Overheating at low speed (new coolant, new tstat, new fan clutch)

I've been asking about this in some other threads but I don't want to hijack them too much. I've done a lot of searching and I can't find any circumstances that match exactly.

My XJ has been overheating at low speeds, especially sitting in traffic and offroad. I realized this when the "check gauges" light came on while GPSing some trails for work. I plugged in my Scangauge and it showed 267°F!! Coolant was boiling out of the overflow tank.

I checked the fans and both were spinning, so I ruled out the fan clutch and went to Sears and got the coolant flushed and tstat changed. I've had the XJ for 2 years and never did that so I figured now is the time anyway.

Didn't fix the overheating though. The next day in stop and go in 85°F weather it went up to 230°F or 240°F regularly, and intake air temp was about 160°F. Once I got on the highway and started going 35-50mph the temp dropped to 210°F-220°F and intake air dropped by about the same amount. To me the high intake temp plus the better cooling at higher speed would indicate a bad fan.

Someone on Expedition Portal said to turn off the engine while it was hot, then try to spin the fan by hand to see if the clutch is working. Well it spun easily, so I was pretty sure the clutch was the culprit.

So I got the clutch changed yesterday at Sears. The tech said that if it's still overheating it could be the water pump.

Well it's still overheating!! I let it idle down the road for a while and intake air got to 130°F with 230°F coolant temp. When I got home I shut down and checked the fan again, and I could turn it by hand easily.

I know it could be another bad clutch, but that seems unlikely. Could it be that the water pump really is bad so the radiator never really heats up, therefore the clutch never really heats up? Isn't the clutch supposed to be heated by the engine mount also?

Would a bad water pump cause the overheating at low speed but not at 35mph+ when the pump is turning faster? What about offroad, when the engine is spinning at 1500-2000rpm but it still overheats?

What do the pros think?

It might help if we know what year XJ you have.
It might help to clean the fins out in the AC condenser----air flow to the rad.
It might help if you replaced the radiator----they do go bad/clog internally that a flush just wont fix.
It might help if you replaced the radiator cap----or had yours tested for pressure.

Wayne

Oops... sorry. I had that info in my sig but my sig apparently disappeared.

It's a 1999 4.0L AW4


I replaced the cap with a 16LB.

The radiator should be pretty clean since I had to wash the hell out of my Jeep before shipping to Hawaii a few months ago. Where is the AC condenser? The AC works perfect, so I would think it's clean.

If the problem is lack of water flow, how can I figure out whether it's the water pump or the radiator being clogged?

Can I test the pump by parking, idling, and using the heater? I would think if turning on the heater cools it down, the pump is fine but there is an airflow problem.

Same problem, and I had very good results from new water pump even though the original still looked fine.

BTW the fan shroud looks incomplete. The top from 10 oclock to 2oclock is there, but below that it looks like someone trimmed it extremely precisely. Is that how the shroud is designed or did someone trim it for some reason?

The problem, if WP related such as an eroded impeller, I would expect it to be worse at higher RPMs--cavitation.

Ok, fan clutch 101: When cold, like overnight, the silicone will seep out of the reservoir and engage the clutch, so if you try and spin the clutch by hand after it has sat overnight it will be a little stiff. Then, if you start the engine and run it for about 5 minutes the silicone will be returned to the reservoir and if you then shut off the engine it will turn much easier. The last step is getting the engine up to full operating temperature, like 20 minutes of driving with the last 5 miles or so in slow city driving. That should raise the temperature enough so that the air flow through the radiator that hits the bi-metal spring will be higher than 170 degrees--the temperature where the spring just starts to open the reservoir--and once engaged a good fan clutch will be quite stiff. When not engaged both the standard and HD fan clutches will spin at 30 percent of shaft speed. Once engaged, the standard fan clutch should be from 60-70 percent of shaft speed, and the HD fan clutch spins at 80-90 percent of shaft speed. FYI, there is no HD fan clutch for the XJ--luckily, the ZJ HD fan clutch, NAPA number 272310, $44 dollars is a direct fit. Not the ZJ MAX COOL fan clutch, it will not fit.

Now, it is fine on the open road so airflow is adequate for cooling then. However, any restrictions to airflow will be greatly magnified at idling/stop and go city type driving. So, as posted above, check the clearance of things up front. Things that restrict airflow--aftermarket bumpers, winches, trans coolers, PS coolers, a/c evaporators, dead birds, mud, bugs, etc.

So, good airflow, good coolant flow, proper coolant mix, and pressure--good cap, those are the elements that make it work.

