The Stovebolt Site Forums The Shop Area Interiors GMC temp gauge in a Chev 235

I have a '40 Chev 235 with the stock Chev gauge with capillary tube. Anyone know how I would make a 40-46 electrical GMC temp gauge work?

Thanks
Dennis

If you have the correct electric sending unit for the gauge, pull the original cap tube bulb out of the engine, figure out what thread adapter is needed to install the electric sending unit, one wire from the sending unit to the gauge and wire the hot side of the gauge to be energized with key on. Is everything staying 6 volt?

Doesn't sound too tricky then. I only have the NOS gauge. I have yet to source the sender. I am 12 volts but that shouldn't matter, right?

I believe you will have trouble finding/matching a sender to the gauge. Then there is the 12V issue...... and don't know if a GMC gauge matches/fits a Chevy cluster.

My suggested options: (headache prevention)
1. Buy a capillary gauge.
2. Buy a 12V electrical gauge and sender set.

It is possible you may find "original" parts here on Stovebolt or Ebay and etc.

Your 6V gauge would need a voltage reducer.

Click

... and the GMC electrical system was positive ground.

Are you saying the GMC pos. ground would fail with a neg. ground system? Would I swap + - posts on the gauge?

If you find a sender that works accurately with your NOS gauge. Please post the part number info here. There are many of us that have been searching for years without any luck.
I bought a NOS gauge myself, thinking that might solve my issue. I went through 5 different used original sending units comparing them to a mechanical gauge that I installed temporarily. None matched. I made notes on each pair. I then used a used gauge and went through the process again. Nothing matched. One more gauge and repeated. A used gauge and a used sending unit came close on the mechanical gauge temp reading. It was strange how every combo was different. It convinced me to go with the mechanical one. As much as I wanted to keep mine original, I wanted to make it reliable and not damage my motor.

DennisM - Since no one else has asked, I'm going to toss this question out. Your signature line says you have a 1940 Chevy 1/2 ton, and you said your engine is a 1940 235. What's driving the train on wanting to use the GMC electrical gauge?

You also mentioned you have a 12V system. Guessing since it's a Chevy that it's negative ground. Just saying that the significant lack of available electrical sending units is going to have you hunting for years (if not decades) and I seem to recall that the Chevy gauges are different than the GMC in appearance. Wouldn't it be much easier to use a correct Chevy capillary tube gauge for what you have?

Don't know, just posing the question. I looked through both the 39 to 50 something GMC Master Parts Books that I have. The electric temp gauge is listed as a bunch of different part numbers over that range of years, but there are NO listings for electric temperature gauge sending units. Like Dan says, finding the right one is going to be tough.

Well, this is turning into the can of worms. Sorry for the confusion. This is for a 1940 Chevy with a 1960 235. I came across a NOS GMC cluster gauge. The size/shape is same as Chevy. No problem. Simple, easy swap. I actually like the color of the GMC vs Chevy so used the GMC decals a couple years back when I rebuilt the truck. This all started when my speedo failed. I rebuilt it myself but kept have issues so I just swapped the speedo. That required another cable, which I had. This is on another thread here. The calibration was off because the Chevy has 0-100mph and GMC is 0-80. Soooo, I'm now using the GMC housing & speedo with '40 capillary tube temperature gauge. AMP gauge is a modified aftermarket voltmeter gauge as described on this site. One more change will be to use the GMC oil pressure gauge since it is 0-80 instead of Chevy 0-30. Fuel gauge is Chevy.

I thank you all for your insight on this. Let's call this one handled.

Thanks,
Dennis

Dennis - Thanks for all the splaining and clearing up with details. All the info helps me see where this all came from and how it sounds like you've been able to finish it up. Sorry there wasn't an easy answer on the sending unit.

Bill - the electric temperature sending unit should be in your books, group 7.5050 P/N 1511734 (1510774 old) 6 volt. From 1939-1955 all gas trucks.

Oddly enough, a web search for GM# 1510774 came back with an actual result. If you want to use that NOS GMC Temp Gauge, click HERE. The source in Holland says they have 2 in stock (looks like left over WWII parts stock) and the pictured sending unit with original GMC box looks like the critter you seek. Be ready to pony up for the asking price plus international shipping though.

Looks like only 1 left now. Price is 86.70 euros or $90.30 at the time of this post

When you have an 85 year old truck, you should be grateful that an original part is available at any price. Buy it.

I did, that was me that gobbled up one! It looks too fat to fit into my '60 engine so will need an adapter. Hope having the probe higher up won't be an issue. Came out to be $93.31. Thanks for finding it Dan. Never thought of querying the part number. I'll remember that in the future. Yeah, me that forgets everything.

Dennis

Dennis - Glad you were able to snag one and hope you can find an adapter to make it work, if needed.

Perhaps jimgmc or Bill Hanlon can confirm what size the GMC head temp sensor port thread size is to compare with the 1960 235 temp sensor port??? Too hard to tell from that picture what size the sender is and their description doesn't provide those details either.

Early (39-54) GMC Master Parts Books show a reducing bushing to screw into the port near #5 cylinder position on the head that the sending unit then screws into. But the MPB has no information about the bushing. Most 55.2 thru 60 GMCs used a port on the lower thermostat housing for the temp sensor sending unit (and I think, but don't know for sure) did not drill and tap the head between cyls 4 & 5 for a sending unit.

I have a GMC head casting number 2193983 that was used on military and '52 thru '62 302 engines (the big port head). I just measured the size of the hole for the temp sending unit at 1/2" - 14 NPT. I'm pretty sure the head on my '52 truck's 228 engine has the same size hole, but I don't want to drain the coolant just to find out.

Another interesting thing about this head is that it has another 1/2" NPT hole at #6 cylinder that is piped up to the thermostat housing. It is used to get additional hot coolant (and any air pocket) away from the imfamous "hot spot" in the head. Most GMC heads have a flat spot here on the head casting, but it is drilled and threaded on the military heads.

Two Jimmies, Here's the info you asked for. Over the years these parts are all equivalent: 1511264, 1511734, 1510774, 1512015 and an old (NAPA) Echlin part number TS-6162. These will work with the 40-46 GMC gauges. I hope this helps.

David