Temp gauge/overheating issue

[warmseth]

'90 325is

The temp gauge is bouncing all over the place when it works at all. And the last few days the reservoir has been near dry when I start the car in the morning. Bad thermostat? What else might it be?

This video shows the gauge bouncing although it's camera shy and behaved itself more when I was filming...usually it's all over the place!

http://www.youtube.com/watch?v=Oo4pYLLHGVE

Thanks in advance all.

[warmseth]

Possibly two separate issues? Temp sending unit and thermostat?

[jlevie]

I can't watch the video here at work, but if the needle is rapidly jumping around the cause will probably be a bad connection where the gage mounts to the PCB in the cluster, a bad SI board, or a bad connection at the sensor. It takes more than seconds for the sensor to respond to a change in temperature.

If you are loosing coolant, there's a leak somewhere and it needs to be fixed before the engine overheats and damages the head or head gasket. If you can't find an leak, have the system pressure tested. If the pressure test doesn't reveal a leak there is the possibility that there is a leak from a cylinder into the cooling system that is overpressurizing the system and causing coolant to be dumped. I.E., a head or head gasket problem.

[warmseth]

Thank you for your good advise.

[kts]

My car started doing the same thing on my way into work this morning and it's done it a few times off and on in the past. Did you ever figure out what was causing this to happen?

My first thoughts were that either my coolant temp sensor was dying or there was a loose connection somewhere, something I plan to dig into this evening.

[warmsquash1]

My 1987 Cabby did this a couple of times. First a couple of things: Make sure there is not a sweet smell or white smoke coming from the exhaust. Second, get the coolant tested for hydrocarbons (use a refractometer or prizm). If any of these things holds true, you're doing a head gasket. If all that checks out, look for the wet spot or rotted/cracked hoses. sometimes its not that easy. My convertible had a pinhole in one of the upper hoses and it was just evaporating before it had time to get anything wet, but it was still losing coolant.. Good luck to you....