View Single Post
Old 05-27-2014, 11:57 PM   #5
ray_mcavoy
Registered User
 
Join Date: Nov 2009
Location: Sherman, ME
Posts: 2,373
Re: Coolant Temp Gauge - What makes it work?

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 View Post
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.
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.

Last edited by ray_mcavoy; 05-28-2014 at 12:09 AM.
ray_mcavoy is offline   Reply With Quote