# 6.2 Diesel running hot



## Huntinfamily (Aug 14, 2010)

Hopefully someone here can help me figure this out. I have an 83 GMC with the 6.2 diesel in it. Two weeks ago it overheated when I was pulling my welding trailer. When I got home and took the radiator cap off the coolant was moving very very slow through the radiator. Figured my water pump was shot and replaced that and the fan clutch, flushed the cooling system and refilled the coolant. Today while driving the engine temp hovered between 200 and 210. After it cooled off I checked the coolant level and saw it was a little low. Before topping it off I started the truck and saw that the coolant is still just trickling out of the spouts in the radiator. Thinking that maybe my radiator is plugged up with rust or something like that. The guy I bought it from used it as a farm truck and usually ran very little coolant mixed with alot of water. Any ideas? Suggestions? 
I know the 6.2 usually runs around 190 but with this huge 4 core radiator the truck has never gotten over 185 when not pulling a load. Btw, it was 91 degrees out today. Not even close to how hot it will be this summer. At the cost of almost $500 to replace the radiator I need another solution.


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## Huntinfamily (Aug 14, 2010)

Ok. I was mistaken. The radiator is flowing great. I only checked the flow at idle. When we revved it up a bit I had great water flow. So it must be something else.


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## Darren (May 10, 2002)

Head gasket leak?


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## bikehealer1 (Oct 8, 2009)

is this a vertical or horizontal oriented core? brass or aluminum core? remember, you can only see a small area of flow looking into the neck. Friend at work had a similar issue with a 2004 GMC a few weeks ago. Ran hot on the way home one night, took it to shop owned by one of his high school buddies. Radiator 85% blocked,water pump killed by a bad fan clutch and stuck thermostat. 

When you drained the radiator for the water pump how much sediment was in the catch pan you used? was the coolant nice and green or rusty brown? was there a build up of rust/crud in any of the hoses you removed? In my experience Chevies seem to have the worst rust problem in the cooling system I have ever seen. I flush my wifes 97 1500 every 8 months trying to get rid of all the build up.


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## rancher1913 (Dec 5, 2008)

your core may need rodded, not just flushed.


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## citxmech (Dec 26, 2011)

Try pulling both hoses on the radiator and putting a garden hose in the radiator inlet wrapped with shop rags to get a seal and see how much flow you get out the outlet. That should tell you how restricted the radiator is. If you can't get a good seal and nothing's coming out the outlet, she's clogged up. 

A head gasket should get you either white smoke out the tailpipe or oil in the water. 

Did you replace the thermostat? You could try pulling it and see what your temps do - If they come way down, put in a new one and see what happens.


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## artificer (Feb 26, 2007)

Another thing to check is to see if the fins are becoming delaminated from the cores. Had a '82 Chevy pickup, and it started overheating. Changed the radiator, and it was good to go. Should be obvious with a quick look.

Another test for a partially plugged radiator is to get an IR temperature gun. Get the engine hot, and shoot temps of the radiator. If you have a variation of more than a couple of degrees, the cold areas are probably plugged.

Michael


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## Yknot (Jan 1, 2012)

Find someone with a combustion leak tester, Napa has them for $50. The 6.2 is famous for the head cracking between the valves. This causes exhaust gases to enter the coolant and cause overheating. A combustion leak test will tell you if you have an internal engine problem. If you buy one it must be for a diesel as it uses a different test liquid.


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## BFFhiredman (Mar 24, 2005)

Have you checked the air flow thru the outside of the radiator? Farm trucks get clogged up with seed heads, pollen, lots of duct and dirt. Gently blow some air thru the fins from front to back then try back to front.


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## Huntinfamily (Aug 14, 2010)

Thanks for all the great advice. Here's what I found. Used my IR thermometer from work and got even readings all over the radiator. Got some of the good quality radiator flush from napa and got a good bit of rust out. Truck cooled off about 5 degrees after that. Pulled the thermostat and made no difference. pulled the grill and fan housing off and pressure washed the entire radiator. Got a friend of mine to use the tester to see if there is exhaust gasses getting into the coolant, was negative. On my way home from work today truck was running right at 200 degrees running about 50 mph when a huge cloud of steam came from under the hood. When I pulled over and looked under the hood my problem was staring me in the face, a nice big leak in the top center of my radiator. New radiator is ordered and should be here tomorrow. These 4 core radiators with the built in oil and trans cooler are expensive.  My Wife pointed out that with the money I have put into this truck I could have bought a decent much newer truck. My responce "Honey after I replace the radiator, with the exception of the steering wheel and passenger door hadle this truck is brand new". She didn't find that comment amusing.


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## Minnesota_6.2 (Sep 1, 2020)

Huntinfamily said:


> Thanks for all the great advice.  Here's what I found. Used my IR thermometer from work and got even readings all over the radiator. Got some of the good quality radiator flush from napa and got a good bit of rust out. Truck cooled off about 5 degrees after that. Pulled the thermostat and made no difference. pulled the grill and fan housing off and pressure washed the entire radiator. Got a friend of mine to use the tester to see if there is exhaust gasses getting into the coolant, was negative. On my way home from work today truck was running right at 200 degrees running about 50 mph when a huge cloud of steam came from under the hood. When I pulled over and looked under the hood my problem was staring me in the face, a nice big leak in the top center of my radiator. New radiator is ordered and should be here tomorrow. These 4 core radiators with the built in oil and trans cooler are expensive. My Wife pointed out that with the money I have put into this truck I could have bought a decent much newer truck. My responce "Honey after I replace the radiator, with the exception of the steering wheel and passenger door hadle this truck is brand new". She didn't find that comment amusing.


any chance you remember where you order the radiator? I’m having a heck of time finding one with 4 core like you’re saying. Hope you’re still active here!


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## coolrunnin (Aug 28, 2010)

Minnesota_6.2 said:


> any chance you remember where you order the radiator? I’m having a heck of time finding one with 4 core like you’re saying. Hope you’re still active here!


Did you try rockauto.com


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## Minnesota_6.2 (Sep 1, 2020)

Yep, ran through all my options through the online vendors. Even went so far as thinking I ordered the correct rad, took it in, and wasn't large enough.

Putting it in a resto project, 1983 GMC G2500 Vandura. Every shop I go to refuses service or falls short finding it too.


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## 67drake (May 6, 2020)

Might not be factory stock, but my hot rod buddies use this place. They specialize in Pontiacs, but will make anything. But expensive!






Rodneyred.com







www.rodneyred.com


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