The Stovebolt Site Forums The Shop Area Engine Shop Temp sender issues

So I finally got my rebuilt 235 up and going. I'm having some issues with the temp gauge and I'm hope you can help. I have tried two temp senders in the engine, one reads like the engine is over heating ( jacked all the way to "H"), the other sender is reading like the engine is running cold ( staying on "C" ). The one that's showing HOT is one I bought from Checker, they sold it to me as one being from a '62 C10 235. The sender that's running cold is one from a box of parts I received when I bought the engine. Both look the same but are acting completely different from each other. I know the gauge is working, because when I ground the green lead, it goes over to H on the gauge. Is it as simple as the one that reads Cold is just bad and the one that reads hot was just not the corect year/model for my engine. Is there a difference in temp senders from '59 to '62 Chevys?
My truck is a 1959 3100 with stock 235, enigine is a '59 to '62 block and the head is a 848

i had the same problem with my sender. i ended up putting it in the oven and tested its resistance vs temp until i understood its curve. Next i figured out what equation represented that curve. i then added additional resistance in the wiring to set up the gauge so it read in the middle when the truck was at 180 degrees.

overheating, but maybe not...

a C reading means an open circuit, a full H reading means a short circuit - checking the new sender a pan of water is a good idea, entirely possible it's defective out of the box - also do a resistance check on your wiring .... OTOH the gauge reading H when you short the lead to ground doesn't have to mean that it's good, you need to put a variable resistance in the line [like a known good sender] to tell that

Bill

I forgot to add that I have an infrared thermometer and all the readings I took were within spec i.e.: radiator, at the front of the block and the back of the block where the temp sender is.

so either your new sender is defective [most likely], the gauge is actually bad, or the wire to it has a short when you hook it up

Bill

Thanks for all the replies so far
Well then it's between the sender or the gauge, because the wirings all new and I checked that as well.
Just bought a new sender, i'll be throwing that in tonight or tomorrow. I'll post what happens then.

So I installed my new temp sender this morning. How tight ( torque ) do I screw it in: 20-25-30 ft/lbs??

I saw this last night and thought it might help.
Bolt torque spec's

After installing the new temp sender, I took a quick ride around the neighborhood. And now the gauge is reading hot again??? I took my IR Temperature gauge and took some readings, all were within normal operating temps: top of radiator 158, just below gooseneck 195, back by temp sender 185. Here is a pic of the gauge:

http://i1236.photobucket.com/albums/ff441/AZ59apacheguy/IMG_1397.jpg

Is this were the needle sits during normal operating temps?????

not on mine, runs a bit below center when well warmed up .... I'd say find a different gauge that shows more of a center reading at correct temps

Bill

Do the aftermarket Temp Gauges work with the temp sensor I just bought and installed?

it might, the sender is just a variable resistance, but usually when you buy a 'generic' gauge it comes with a sender .... post in the parts wanted for a used original, you'll find one that works better, and keep in mind these gauges are just a general idea of things, checking against your IR gauge tells you what the stock gauge is saying and if it acts different sometime you know something is up

Bill

Sound advice, except mine did not have much farther to the right to go to tell me if it was over heating or not LOL

So I picked up a new Temp gauge from Grumpy's Trucks here in Phoenix. Installed, test drove and so far the temp is sitting RIGHT IN THE MIDDLE of the gauge, BOY was it nice to see that!!!! With the same distance traveled, the other gauge was reading very hot temps ( picture earlier in my thread ). It's also over 100 deg F here in Phoenix, so it's nice to know my radiator is handling the heat as well. Even small victories feel good.......

I installed gauges and a new sender and it was a tad short so it read head temps and reads 20 degrees high. i put a radiator cap on that has a thermometer in it and i check it periodically.