Temperature sending unit

[kmartin83]

My temp gauge wasn't working, so I removed the wire from the temp. gauge sending unit and tested the wire. Gauge works. So I ordered a new temp. gauge sending unit. I replaced the old unit with new one and the gauge still doesn't work. I have also replaced all the fuses. Any thoughts?

[rod shiftright]

you say you tested the wire and the gage worked? By this I guess you mean that you took the wire loose from the sending unit and touched it to ground with the ignition on and the gage pegged out. Thats the normal test for a gage. Did you touch the wire to the cylinder head,or to some other ground? The temp sending unit itself MUST be in direct contact with the cylinder head (i.e. no teflon tape!) or it won't work. The temp sending unit is what is sometimes called a "thermesister", and I probably just spelled that wrong,but it is an electrical device whose resistence drops as tempeture increases. Your temp gage is actually measureing the resistence of the sending unit as it heats up, and expressing the change in the temp units resistence in degrees of tempeture instead of ohms of resistence. If the sending unit doesn't have a good "connection" to ground,the poor connection will result in high resistence,which the gage will read as low or no tempeture. People are in the habit of putting telfon tape on screw in devices that might leak water but with a temp sending unit,too many wraps of this tape might insulate the unit from the cylinder head,preventing a good ground to the unit. A simple way to check for this would be to run a wire from a good ground on the body,like maybe one of the studs for the hood latch,and strip enough insulation off the other end of the wire and wrap it arround the base of the sending unit. Turn on the ignition and run the engine for a few minutes untill you know it's warm enough to be showing some tempeture. If this works, then you have either insulated the unit,or the ground to the engine isn't very good. I've had so much trouble with poor grounds damaging the electronic ignition system on my car that I ran a seperate ground from the exhaust cam shaft housing to the coil bracket, and have had no further trouble. Hope this helps.

[kmartin83]

Yep, when I touched it to the ground the gauge pegged. I didn't use any insulating tape; the previous gauge didn't have any. I haven't had a chance to check the ground to the engine, but haven't had any other electrical issues with the car. Thanks for all the info. Kathie

[spider2081]

I think you are checking the correct wire if when you ground it the guage pegs. Is it possible the sender you installed is an over-heat switch. It is an open switch until the temp gets up to around 250 then it closes and lights a temp light or pegs the temp guage. The guage sender is a variable resistance that as already stated decreases as the temperature goes up. Both are located in the head but I don't remember their positions. If you guage is staying on zero when connected it sounds like the sender you are connecting the wire to is bad. Maybe someone knows the resistance value so you could check it.

[kmartin83]

Thanks for all the help! I went ahead and got another sending unit because everything else looked like it was working fine. Of course the new sending unit works great and the gauge works! Now, on to the carb.