I agree with what Rich posted about the GM #1513321 sending units.
However, GM only used the #1513321 up through 1978. They changed to a different temperature vs. resistance curve for the gauges & sending units starting in 1979. And based on your
BigBlue86K30 name, I assume your truck is a 1986, correct?
The 1979 & newer temperature gauges are designed to work with either a GM #8993106 or #8993146 sending unit. The #8993106 has 1/2" NPT threads while the #8993146 has 3/8" NPT threads. They're both approximately 1425Ω at 100°F and decrease to around 147Ω at around 220°F. Those are nominal ratings and can vary ± 10% or so.
The #1513321 sending unit (for 78 & older) has lower resistances across the whole temperature range and will therefore make the 79 & newer gauges read too high.
Quote:
Originally Posted by BigBlue86K30
I am curious as to what ohms would show 100, 210 and 260 on the gauge, if I knew that I could use my test tool to check the gauge.
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Based on testing some sample gauges, here's what I've found for the later 80's gauges that have the 100, 210, and 260 markings:
Anything in the 1500 to 1200Ω range will make the gauge read close to the 100°F mark.
Around 105 to 110Ω will make the gauge read close to the 210°F mark.
Around 58 to 60Ω will bring the gauge up to the 260°F mark.