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Discussion Starter · #1 ·
So I try to take it upon myself to do as much as I can on my own vehicles (mechanical wise) but I have always had problems trouble shooting the engines cooling system. Here's what she's doing......

I remember back in February, while driving, the truck would get hot. The needle would move indicating it was getting hot, but only while stopped, or coasting. While driving the truck would cool down, and the needle would go back to it's place. It did this once, and it stopped.

Fast forward to today. The truck has been sitting since March, and now that I've fixed it up got it running better, the problem is back. I was driving around, went to slow down and stop, and the truck got hot again. Once I got going the needle went down and back to it's normal operating temp.

I got her home and checked under the hood. There was a little bit of a smell but no visible leaks. Do you guys have any ideas as to what it could be? Thermostat? Water pump? Clogged radiator?

Thanks guys!
 

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Possibly air in the system. Put the front up on ramps so the radiator is above the engine and check the antifreeze level at the radiator after its cooled down of course.

A pin hole leak can let air in without you noticing a leak until it starts to act like what you describe.
 

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johnnie59 said:
Possibly air in the system. Put the front up on ramps so the radiator is above the engine and check the antifreeze level at the radiator after its cooled down of course.

A pin hole leak can let air in without you noticing a leak until it starts to act like what you describe.
That would explain the smell,assuming its a coolant smell.
 

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Being a 98 model year, I have to say, if the thermostat and radiator are original...it's time for them to go, irregardless which one is causing the problem.

The factory radiators only seem to last 7-10yrs or so in these trucks, I have a 97 model year, I ditched my factory radiator over 3yrs ago....even with regular antifreeze flushes/drains, they still grow crud and become clogged and rot out internally.

Also check your clutch fan, that could be on the downside as well.
 

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x3 on the fan clutch. When you are moving the air is forced over the radiator but at low/no speed the fan is the only thing moving the air.

As others have said the radiator is old and so on but as long as it is cooling ok when the truck is moving it seems unlikely swapping the radiator and/or thermostat will have any impact on your immediate problem.
 

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The only Isuzu one I have had fail failed with the clutch locked up so it spun like crazy at any RPM.

One that fails open like I suspect yours had would seem to spin really freely when the motor isn't running and then would continue to spin longer than normal after you shut the motor off.

Do you maybe have someone with a similar truck you could use to compare the two? If not maybe I can get a video of mine (is 99 Troop but same behavior) and get it to you.
 

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Discussion Starter · #9 ·
Unfortunately I do not.

When I got home from work I checked to see how much play is in the fan, and I could move it freely with my hand. I thought that when an engine was turned off that a clutch fan couldn't spin? Is that correct?
 

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Discussion Starter · #11 ·
Ok, well it does have that feelin to it. Well it has behaved for the last few days, so I guess I'll drive it a bit more and see if it comes back.

Thanks a ton guys!
 

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Discussion Starter · #12 ·
So I was reading around, and someone had mentioned that when you turn the motor off the fan should stop with the motor, so I had someone turn on and off to see if the fan would keep spinning. It did, so now I'm wondering if that's a normal thing, or do I need to replace it?
 

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usualy like 1 maybe 2 turns it might spin after shut down buy anymore then that its out or going out
 

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Discussion Starter · #14 ·
Alright, well this thing is spinning freely after shutting it down, so it looks like I will need to replace the fan.

So for my last question, would you all recommend I replace the clutch fan? Or would an electric one be better?
 

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Canuck said:
So I was reading around, and someone had mentioned that when you turn the motor off the fan should stop with the motor, so I had someone turn on and off to see if the fan would keep spinning. It did, so now I'm wondering if that's a normal thing, or do I need to replace it?
It may spin a little bit after the engine shuts off, depends how hot it is. The fan clutch is a fluid coupling that gets tighter as it heats up.

So when your engine is cold the fan may only be spinning at 50% of the input rpm, but when your very hot/overheated it would be spinning at 90-100% of input rpm, and it will be very loud.
 

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Canuck said:
Alright, well this thing is spinning freely after shutting it down, so it looks like I will need to replace the fan.

So for my last question, would you all recommend I replace the clutch fan? Or would an electric one be better?
No and No, just replace the clutch if you need to. If there is nothing broken on the fan no reason to replace it. And engineering an electric fan in there will be more trouble then it's worth. The thermal clutch fan works fine.

You can test your fan clutch just by seeing if it has the same resistance when hot and cold. If it turns as easily hot, as it does cold, it's broken.
 

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I had this same problem with mine. Sags is right, if it makes 2 or more full rotations after you shut it down (at normal operating temp) then its bad.

Replacing it doesn't take 10 min.
 

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Hayden makes some good products, if it were me I'd go with that one.
 

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Holy crap please don't buy the Hayden. Your truck will sound like a semi (trust me) and your neighbors may not appreciate it . The Hayden is pretty much the loudest clutch I've ever heard. I exchanged mine for the 4 seasons as it was so much quieter.
 
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