Temperature gauge

[miket007]

Hey guys-


I am hoping you can help me out...I just bought a 78C10 with a 350 HO crate motor. The temperature gauge barely moves after driving the truck for a while...even in AZ with AC running. I verified there is a good lead running to the sending unit on the drivers side head. Is there a good way to test the gauge and the sending unit? Is there a compatibility issue between the older gauge and a newer sending unit? I have no overheating issues.

I am trying to fine tune the motor but I need to benchmark the full operating temp.

[bd]

Assuming you've covered the basics and verified actual engine temperature with a thermometer in the radiator, see the thread: "Correct temperature sender and connector" by member, Rich Weyand.

[miket007]

Assuming you've covered the basics and verified actual engine temperature with a thermometer in the radiator, see the thread: "Correct temperature sender and connector" by member, Rich Weyand.

Perfect! Thanks...exactly what I was looking for.

[Project86]

I'm having a similar issue with my 86' 305 engine with OEM gauge. The gauge itself test out at 240 ohm @100 degrees and 40 ohm @ 260 degrees, any idea as to the correct sender I need? I've tried a couple from the auto parts stores that say they're the correct one for my truck but they read hot on the gauge. If I remember it was reading 225 ohm @ 160 degrees. Any help on a sender would be much appreciated. Thanks.

[miket007]

Well I have finally been able to track things down abit. The temp sensor is likely the culprit and it appears to be a 3/8" NPT which I think is a TS-76 (GM #8993146). Makes sense as this has a vortec head crate motor. At 110 degrees it was at approximately 1100ohms.

Does anyone know what the correct ohm rating on the sensor which works with the original temp gauge?

Anyone know by chance what temp sensor in 3/8" works with the stock gauges?

[miket007]

I did some more looking and found this post on here that gives us an estimate fo the ohm swing for the stock gauge. (http://forum.73-87chevytrucks.com/smforum/index.php?topic=25339.0 ) which appears to be 350 ohm cold to 46 ohm hot.

I have a TS-6 but it is 1/2"npt which is too big. Here is data on the TS6...resistance is close...

Temp sensor: TS-6
Thread: 1/2-14
Ohms @100 deg. F: 368
Ohms @220 deg. F: 80

However the TS-76 is 3/8" NPT but the wrong resistance.

Temp sensor: TS-76
Ohms @ 100 deg. F: 1425
Ohms @ 250 deg. F: 147

So really I need a 3/8" NPT sending unit with a resistance swing of 350-46 ohms roughly.....any ideas?

[miket007]

Well, I think I found a work around.

Instead of trying to find a sending unit to go in the head, I decided to use the TS6 (1/2") and put it in the manifold...there is a 1/2" threaded port already there for it. Will know how it works tomorrow!

[miket007]

All done...moved the temp sensor right up near the thermostat housing...used a TS6 which is 1/2"...wire was just long enough with the right connector...put a 160 thermostat in it...and its doing fine!

So for those with older trucks and gauges and vortec heads...don't drill and tap the head, don't machine down a TS6 to fit the vortec 3/8" hole...just move the sensor! 

[blazer74]

I have also done this, the only diff I see is the temp initially reads higher until the thermostat opens then reads normal.


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[78BIG-TEN]

I know that GM had a sender with the smaller thread size to work with the older gauges.The replacement motors back in the day(Target and later became Goodwrench).Whenever I purchased one the dealer would send a sending unit with it