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**MikeB** · 04-21-2024, 05:21 PM

I had the same problem with an LMC gauge meant for a square body truck, and ended up with a shunt resistor that sort of helps. Still, the needle barely starts moving at 160-170, then it's straight up at 190-200, but then moves rapidly to the right. Haven't got up to higher than 190 yet, but I think 210-220 would be around 7/8 of full scale.

I used a bi-metal thermometer in a thread port to do the calibration. Also used a potentiometer as the shunt resistor to determine 100 ohms was a good value. It's been a while, but I think I used a 5 watt wire-wound resistor.

Edit: I read in a few places that using a temp gun on the manifold surface isn't accurate. But I found no more than 1-2 degrees difference between my two guns and the thermometer, when I pointed the guns at the base behind the t-stat housing, out of the fan's airflow.

04-21-2024, 05:21 PM	#6
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,666	Re: Erroneous Temp Gauge Reading I had the same problem with an LMC gauge meant for a square body truck, and ended up with a shunt resistor that sort of helps. Still, the needle barely starts moving at 160-170, then it's straight up at 190-200, but then moves rapidly to the right. Haven't got up to higher than 190 yet, but I think 210-220 would be around 7/8 of full scale. I used a bi-metal thermometer in a thread port to do the calibration. Also used a potentiometer as the shunt resistor to determine 100 ohms was a good value. It's been a while, but I think I used a 5 watt wire-wound resistor. Edit: I read in a few places that using a temp gun on the manifold surface isn't accurate. But I found no more than 1-2 degrees difference between my two guns and the thermometer, when I pointed the guns at the base behind the t-stat housing, out of the fan's airflow. Attached Images __________________ Mike 1969 C10 LWB -- owned for 36 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- converted from 250-six to roller cam 350, Vortec heads -- sold 1981 C10 Silverado LWB, 305, TH350C -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 04-22-2024 at 10:26 AM.