BMW E36 engine does not warm up or overheats (thermostat)
Why does the E36 engine not warm up or the cabin get no heat in winter?
Usually the thermostat is stuck open. With a working thermostat the temperature gauge stays in the middle range. If the engine warms up but the cabin gets no heat, the heater water valve may have seized from lack of use.
How do I free a seized heater water valve?
Turn the temperature control to full with the engine running and tap the valve at the bulkhead, under the intake manifold. This can free the valve, and the heating starts to work.
How is the thermostat replaced and what should be noted?
On the M52 the thermostat is at the front of the engine, and removing the viscous fan clutch and the plastic frame is enough. The housing gasket does not usually come with the thermostat, so buy it separately. The opening temperature is stamped on the thermostat body.
What if the engine overheats or there is no heat after the new thermostat?
Bleed the cooling system first: do the bleeding with the nose raised for about half an hour. The lower radiator hose must be cooler than the upper hose. If the thermostat has no bleed hole, a 1-2 mm hole can be drilled at its highest point.