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Discussion Starter · #1 ·
This isn't a question. It's notes about my 99 Trooper overheating problems, the ultimate cause, how I found it, and how I resolved it. Hopefully it saves someone some time/money.

My trooper was overheating. I have a nice OBD-II-to-Bluetooth adapter that lets me view precise coolant temperature on my cell phone. It would climb regularly WELL over 100C.

My temporary fix for my overheating problem was to turn the engine off as I was cresting a hill, and allow the coolant in the radiator to drop a few degrees on the way down. I would then turn on the engine to climb the next hill or maintain a reasonable highway speed on a flat area. Incidentally, I tried this once in my 98 Rodeo and it was a bit unpleasant. With the engine off at speed, a loud ratcheting noise could be heard.
QUESTION :?: : Could the loud ratcheting noise be a functioning fan clutch being torn between a still engine and a fan that is being forced by the wind to turn?

A trick I've used in the past on my Rodeo during overheating at stop lights was to put it in neutral and rev the engine to 3500 or so to get the fan to spin faster. This trick wasn't working on the Trooper. That should have given me a clue as to the real problem. But it didn't at the time.

I needed a permanent fix and assumed it was the thermostat. The thermostat on the V6 (3.2 and 3.5) is underneath the intake plenum ('common chamber'). This makes it hard to reach. If you do it, you might as well replace your intake manifold gaskets at the same time. They get very brittle with age, and if you miraculously manage to avoid cracking them while replacing your thermostat, you will still surely shorten their lifespan. Incidentally, I've replaced these gaskets three times on my isuzus and have still never cracked open the common chamber to replace the paper gasket in the middle. (So now I have three of the gaskets laying around from the sets I've bought.)

After replacing the thermostat, the overheating problem remained. I assumed the duralast thermostat was junk. So I did it AGAIN. (this time with a more expensive thermostat, and this time completely removing the intake manifold and replacing all injector O-rings as well.)

After the second thermostat, the overheating problem remained. I assumed the remaining possible solutions were: Blocked radiator, bad water pump, or bad fan clutch. I am not sure how to test a radiator's flow, but filling the cooling system went pretty quickly, so I assume no blockages. I wasn't sure how to test the pump either. But a little searching led me to a test for the fan clutch. Get the car up to temperature (or overheating :) ) and turn off the engine. Now try turning the cooling fan by hand. There should be resistance. Another test is audible. When you start up the car cold, rev it to 3500 or so. Make a mental note of the noise level. Now let it idle until hot. Rev it to the same rpm, and compare sound. If the fan is not obviously LOUD compared to cold, then the clutch isn't working.
My fan was not resistant to hand-turning after warm-up. The noise wasn't there. My new diagnosis was a bad fan clutch.

I ordered a fan clutch on clearance like this one. It isn't here yet but I need to drive the car without turning off the engine every 30 seconds, so I needed a hack to get it working. So I 'bypassed' the fan clutch. How?

The plastic fan is mounted to the output side of the fan clutch with four 10mm nuts. The input side of the fan clutch is mounted to a pulley on the engine with four 12mm nuts. I took the clutch off of the engine, (a long screwdriver or breaker bar holds it in place when breaking the nuts loose) and the plastic fan off of the clutch. I then took some plumber tape (roll of .75" soft metal strip) and trimmed off two equal lengths with tin snips. I attached one end of each strip to two of the clutch's four studs to which the plastic fan mounts. I then mounted the plastic fan back onto the clutch, on top of the strips. The other end of each strip was mounted to the front of the pulley, between the pulley and the clutch. I had to drill out the holes in the strip for the 12mm studs.

The basic idea was to use anything available to keep the front of the clutch from turning independently of the back of the clutch. Using wire, strap, cord, or whatever to connect a front mounting point to a back mounting point seemed the logical way to go. I put two straps in (on opposite sides) for symmetry and strength. I assume you could use one strong strap or 4 straps and have the same result. If you can limp to a hardware store or a Wal-Mart you can probably find something usable.

The only danger I can imagine this might introduce would be if the plumber strap failed and damaged your serpentine belt or fan blades.

So now no matter what the temperature, when I rev the engine the fan is forced to turn and roars. After finally hearing it again, I'm shocked that I ever forgot to expect that sound.

Again, this is temporary; once the clutch arrives I'll fix it for good.

plumbers tape
 

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on the many izusu's rodeos ( 7 ) i have had i would guess i have seen 3 different types of fan blades on them , some have different numbers of blades , some have different pitch on the blades .

i realize that with fewer blades a bigger pitch would pull the same amount as more blades with less pitch , but even with the same number of blades i have seen different pitch blades .

i guess what i'm saying , the short term fix you did will pull your mpg down at least 10% a chanch of knocking out your water pump .

keep your eye on ebay for gm/isuzu cooling fans , you will find one with 9 blades and a high pitch on it .
 

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Discussion Starter · #3 ·
I expected the drop in fuel economy but I don't understand how the water pump could be damaged. Can you explain?
 

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i think the water pump and fan pully are together in that any vibration from a miss balance of the fan will effect the water pump , even thou you won't be able to feel the vibration the wp will .
 

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Discussion Starter · #5 ·
Ah, that makes sense. Incidentally, this fix did not hold for more than a few start-ups. Plumbers tape was too soft and tore. Clutch should arrive in a day or two so will just wait for it.
 

