temp guage- need help with correct sensor

[knightowl73]

Ive been trying to get the temp guage towork in this truck since i started driving it and no luck. I thought it was th eguage , so i swapped it for the one from the original 73 truck that the motor came from, but nothing. then I bought the temp sensor that goes in the head for the 84 with a guage, but the sensor is too big. the heads are 87-up and the hole is smaller.

Now i want to put the other guage back in so the scripts are all the same , but i dont know what guage sending unit that will work and fit. anyonehad this prob before? I have centerbolt heads and i dont know what ohms or anything the original 84 sender was supposed to work between so im lost. all i know is that it works off ohms and grounding the wire only tests the guage to see if it moves, and it moves then, but never when hooked up to any of the 3 senders that i have tried.

[raws67]

They make a small sending unit and a large sending unit just tell the guy at the parts counter you need the small one. I believe they are all the same function wise.

[78 Chevyrado]

Get one for an 87. I think the only thing that really changed over the years was the amp/volt guage and the oil psi guage. other than the fonts they should be the same.

[knightowl73]

ok thanks, ill try that

[87Bob]

There must be a difference in the years. When I got my 85 from my father-inlaw the temp gauge always read cold. I got a new sender and then it read right. Now I swapped out the gauges and put one in from an earlier year with a Tach and it reads cold again. I only swapped the sender and the later the gauges. Go figure. Maybe one of our electric Gurus will jump in.

[raws67]

the sending units are all the same as far as how they read out the only difference is the pipe thread size. Same goes for fuel sending units I believe pretty much all chevy fuel sending units are 90 ohm. My 78 c10 with a 350 uses the same one as my 82 c-30 454 and my 67 chevelle with 396 uses the same one. The only real difference you get in reading will be if you have the sending unit installed in the head or the intake manifold. Usually you will get a cooler reading if its installed in the intake but other than that they are the same. Look up the part for various years on a web site like rock auto and you will see what I mean. Its not general motors for nothing.

[Slonaker]

I had a similar problem when I did my engine swap. The sender are NOT all the same. I used one that fit the engine, and it read very high. I used an adapter bushing to allow me to put the correct one for my year of truck on the engine, and it works perfectly.

Use the one for your truck the gauge came from, not the one for a different year of engine.

Slonaker

[raws67]

ok looks like you are probably right. I looked up the numbers and the part stores list sending unit from 57-77 then 78 through 90's so maybe there is a difference.

[Slonaker]

When I put the crate engine in my truck, it had a different size hole in the head for the sending unit. I bought one for a 70s model truck, and fit perfectly.

When I was breaking in the engine, it quickly overheated according to the gauge. I asked around here, and was told it might be different. I bought a new sender that was correct for my year of truck, and got a brass adapter from Lowes to make it fit. Temps were right where they were supposed to be.

Since then, I have seen the issue pop up on the board several times, and changing to the sender that matches the gauge has always resolved it.

Slonaker

[Thealien]

The temp senders are definately different. Just take an ohm meter and measure the resistance of a few different ones and you will see a difference. I have a handfull of senders trying to get a newer sender to work an older gauge and it doesn't work!

[knightowl73]

i will try out the sender that goes in the truck tommorrow. Is there any way to check the gauge itself? the one i took out was all the way to the right, even after i took it out. is this bad? should i be concerned with it reading correctly? thinking i may need to get the radiator capp with the guage in it too just to be able to verify if it reads right, but that is like 35 bucks too.