Temp gauge problems

[VintageAutobahn]

I got in my car this morning to go for a little drive early this morning when my temp gauge said that my car was overheating. I dont think the car was actually overheating as I drove less than a quarter mile before i noticed it was rising really quickly and turned around. The outside temp was about 55 degrees and I drove it earlier this week in 95 degree weather with it sitting just over mid way up the gauge the entire drive. I pulled into the driveway with the gauge a little below the red. I then opened the hood and popped the radiator cap and saw the coolant level was full and very little pressure was let out (like not even half a second of pressure release time). I was thinking maybe my thermostat is stuck but I dont think it would overheat that quickly if that was the case. I know people are going to say "swap to a 320 radiator" but that doesnt make sense to me when it was fine in such hot weather and the problem arises in cool weather. Anybody who has any ideas I would be very appreciative.

[ifayeoh]

check the connection at the sender and install or secure ground on back of gauge in cluster.

[boldtu]

I also had a problem with the pigtail connection from the battery to the block (ground)

chet

[Guest Anonymous]

Other posters have covered the issues. Since the temp guage is electric, any oxide or frayed wires can increase the ressistance of the circuit. Remove sender at water jacket splter. Clean oxide off disconnect, and threads. Make sure there is no teflon tape on threads or other gasket sealant. These threads must connect the manifold ground system for proper reading. Temp senders rarely fail however you must make certain that the sender is the correct one for this vehicle and that it is functioning properly. Use an ohm meter (DMM) for a resistance measurement at cold temp and boiling water. It should show a smooth transition from cold to hot.

Then look at the connections on the rear of the instrument cluster. Open grounds are suspicious. An open ground can cause the indicator to 'float' and that might explain your incorrect reading. Remember, since these are old style D"Arsonval meter movements, they are susceptible to stray magnetic fields which may cause an erroneous offset. Methods of bypassing this stray induction are not completely satisfactory. Use of a rf capacitor or multiple grounds from instrument cluster board to chassis ground have been tried. They seem to work in weak interference situations but not in strong interference situations.

[jonny]

check the connection at the sender and install or secure ground on back of gauge in cluster.

Also ground to firewall and jump to block.

I thought for years my car was overheating. I finally put a candy thermometer in the rad. = it wasn't.

Adding the above grounds solved everything...including the jumpy needles (fuel & temp. gauges) when activating turn signals and/or highbeams.

[yeewiz]

ditto everybody above. also see my own experience at:

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,323234/highlight,/