Author Topic: Temp gauge not working and no heat (Read 2884 times)

ecuastyle84 · « **on:** February 08, 2012, 07:34:06 PM »

I own a 91 318i and recently installed a stock m42 motor due to the previous one having a cracked head. Anyway the motor runs great but my temp gauge doesn't work nor do I have heat blowing out the vents, just cold air. I replaced the temperature sensor for the gauge read out off the old head which keep in mind the temp gauge worked with that old motor. Is it possible for that temperature sensor to go bad or could it just be the vdo?
Any help will greatly be appreciated.

ecuastyle84 · « **Reply #1 on:** February 09, 2012, 01:44:03 PM »

Anybody?

I bled the system again and now I have heat but the temp gauge still doesn't go up, doesn't even move. The only time it moves is when I turn the key on and the needle goes to fully hot. When I turn the car on the needle drops to cold and doesn't move after that.

Also the left rad hose is still cold after having the car run for several mins, I even drove it up and down the street for abit. The only time the tstat opens is when I turn off the car, and hose is hot now...I don't get it

danlolasdad · « **Reply #2 on:** February 09, 2012, 05:37:31 PM »

left hose should be cooler its the return from rad. you might have a thermostat stuck open or removed by previous owner to mask overheating. is your fan stuck on?

DesktopDave · « **Reply #3 on:** February 09, 2012, 06:57:12 PM »

+1 on the missing/stuck thermostat - these engines commonly get coolant leaks and the PO might have removed the thermostat entirely, or used a low-temp 80degC one. You could be losing pressure off the rad cap too.

It's good that you have heat...at least coolant is flowing around and you know the pump isn't air-locked. The M42 is a PITA to bleed, especially if the little passage in the thermostat housing gets plugged up with silicone make-a-gasket (don't ask how I know). BMW doesn't use jiggle valves like many other (lesser) cars do. My car takes a while to heat up nicely, and even then the hoses aren't really hot...just warm.

As for the gauge...when you swapped the motor, did you make sure the plugs were right? All three share the same two-pin plug type. I accidentally plugged my oil sensor into the DME temp sender after I did the hose delete mod. The oil pressure light was on (but dim) and the temp sensor didn't seem to work. Gave me some high blood pressure there for a bit. Swapped them around and all was better.

ecuastyle84 · « **Reply #4 on:** February 10, 2012, 02:09:54 PM »

Thanks for the reply guys, I'm going to replace the tstat first cause it was given to me when I bought the car so I don't know if it's good or not. I'll keep you guys posted. Thanks again

DesktopDave · « **Reply #5 on:** February 10, 2012, 04:00:02 PM »

Don't use any of that silicone goo! Just the cheap OEM paper gasket...it works perfectly if the housing surfaces are cleaned up nicely. Some non-curing gasket sealant is all I'd consider.