Should I hear the radiator fan when it's engaged? (1989 4.0)

[gummycarbs]

Hi everyone,

 

I'm driving a 1989 Comanche 4.0.  It's at almost 278k miles and has no modifications, aside from maintenance and collision repair. It's a stripper model, with no A/C, so no auxiliary electric radiator fan.

 

Last summer, it began to overheat when idling for extended periods.  I flushed the cooling system and replaced the radiator clutch fan.  If I recall correctly, I used the old "push a stick against the fan when it's hot and idling and see if the fan stops spinning easily" test to determine that the old fan clutch was bad.  Also, I could see coolant flowing pretty well into the overflow tank, so I assumed the water pump was good.

 

Well, here it is summer again and it's overheating again.  One thing I've noticed is that I never hear any kind of roar from the radiator fan.  My old 1995 ZJ would roar for a bit right after starting up, then I'd intermittently hear the fan clutch engage and more roaring during prolonged idling.  So, should I be able to hear the Comanche's radiator fan?

 

The last time it started overheating, I gave it a bit of throttle and noticed the gauge begin to drop a bit.  I held it at maybe 1,500 RPM for twenty seconds or so.  I've read here that this indicates a failing water pump, but I chalked it up to increased radiator fan speed from the parasitic drag of a non-engaged fan clutch.

 

Regarding the temperatures, I've seen it get *almost* to the start of the red zone.  Now that I know it can happen, I keep a close eye on the gauge and shut the engine off when it gets close to last white tick mark.  In years past, it would be rock-solid in the 195-210 range.  Seeing it at 210 (the middle mark) was a notable occasion!

[schardein]

I never notice the clutch fan on my 91 XJ or 91 MJ.  I generally do not even notice the electric fan when it kicks on, until I park and get out with the engine still running, then it's noticeable.

 

Is your fan belt tight?  Engine oil level correct?  No damage to exhaust system?  I've had all of these contribute to an overheating situation (along with a bad fan clutch, dry rotted radiator from salt air) and might be worth double checking before replacing a water pump.

[Rockfrog]

Check the cat/muffler for blockage. The stock fan only spins about 60-70% of engine speed. An upgrade is a Hayden 2737 which spins 90%

Is the rad fins full of dirt/Grime at all?

When was the last time the water pump was changed? If the fins are rusting out ... Well you can guess what happens there.

 

 

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[onlyinajeep726]

Check the cat/muffler for blockage. The stock fan only spins about 60-70% of engine speed. And upgrade is a Hayden 2737 which spins 90%

Is the rad fins full of dirt/Grime at all?

When was the last time the water pump was changed? If the fins are rusting out ... Well you can guess what happens there.

 

 

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That right there is what I did... You'll definitely hear it then lol.

[gummycarbs]

Thanks for the responses. The belt is tight, I topped the oil up last week, and the radiator fins are about as clean as can be.

 

The catalytic converter and exhaust is an interesting idea. The cat has recently started to rattle at low RPMs, so it's breaking loose if not completely broken up. I have no idea how that might be affecting flow. It's never been off-roaded and the exhaust is at least visually in pretty good shape.

 

The Hayden 2737 fan clutch might be a good stop-gap measure while I decide whether or not I want to do an engine swap. There's an 80k mile 1988 motor for sale locally.

[Rockfrog]

My XJ has the YJ/TJ stock fan (also the ZJ max cooling) aka Hayden 2737. You definitely WILL hear the fan I guarantee it. I don't even notice it now, but when it first went in. But it only makes it sound like a YJ/TJ so really not a major deal. It's just that the stock fan is so quiet is all.

 

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[DirtyComanche]

Normally if your cat is plugging up you will experience low power with it.  If it is gradual you may not notice it though.

 

I think you should change your waterpump.  The stock fan, which cools adequately when the rest of the system works correctly, does not make a lot of noise.

[Eagle]

If the overheating is only at idle or low speeds, and the temperature drops back to normal once the truck is moving along at 25 MPH or faster, the viscous fan clutch is the likely suspect.

[coathanger37]

I my experience most of the time idle overheating is almost always the water pump. I always change the thermostat when changing the pump. If you see a lot of crud the do a coolant system flush when your done before filling with antifreeze.

Just my 2 cents

[gummycarbs]

Just a followup:  I went ahead and replaced the water pump.  Amazingly, there was no change in the idle overheat behavior.  The last water pump I can find in the records was at 132k miles in 1997.  Now at 279k miles, the old water pump's fins looked just about exactly like the new one!  No noticeable corrosion, and no perceptible play in the shaft.  Kind of amazing, but maybe water pumps last indefinitely when they don't have to support a radiator fan...

 

Like a fool, I didn't replace the thermostat while I was in there.  I've also noticed some coolant around the reservoir, so I think the cap is shot.  I ordered a new cap and if that doesn't fix the issue, then I'll replace the thermostat, and if it still overheats, then I'll replace the radiator.

[Rockfrog]

Stop beating around the issue, the fan clutch is done and needs replacing. You described the exact symptoms of the problem.

The clutch is 1/4 the price of a rad so it's also the cheaper route.

You can't "feel" a bad clutch on these as the lockup is only 60-70% ... A bad clutch generally feels just like a good one, if you get lucky you may have one freewheel when hot (like tapping the red, hot).

 

As for waterpumps, my stock 2000 XJ water pump still cools my 1988 MJ after is replaced the XJ's entire cooling system a couple years ago. It also has the stock 2000 radiator in it as well. The fan clutches in both vehicles have gone several times over the years though (XJ has had 4, MJ on it's third now).

 

 

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[gummycarbs]

As I said, I replaced the fan clutch last year and it had absolutely no effect on the behavior whatsoever.

 

After replaced the reservoir/expansion chamber cap, the needle hasn't yet passed the 210 mark.

[gummycarbs]

Update:  it was the thermostat.

 

I used my IR temperature sensor and noticed that the radiator temperature wasn't getting over about 170 degrees, while the temperature gauge showed 210 or more.  If the radiator isn't getting hot, the fan clutch isn't going to engage.  I did a Prestone 3-day flush.  It improved the situation, but didn't fix it.  The temperature differential was still higher than expected.  I replaced the thermostat (Stand 195-degree 'economy' thermostat) and it instantly resolved the problem.  Now, the top of the radiator shows almost the same temperature as the thermostat housing.  I did two more flush cycles and replaced all the rubber components, but the thermostat was what completely changed the behavior.

 

The fan still isn't audible at idle.  It is audible, however, if I've been idling for awhile and begin to accelerate.  It simply sounds like a slight 'roar' as RPMs approach 2k-ish RPM.

[omega_rugal]

if the engine is overheating, touch the radiator, if it`s cool enough to hold your hand on it, coolant is not flowing, make sure coolant is even moving before start changing parts...

 

i learned that the hard way...

[GrayWolf]

Went through some of these same fixes recently, Post: "Overheating and Power Loss over 2000 ft".  27-June-2017. I won't go through all of it, but the one thing I had not added to my last post was returning to my original clutch fan, instead of one that was attached to parts from a WR.  Some of the things I did might help.  I'm now running cool and consistent no matter load or elevation.