Water flows in the bottom, and out the top of your engine. If bottom is cold, not just cooler than the top, could be a plugged radiator or failed water pump.
thermostat typically stays closed til about 170 deg F to 185, to warm the engine. When it opens, top hose gets hot quick. Thermostat sounds fine to me.
Hi Michelle
it sound like the thermostat is playing up, replace the thermostat and your BMW will be OK.
This sounds like a coolant flow problem. possible rad plugged or water pump problem.
SOURCE: 1998 jeep grand cherokee cooling problem
Your thermostat is stuck closed. It needs to be changed right away. By the way the operating temp on that motor is 160 degrees so you are running hot you have just been lucky so far. Good Luck
SOURCE: 1991 honda accord is overheating. Installed new
When the car is completely cool,check the electric fan(s) for smooth rotation.
Clean/check/change the thermo sensor,contact and wire.
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Excavate air pocket in coolant system / check for head gasket leak
This test will kill two birds with one stone.
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MAKE SURE THE COOLANT SYSTEM and ENGINE IS COLD!
RAN THIS TEST IN A WELL VENTILATED AREA ONLY!
You will spill some coolant during this air pocket purge test.......BE
KIND TO THE ENVIRONMENT and ANIMAL please clean up after the test!
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Put the front end on a pair of ramp or park your car on a VERY STEEP HILL (radiator facing top of the hill) .
Top of the coolant reserve tank
Let it ran for 10-15 minutes.
Monitor for air pockets escaping from coolant reserve tank.
Small amount of bubbles is OK at 1-5 minute mark
After the thermostat open up (after 195 F warm up) at
5-12 minute mark or after high idle you should see less bubbles.
If you do not see any in rush of bubbles then your thermostat may be
partially stuck or rusted badly inside the thermostat hosing.
Give the thermostat host few gentle taps.
If you see larger bubbles surfacing after 15 minutes then should do a
hydrocarbon (HC) dye test to test for potential head gasket leak.
Let engine cold down and top off coolant reserve tank.
Start monitor for coolant lost
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A coolant flush is require every 2 years or 24,000 miles.
I recommend the thermostat that has a relief pop-let to reduce the change of burst radiator and coolant hoses.
Make sure you get a new thermostat gasket,black RTV and fresh coolant for the job.
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SOURCE: 1996 VW Passat VR6 is overheating
Thermostat is most likely. Try that first, then my next choice would be water pump. Good luck.
SOURCE: car overheating, coolant in resevoir cold,
First-change the thermostat and bleed the system.If the problem is still there change the water pump.
SOURCE: top radiator hose hot and lower hose cold. car
Either the water pump has failed, the radiator core is plugged, or the lower hose has collapsed and blocking the flow of coolant. Hope this helps!
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