I have a 85 Blazer with the 6.2 Diesel. Driving it around town it runs at 180 or so, never overheats. We took it on a trip last week and every little hill we came to would cause the temp to shoot up.....on one particular hill (6% grade for 6-8 miles) it jumped up to around 240, as soon as we leveled off it went right back down. I checked the radiator when it cooled down and it looked like it had nothing but straight antifreeze in it. Does anyone think that the straight antifreeze could be what is causing it to over-heat?? Oh and I think the over-heating fryed some of the glow plugs because after we got back, the GF used it one time the next day and now the wait light stays on way too long and it won't start. Does the over-heating sound like a logical glow plug killer?

Glow plugs don't need a reason to die. Same with the Relay/timer.

As to the Overheating, First, I'd change the thermostat, because that's the cheapest place to start. Get one of those cheap antifreeze testers, and find out if that's strait antifreeze in there. If it is, Dilute it. What kind of fan are you running? if it's the factory clutch fan, the get the motor hot, SHUT THE MOTOR OFF, and try to move the fan back and forth. if it's tight, and hard to move, cool. if it's easy to move, then your fan clutch is toast. if you're running one of those aftermarket flex fan thingys, then throw it as far away from your diesel as you can, and replace it with a factory clutch fan, or a pair of good electrics. Is your fan shroud intact? If not, fix/replace it. Do you have the four core radiator? if not you need one. What kind of anti-freeze are you running? If it's the Orange stuff, get it out of there! That stuff will clog a radiator inside a couple of years. Also, the waterpump could be going out. That's about everything I can think of. Hope this helps.

Also, have you noticed it black smoking more than normal?

Thanks for the tips. And there's no more smoke than usuall.

Additionally; most basic replacement tstats are troublesome, look for a genuine AC or Robertshaw for max flow.

If you have straight anti freeze that will cause you to get an "iron hot" condition and it will cook the relay at the back of the head that runs the glow plugs. it may have burned some out so once you replace the relay then test for bad plugs. and the when you delute it make it about 50/50 water & anti freeze.

by the way has the radiator been flush recently? it could be plugged a bit and causing it to restrict the flow. if you lower the coolant level do you see white crustys on the end of the cores? if so you may want to have professionally flushed

rread your anti-freeze jug it gives ratios for a reason. straight anti-freeze about the wors't thing youcan use behind straight water

Thank you guys for all the help. Just to let you know, I'm not the one that put straight antifreeze in it.....the guy I bought it from a couple of weeks ago is actualy from, where else....California :flipoff2: Just kidding. He is part owner of a tranny shop in San Diego and owns a cabin(where he kept the Blazer) in Oregon.