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Discussion Starter #1
About a week ago in 93 degree sunny weather I had our dog in the P38 along with my wife. The AC works well in the 98 RR 4.0, and even better when it's set to recycle to keep the hot air out.
But during along idling stop after about 10 minutes, while my wife went into the store for milk, the RR stared getting hot.
The temp got up to almost max, so I drove around the block. The temp got back to normal quickly.

The radiator fans never came on, so I want to connect a wire to a 12v dash aux plug to the fans so I can just plug it into the cigarette 12v aux hole when idling or stuck in traffic.

ANY ideas?
 

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The fans are not for engine temp or radiator cooling. The fans are for the A/C condensor and one comes on when the A/C is under a heavy load and assists the condensor with air flow. If the A/C is under a ridiculous load the second fan will be activated. All of the P38s I have had one fan come on in Eastern Washington when over 100 and of course when in Phoenix in July and August I've had both fans on. I remember on technical and very steep difficult hill climb with my mother in the rig so I was not about to turn off the A/C. Engine only went about two needle widths above centre on the temp guage, but both fan were blaring and the A/C was ice cold.

There are few write ups on manual operation and how folks have done it. Personally I prefer not to muck about with things that already have a job to do.
 

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Assume you are referring to the auxiliary fans that RRToad is also talking about. The engine fan must be spinning underneath that shroud. The aux fan operation remains a mystery, I've never actually seen mine operate so your problem is probably elsewhere. Poor cooling at idle suggest a water pump on its last leg or a partially clogged radiator or both. Most P38's would have had both replaced by now. What the status of those?
 

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Discussion Starter #4
Assume you are referring to the auxiliary fans that RRToad is also talking about. The engine fan must be spinning underneath that shroud. The aux fan operation remains a mystery, I've never actually seen mine operate so your problem is probably elsewhere. Poor cooling at idle suggest a water pump on its last leg or a partially clogged radiator or both. Most P38's would have had both replaced by now. What the status of those?
I replaced the water pump 2-3 years ago and changed the thermostat last December.

My 91 suburban would overheat in slow traffic for two years and I finally found the radiator fan wire was grounded. I pulled it lose and the fan came on and never over heated again. I know the fan is for the AC system but does it not help with the engine cooling too?
 

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Discussion Starter #6
I have put 70K miles on this RR and have only know of one time the A/C condensor fans came on, and it was 60K miles back. We were in the RR and heard the A/C condensor fans come on. And never since.
I have to try something to help with the engine cooling. The A/C system works fine. And it appears to work without the AUX fans engauged at all.
.
 

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Whenever the AC compressor clutch kicks in the fans come on in series so run but only slowly. They run in parallel, so at high speed, if the pressure in the AC system gets too high so it will only happen very occasionally.
 

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I have to try something to help with the engine cooling.
A properly maintained P38 cooling system will easily handle temps over 110-115 traveling through hilly terrain. As close as you are to the coast you rarely would see over 100. You did not respond to NorCal on the condition of your radiator.
 

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+1 on the radiator.
Also, a new water pump could easily be a bad water pump......
Generally, you will be offered a choice of 2 pumps at the parts house, and indeed from AB and others online...
GET THE EXPENSIVE ONE!!
The one that costs about $140.00. Not the sub 100 buck job.
Problem with the cheap one? Yes! They have been known to last as little as 3 months.
Sometimes even have a plastic impeller. If you used the good one, then go to the radiator next.
Just today, I idled in 105 deg heat for 20 min, and had no issues whatsoever.
Put in the good water pump a few months ago, and did hoses as well.
If you have not done hoses in the last 100k miles, it is advisable to do them as well.
Last, but certainly not least, Boogering with the wiring for the AC system will cause more problems than you really want.
Not to mention, you will fry the ciggie lighter wiring trying to run the fans off that circuit.
Band aid fixes will just fester. Find out why you are overheating, and fix the issue.
Good Luck!
 

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It sounds like you have poor coolant flow in the system since driving around the block solved your issue (vs. highway speeds that increased airflow). Speeding up the engine increases coolant flow. So adding airflow is unlikely to help even if you bypass the electric fan controls and run them more. Even if it did, do you want to depend on noticing a climbing temp gauge and manually switching on the fans? Poor coolant flow is pretty much a clogged radiator, a failing water pump, or bad thermostat. A thermostat usually fail in a spectacular way, not warming up too much at an idle cured by driving.
 

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Discussion Starter #12
I may have found the radiator/overheating problem.

Last week I found a pinhole in the top of the radiator. It would only leak after the engine was turned off.
The new radiator came in and it's installed now.

Thanks for the suggestions,
 

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Thanks for the follow up.
Please let us know if this has indeed solved the problem for you.
It is so common for folks to jump straight to the wrong solution for cooling system issues like this.
Be very glad you have not messed with the fan circuit, as it would not have helped the issue and you would now be trying to work out why the A/C is now screwed up:roll:
Happy Cooling!
 

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Discussion Starter #14
Just to help someone else who has a problem with removing the radiator from a P38

The nut holding the radiator in place at the bottom was my only problem. The nut inside the plastic bracket at the bottom of the radiator was frozen to the bolt. The passenger side bolt came out easily, the drivers side was hell.
The nut kept turning with the bolt and quickly stripped out the plastic bracket. I ended up using a narrow but sharp wood chisel. I chipped away both sides of the plastic until I could get a grip on the bolt with an open end wrench, but I could not get the wrench around the nut.
I shaved the tips down on the open end wrench on my grinder so I could get the wrench to bottom out on the nut. Two hours later the bou came free of the nut.
I'll try to post of each.
 
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