Temp gauge not working and no heat

[ecuastyle84]

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.

[vpilarrt]

I would suspect the wire between the sensor and the cluster. In case you don't know there are 2 temp sensors right next to each other on the head. The front one (2contacts) is for the computer, the rear one (single contact) is for the gauge.

[ecuastyle84]

I would suspect the wire between the sensor and the cluster. In case you don't know there are 2 temp sensors right next to each other on the head. The front one (2contacts) is for the computer, the rear one (single contact) is for the gauge.

I could grab that 2prong sensor off my old motor, you would suggest I try that to see if that works?

Can this also be a reason why I have no heat blowing out my vents? Or is that a different not related to this?

[vpilarrt]

No - the 1 prong sensor is for the gauge, try that one.

I would suspect you don't have the cooling system bled properly. Do you know the procedure/have you searched in this site on how to do it?

[ecuastyle84]

No - the 1 prong sensor is for the gauge, try that one.

I would suspect you don't have the cooling system bled properly. Do you know the procedure/have you searched in this site on how to do it?

I did swap the 1prong off the old motor and still doesn't read it...the system was bled properly but even if it wasn't wouldn't I notice the gauge reading overheating?

[vpilarrt]

Try this - disconnect the sensor wire connector at the sensor, ground the contact, with the key at ON the gauge should go to full hot. If it doesn't something's wrong with the wiring or the gauge.

[ecuastyle84]

Try this - disconnect the sensor wire connector at the sensor, ground the contact, with the key at ON the gauge should go to full hot. If it doesn't something's wrong with the wiring or the gauge.

Ok I'll try that tonight thanks

[Carib]

Is the temp gauge not giving a reading at all or is it just moving a little but not reaching the normal operating temperature? If the latter is the case, then the thermostat is most likely stuck in the open position and so you wouldn't get any heat and a cooler than cool reading on the temp guage.

If the temp guage is not giving any reading what so ever, then a couple of suggesting post earlier could be the problem. However, the no heat issue could still be the stuck thermostat.

[Kvasi]

If the sensor and the heater core is all air it should be like that. Tried to bleed it properly?

[ecuastyle84]

Is the temp gauge not giving a reading at all or is it just moving a little but not reaching the normal operating temperature? If the latter is the case, then the thermostat is most likely stuck in the open position and so you wouldn't get any heat and a cooler than cool reading on the temp guage.

If the temp guage is not giving any reading what so ever, then a couple of suggesting post earlier could be the problem. However, the no heat issue could still be the stuck thermostat.

temp gauge doesnt move at...ran the car for awhile the lower rad was still cold maybe alittle warm but soon as i turned off the car the hose was hot to the touch which means the tstat did open up?

[ecuastyle84]

If the sensor and the heater core is all air it should be like that. Tried to bleed it properly?

I'm going to try to bleed it again. I know these m42 rads are a bit tricky. I've searched online on how to do it but everybody has a different way of doing the procedure and I'm not sure which one to follow

[vpilarrt]

One trick I found to help dislodge those gas bubbles is to squeeze the radiator hoses (wear gloves so you don't burn yourself) in a pumping motion. You should be able to hear the water sloshing/flowing.

[ecuastyle84]

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

[Ryann]

First, do this.

http://www.r3vlimited.com/board/showthread.php?t=230380

[3bvert]

a bazillion years back I used to work at a foreign car dealership. one of the old fac trained jag mechanics use to do this ( below) and I have been doing it since

Ill make this relevant to the m42

when replacing the thermostat, use a small drill bit and drill a hole in the flat part . its a small hole about toothpick size ( sorry not enough coffee yet) then when installing thermostat place thermostat in block with the small hole at 12 'oclock.

what this does and does not do
when filling blocks and etc slowly lots of the air can pass through the hole you made in the thermostat making it so there is not a airblock in front or inback of the t-stat.

what it does not do: the hole is small enough that it does not allow enough water to pass to alter the function of the thermostat

reasonsing for me: when I began twisting wrenches the thermostats used to come wiht the hole in em, some brands still do, some brands have a modificatin of this, and the first time I pulled a thermo out of a m42 it had a hole in it, so when the suppliers started sending thermos without and we were having bleeding problems we started putting the hole back in. and of course some cars now have a small built in thermo bypass hose to allow some water to move.

does it really help, to me reason says yes, can it hurt, dont know how

some old habits are hard to get rid of