What happened? (84 GMC 6.2 temp gauge started going up and away)

Hello all...

Truck in question is a 1984 GMC Sierra with the 6.2L Diesel underhood. Runs like new and drives well, but it doesn't get out a lot as the body is bad and I only have a makeshift door on the driver's side. It gets started and moved around to keep the batteries up and people from complaining. I'm remodeling a house and sometimes use it to move heavy trash cans. Would like to restore it at some point, but I'm not there yet.

Today it did something strange. All of its life, the temperature gauge has reported 200 degrees F when fully warmed up. I started to back it up with the heat on. It was about halfway warmed up. When I parked it a few minutes later, there was cold air coming from the heater/defroster and the temp gauge was going up rapidly. It got to 215 degrees before I shut it off.

Am I right in thinking that this might be a stuck thermostat, or is it something more sinister? The truck shows no sign of having suffered a major cooling system failure (no coolant smells, milky oil or green puddles, plenty of coolant in the radiator and some in the expansion tank) and it cooled off pretty quickly once it was shut off.

William

Reply to
William R. Walsh
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Could be a stuck stat or any of a number of things. Check all the obvious of course.

Suck stat would be my 1st guess. Of course check the coolant level, and look for any gunk or build up. Don't know about all the modern coolants, but I have seen coolant in vehicles that have been parked for a while turn into gunk that will obstruct water passages. Fortunately, it blows out easy if one takes the time to make a pressure flushing adaptor. (remove stat before flushing engine)

Sorry, I'm not up on diesel much, but gas engines will get hot if run too lean. I have heard that diesel will grow an algae scum in it if it sits for a while. A sludge that can plug filters and injectors and things causing a lean engine condition. I've heard that folks that have to store diesel for a long time, like for backup generators that only get used a couple times a year, add some kind of algicide chemical to their fuel and put in huge prefilters.

Reply to
Bob La Londe

Greetings,

Try the quick and easy stuff first - replace the thermostat and radiator cap and check your coolant level. Also be sure that your radiator has free air flow and that your fan clutch is still good (with the motor stopped if you can spin the fan by hand it's probably time to replace it).

Cheers - Jonathan

Reply to
Jonathan

William,

Maybe try and start it up again and se if it repeats first. One day last winter coming home, about a mile from house I got cold air and the temperature gauge went higher than normal. About an hour later I took it back out and it ran normal. Never did have a problem since. I figured I got an air bubble blocking the flow and letting it rest, let buoyancy do its job.

R> Hello all...

Reply to
Ronald Thompson

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