I have a overheating problem on my 1998 523iSE auto saloon. The engine is running fine but overheats after approx. 5 miles. Work has been done by two garages, a new water pump has been fitted plus bits around the radiator. I am unsure whether the water pressure is operating correctly, as the valve on top of the water pump will steam up after approx. 15 minutes. The top hose gets hot after apprx 5 to 10 minutes while the bottom hose stays cold. I am unsure whether the water is flowing through. Could it be that the thermostat is not opening for the water to flow through the system. After running the engine, the temperature gauge warms up to the normal centre point, but on continual running, after approx. 15 minutes will go into red and overheat. The steam increases from the pump, but the bottom hose remains cold. The fan seems to be operating ok, as it should. Your thoughts will be appreciated, regards, ***** ***** tel: XXXXXXXXXXX, LE7 9DB, Leicestershire
Neither garage is a BMW agent as such, but both are reputable and I have used them for many years.
The invoices for the work as such, do not specifically mention that the thermostat has been replaced. I can ask them tomorrow if they have.
I am unsure whether on fitting a new water pump, that this is supplied with a thermostat. It has not been priced separately.
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the problem is most likely the thermostat
it sounds as thought it was not replaced with the waterpump. Best practice on a BMW is to always replace the two together, so if this was not done, I would a little concered with the garage's familiarity with BMW.
the other possibility is that the head gasket could be blown, so you should also have this tested for.
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