thermostat

My 88 4.0 I6 is running a little on the Hot side...and when i say little we are talking like at highway speeds it sits at 210 but at idle for three minutes at a train crossing it redlined on me. When we started moving agian it dropped a little but as soon as i stopped at a light it would jump right up. When i stopped to talk to a friend at a parts store i cut it off. Well come out and i smell Anti Freeze. now i have plenty anti freeze in the over flow bottle. So i was thinking of pulling the T-stat for the summer and put one back in in the fall. Any thoughts?? Good or Bad???

Bad idea. At best, all it will do is mask the real problem. And running without a tstat will only cause the engine to run super cold, compared to what it should be running.

If you can smell antifreeze, it's escaping somewhere. Maybe the overflow, punctured hose, failing waterpump, etc. But it's coming out SOMEPLACE.

Given the age, you probably want to check the fan clutch. If it's original, it's probably bad, and maybe a significant contributor to your overheating.

Your overheating may also a thermostat that is failing to open properly.

ChiXJeff

Classic case -- overheats when not moving, cools down when moving.

Replace the viscous fan clutch on the mechanical fan. Removing the thermostat won't do anything for you. It's open at 200 degrees or so, so how's removing it going to help you if the temp is higher than that when you're not rolling?

There was a thread just a couple or three days ago in which someone (Martin???) posted which replacement fan clutch will fit. The ones from Auto Zone and Pep Boys are listed for the XJ but often are just a tad too deep and won't fit.

old88XJ,

You need to do a couple of things to your 88 XJ. You need to install a new Mopar 195F thermostat and a new fan clutch for the mechanical fan.

You did not say how old your radiator is but if it is the stock radiaor is may be partially plugged and installing a new radiator.

This subject was discussed in the past week on here, see what the older post says.

Martin

Running with no thermostat or a low temp one isn't good as they say. The one thing that you'll notice the most is a loss in power and bad gas mileage...enough argument for me!

How 'bout your electric fan as well (providing you have one), is it working? I'd say you're due for the clutch, a check of the electric fan, and finding the leak (ever changed the XJ's water pump...if not then you should do it just because of it's age, doesn't hurt to be proactive) Also, the system is pressurized, your "overflow" is actually a pressurzied tank, those are known to crack, look for green on the hose that comes out of the bottom of the bottle. Another thing, get a new cap for the tank, it's probably bad.

If the radiator is suspect you may find it easier to convert your system to a later model style "open" system, get yourself a GDI 3-row open radiator if you do, they're quite cheap.

I don't have my links on me, but bleeding the system is IMPORTANT with the closed system, somebody here will have the best procedure on hand...

Sequoia

Time for some pmcs of the cooling system.
1 Mopar OEM tstat, one OEM mopar pressure cap, new fan clutch, two gallons of antifreeze, two gallons of distilled water, 1 prestone back flush kit, 1 can of prestone super 7 hour flush.
1 replace fan clutch and pressure cap.
2 drain system, refill with water and super flush. Go for a long drive.
3 Drain system, backflush, replace tstat.
4 refill with one gallon of antifreeze and one gallon of distilled water, mix remaining antifreeze and distilled water so you have two 50/50 mix bottles.
5 burp system.
Don't screw around, summer is coming, this sat is my pre summer maintenance, cooling system, plugs wires cap and rotor. Might even do the belt, it's got 170,000 on its original belt so I guess it might be time. Might even rotate the tires and check the brake shoes n pads.

Thanks for the advice...but i replaced it with a 180 tstat and flush and fill and it runs right.....fan was kickin in like normal so that wasn't the prob.

old88xj said:

Thanks for the advice...but i replaced it with a 180 tstat and flush and fill and it runs right.....fan was kickin in like normal so that wasn't the prob.

Click to expand...

When (not if) it next overheats in traffic and then drops to normal when you start moving, remember that you were advised to change the viscous fan clutch and chose not to do so. Running a lower than recommended thermostat is only masking symptoms, not solving the problem. It isn't summer yet.

Things to check...

Fan clutch - usual lifespan is about 5 years. Should spin freely when cold, and resist movement by hand when hot (engine off, of bloody course! No sense losing pieces you don't need to...) Aftermarket replacements are often about 1/8"-1/4" longer than OEMR, unbolting the upper crossmember over the radiator will give you enough tilt to get it in there, and there is no significant interference issue with the aftermarket unit in place (I've done this a few times...)

Radiator - Renix rads tend to pop about 150K, I am told. Go with a good 3-core replacement. Most here will tell you GDI, I swear by Modine. Go with whichever is easier to get.

Check hoses - they have a useful life of two years or so. If the hoses are gone, do the belt as well - you're in there anyhow and probably don't know how old it is.

Electric fan - there are two critical components here - the thermal fan switch (driver's side radiator tank) and the relay (I'd have to look it up, but I think it's left fenderwell.) You can backcheck the relay by disconnecting the fan sensor and shorting the two terminals in the wiring harness together (key on, hands out of the way) and noting whether the fan comes on - it should. Also make sure that turning the aircon on also act ivates the fan. The sensor needs to be removed to be tested (thermometer, boiling water, meter,) but should probably be replaced anyhow. If the fan doesn't come on, a meter across the fan leads will tell you if the armature is shorted or open.

Also, that "football" tank at the right rear tends to crack slightly with age, and I've usually seen them leak near the bottom hose fitting. In the beginning, they will only leak when the system is hot and at or near operating pressure (16psig.) Check Quadratec for this one, and a new cap probably won't go amiss either.

Bearing failure is usually accompanied by noise, and you don't mention any new noises.

