Hey everyone I’ve been having problems with my 325xi overheating. I had the thermostat replaced a few months ago and since then I’ve had no problems with overheating until now. At first I thought it would be an issue with the water pump but when I grabbed the coolant return line it was barely warm while the oil line and filter housing was scalding hot. The radiator fan turns on and blows fine, the belts are all in good condition. I can’t figure out why the coolant is barely warm while the oil gets super hot. The oil was just changed about 3 weeks ago and the car started overheating about 2 weeks ago. The oil was changed by the bmw dealership along with replacing the transmission fluid pan. Anyone have ideas? I just brought it to a mechanic and it was there for a week and he replaced the valve cover gasket only because I knew that needed to be replaced and he said the car wouldn’t overheat for him but on my 20 minute drive home it overheated right at the end. When I opened the hood, there was no coolant and it was full before I drove home.
First off, fill the system and bleed it properly. I'm sure you can find out how via this forum, google, and/or YouTube. Second, you may need to find a new mechanic if he doesn't know how to fill/bleed the system. Third, you need to check for any fault codes with a proper BMW-specific scan tool. If there is water pump fault codes stored, you will need a new water pump.
ASE and BMW Master Certified Technician
Also, be aware that the engine oil IS part of your cooling system. It should reach 200+ degrees after a period of driving. This is also a reason that some cars hold 6+ quarts of oil - not because they need that much oil in the engine to lubricate, but because the oil is a heat sink and helps cool the engine.
I suggest you disregard the oil and focus on the codes, radiator, water pump and bleeding the system properly.
Check for faults it's probably your electric water pump
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