Diesel Temp Gauge Accuracy

[RLC2020]

Pic below of my temperature gauge after running at 45mph for 20+ minutes, the gauge never gets above this point and it starts out right at the cold mark so I know it's at least reading something. What temp thermostat is stock and/or what should I run for the 6.2? I'm going to order a new one before I take it apart. I'm assuming it's stuck open, but anyone else with a diesel can chime in with where there gauge sits normally. Too cold is better than too hot, but I want it to be right.

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[Blue Ox]

I believe the 'stat is supposed to be 190°. I've had trouble with a lot of aftermarket thermostats because they're a plate style instead of a sleeve (or something like that. Not sure of the terminology) that the coolant flow can push shut at high RPM. Installed the proper Delco and it solved the overheating problems.

 

[RLC2020]

Delco 190, Thank you very much. I'm guessing yours runs hotter on the gauge then the picture I put up?

 

[Blue Ox]

Yes. My gauge has numbers on it, but when it was working right it usually ran just slightly to the left of straight up. So 190°. Ignore what it looks like right now. Something's gone wonky.

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[BKING33]

I have a mechanical gauge on mine and it runs around 190 to 200 at normal operation

 

[highdesertrange]

first off why are you going replace parts that you don't even know are bad. you need to troubleshoot this and find out what is actually happening. I would start by finding out exactly what temp it's running at. remove the radiator cap and put a known good thermometer in the water and see what it's running at. next check the sending unit with an ohm meter then check the gauge with the correct resistors. this will show where the issue lies.

remember if you just start replacing parts willy nilly you might be replace better parts with inferior junk parts.

highdesertranger

 

[75gmck25]

GM changed the resistance profile of temp senders over the years, so you really need to know the actual engine temp before you try to fix the gauge. I finally installed a mechanical temp gauge under the dash and used that for troubleshooting until I found the right sending unit for the dash gauge.

Stock thermostat would be a 195. I recommend using a Stewart high flow 195 degree thermostat, or similar design. With that thermostat and a good OEM thermal clutch fan the engine will always run in the 195-200 degree range, which is exactly what you want.

Bruce

 

[RLC2020]

all going points. I'll take a temp reading before I do anything. I can also test the thermostat that's in there to see what temp it opens at before I start replacing things.

 

[NCBurb]

Jumping in here because i also have a 6.2 with wonky temp gauge. Where is/are the best places to measure temperature for reference? With engine warmed up and running I assume, just shoot an infrared thermometer at the radiator? block itself? Where?

 

[highdesertrange]

infrared thermometers are a great tool but you must remember they are not measuring the true coolant temp. they will get you in the ball park. remember an infrared thermometer will not accurately measure a liquid. you can't take the radiator cap off and point the thermometer into the coolant, it will not give you an accurate reading. a mechanical gauge in the head will get you the coolant temp in the engine.

I like to put a regular thermometer in the coolant in the radiator then compare that to the factory gauge.

highdesertranger

 

[NCBurb]

good point. So basically warm up the engine, then pull the cap and stick a thermometer in while it's running? That should be within a few degrees of the temp circulating through the engine, right?

 

[highdesertrange]

yes and then take a ohm reading of the sending unit at the same time. that will probably answer a few question. to get real precise hook a resister up to the sending unit wire and see if the gauge respond like it is supposed to. I have a resister box so I can adjust the resistance in real time to check the whole gauge circuit. somewhere on here is the chart of what the sender should read in ohms. hope that helps. highdesertranger

 

[Blue Ox]

Aside from trying to open the cap on a hot radiator it should work.

I would probably just start with the IR gun if you have one. It may not be super accurate, but you're talking about a 100° temperature difference between the C and the middle of the gauge. It would steer you towards whether you're chasing a cold engine or a false temp reading.

 

[Grit dog]

20min straight driving in your weather OP, would get it up to operating temp, even with an open tstat I bet. Surely you’ve driven it a little harder than that? Gauge stays the same? If so I wouldn’t worry about it. Hell , it works. So wherever normal is, is “normal.”
Although you may put in a new temp sender. It could be original and not reading right. Cheap fix for an otherwise old unknown part anyways.