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Discussion Starter · #6 ·
Clutch arrived. Installed it. Drove 30mi on the highway. Overheated.
Looks like I got too cocky about the fan.
When I stopped (with the car overheated) I checked the fan and it had a little resistance when I pushed it with my hand. It stops when I stop pushing; no freewheeling. I'm not sure how locked up the clutch is SUPPOSED to be but the amount of resistance I experienced did not seem enough to get the fan really spinning fast. This is with the new clutch.

I've replaced:
Thermostat (twice)
Fan clutch

All that's left is the pump and radiator. Time to google.
 

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Well here are a couple of thoughts of mine. Have you checked to see if the lower radiator hose is collapsing because of the suction of the water pump restricting the coolant flow. Next I would pressure test the cooling system and a combustion gas test to check if it might be a head gasket leak. Also a restricted exhaust system, bad cat or collapsed muffler baffles can cause over heating problems.
 

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Discussion Starter · #8 ·
Thanks. I dropped it off at a local shop to have them do a pressure test. If they don't come up with anything I'll check the lower hose and also buy a gas test kit. I don't know the age of the exhaust components but will look at them as a last resort and replace anything that looks ancient.
 

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I'd swap the radiator. While the radiator is out use a hose or pressure washer to make sure the A/C condenser isn't obstructed.

If it overheats at high speed it isn't the fan.
 

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Discussion Starter · #10 ·
The shop told me the center of the radiator was cold even after running for 30min so I let them replace it. I've turned down a few estimates from them so I figured it was time to let them make a few bucks. $350 isn't too bad considering the radiator would be around $150 shipped if I bought it.

We'll see if that fixes it finally.
 

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Hi, I'm having the same issues with my Trooper 98 - 3.5 - Did you ever solve the problem?
Mine is driving me crazy, Changed radiator, water pump, radiator cap, thermostat.
After 20-40 min driving the temp gauge starts going Max and coming back to the middle. Back and forward. Not funny.
Any ideas?
 

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Alejandro said:
Hi, I'm having the same issues with my Trooper 98 - 3.5 - Did you ever solve the problem?
Mine is driving me crazy, Changed radiator, water pump, radiator cap, thermostat.
After 20-40 min driving the temp gauge starts going Max and coming back to the middle. Back and forward. Not funny.
Any ideas?
Your issue sounds like you need to bleed the cooling system, make sure your jiggle valve on the t-stat is in the 12 o clock position. To the top.
 

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Hi Guyana00,
Thanks for the reply. My mechanic took out the T-stat to make sure it was not acting. Actually modified one removing the closing valve and leaving the housing. So I know the T-stat is not closing for sure.
The problem still happening. I tried to bleed the system like in the forum someone said, idling the car for an hour inclined (front up) radiator cap out and adding water. Accelerating it to 2200 rpms. But it still happening.
Do you have a better way to bleed it?
At this time the only thing left is that the head gasket is blown, according to my mechanic :(
Thanks again,

Alejandro
 

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Alejandro said:
Hi Guyana00,
Thanks for the reply. My mechanic took out the T-stat to make sure it was not acting. Actually modified one removing the closing valve and leaving the housing. So I know the T-stat is not closing for sure.
The problem still happening. I tried to bleed the system like in the forum someone said, idling the car for an hour inclined (front up) radiator cap out and adding water. Accelerating it to 2200 rpms. But it still happening.
Do you have a better way to bleed it?
At this time the only thing left is that the head gasket is blown, according to my mechanic :(
Thanks again,

Alejandro
Has your coolant ever boiled? Check your coolant for oil or foam and vice versa. That's pretty much how I bled mine. I bounced the front as well it helps. What have you tested or replaced so far.
 

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Yes. That is what we discovered last time. Before the gauge gets to normal temperature the radiator push some water to the reservoir. Of course the reservoir water stays there boiling. After the radiator pushes the water out, it is with 1 or 2 quarters less, so the engine starts overheating. I never got oil on the coolant or foam in the oil. That is why it is so difficult to diagnosticate, according to my mechanic.
Last test where he was conclusive was, he kind of build a radiator cap that don't let water out, just to see what kind of pressure we were talking about (and to exclude the possibility of a bad radiator cap) and 20 blocks of testing we blow the radiator.
So he told me that kind of pressure can only come from the combustion, meaning the head is blown.

I changed radiator, water pump, radiator cap, thermostat and fan clutch.
 

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Hello dewzenol

I have a friend with a 2000 trooper with a 3.5 that is starting to have over heating issues, did you ever find the problem with yours? His truck sets all summer and drives all winter, last spring I replaced the thermostat because of this problem but it did not fix it so he just put it in the barn for the summer, well it is out for the winter now and it did not fix itself over the summer, it is still running hot. looking for help. thanks
 

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Hi there crew:

I have a 2001 Trooper LS with 135000 miles. The temp gauge starts to rise when the AC is on, moving slow in traffic, and outside temp is in the 90's. I turn off AC and use old school "windows down" cooling; temp returns to normal. Never actually had a full pegged temp gauge with coolant spraying everywhere, only a rise in temp. Other than that no issues with over heating. I do have an OBD "P" code that is indicating some sort of Thermostat issue (cant remember exact number). I live in the Central PA area so we will not see 90 until May or June but I expect to be stranded on side of road since this issue is not going to get better or fix it self. Will keep this thread updated with further developments.

Kent
 

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I replaced the radiator on my 95 earlier this year. It was less than $100 shipped. Well worth it. Radiators just don't last that long, yours is 13 years old.
 
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