T-shooting cooling problem

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In my '97 Dodge Ram Van 2500 (3.9L V-6),
The symptom is that the van runs hot: creeps up toward 3/4 on the gauge on the street, and when pulling a hill (naturally I live atop a large hill) shoots toward the top of the
gauge. The short-term fix has been to use the heater; at full blast, the gauge usually stays at or below 1/2 until I get to my hill, then stays at or below 3/4 until I get home. (I run it at idle, still with the heater full-blast, until it's about 1/2 on the gauge... then shut it off.)
I don't want to "shot-gun" troubleshoot, but I'm not sure where the problem might be. At first I suspected the water pump, but the van doesn't leak when cold, only when the gauge is near the top. What's a good troubleshooting approach? I plan to flush the radiator this weekend, but don't have any confidence that flushing it will address the problem. And of course I'm broke... and a little put off by the idea of pulling all that front-end hardware to start swapping out thermostat, water pump, ...
If it matters (how could it?) I had a limited-slip differential installed, since I live on a steep gravel road. This van is new to me, I've had it about two months and it's always exhibited this problem.
(BTW thanks to the two of you who enlightend me that the AC *is* active when the defroster is active... news to me, this is my first vehicle with working AC!)
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I would check the fan clutch. Sounds like the fan may not moving enough air. It could also be the radiator itself, especially if someone before you loaded it up with stop leak. Watch for leaks to appear when you flush it out. Check the outside of the radiator as well and make sure that the fins are not plugged up with dead bugs and other debris. The fact that the heater core (a tiny radiator) is helping to keep it cool shows that the problem is probably not in the pump
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"just another" < snipped-for-privacy@noaddress.com> wrote in message
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wrote:

Thanks, I was wondering about the fan... it seems slow to me but it is turning. But this is my first clutch-fan (I've had vehicles with electric fans, otherwise). Any specific tests I can do?
Doesn't appear to be any debris in the radiator; has a small radiator in front of the main one; I think it's for trans fluid.

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With the engine running at operating temp, watch the fan as someone shuts the engine off. If it stops turning almost immediately, the clutch is doing it's job, and is engaged. If it freewheels for a while, the clutch is shot, and needs to be replaced.
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Did this & the fan seems okay. When the van overheats, sitting at idle for a few minutes with the heater going full-blast does bring the temperature gauge back down to the middle.
I had the radiator flushed; seemed like the thermostat must be working right, it did open. Guess I'm starting to suspect the radiator itself, even though it looks to be in good condition.
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If overheating occurs only at periods of extended idle then my kneejerk shadetree diagnosis is the radiator itself may have become internally choked with rust and deterioration, such that the volume of coolant able to circulate through it is significantly reduced.
A "radiator shop" is probably going to cost you less than taking it to a dealership.

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wrote:

Thanks, that's not it; periods of extended idle let it come back to a normal temperature range. It's pulling hills (& running the AC) that cause the overheating.
However I'm leaning toward a radiator prob. at this point.

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Symptoms which point to either an airflow problem or a constricted flow volume problem. A partially obstructed radiator (or hose) would give these exact symptoms. Replace the radiator. Also make sure you have the right water to antifreeze fluid ratio.
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Thanks for everyone who replied to this thread.
Replacing the serpentine belt *partially* fixed the problem. It still gets too hot pulling a hill, i.e. the hill up to my house. However it seems okay on the freeway now... at least during this cold-weather spurt we're having.
The serpentine belt seemed fine when I checked it, little wear evident & few cracked v-grooves (none of the long cracks the Haynes manual warns against). I was surprised that changing it made any difference at all. So there's still some problem, but not as bad.
I can only suspect the radiator now, & I'm trying to find a radiator shop with a good reputation (not as easy as it sounds!). Just trying to get the van reliable enough to take on a couple of pending long trips. These vans were designed to last a quarter million miles, weren't they? (i.e. the Ram Van 2500) Mine's less than half that, but I'll say that the overheating is the only problem... everything else about it is terrific!
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just another wrote:

Does it bubble in to the overflow tank? If so, might be a blown head gasket.
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Not that I've noticed, in fact the overflow tank seems hardly to be in the circuit... i.e., when it gets hot I would've expected the overflow tank to fill, but that doesn't happen. Levels are fine there, in fact a little high but stable, cold or hot. So the only shot-gun approach I've tried is to replace the pressure cap, hoping to see more action in the overflow tank. (Just replaced it today, we'll see how it behaves tomorrow...)
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The fins in the water pump are just sheet metal and they corrode off until there is little left and are unable to move enough fluid.
beekeep
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Thanks, seems like the flow is okay, though. (Per the guy who flushed the radiator.)

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(beekeep)wrote:

What you need to do is determine what is happening. Either the radiator is getting too hot, or it isn't. It's that simple. When the engine is overheating, there should be a lot of hot air coming from the fan, and if you rev the engine the fan should roar. If the air is just warm the radiator is not hot. Before you start laughing, if the radiator is not hot, it's a problem with water flow. Water pump, collapsed hose, plugged radiator, or thermostat. If the radiator is hot, it's a problem with air flow.
Al
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If it were a flow problem due to the pump, turning on the heater would have little to no effect.
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"Big Al" < snipped-for-privacy@qwest.net> wrote in message
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wrote:

Agreed, & turning on the heater effectively makes the radiator *bigger*, right?

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In a way, yes, since it is in fact another radiator. Actually, it is in itself a miniature cooling system that is for the most part independent of the radiator and bypassing the thermostat. If you have replaced the thermostat then it is looking more and more like the radiator or cooling fan as the source of your problems. If you are sure that the cooling fan is operating properly and there is nothing wrong with the radiator hoses (such as a collapsing lower hose), it almost has to be the radiator. IIRC, you did say that this is a used vehicle and if so, the original owner may have dumped a shit load of stop leak into it at one time or may have neglected the system to the point that the tubes are plugged with rust and debris. I would bring the radiator to a radiator shop and let them clean it and look it over for potential problems.
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"just another" < snipped-for-privacy@noaddress.com> wrote in message
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This was good advice, I spent a lot of time thinking about what you've said. Unfortunately, there's not a *firm* failure... pump/hose/radiator/thermostat all indicate that they're working... to some degree! Somehow there seems to be insufficient flow... must be the radiator, is my current thinking (any other component would *noticeably* fail, right?).
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More than likely it is the radiator. For kicks, check the radiator cap.

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I would check for proper operation of clutch fan first.
Xclimation wrote:

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