Highway Overheating - again

Hello all! I have been struggling with this overheating issue for quite some time but I need to finally fix it and I am hoping you all can help me with it. First, I have a 88 Jeep Comanche and a new stroker engine (1 year old) and a 91+ converted cooling system with a new 3 core radiator, new ac condensor, 1 year old stock water pump and dual electric fans (flex 110 and stock fan). When the ambient air temp goes above 95 degrees, my comanche overheats on the highway or hills with the ac on. Am I just not getting enough air through my radiator with my flex 110 or do I have another problem? I would think that on the highway I would need less fan cooling but looking through several seaches here, many jeepers say you still need a 2500cfm+ fan. Other suggestions? Anyone else have this issue? Thanks in advance!!!

Well, a standard or HD ZJ clutch fan setup will not engage until the air flow through the a/c condenser and radiator hits 170 degrees at the bi-metal spring on the front of the fan clutch.

I don't have any CFM numbers for a standard fan clutch (operates when engaged at 60-70 percent of shaft speed) or the HD ZJ fan clutch (operates when engaged at 80-90 percent of shaft speed)--I wish I did. Flex-a-lite says there puller 110 moves 1250 CFM, and I don't have any idea what the stock efan pulls, but you could upgrade to the later style efan, or dump the 110 and the standard efan and try a dual Flex-a-lite 220 that would move 2500 CFM.

Also, you didn't specify at what temp your fans are set to come on at. Seems that from other posts on that can be anywhere from 213~230 degrees. You can wire them to run 100 percent of the time--not recommended, or you could run both on a command switch--not recommended (operator error don't you know!), better yet rig the 110 Flex-a-lite to come on at 200 degrees coolant temperature (same as 170 degrees at the bi-metal spring of the fan clutch), and have the weaker standard fan (an assumption on my part that it moves less CFM) kick on around 210 degrees.

You didn't mention your transmission. If an AW4, do you have an external cooler?

do what joe says like he has you looking down the barrel of a gun. he'll fix you up.

Thanks Joe for the info. I have a manual transmission and I have both the stock fan and the flex coming on at the same time at around 200 degrees. Am I not moving enough coolant through or am I not moving enough air through to cool the water. Go Jeep says that you need 2500 cfm + the stock fan. But he also says that his fans dont come on much when he is on the highway so I cant figure out my overheating issue.

$700later said:

do what joe says like he has you looking down the barrel of a gun. he'll fix you up.

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That sounds intimidating!

Well, for what it is worth I found a comment on another jeep forum that the standard XJ fan and fan clutch will move about 4000 CFM. That would mean the Flex-a-lite 110 is 2750 CFM short of what it left the factory with.

Now, I will try and get some actual CFM numbers from Chrysler or another reliable source, so until then treat the 4000 CFM stated above with judicious caution.

One popular conversion is the dual-fan Taurus setup, and here again I don't have any CFM numbers for that.

TexasComanche said:

Thanks Joe for the info. I have a manual transmission and I have both the stock fan and the flex coming on at the same time at around 200 degrees. Am I not moving enough coolant through or am I not moving enough air through to cool the water. Go Jeep says that you need 2500 cfm + the stock fan. But he also says that his fans dont come on much when he is on the highway so I cant figure out my overheating issue.

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Two options, as I see it:

1. Increase air flow through the radiator.

2. Reduce the load on the cooling system.

Start with #2 first--no help there, I was kinda hoping you had the AW4 and could eliminate the transmission from the equation by running those cooling lines only through an aftermarket cooler.

Now #1. Any accessories on the bumper? Winch, off road lights? Have you checked the a/c condenser and radiator fins to ensure they are not bent or full of bugs/debris? Do you have the plastic(?) front splash guard or the front skid?

It has been suggested that removal of the plastic(?) front splash guard or the front skid can contribute to air turbulence in the engine compartment, making the fans less effective in pulling air through.

Also, and this is just a germ of an idea I had, you could try and "funnel" the air in front of the radiator by making some cardboard cutouts and duct taping them behind the grill to try and direct the air flow to the radiator more efficiently. Of course, if this silly idea was to work, you would want to replace the cardboard with something weather resistant that will last.

I have a hard time believing a fan does anything but restrict air flow at 65MPH. If you put your hand out of the window, or stand in a 65MPH wind, you almost get blown over. (or ride a motorcycle at 65 without a fairing). If you (carefully) check the air flow coming out of your fans at idle, it seems like about a 15MPH wind. We made fan shrouds for BMW that had little shutters that would open (presumably for the Autobahn - zoom, zoom, farfignugen and all that sheisse) at speed and close back up from gravity and vacuum at low speed / stationary. So when people say they are overheating at 65MPH, I can't see the fan as being a problem (unless the huge blades are blocking too much air).

