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Overheating


Chucktkd's Avatar
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05-13-04, 06:02 AM   #1  
Overheating

1995 Dodge b2500 cargo van with the 3.9 6 cylinder. It overheats when it is over 60 mph and it's only 80 degrees outside with no load in the back......It is fine in stop and go traffic even with the AC on and at moderate speeds. I just replaced the water pump and no change. The radiator cap is working properly....The radiator is clean on the outside and the inside doesn't appear to have any stoppages.....I just flushed it as well.....There are no leaks and the water level is correct...

This is an engine I had installed January 2003 from a junkyard and it had 88,000 miles on it. It now has 160,000...I drive a lot.......When I replaced the motor I had the thermostat replaced...I have put 70,000 miles on it since the engine and thermostat were installed....It was doing this last summer as well...

I'm thinking it's the thermostat......

Any ideas??? Thanks!!!!

Chuck

 
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05-13-04, 08:16 AM   #2  
it's not likely the thermostat,

as a bad stat wouldn't just cause a problem at highway speeds. it really sounds like a radiator problem to me. it doesn't take much internal blockage to compromise a radiators ability to transfer heat. the thing to do wopuld be to use an infrared thermometer and check for temp variation all over the radiator...esp when it begins to run hot. it should be uniformly hot on the inlet side from top to bottom and cool evenly all the way across to the outlet side. hot spots and cold spots indicate a partially plugged radiator. if this is the case, don't consider having it repaired, flushed or rodded out. replace it...that's an easily justifiable expense based on your driving habits. not to mention, that engine is only going to take running hot for so long...

 
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05-13-04, 09:45 AM   #3  
Bugalou
Is all the baffling in place in front of the radiator so the incoming air is directed through it and not around it?..is the belt for the fan/waterpump loose, worn??.a slipping belt at high speed could cause your situation..Also at high speed the impeller in the water pump could be worn enough to not push enough water through the engine...

Bug

 
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05-13-04, 09:59 AM   #4  
there is no...

...special "baffling", nor is a van a "bottom breather" like a car with no grill. a belt THAT loose would surely be causing other issues and the water pump has already been replaced.

 
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05-13-04, 08:22 PM   #5  
I replaced the serpentine belt when I replaced the water pump....One thing I forgot to mention......When I'm at 70 mph and it starts to overheat, if I start down a hill and put the van in nuetral for just 30 seconds it will cool the engine down about 20 degrees.....

 
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05-13-04, 08:57 PM   #6  
I agree with carguy - check for an internal radiator restriction. Also, if coasting cools it down somewhat, check the operation of the fan clutch. It should freewheel when cold, and tighten up considerably when at operating temp.

 
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05-14-04, 02:31 AM   #7  
carguyinva is right on, as usual. The radiator is about the only thing that will act like that. I'd change the thermostat at the same time, just for accuracy but that's not causing your problem. Neither is the fan belt or water pump.

 
Chucktkd's Avatar
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05-14-04, 04:02 PM   #8  
Thanks guys, it was the radiator...

 
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05-14-04, 09:30 PM   #9  
mike from nj
did the radiator look something like thisCLICK HERE


it never leaked, wasn't clogged, the thermostat wasn't stuck open or closed, the fan worked perfect, yet i wonder why it kept overheating at highway speeds. note: this is one of those cheap chinese $99 radiators i speak of every so often. it was new 4 years ago. a properly built american unit which cost slightly more lasted a lot longer. this is how the stores make money, make something extremely cheap quality, and make the price competitive. people think they're saving money, yet it costs more in the long run.

you pay for cheapness over and over

you pay for quality once!!

*I* learned it.




glad to hear it's fixed chuck, just don't overload that 3.9L too much, the exhaust valves don't like it that much(but i do)

 
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05-16-04, 04:45 PM   #10  
Actually I was mistak in my check.....There was some paper blocking the bottom of the radiator that I couldn't see because it was so black it matched the radiator and my eyes aren't what they used to be. I found it when I went up under it to see whether the transmission lines were attached by hose clamps or screwed in before I went searching for a radiator so it didn't cost me anything.

I don't haul much cargo over 500 lbs. and when I go over the Appalachians I use a higher octane. My first van with the 3.9 I got 350,000 miles before I donated it to the V.A. and it still ran fine. I wound up replacing the engine on this because a spring broke and then other things went wrong. I keep it tuned up with the Bosch +4 and I get 16.5 mpg. It's a good work van....The only thing is that obnoxious rattle from the oil deflector...

Thanks again.....

 
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