temperature guage problem

[71lwb]

i have a 71 chevy with guages. i cannot get the tempurature guge to function properly. i have replaced the old broken guage with a reproduction guage. as the engine warms up, the needle goes all of the way over to the stop just past the red. my mechanical aftermarket guage verifies that it is running at 180. i can pull the cluster out and ground the guage out with my self powered test probe, but as soon as i restart and rewarm the engine, it pegs again. i have read on previous threads, that there are variable resistance senders. i am leaning toward this being my problem, but i would like some opinions on this problem before i do any more to it. if anyone believes this to be my problem, a proper part # would be very helpful. any help on this matter will be much appreciated. thank you

[davepl]

If you search the forums there is an old post about resistance vs temp on old and new sending units. If you've seen it on two gauges, likely the sending unit is bad.

I have the opposite problem (indicates unrealistically cold) which can be bad connection between the sender and the head, but you've got too -much- connection, which I'd think would have to be a bad sender.

[VetteVet]

Take the wire off the gauge sender and turn the key on. If the gauge goes back to cold then the sender does not match the gauge and if the gauge continues to read hot then the sender wire is grounded or the gauge terminal is grounded.
If the gauge goes to cold then ground the sender wire to the block and see if the gauge reads full hot.

[71lwb]

thank you all for the tips. i'll try these things out tomorrow and post my findings.

[chevytruckluver]

good luck finding the problem, if you still have trouble dont be afraid to ask for more help.
Welcome to the site!

[schurg]

just to rule out an odd potential issue...could your sending unit be for idiot lights or one for actual gauges? the ones for I-lights are more or less on/off rather then a varying resistance.

[chevy88]

If this is not the original motor and motor is 1973 or newer, then you would need water temp sender for gauges 1956-72 chev trucks part # 53-811 for $8.95 from Classic Trucks Of America PH# 1-816-741-8029. This will give you the correct resistance for your gauge.

[davepl]

I thought about the idiot light sensor, but if that were the case then it would read full cold until (and only if) you exceeded the warning temp, then full on. At least I think.

But they did switch the resistance maps (perhaps 1973 as someone suggested), the old post I refer to has graphs of them both.

[DANTIP]

This may sound odd, but check your charging voltage while running. If your regulator is bad you could be overcharging your battery and while it's cooking your battery, your temperature gauge will read excessively high!! The other way to check (without a volt-meter) is to turn your warm truck engine off, then turn the key back to the run position without starting the engine. If the gauge reads correctly, your problem is high voltage fooling the gauge and cooking your battery.

[71lwb]

thank you everyone, for the advice on tracking down my problem. after following all of the testing procedures i was led to my problem and was able to fix it at no cost. the ground wire for my instrument cluster was open. after properly grounding the wire, the guage functions properly. thanks a million for all of the help!