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  #13  
Old 04-13-2014, 12:00 PM
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Re: '99 4.0 Overheated

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Originally Posted by Frango100 View Post
You are probably talking about the viscous clutch fan mounted on the water pump, but not the electrical. The viscous clutch fan idles at a out 300 rpm and goes to high speed when the engine coolant temperature rises too high. It should work in combination with the electrical fan, so could be the problem in case of overheating.
Nope, I'm talking electrical fan as there's nothing attached to my water pump. The fan kicks on a low speed when the engine starts. Once it gets up towards 200*F, it turns onto a high speed (you can easily hear it) and it brings the temperature down and then kicks back down to the low speed. If the electric fan doesn't kick into high speed then it will overheat while sitting stationary as it cannot get enough air through the radiator. When the vehicle starts moving it will force air through and cool it down.

Here's a picture taken from the driver's side of the water pump and electric fan. As you can see, nothing attached to the water pump.


Quote:
Originally Posted by JGiardino89 View Post
OK, so the jeep overheated again, and the fan wasn't running. Would that be the relay / resistor under the passenger headlight ? Or what else could it be.
That's where I would start.
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  #14  
Old 04-13-2014, 02:24 PM
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Re: '99 4.0 Overheated

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Originally Posted by JGiardino89 View Post
OK, so the jeep overheated again, and the fan wasn't running. Would that be the relay / resistor under the passenger headlight ? Or what else could it be.
If the electrical fan runs with AC on, the fan and relay should be ok. Not sure if the temperature sensor can be the problem, since it seems that the temperature indication is working.
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Old 04-13-2014, 05:05 PM
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Re: '99 4.0 Overheated

Fan does not come on with A/C Anymore. I replace the fan relay just now. Fan still did not come on, going to put direct power to the fan tomorrow and see if it comes on.

If not, I'll replace the fan. If the fan comes on with direct power, not sure where else to go from there.
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Old 04-14-2014, 04:57 AM
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Re: '99 4.0 Overheated

Did you check the fan fuse? Many times the relay fries due to the fan which draws too much current.
The PCM will send a fan on signal to the fan relay when switching the AC on. You could measure the voltage at the fan connector to see if that part is ok.
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Old 04-14-2014, 05:03 AM
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Re: '99 4.0 Overheated

Visual check of the fan fuse was good.
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Old 04-14-2014, 02:19 PM
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Re: '99 4.0 Overheated

took the fan out. gave it direct power from the battery, and it came on.

Now I'm stumped. Fuse is good, brand new fan relay, fan turns on with direct power, but the fan wasn't turning on when it was overheating...
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Old 04-14-2014, 02:38 PM
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Re: '99 4.0 Overheated

I am also getting a full 12v and the radiator fan connector.
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Old 04-14-2014, 02:47 PM
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Re: '99 4.0 Overheated

Might just go with this instead of trying to hunt down a bad wire or short.

Mechanical fan upgrade.
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Old 04-14-2014, 02:50 PM
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Re: '99 4.0 Overheated

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Originally Posted by JeepMe View Post
Check the fan and make sure it is kicking on both speeds. When you start the Jeep from cold it should come onto low speed. Once it gets to operating temperature it should engage into a second and you should hear a difference (it's VERY noticeable). If you cannot hear the fan change speeds, that's your problem.
Excellent point on that cold start fan noise. It should sound extremely loud when started after being left off some time. Don't recall the time it takes, but first thing in the morning the very first start should result in a rather loud roar from the fan that goes away reasonably quickly.

I'd spend the money for a professional flush before springing for a radiator.
Or get a good reverse pressure flusher...

Just because the water is clear doesn't mean there isn't a possible plugged coolant passage either in the block, or in the radiator. Theoretically it is possible to take
the radiator apart and clean the passages... never tried it with a plastic tanked one.

When you finally fill it, make sure you replace any weak hoses, and burp every one thoroughly, or fill it from the bottom drain and a pump.
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Old 04-14-2014, 03:00 PM
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Re: '99 4.0 Overheated

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Originally Posted by lstowell View Post
Excellent point on that cold start fan noise. It should sound extremely loud when started after being left off some time. Don't recall the time it takes, but first thing in the morning the very first start should result in a rather loud roar from the fan that goes away reasonably quickly.

I'd spend the money for a professional flush before springing for a radiator.
Or get a good reverse pressure flusher...

Just because the water is clear doesn't mean there isn't a possible plugged coolant passage either in the block, or in the radiator. Theoretically it is possible to take
the radiator apart and clean the passages... never tried it with a plastic tanked one.

When you finally fill it, make sure you replace any weak hoses, and burp every one thoroughly, or fill it from the bottom drain and a pump.
Why would an electric fan come on when an engine is cold ? that doesn't make any sense. There is no heat to be dissipated.

I flushed everything very well, I am sure that I got most, if not all of the old stuff out.

Would a bad temp sensor cause the fan not to come on ? "Check gauges" came on, temp was pegged, but I looked under the hood and it was not over heating. But the fan was on.
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Old 04-14-2014, 03:49 PM
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Re: '99 4.0 Overheated

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Originally Posted by JGiardino89 View Post
Fan does not come on with A/C Anymore. I replace the fan relay just now. Fan still did not come on, going to put direct power to the fan tomorrow and see if it comes on.

If not, I'll replace the fan. If the fan comes on with direct power, not sure where else to go from there.
Google on
1999 Grand Cherokee fan relay location
1999 Grand Cherokee fan clutch replacement

e.g. Part 1 -Jeep PWM Fan Relay Test Troubleshooting an Overheating Condition

And there are a few YouTubes as well.

It appears to have a very high pita factor....
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Old 04-14-2014, 04:01 PM
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Re: '99 4.0 Overheated

I don't have a scan tool...
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