Aux Cooling Fan Q

My radiator was knocked out among a number of other components, by a stupid teenager who backed into me. Since the repair, my 94 4.0 XJ has been overheating. The Aux cooling fan has only been coming on intermittently and rarely. When it does come on it cools the 4.0 almost instantaneously. I was told by the body shop that the AUX cooling fan is only there to cool when the Air conditioning is in use and that the mechanical fan should be more than adequate to take care of the radiators cooling requirements. He also told me that the Temperature sensor may have gone bad because once the engine overheats, it has to be reset by replacement and that the temp sensor controls the auxilliary fan as well. He assured me that the replacement radiator was the identical capacity as the original,..... even though I asked him to put in a 3 row. Can anyone make any sense of this? While my temp meter used to sit rock solid at 220 degrees now it rises and will eventually go into the red if I let it. Tomorrow it goes to a real mechanic. TIA

air pocket

Hey Dirt,
I forgot,..... that's what they told me at first and theoritically took care of it. maybe they didn't get all of the air out?

they can be a real SOB to get the air out of. i've modified my heater hose and put a bleeder valve in line so that helps. but before that i would take the heater hose off the t stat housing and fill with coolant then fill the heater hose you have off with coolant and put it back on real quick. the thermostat has to be open to do this. then just let it run with the heater on and the cap offfor awhile. give it some throttle in ten second intervals and hope for the best. hope this helps Dirt

sorry fill with coolant till it comes out the housing then do the same with the loose hose.

The aux cooling fan is (OEM) triggered by one of two events - either the AC is turned on (AC REQ) or the thermal switch/sensor reaches a predetermined temperature (RENIX has a dedicated TFS - I don't recall how later models work at the moment) that trips the relay and turns the fan on until a (lower) temperature is reached - I think for RENIX, it's ON at about 215-220 and OFF about 190.

If the thing has to be reset, there's something silly I should look in to...

Problem with most shops - especially if it's insurance work - is that they'll only install OEM-equivalent parts unless the swap is documented with the underwriter for your vehicle. Therefore, your telling them to install a 3-core was just wasting air - they HAVE to install whatever was in there when it left the factory, as I recall.

The secondary fan should not run all the time - only when you get past 215 or so. If it's coming on much hotter, you'll probably want to change the sensor and/or check the wiring.

Meanwhile - if you want the system to "burp" easily, drill two holes in the thermostat flange like I keep suggesting - one hole at the top, one at the bottom. Air will pass thru the top hole, displaced by water thru the bottom, and the air will make its way toward the radiator cap so it can be easily purged. About 1/16" is right for the holes.

5-90

OK, I got the Jeep back from the mechanic. They said they couldn't find anything wrong and that maybe there was an airbubble that burped out. Ideed it is running much better and the only time the temp gauge goes over 210 degrees is when sitting at idle with the air conditioning off. Then, it rises to about halfway between 210 and the "Red" zone. At that point the electic fan kicks in and brings the heat back down to 210 again. It never did this before. I thought that the mechanical fan was supposed to be able to hold its own and that the auxilliary fans' sole purpose was to cool when the air conditioning was on. Am I wrong on this?

Theoretically, that is correct. However, practise is not always perfect - and that's why there's overkill with the two fans running.

If it was never going to happen, the radiator wouldn't need the extra fan (it doesn't come on for the radiator proper with an AC REQ anyhow - it's for running extra air over the condenser. The extra heat load on the engine is minimal.)

I'm still curious about this - mainly because there's so much difference between operation before the crash and after. What parts where there before you got hit - had anything been replaced?

5-90

What was replaced? The front bumper, grill, the header between the grill and the hood, the radiator, the part that the lights and grill and everything screw in to, a lens, that's about it. Quite frankly I'm suspicious of the radiator itself. Its a 2 row replacement that the parts guy swore up and down was the exact same capacity as the original. Unfortunately I told the guy I wanted a GDI metal 3 row and instead he replaced it with a no-name metal 2 row thinking that I wanted it to be metal rather than plastic like the original. He didn't understand that I wanted the 3 row which just happens to be metal. So now I have the worst of both worlds. I am still suspicious of the replacement radiator but have no way to really test/prove it without replacing it..

The other change that I failed to mention is that prior to the accident, as the engine warmed, the temp guage rised very steadily up to 210 degrees. Now it is up and down, up and down as though each time more coolant is allowed through the thermostat, the engine is cooled a bit and then reheats. This whole thing is SO annoying.

hey 5-90, I'd really like to see some pics of the way you drill the t stat housing. I see your point and it sounds good in theory i just can't picture it in my head. like I said I installed a bleeder valve inline. but I would really like to see an example. TIA Dirt

Take the thermostat, drill a hole at 12 and 6 o clock... on the flange part.

yardape said:

Unfortunately I told the guy I wanted a GDI metal 3 row and instead he replaced it with a no-name metal 2 row thinking that I wanted it to be metal rather than plastic like the original. He didn't understand that I wanted the 3 row which just happens to be metal. So now I have the worst of both worlds. I am still suspicious of the replacement radiator but have no way to really test/prove it without replacing it..

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You don't want a GDI Do a search on here and you will hear a lot of negative stuff about them. They are crap since they got bought out.

Atl XJ said:

You don't want a GDI

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I agree. The two row you have likely has larger passages and should work just fine......and probably last much longer than the GDI.