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I have installed new expansion tank cap-installed new
If let the car run in driveway a long time the fans do work, the fans will run and stop andin
sort time they will run again and they will do this all day setting steal,
if I drive it about 10 miles at 70, it get hot, steam will come out of the
expansion tank and the FANS ARE NOT
RUNING. If I drive 60 ok if I drive 70, runs hot in about 3 min, if I go back
to 60, temp is ok
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Most systems are self bleeding but with the car on a slight incline the driveway turn heater on start car and run with the radiator cap off (cold engine) level of water in radiator should be down about 2-3 inches will warming up it will expand then drop again after hot top off system place cap on done .with Degas bottles (divorced radiator cap) it has a hose that runs from radiator to tank this bleeds the air out. heater should be hot after done.
When coolant level drops, system becomes airlocked, so simply adding coolant wont work. First sign of loss is usually heaters blowing cold air. Firstly look on the RHS of engine at gearbox end of cylinder head. You will see the thermostat housing. Its seal leaks and causes the problem over a period of time. Dealer will supply you with a revised housing complete with improved seal. Job for a garage.
Meantime, note the black, round, cross head plastic bleed screw on top of thermostat housing and possibly one on the rubber hose above the alternator. Loosen them off a couple of turns. Remove filler cap from thermo housing (not expansion tank) and add coolant. When coolant runs out of the lower one, tighten it, start engine and keep adding coolant till it runs out of the remaining bleed screw. Then tighten it up, top up coolant, replace cap, fill expansion tank to level. Sit in car and hold revs at 2000 rpm for 2 minutes with fan on and heat at maximum. If it dont feel like a sauna now, repeat the process.
Then allow the engine to run till normal temp and observe that the radiator fan operates before engine gets to max temp. Get the housing replace ASAP before the engine gets cooked. (not unusual)
might sound stupid but did you check the impeller by holding the drive shaft and trying to turn the impeller asnif its a plastic one they tend to come loose on the metal drive shaft and loose power so they are not circulating the coolant ??
A BMW that is hot after only two or three miles generally has air in the cooling system. Did you turn on the key and turn up the heater to open the heater valve, and then pour water unto the expansion tank until pure water came out of the bleed screw?
Overheating can be numerous things: Fans not working, water pump, thermostat, overflow cap, and the list keeps going. When the engine is running and heats ups, feel the heat of the top hose, if the hose isn't hot, the thermostat is most likely stuck open and needs replaced. If it is hot we know you have circulation. The cap on the expansion tank may be defective, if it can't hold the pressure of the water, it will release at the overflow cap if the cap is bad. Also check the coolant level.
We have had some similar problems with some BMW's,the last one we replaced the expansion tank.Before we attached the upper radiator hose to the radiator we filled the engine with antifreeze through the hose.Install the hose and fill your expansion tank to the proper level and run the engine to operating temperature.
Take rad cap off when cool & run it for a while with the heater on (not defrost) and top up coolant as needed in rad, about an inch or 2 from top of rad. Let it run until you see rad fan come on & off about 2 or 3 times at operating temperature. Then replace cap, top up return bottle to proper level, and try that. Probably still air in system. If that doesn't cure it, I'd look at faulty or incorrectly installed thermostat, which would be a trip to shop that installed it, if it were me.