The Stovebolt Site Forums The Shop Area Engine Shop GMC coolent Temp probe/sensor location?

Hello folks,
I just got a rebuilt gauge cluster for my '49 GMC 1 ton w/ a 228 engine. The original temp gauge didn't work, and the previous owner just stuck a modern after market temp gauge under the dash. It's probe runs to hole way up near the water pump. The rebuilt temp gauge I got comes up about 18" short. I noticed there are 2 threaded plugs in head near the firewall that the new probe could reach. They are not willing to unscrew too easily, so before I bust knuckles to get one out, does anyone know if they are for temperature probes? Where is temp probe supposed to go? I got it from Jim Carter and the offered to lengthen the probe tube for me, but I would rather not have to pull the gauge out again/ship back/reinstall. Thanks in advance for any ideas or suggestions!
Greg

Greg
In your '49 GMC the temperature sensor was probably an electric one mounted in the thermostat housing as shown in this photo. '49 temp sensor In my '52 the temperature sensor is a mechanical bulb that is mounted in the cylinder head. It is located behind the carburetor in this photo. '52 temp sensor The bulb screws into a bushing that is screwed into the head. Most of the vendors carry this bushing if you don't have one.

Huck,
Thanks for the very useful info. The original broken gauge did have wires coming from it, so now it makes sense why. Does that threaded bushing have a common name I can ask/search for? Is it common to a hardware store, or is it mostly old truck related? Thanks again!

get one from carter. while your waiting for it to arrive heat up a pan ful of water and drop a thermometer in the water along with the bulb and slowly raise the temp of the water to 180-200 to see if the bulb somewhat matches your thermometer. while your at it, drop your thermostat in too and observe its operation in regards of temp with the bulb and thermometer from closed to fully open. it will keep you from guessing later.

51 Ashton,
I see the part on Jim Carter. I think there actually is one already in the truck being used with the existing gauge. I'll have to take it out and see how it fits with the new one, and if it fits in the head.
Good advice on doing a controlled test with the 'stat and new gauge - thanks for that one!
Greg

HI

Just remove the sending unit and adapter from the thermostat housing. Use a 1/2" drive 6 point socket to remove the adapter.

Remove the pipe plug from the head just behind the carburetor. Use a 1/2 drive square socket (4 or 8 point) to remove the 3/4" pipe plug.

Use the pipe plug, to plug the hole in the thermostat housing and reinstall the adapter in the hole in the head. Both are a 3/4 inch pipe thread.

Then connect you new Temp gauge sending unit/probe to the adapter behind the carb.

Good Luck,
GMCPic