how accurate is the coolant temp gauge?

[thedave]

The temerature sending unit on the 91 4.0 ranger I picked up a few days ago was trashed, would barely get to the N on normal. I replaced it with a new sending unit and now it is reading very high. After flushing the coolant and changing out the thermostat for a new 195 degree one it sits on A and will climb to about 1/8" past L before dropping back to A. I have tested it so far at idle and at speeds up to about 30 mph, have not had a chance to hit the highway.

I should have access to a thermal temp gauge tomorrow but I'm trying to find out if I do have a problem or the new sending unit is simply reading high.

 

[ForOffRoadDriving]

mine has always read very cold on the temp scale, but when i put a real temp gauge in it always runs around 190-210

 

[locovaca]

Working properly they're as accurate as they are on any other FoMoCo product as almost all of them of that vintage us the same sender. Mine was always cold until I stuck in a new sender and from that point on it was "accurate"- meaning it stayed in the normal range when it was normal and you could see when the thermostat opened up when first starting out

 

[calypso93]

This was in response to a slightly different question, but may have something for yours in it---

"I used a non contact thermometer (IR) aimed at the t'stat housing, just about where the upper hose connects. It read from 185-210 while the dash gauge read between "N" and "O". Getting an idea of the actual coolant temp may help in finding the real problem.
An even better tool is a thermal imaging camera. Found a few cooling system problems with one. Lucky we have a bunch at work. Check with some of your fire department friends. They may have access as well."

 

[thedave]

This was in response to a slightly different question, but may have something for yours in it---

"I used a non contact thermometer (IR) aimed at the t'stat housing, just about where the upper hose connects. It read from 185-210 while the dash gauge read between "N" and "O". Getting an idea of the actual coolant temp may help in finding the real problem.
An even better tool is a thermal imaging camera. Found a few cooling system problems with one. Lucky we have a bunch at work. Check with some of your fire department friends. They may have access as well."

Yeah I never updated this, I put a infrared thermometer to the thermostar housing and at the A in normal is right around 195 degrees. I guess te sending unit I put inreads high which is odd but it doesn't waver too much from the A so I can live with it.