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  #1  
Old 08-03-2012, 09:37 PM
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Hydraulic Radiator Fan 4.7L Questions Please

Hi all I have a 2001 Grand Cherokee Limited with the 4.7L engine 2wd if that matters.

This one has the Hydraulic fan which blows me away. I spent a good deal of time trying to figure out where the relay was ands there is not one.

Anyway my unit is running hot after idle for say 5-10 minutes. As soon as I start moving it cools down.

Fan comes on and runs when engine starts heating up. Perhaps not coming on sooon enough? When the fan is running the engine continues to overheat.

Any suggestions?

I'm not finding much about this on the net as most seem to have the electric fan.

Thank you in advance!!!!!!!!!!!!!!!!!
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Old 08-04-2012, 06:39 AM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

Blue Marvel,

I have a 2002 GCL 4.7L with the hydraulic fan and it has continued to work great. I had at one point considered swapping it out for an electric fan, since I am more familiar with those, but the hydraulic unit has continued to perform admirably.

The fan always seems to be turning at some speed, even when cool. This may be due to it always having some hydraulic pressure from the power steering pump. I checked it while the AC was on last week and it really speeds up for additional cooling then. It could suck a few small birds into the grill at that point. This is actually the only time where in which the fan has an audible pitch.

The fan has a solenoid that varies hydraulic pressure so to increase fan speed when necessary. As I previously stated, it is activated when the AC is operational, but also when the engine reaches various temperatures. I have never heard my fan reach the high speed setting for normal cooling. Normally I am wondering if it is running, but my temp gauge never moves, even in +100 degree temps.

Does your fan speed increase when you activate your AC? How is your power steering fluid level and it's operation? If your Jeep is running hot while sitting still your fan must be near non-functional.

I will see if I can locate the operation explanation for the fan...

Regards,

Carlos
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Old 08-04-2012, 08:06 AM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

Sounds like maybe a plugged rad or thermostat. These jeeps tend to run a bit hotter to begin with so I put a 180 degree t-stat in mine when I was chasing my cooling issues recently.

More info. Have you done any work recently? When was the last cooling system flush?
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Old 08-04-2012, 12:08 PM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

The hydraulic cooling fan runs at 500 rpm as soon as the engine is on, as soon as the engine temperature rises above a certain level, the PCM will command the hydraulic fan solenoid valve more open, to ramp up the fan speed.
If the engine coolant temperature is ok when driving, but overheats when standing still, there must be something wrong with the cooling fan and not with the radiator, thermostat or pump.
To test the cooling fan to see if it will go to full speed, you could disconnect the coolant temp sensor connector ( in between the alternator and AC compressor). You only get a "check engine" light, which must be reset with a scanner after reconnecting the temp sensor connector. Best is to disconnect the sensor with engine off and cold. When working there with the engine on, keep hands and clothing away from the fan and acessory drive belt.
But first check the hydraulic cooling fan control fuse # 16 in the PDC. When that one is blown, the fan just keeps at the 500 rpm speed and you will indeed overheat after standing still for a while.
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Old 08-04-2012, 02:56 PM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

If your cooling fan is taking off then thats not your problem... I just had one about 3 weeks ago now that had the same concern, i popped the radiator cap off and it was almost empty, an instant indication of head gasket failure as i find typically an external leak will suck all the coolant out of the overflow tank where as a failed head gasket wont and it will just drain the cooling system leaving the overflow tank full. A simple block test confirmed my suspicions.
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Old 08-04-2012, 08:56 PM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

Hi Guys,

Thank you for all the replies, Lots to check here. I will try to do some of this soon.

To clarify, the fan does speed up when the engine starts heating up after idle for a few minutes. It gets really loud when it speeds up. Also the coolant is full and the engine is fine.

I would surely like to fix what is broken without changing things that aren't but at this point I'm not sure what's wrong.
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Old 08-04-2012, 09:18 PM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

Have you opened the bleeder? It's right where the top radiator hose connects to the motor. Open that and see if you have air or coolant come out. You may have some air in the system.
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Old 08-04-2012, 10:12 PM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

It is always guessing, but could have to do with the water pump. When you start moving, the temperature goes down. Or that is because of the airflow through the radiator, or it is because of the higher coolant flow from the waterpump. You could test this when idling for a while and when the temperature goes over the normal value to rev the engine to 1500-2000 rpm. If the temperature would drop, it could be a sign that the waterpump is the culprit. It can happen that the impeller gets loose on the axle, reducing the impeller rpm and thus reducing the flow.
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Old 08-05-2012, 08:05 AM
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I have a hydraulic fan and wish it never did.. but oh.well

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Old 08-05-2012, 04:03 PM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

Quote:
Originally Posted by Dustinmk4 View Post
Have you opened the bleeder? It's right where the top radiator hose connects to the motor. Open that and see if you have air or coolant come out. You may have some air in the system.

I have done this. There is plenty of coolant.
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Old 08-05-2012, 04:03 PM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

Quote:
Originally Posted by Frango100 View Post
It is always guessing, but could have to do with the water pump. When you start moving, the temperature goes down. Or that is because of the airflow through the radiator, or it is because of the higher coolant flow from the waterpump. You could test this when idling for a while and when the temperature goes over the normal value to rev the engine to 1500-2000 rpm. If the temperature would drop, it could be a sign that the waterpump is the culprit. It can happen that the impeller gets loose on the axle, reducing the impeller rpm and thus reducing the flow.

Good idea I will try this.
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Old 08-06-2012, 03:42 PM
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Re: Hydraulic Radiator Fan 4.7L Questions Please

I ran the rev up test. I let the engine run until the temp started climbing a 1/4 click up the gage. Then I rev-ed the engine to about 3,000 RPM. It immediately cooled down. So for what ever reason either A the water pump is not pumping enough flow at idle or B The power steering pump is not causing the fan to blow fast enough or C the radiator is restricted enough to not allow flow though I doubt that's it because if it were restricted it would still be restricted when rev-ed up.

This is where I'm at right now. I picked up a water pump at Car Quest. The standard unit from them new not re-manufactured has a metal impeller. Most of them these days have a plastic impeller, I believe from what I'm seeing.

This may or may not fix the problem. I will check back in after I get it changed and tested.
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