overheating

[asmith88]

my engine has been recently overheating, e30 318is m42...

it used to overheat slightly, and i put this down to the scrap viscous coupling..

however today, it overheated quite close to the red, i turned the heater blower on and there was no hot air, so i assumed low water, i checked it, and there was plenty of water,

i havent muddled about with the cooling system in a while so i dont think its an airlock, i was thinking maybe a sticking thermostat?

any ideas?

thanks.. andy

[DesktopDave]

Could be a bad heater valve, but I'm betting on there being a bubble somewhere in the system or a pinhole leak.  If you have a little leak in the system it might be pulling air through the expansion tank.

You don't see anything odd in the coolant?  You're using distilled water & BMW or Dex-Cool coolant?

[asmith88]

hi, im not sure, as i said, it used no water, so i dont think theres a leak anywhere..

i use renault type d coolant.. handy from work

[locknload]

Future reference:  In an overheat situation, switch on the A/C to activate the aux fan for cooling.  Your aux fan should have come on automatically near the 3/4 mark on the water gauge.  If it didn't, you need to be checking the water temp switch as well.

As far as your overheat problem goes, I'd be replacing the thermostat and water pump.

[DesktopDave]

+1...That aux fan resistor and the radiator switch have failed on my car.  To test, pull the connector off the radiator switch (carefully) and jump the contacts to test the high and low speeds of the fan.  You can test for a dead fan motor with the A/C switch too, it'll turn the fan on low regardless of motor temp.

You can also use a different temp range switch & some surfactant like Water Wetter to 'delete' the clutch-driven fan entirely.  Google "e36 fan delete" or read this Bimmerforums sticky.  Most every BMW I've ever seen has the same switch with many different temp ranges.  They even sell a little motor jewelry to cover up the clutch fan stud.