I can drive all day unloaded with no issues. I can pull several tons around with no problems either - until I pull a long grade and then the temps climb and I reach 250* in just a couple minutes. Exhaust temps stay normal.

I know my head gasket weeps ever so slightly so I'm going to replace that. I keep the coolant topped off. With about 170K miles I'll also put in a Cummins water pump and thermo. I'll flush out the block while everything is down & open.

Just wondering what is causing the overheating exactly since the headgasket doesn't seem to be it. There's no coolant in the oil, no oil in the coolant and my exhaust hasn't changed color. So I figure its leaking out not in as well.

The radiator fins "look" clean, from reading searches this has been the problem for several. My truck is not oily. Inside "looks" OK although I can see some scale. But when running the top hose never gets hard or pressurized. The heater works good. The cap is new (flip top). Fan runs even when cold (thats not normal is it).

Using an infra red thermo the radiator is flowing, but maybe not enough under a load? The last time it overheated I didn't have it with me to check. The day started in the 30*s but warmed to the 40s* and I had 1/2 the radiator blocked which is normal and never been an issue before in our mild winters.

NAPA wants $300 for a new rad. With the truck being 20 years old I guess a new one isn't bad preventative maintenance but at the same time I'm not want to throw $$ at a problem until I eventually find & fix the offending part...

Any ideas? I can't see the forest for the trees...

 

These symptoms ring of clogged up radiator, with enough capacity with no load, but heats up under load. I have seen this before. IMO, of course...Mark

 

Mine did basically same thing when the head gasket was leaking on mine too. Just a light load on a 16' trailer would make it get hot on the highway. I replaced it and it don't do it any more. Hopefully that fixes yours. Good luck.

 

I had the same problem with mine. All was great until I pulled the toy hauler around, 10k lbs loaded. The truck would just rev pulling grades, sending the temp gauge to the hot side. The tranny temp switch would then kick it out of OD. I figured the converter was getting everything too hot, with the higher stall speed. I installed a goerend with a lower stall speed and it really gets the power to the ground. Just my experience, but all seems good now.

Mike

 

I would try cleaning your rad, even if all the cores are 75% plugged it will still look like its flowing properly on a thermo. The best method I've found is taking the rad out, laying it horizontally on its front and filling the rad to the top of the hose couplers with a good rad flush. Then every once in a while hold your hands over the hose couplers and swish it back and forth. After sitting for whatever time it says on the bottle flush it both ways with water until junk stops coming out. You will be surprised at the crap you get out. Doing this has saved me getting a antique rad rodded many times

 

I'd fix the head gasket first. If that doesn't solve the overheating problem, get the radiator serviced or replaced.

Head gasket needs fixin' anyway, and it might be the problem. It's just a matter of economics.

 

Are you sure that your fan clutch is working? I don't tow much so I don't hear my fan clutch hook up often, but when it does it roars.

JP.

 

I'd go ahead and replace the headgasket. While the truck is down during that, have the radiator cleaned up. If not, a new Spectra radiator from Rock Auto will only cost you about $200.

 

To me it sure sounds like a cooling issue, or lack of air flow. As others have suggested the cheapest would be to remove the rad and back flush it. I do this every time I take my rad out. I turn it upside down, hand over upper rad opening, then fill with water, then let the water rush out. Then fill it part way and swish it up and down, back and forth and flush it again. Alternate filling and flushing from top and bottom.

But it could be the clutch fan as suggested as well. When she's running hot on the highway maybe pull over and quickly shut it down and check the clutch. It should be almost 100% locked up. If the blades move more then an inch or so I'd say your clutch fan is toast. Again a cheap fix as well.

You are running a fan shroud?

 

Appears that I'm hunting the right trail. Concensus says head gasket/radiator or air flow.

Is the Spectra radiator a good one?

I'll proabably not replace mine unless I can't clean it out good enough. Water flows in the top and out the bottom right?

How does the fan clutch work? Mine is spinning all the time, even when cold. I'll try to spin it once warmed up & see. And yea, I still have the shroud.

I'll call Tuesday and see what the shop I use wants to check and redo my head. Already priced the gasket & bolts from Cummins.

BTW - my trans temps are staying good. Totally unaffected buy motor temps.

Thanks for all of your alls observations and advice. Its alway good to get a different perspective. Sometimes when you're studying a problem so hard you overlook something simple.

Happy 2012

 

You can do the head gasket yourself. I did my first one last year and took me 9 hours. Saves the $$ by not paying someone else to do it for you.

Happy New Year !

 

I plan to. I'll just have the shop check the plane and valves if they're cheaper than a swap with a new one from Cummins. I hear they are heavy huh?

 

Yes, they are heavy. I used a friends cherry picker to help get mine off.

May as well while you have it off, put new seals in it, check the valves. Thats what I did, but mine had around 300K on it when the head gasket finally went out of it, up by number 1 cylinder.

 

Got the head off. Was warped a bit so they took 0.12" off.

 

That's normal. They're always gonna be warped most on the exhaust side, too. When I had mine off, they machined .006" off of it. They also gave it a valve job and replaced the seals.