dr4

C1500 2WD, 5.7 liter, 275,000 miles, never warms up fully. Temp on guage varies between about 150-175. Also slowly loses water but no visible leaks. Have changed out thermostat, radiator cap and temp sending unit. Changed out fan clutch several years ago and suspicious of it. Any ideas would be greatly appreciated.

bandit_601948

is the temperature really low of just shows it's low ? maybe the coolant sensor is going bad !

dr4

Thanks for the suggestion! The connector on the sensor was bad so I changed it out too. The temp at the radiator cap is only about 125 so that's what's got me baffled. I'm still thinking maybe the replacement fan clutch has already locked up, because when it's cold I don't hear it cut on and off on warm-up.

Suburban Dude

Hi. What temp rating was that thermostat? It’s not likely the fan can cool the motor to the to the point of overwhelming the thermostat. Case in point, even at 40 below the thermostat will made the temp rise to the rating of the thermostat. I would recommend two things. Purchase a infrared temp gun (the one with a laser pointer. ) Check the temperature on the engine, at the manifold, the rad cap and the engine bock. Once you confirm the temps, if they really are low, buy another thermostat and install it. You probably have a bum thermostat.

Does your Burb have a rear heater? If so, go under the truck and check the lines from the front of the truck to the rear. If you don’t see a leak, pull the cover of the rear heater assembly and take a look at the rear heater core. Good luck.

SD

oilcanhenry

Have you checked the true temp with a thermometer? Could be a bad sending unit or the gauge isn't reading correctly. You can up the temp by blocking off part of the radiator with something like cardboard or vinyl, like the truck drivers do in cold weather, also. Wont go into the thermostat, as the others here already covered that.

I had a small coolant leak myself on a 4.3 Liter Chevy pickup. Never could find out where it was leaking, but it wasn't into the motor oil. Likely a small head gasket or intake manifold leak. A can of Alumaseal put a stop to that for good.

dr4

Thanks for the replies, sorry, they got sent to spam for some reason.

I think i'm mistaken--the air coming out of the dash heater vents is as hot as ever, so it's probably coming right up to the rated temp and just not showing on the gauge. Might see if I can wire in an under dash temp gage and just see if it reads the same.

The thermostat is the one recommended, 185 degrees F if I'm not mistaken. Just changed it out recently, and tested it in a pan of water on the old coleman stove. It opened and closed with 2 or 3 degrees either way of what it was rated.

Next step will be to check the rear heater core. Thanks for the idea--never thought to look there. The front heater core is not leaking, but if the back one was I'd probably never know it.

Alumiseal will be next if there's not a leak there.

Thanks, guys.

dr4

Forgot to pass on something else I tried. One recommended test of the temp sending unit is to unplug it and jump the connector on the harness side. Turn key on, not running, temp gauge should top out to high side of gauge. Mine only came up to about where it does when running (150 +/-). I think this means the gauge is bad, since the other voltage test of the sensor itself which was new, came out okay.

Hope this helps somebody else trying to figure out wth is goin on with temp gauge.