes the problem, although the old water pump looks good. One thing I notice is that Im able to stop the fan with my hand even if the car is hot, but the clutch its new, I also notice that the car builds up a lot of pressure on the hoses but not with antifreeze just with air and when I open the bleeder screw the air escaping from it its way too much, it keept getting air out for about 15 mnts. Im running out of ideas help please!
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Franxua1
July 18, 2012.



Have the engine tested for a leaking head gasket. It involves drawing air from the radiator through a glass cylinder with two chambers filled with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow. That air will prevent the thermostat from opening. They open in the presence of hot liquid, not hot air.

Caradiodoc
Jul 18, 2012.
But in that case? Wouldn't the hose that is going from the water pump to the radiator be full with water? Because it only has air, I took that hose off after turning the car off and there was nothing but air? And the one that comes from the thermostat did have water, so I thought the thermostat does open. And why am I able to stop the fan with my hand even when the engine its hot?

Tiny
Franxua1
Jul 18, 2012.
I wouldn't be concerned with where you find the air. The fact it's there is a problem and there's no place for it to come from other than a leaking head gasket. Don't knock yourself out looking for an elusive cause of the overheating until you eliminate the real common one.

Caradiodoc
Jul 18, 2012.