Checking engine temp gauge

[earl84]

My truck has not been run all that much, but it has been run a little. I just finished doing the entire AAW wire harness install and have run the engine since then and the temperature gauge stayed in normal operating range. Prior to that, the PO had an aftermarket gauge on it and it ran in the normal heat range. I removed that (now I wish it was still installed) because I want to go back to close to original look.
Anyway, I got my heater core fixed at a locla radiator shop, reinstalled it, and connected everything up. This was sort of the last thing of MANY little projects to do prior to calling it roadworthy. Well, I went for a very short drive, and the factory temp gauge was quickly heading to the danger zone. I pulled over and let it cool, then brought it back home. Checked coolant level, good. Checked for any water in oil, good. Keep in mind, it has run before and there were NO issues. The engine was not overheated, didn't smell hot, nothing.

There were only two things different than prior when it was running normal temp. One was the heater core, so I bypassed that and the temp gauge was still showing it getting hot. The heater core was flowing water through it just fine when I shot a water hose through it.
The other was that I pulled the gauge cluster out to clean up some other wiring, and also had to mess with the wiring that ran to the back of the alternator and the temp sensor on the engine (they run together in some nylon braided sleeving. So maybe I pinched the green wire for the temp sensor to the temp gauge. Hope not.

So what is my question after that long diatribe? Is there an easy way to check whether my temp gauge is bad? Or my wiring? I guess I could check for continuity and/or run another temporary wire in the engine compartment and see what happens.

I am thinking of getting another cheap temp gauge and installing that, just for troubleshooting purposes. Is there a better/easier alternative?

Sorry for the long post, just thinking as I type and trying to give a complete picture of what I have done and am thinking.

[Captainfab]

What I have done in a situation like this is use my infared temp gun to check the actual temperature of the engine. If you don't have one, or know someone that does, Harbor Freight has inexpensive ones. Although I do not know how accurate they are.

[earl84]

What locations are you aiming at to check the temperature? Are you expecting to see the same temps that would be diplayed on a temperature gauge, like around 180 or so?
I have been so close to buying one of those guns in the past, wish I had now, dang it.

[theastronaut]

Could use a meat thermometer in the dipstick tube. Check the accuracy of the thermometer in a pot of water, boiling is 212*.

[Jared102000]

I have a similar problem. I replaced the part that screws into the block and still have this problem. I didn't have one of the temp guns so I bought an aftermarket temp gauge at O'Reilly's for $22 and it ran right at 195 degrees which I think is normal. Just an alternative for now until I find the real problem.

[earl84]

I think I have figured out my problem. The truck had been sitting for a while before I got it almost a year ago and I have porbably only driven it about 30 miles. I think some of the gunk broke loose and was slowing the flow of water down, and the thermostat was not opening correctly. Got a new thermostat and replace it first, same problem, but that's when I saw how nasty the coolant was. I did change that along with all the other fluids when I first got the truck. Anyway, flushed it all out about 6 times, water running clear, then found out I had a 195 degree thermostat. Had to go back to the store and get a 180 degree.

Still runs on the high side of the gauge,but not redlining. Gonna drive tomorrow and see what happens. I may have to get a cheap temp gauge and install just so I feel safe, at least for a little while.
Thanks for the replies, guys.

[luvbowties]

Originally Posted by earl84

I think I have figured out my problem. The truck had been sitting for a while before I got it almost a year ago and I have porbably only driven it about 30 miles. I think some of the gunk broke loose and was slowing the flow of water down, and the thermostat was not opening correctly. Got a new thermostat and replace it first, same problem, but that's when I saw how nasty the coolant was. I did change that along with all the other fluids when I first got the truck. Anyway, flushed it all out about 6 times, water running clear, then found out I had a 195 degree thermostat. Had to go back to the store and get a 180 degree.

Still runs on the high side of the gauge,but not redlining. Gonna drive tomorrow and see what happens. I may have to get a cheap temp gauge and install just so I feel safe, at least for a little while.
Thanks for the replies, guys.

Have u thought about how accurate your sending unit is? Keep in mind that new doesn't necessarily mean accurate or good! As posted already, checking actual temp with a temp "gun" will answer lotsa questions. I've used an inexpensive one from Har Frt for years, and been pleased with it. When I 1st got it, I 'verified' its readings by comparing with several cars whose gauges I comfortably trusted.
Sam

[earl84]

luvbowties, I have run it before with the current sending unit and the temp gauge stayed in the normal range. So, I am thinking this isn't it. It was a new sending unit, though. I think to really feel comfortable, I just need to get another gauge and put it in temporarily, and also get one of the HF temp guns.
Gonna be a few weeks before I can nail this down, heading out of town soon.

[luvbowties]

Earl, often when a new problem arises, we need to verify the last changes we made to our ride prior to the prob's appearance. You stated, " The other was that I pulled the gauge cluster out to clean up some other wiring, and also had to mess with the wiring that ran to the back of the alternator and the temp sensor on the engine (they run together in some nylon braided sleeving. So maybe I pinched the green wire for the temp sensor to the temp gauge." To check for a partially-grounded green wire, disconnect it from the sender AND the dash gauge. Replace it, temporarily, with a new wire, routed directly from the sensor to the temp gauge. Will tell u quickly if this "only thing different" has caused the now-higher reading--and maybe save hours and dollars spent on aimless/useless/wasted testing. Good luck on solving one of the most likely toughest problems to diagnose--an electrical dilemma.
Sam