That's right, if you are overheating on highway you have some other big problem

It seems like it should already be getting all the air it needs at 65mph but when my jeep starts getting hot on the fwy at those speeds and I turn on the aux. fan, it cools it back down. Fans are still working at those speeds.

If your overheating on the highway you either have a coolant flow problem or something blocking the radiator. My 2000 was overheating on the highway and it turned out my radiator had a blockage so the coolant wasnt flowing very well. My waterpump also wasn't in the greatest shape. Combine that with all the tiny rocks jammed in the front of my radiator and it made for a useless cooling system. The fans only really do anything when the jeep is idleing at a stop light or when you are driving around town and not much air is flowing through. I did the ZJ fan clutch upgrade and it keeps the jeep cooler around town or when accelerating from a stop (and sounds like a jet). The jeep runs exactly the same on the highway because like stated above the airflow going through at that speed is more than what the fan would pull.

jeepkid03 said:

If your overheating on the highway you either have a coolant flow problem or something blocking the radiator... The fans only really do anything when the jeep is idleing at a stop light or when you are driving around town and not much air is flowing through...

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I'd say X2 on this post. A restriction of coolant FLOW would be the first thing I'd look at for highway overheating. At 65 mph you have enough air moving. The fans are designed to assist in slow moving traffic, idling and wheeling/crawling if you're so inclined.

Also the load of the A/C can't help. What temp are you running at when it overheats?? A skosh over the 210 mark is to be expected in hot weather driving an XJ.

I'd check the water pump and/or flush the system.

Actually, you are not overheating unless you are boiling over. 230+

I have an 88, after replacing the bottom radiator hose and installing the coil inside of it, it would overheat at highway speeds.
The coil slipped to one end of the bottom hose leaving about 4+ inches of the hose without reinforcement. And when I ran it up near redline in the driveway the bottom hose partially collapsed. It was just luck I noticed with the air box in there, I was just lucky, had a good angle and caught it in the act.
One easy way to check if airflow is your problem is to stick some washers under the rear hood hinges. Leave a gap at the rear of the hood and see if it helps. Mark the hood hinge location with a magic marker before messing with it, makes it easy to return to the stock location. The washer stacks need to be unequal heights to allow for a slight angle, a little trial and error may be necessary.

my jeep was running warmer than i wanted it to, so i built a lower engine cover to replace the mud flap that the engineers decided to put in there. i used .025" aluminum sheet and and cut it to clear the steering box and oil pan and bolted it in using some existing bolt holes in the frame rails. it went from running just above the 210 mark to just below the 210 mark.

as was stated above, the air traveling under the jeep whips up into engine bay and causes an "eddy", or a high pressure area. this can cause an overheating condition because air flow through the radiator is reduced. this is also why you don't overheat at lower speeds. the "eddy" hasn't doesn't form until x mph.

zedpapa

Mmmm....some interesting ideas. I have a new lower radiator hose but it doesn't have the spring in it. I read about the spring issue but never fully believed it. I'm going to try to find a place to purchase it this weekend. The eddy idea is also interesting - I may have to look into that as well. So with my flex 110 fan and aux fan - I should be able to cool properly on the highway? No need to upgrade my fan? Thanks everyone again.

I just made a discovery.... the temp gauge on the dash is useless. My Scanguage II showed 229F sitting at traffic light, while the gauge still read slightly over 210.

The moral of the story is that you shouldn't assume you have good temperatures because the gauge says so!

Well sometimes the sensor is wrong too. You need to put it in boiling water with a real thermometer and compare that to the voltage you get.

This doesn't work with the old-school one-wire sender because those have to ground through the body and stainless cookware does not have the same resistance.

Ok - ordered what Jeep tells me as the last 1988 lower radiator hose in the US from South Dakota of all places for $25. Should be here in a few days and then I will let everyone know how it does. Reading through several other posts, many others without the spring inside report no problems so I am still a little doubtful about this replacement. Just not sure what else to do since it is only a year old engine (rebuilt), year old water pump, year old radiator, and its a brand new ac condensor - so no debris blockage. I have also read several other posts where the flex fan 110 has worked fine so this issue I am having is a weird one.

ehall said:

Well sometimes the sensor is wrong too. You need to put it in boiling water with a real thermometer and compare that to the voltage you get.

This doesn't work with the old-school one-wire sender because those have to ground through the body and stainless cookware does not have the same resistance.

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Hallo. You can better test the gauge and the sender with resistors.
1365 Ohm gives 100F, 100 Ohm gives 220F and 50 Ohm gives 260F.
Put the resistor in series between the wire and the manifold. :laugh3:
or use this tool:

'92 XJ

You shouldn't really need to do this, but most newer vehicles have much better seals aroung the radiator to the body. I looked at mine yesterday. You could fab up some aluminum strips to seal better between the body and the radiator to get more of a "ram air" effect through the radiator. Obviously most Jeeps run OK without this, but you might see some improvement.