steinboy56

My Temp Guage rises to about 120 degrees and stops. To take out the Brass Temperature Sender on the intake do I just unhook the wire and wrench it out? Is that piece still available from GM?

Chuck Gongloff

In essence, yes. BUT, use a 6 point deep socket and be careful. If you reinstall it, don't use teflon or other thread sealants on the threads. It's tough to find a correct reading temp sender. There are MANY threads on this. Did it work before? Could the gauge or the wiring be bad? Chuck

62fuelie

With the ignition on, momentarily ground the sender wire at the sender end. The gauge should read full scale (hot). If not, your problem is in the gauge or wire. If it does read full hot, take the sender out and clean the threads so it make good electrical contact with the manifold. If it still reads low, you need a sender. Autozone sells a sender, Wells TU5, which will work with all C1/2's for six bucks. It looks like the original but has no markings. It will do until you find a correct one if that sort of thing matters to you. FYI, a correct sender will read about 700 ohms at room temperature.

JF244

Using an after market sending unit from a reputable corvette supply house, I was having just the opposite problem, running at 210 then pegging at 250 but never boiling.

The GM part is available and this is relatively easy to do yourself. I agree, no teflon or sealer. Unless you've drained the coolant some, have a couple of towels stuffed in there to soak up some coolant when you pull the old unit out.

Over the past several days there has been a good string about this on the NCRS technical board at http://www.ncrs.org. After reading these comments I ordered a GM replacement unit this afternoon for $12 and it will be at my dealer on Monday morning.

:cool:

ghostrider20

For the six bucks if I took it out, a new one is going in. You will have to drain some coolant out, unless you don't mind it running out the hole.

I used the Teflon tape because I did not know any better, but will never use it again. Mine temp gauge/sending unit works perfect with the Teflon tape, but it may be one in a hundred. (I think the threads cut through it enough to make contack). I also replaced the wire from the firewall to the sending unit. I bought some green wire so it looks stock. I think my problem was in the wire more then anything, but I never did any of the checks. The wire was baked and brittle. I used small black nylon ties and hid the wire on the back side of the vacuum advance line and then to the base of the coil mount. This keeps it from laying on the intake and unless you look, you can't see it. My car is all numbers matching but stuff like this gets replaced so it works. The next guy can install the original one back in if they want.
Mark.

foliva

My suggestion would be to go to Radio Shack & buy 2 things:

(1) 50 ohm fixed resistor -- about 1/2 to 1 watt
(2) 0 - 1k variable resistor -- about 1 watt

Wire the fixed resistor in series with the variable. Remove the sender
wire from the sender & connect one end of your resistor combo to the
sender wire, the other end to ground.

You now have a temp sender emulator. The 50 ohm resistor will protect
the gauge from overcurrent in the case of you adjusting the variaable resistor to 0 ohms.

With the engine on or the power applied to the gauge, adjust the variable resistor thru it's entire range. As you DECREASE the resistance, the gauge reading should INCREASE.

If, when you decrease the resistance to it'x max, the gauge does not read at maximum, then there is excessive resistance somewhere in the circuit.
Probably, this is due to a bad connection somewhere. The first thing I'd check is the bulkhead connector on the firewall.

Before buying a new sender, you may want to check your old one. Do this
by placing your sender in a pot of water on your stove. You will have to
find a piece of sheet metal. Drill a hole in the sheet metal so the sender
will stick thru but will stop from falling thru by the hex nut. Then, place the
sender & sheet metal in your pot of water. Attach one lead of an ohmmeter to the brass case of the sender, and the other to the top terminal (doesn;t matter which lead is which).

Apply heat to the water until it boils. The sender resistance will start at
around 600-800 ohms at room temp & to around 120 - 140 ohms at
180 deg. Sorry, but I cannot remember the resistance past 180 degrees F.
If you sender follows this behavior, it's ok. The problem, as you can see is the wide variation of acceptable sender readings. This causes for extremely innaccurate guages. There are, however, ways of matching the
sender characteristic to the gauge characteristic for a fairly accurate gauge.

Hope this helps -- sorry for the long post.

Fred Oliva

JohnZ

Thanks, Fred - another very informative post!

For those of you who may not know him, Fred is the "guru" of temp senders, and is also the craftsman who rebuilds those long-discontinued original GM fan clutches.

Chuck Gongloff

Thanks Fred. I printed out your response for future reference. Chuck

Kid_Again

fred...very nice post...thanks :yesnod: