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Old 01-22-2012, 05:21 PM   #1
ecuastyle84
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Default Temp gauge not working and no heat

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.
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Old 01-24-2012, 02:50 PM   #2
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Top heater hose at the firewall goes to the thermostat, Bottom hose goes to the back of the motor. Did you bleed out all the air from the radiator with the heater turned on hot/high? If the solenoid valve by the driver's feet goes bad it shuts off the flow to the heater core. Check to see if you have electricity to the solenoid valve when you turn it to hot. Are the radiator hoses warming up otherwise? How old is the thermostat?
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Old 01-25-2012, 11:43 AM   #3
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Usually no heat in an M42 comes form not being bled properly.

The gauge can go bad, although it isn't terribly common. If it worked fine with the other motor, there is a chance that it is working and your thermostat is either stuck open or there isn't one there, causing it not to do anything. Or you have some wires switched somewhere, so it just isn't plugged in.
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Old 02-01-2012, 01:57 PM   #4
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x2 on the thermostat. if you dont bleed the coolant system correctly there will be air left in the system that will cause problems.
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Old 02-09-2012, 02:30 PM   #5
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UPDATE:

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
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Old 02-09-2012, 02:55 PM   #6
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Maybe you have to flush your system. Might have to flush the heater core separately from the rest since it would be bypassed if clogged.
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Old 02-10-2012, 02:36 PM   #7
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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
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Old 02-10-2012, 03:27 PM   #8
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try grounding out the wires going to the temp gauge to see if it works. I am not familiar with the m42 engine but on an m20 it is easy to get the plug for the temp switch confused with the plug for the temp gauge. Sounds like these 2 problems are independent from each other. Also check your engine grounds, I pulled my motor out one time and forgot to hook it back up, ran like poo and all the gauges went funky.
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Old 03-23-2012, 12:27 PM   #9
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Interested also why my temp gauge isnt working... tried two clusters and 2 motors and still dosnt work.. even though the car i got the cluster and motor out of did work..
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Old 03-23-2012, 06:28 PM   #10
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have you tried swapping out the temp sensor?
they're fairly cheap, and easy to replace (vs a cluster)
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