In this order, check -

Fan clutch
Hoses
Pressure cap/"football" tank
Radiator
Electric Fan

Anytime you overheat (225* or more,) automatically assume the thermostat is shot and replace it. I suggest the use of brass or stainless replacement screws (Brass is better) so you don't have the rust issues you will see when you get the old steel screws out. They are, IIRC, 5/16-18x1" and 5/16-18X2.5", and should be readily available. Be careful removing the thermostat housing screws, hot steel + hot water = corroded metal. Fortunately, the block holds its own against corrosion.

5-90

5-90,

We will wait to see, I think old88xj will be replacing the fan clutch the next time his XJ overheats in traffic, then he will be replacing the fan clutch as well as the thermostat.

The advice you give is good but I have to disagree on the mechanical fan clutch. I do not think there is a test that works a 100% of the time, like you said change it due to age.

When I changed my fan clutch 3 years ago I went through this drill. I did buy one of those imperial brand but as you talked it too tall to fit. As you also talked you have to remove the radiator top support, tilt the radiator, install the new fan clutch, then reassemble.

I then ended up at carquest and got a new clutch which was idential to the OEM AC delco clutch I was removing.

This is my own opinion but new parts that require me to remove additional components to install it not worth it. I'll spent an extra $10 and get the part that looks just like the one I am removing and goes on in the reverse order.

I am also concerned with the additional rotating mass of the imperial brand clutch. I figured the bearing was not designed for that load.

I must be lucky on thermostat housing bolts, mine thread in and out with no problem. Mine still have all the black oxide coating on them. If I had problems I may go to the dealer or junk yard to get replacements.

Martin

You are correct that there is no 100% test for the fan clutch - but that will give you a good idea. If you think it's 5+ years old, replace it. If you KNOW it's 5+ years old, replace it. Besides, I think we're all agreed that it's shot based on the symptoms he's having.

I've been running an Imperial HD fan clutch now for 2.5 years with no problem. The rotating mass being different is not so much at issue provided it is still properly balanced. If the balance is correct, the mass issue is academic. I wound up with the Imperial because OEMR would have cost twice as much - dealers in CA are rather proud of their parts, and the pricing reflects that.

The brass hardware is a matter of course for me - I don't like having trouble, and that is just one more way to prevent it. Besides, I bought my XJ's used, and when I don't know the history of something, I like to start over.

5-90

Fan Clutch

I have just installed the imperial on my 89 with the stock radiator and it was a tight fit but it went in without removal of other components. I can't tell any difference in temperature but just replaced it due to age. I run 190 on warm days and 200 on hot days at a stoplight. One way to check the fan clutch is to get the vehicle hot and put your hand behind the shroud(be careful) at idle with parking brake engaged and feel the quantity of air you are moving. It should be noticeably more than the electrical fan moves. I simply cannot tell any difference in blade resistance from my 12 year old OEM clutch and the new fan clutch. Resistance to turning is light for both on a warm engine. The radiator cap is a $16 rip off. I had a slight seepage and bought a new one and it leaked worse than the old. I took the gasket off the new one and put it on the old cap and it has worked fine since then(3 months ago). If you could find the proper gasket you could replace the one in the exist cap and try it. If you put a rag over the cap with the engine hot and just give it a little nudge open(be careful) you should hear the pressure being released. If you do not, you have a cap or bottle problem. I think the long term solution is to eliminate the plastic bottle. There is discussion on here concerning this.

How to test the fan clutch:

1) Hook up a timing light tester.
2) Drill a small hole in the fan shroud – top center.
3) Install a thermometer into the hole. I used a foodservice thermometer that went up to 250degrees. Make sure that the thermometer is located BETWEEN the radiator and fan blades.
4) Disconnect the electrical fan power cord.
5) Start the vehicle and get the rpm up to 2000-2400.
6) Block the airflow – get some plastic grocery bags or something like it and put on outside of the grill. This will block the airflow going through the radiator.
7) Put the timing light on the fan.
8) When the thermometer reads 195degrees (+/- 3degrees), the fan will quickly speed up. You will hear it get louder, you will see it go faster, and you will FEEL it put out 2-3 times as much air.
9) When the fan clutch engages, quickly remove the plastic and let the engine cool down.
10) If it does not engage at 195degrees (+/- 3degrees), you can consider the fan clutch bad.

I know that there’s another test that you can do to the fan clutch while you have it off the vehicle, but I don’t recall the steps at this time – it’s in the service manual.

The OEM fan clutch and what is sold on the aftermarket as "heavy duty" replacements have a bi-metallic spring to engage or disengage the clutch. The procedure given above can only check that. The problem with older fan clutches is that the silicone fluid used inside the "torque converter" hub (since that's what it is) loses efficiency and even when ehgaged doesn't spin the fan as fast as it should.

There is NO definitive test for this. I have discussed this with technicians whom I trust at my current dealership and also with a close friend who spent his entire working life as chief mechanic and then service manager at an AMC/Jeep dealership. They all agree that you cannot test the fan clutch. When you see symptoms such as described in the opening post of this thread -- i.e. overheating when stopped, cools down as soon as you start moving -- that's when you know it is time to replace the fan clutch.

Eagle, you're right. The test procedure that I listed was from the service manual, but it will only check to see if the unit is responding. But what it cannot tell is by HOW MUCH. The only true test would be to construct a device that could measure the volume of cubic feet of air per minute that was output by the blades and clutch. I don't believe that there's any device out there like this - you would have to either make your own or take it down to the local wind tunnel at Boeing. Somehow, I don't think that they're gonna let me in.... too bad
-peace...

If you wanted to, it would be pretty easy to compare with a known good fan clutch. All you need is a handheld anemometer to compare airspeed of the air that is pulled through the radiator. My homemade anemometer is just a small fan blade on a tiny DC motor from the hobby shop. The motor ends up being a wind powered generator and I measure the voltage output with my DVM.