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Discussion Starter · #1 ·
I have had a 99 cummins for 6 months now. It has 175000 miles and ive had a few computer problems but have it runnning fine now. I haven't towed anything with it until this weekend when i pulled my new fifth wheel toy hauler about 150 miles. The temp climbs when doing hills. The check guage light came on once. I was taking it easy and babying it. It has more power but the temp will just come up. Any suggestions? It has good coolant. Right level. If it wasn't for this problem i could have kept up with my dad's 07.5 duramax.
 

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Doesn't sound like a t-stat issue most likely it's just the weight of the hauler. I assume it's not to heavy.
 

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You could try doing a coolant flush although i dont really think thats the problem. Im not saying its a known issue with all owners, but the 3 24valves i have had experience with all had to have the t stat replaced.
 

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I thought the coolant flush would be a good idea also. Not disagreeing with ya but my experience has been if a t-stat is bad it will cause problem with or without a load. Might also want to look at keeping the trans. cooler.
 

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More than likely your radiator is clogged. The puke bottle likes to overflow and then the oil gets into the fan and then shoved into the radiator. Pull the radiator and you'll see a circle of oil where the fan shot it in. There a picture floating around of one that is like this.
 

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Discussion Starter · #7 ·
While looking over the engine, I found a cracked exhaust manifold. Obviously I have to replace it but could this be part of my problem? I'm still camping and I will have to limp it home in the condition it is in.
 

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When it gets warm, does the fan clutch sound like an airplane trying to take off? If not, it needs replacing. Having same problem with mine, fixin to replace it.
 

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Coolant, Thermostat, Radiator Condition (Inside and Outside), Fan Clutch, Radiator Cap, and Water Pump.

These are the only few components to a cooling system.

My money is on the idea the crankcase breather bottle has coated the radiator with greasy gunk and can't cool anymore...
 

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i had the classic from factory missplaced coolent clamp where it meets block on passenger side.This is a common on 06's so when she decided to spew, at 12 at night i got some mixes with all coolant/added, seemed to have air in lines i couldnt purge, now i have a overflow bottle thats creeping up to full, temps seem to stay in check,it be changed if itll stop raining, also my temp guage doesnt climb right anymore it stays cold then jumps to attention when i am going T Stat?:popcorn:
 

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99% likely your radiator fins are completely full of oil and dirt.

These trucks have big, efficient radiators and if the truck doesn't stay cool ( under 210*) with the A/C on and in warm temps, then something is wrong.

You need to actually pull the radiator out, (NO, trying to hose it out with it still in the truck doesn't do much). It's fairly easy to remove anyway. Then take it down to the car wash with the hi pressure soap/water and blow all the brown oil/dust gunk out until it's clean, then reinstall.

That should take care of it, but it wouldn't hurt to change the T-stat if you know it's fairly old. Get one from the dealership that is a Cummins part, they have a bigger mouth than the original stat and are better than the auto parts store stats.

Furthermore, I use 2 gallons of antifreeze, pint of nowcool (anti electrolisis additive), one bottle of water wetter, and about 2.5 gallons of purified water.

I can run up a hill with a trailer in the summer, A/C on, and likely not pass 200*.
 

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That many miles and being nearly a decade old, I'd give heavy thought to replacing the cooling system. Copper radiator, fan clutch, etc.. Typically the aluminum rad will go away at the coil/end cap interface or just plug up and you can waste a lot of time trying to fix it (you may get lucky though). Rodding out an aluminum rad isn't cost effective. Consider if it overheats you'll have the pleasure of replacing the head gasket which will also give you the chance to replace the exhaust manifold and most likely do a valve job to freshen up the head.. mercy.
keep smokin'
pc
 

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Discussion Starter · #14 ·
I made it home. 45 miles from the house i had power loss and started smoking black. I found the tube going to the turbo (not the air intake) had come off. So i got a hold of that smoking/ power loss issue (i also changed a dirty fuel filter).

I got the t stat on order from the dealer (thanks RJF) it's only $20 more than the cheap one from checkers. The outside of the radiator is clean I don't think i'll rip it out. Coolant flush after i change the t stat should hopefully take care of it.
This winter when it was really cold out, i had problems with the t stat. No matter how long i would let it warm up, the heat would shoot up until i let off of the throttle then it would sit at 190 (where it always does). When it got nicer out, it didn't do it so i forgot about it. So i know it needs replacement. I'll write on thursday or so and let you know. Thanks for everyones ideas.
 

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Discussion Starter · #15 ·
I don't know if it was the thermostat or the radiator flush but i came out camping this weekend. Only 20 miles from the house. But there was some decent grades and hills. With the ac on, the temp never went above 190. The new cummins thermostat is set a 180 which is ten lower then the previous thermostat. I ran it hard. Problem solved. Thanks. Now i can keep up with my Dad's 07.5 duramax.
 
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