If it was mine, I would check the oil for coolant contamination--remove the filler cap, pull the dipstick--any sign of mocha, head/gasket issues. I would also check the coolant for hydrocarbons, you buy the chemical and rent the tester--positive and its a head/gasket.

As you hit 267 degrees I would replace the thermostat, once overheated they can get funcky. I only install, and only recommend, the Stant SuperStat Premium 195 degree.

The life of a WP is about 4 years for a vehicle driven daily--after that and you are running on borrowed time. If you replace the WP PLEASE don't buy a reman, they are purely a waste of time and I don't give a damn if it comes with a lifetime warranty--you will get real tired real quick when you have to keep changing them each year (if that long)!

There is one problem with having a shop do a coolant flush--it really is more of a coolant exchange. What you want is a commercial grade flush, the kind you put in and run for 500 miles, then flush with tap water, followed by a neutralizer and another tap water flush. Then fresh 50/50 mix of coolant and steam distilled tap water.

You mentioned "both fans" so you have an aux fan. If it is old--like yours--it may not be moving enough CFMs to earn its keep.

Do you have the mechanical fan shroud in place?

^ pretty darn cool (pun intended) for you to throw down some info like that Joe.

winkosmosis said:

BTW the fan shroud looks incomplete. The top from 10 oclock to 2oclock is there, but below that it looks like someone trimmed it extremely precisely. Is that how the shroud is designed or did someone trim it for some reason?

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http://www.partsgeek.com/gbproducts...ontent=AYY&utm_campaign=PartsGeek+Google+Base

Thanks for the comprehensive post joe_peters.

I'll check the oil for mocha. I would think if it was the head gasket it would overheat all the time though.

The tstat I had replaced at Sears. They used whatever NAPA or Checker sells because those are the only two parts shops nearby. I'd love to use a Stant but what you want is always hard to find on Maui. If NAPA had the "ZJ" clutch in stock I might have asked Sears to use that. I may do that upgrade now that the bolts aren't stuck-- I don't need to have a shop do it, I just need to buy box ratchets.

When I tested both the old and new clutches, it was after low speed driving when they would have been well heated up. Under the hood was HOT, and the intake air temp was 140F according to the Scangauge. Should the clutch work regardless of water pump performance?

One thing I thought of was that the front skid plate is restricting flow. But there is plenty of room between it and the axle for air to go.


I found that same shroud pic by googling but it doesn't help. It looks like someone trimmed rectangular sections out of the rim except for the very top. In other words the shroud doesn't completely enclose the fan.

BTW, NAPA does list the ZJ clutch as also being for the XJ.

The NAPA Premium thermostats ARE Stant--most of the underpaid and under trained "Counter Dudes" aren't aware of it--you can verify this on Stant's website.

Yeah, low speed is good for the test. The FSM test has you place a blanket over the grill to restrict airflow.

I would want to replace the shroud, but I doubt if it is the sole source of your issues.

I hope the Stant is what they put in. I asked them to get the premium option if there was one, but I don't know where they got it.

How can I tell whether the problem now is the radiator or the pump?

You could pull the radiator and have it checked at a radiator shop, or use the commercial flush I described above to see if things improve. How long have you owned this XJ, and do you know when the WP was last changed? As I said above 4 years is about the useful life.

I've had it for 2 years and I don't know how old the pump is. I can't flush my radiator because my lease forbids that kind of stuff. For the cost of having the radiator pulled and tested I might as well get a nice new aluminum one put in!

As joe_peters has been highlighting .... Your main issue would appear to be airflow.

A thermostat doesnt cool an engine ... It sets a predetermined, minimum hot temp for the engine to run at ... a faulty one not opening fully will contribute to higher running temps.

The factory skidplate/bashplate wont cause airflow issues .... Have had mine off and on with no differences in temps. In fact, having it fitted should reduce turbulence effects behind the radiator and allow the fan to perform as best it can.

The fanshroud ... poor as it is, it needs to be in place - for the small diameter fan to have any chance of operating with any real effect. If yours has been modified it might be wise to replace it.

Clutchfans ... I hate the things ... and replace them at the first hint of an overheating issue on any vehicle ...

Fanclutches are also meant to be stored vertically as far as I know .... Yet how many parts places have them laying on their backs on the shelf ??? ...

I agree with the point that your waterpump is probably not at fault, in regard to your low speed / high temp issue .... but its only a coupla bolts, a gasket, and some RTV to inspect the thing and see if the impellor is corroded ... or the circular area below the impellor has been corroded to an egg shape or similiar. 4yrs lifespan as per joe_peters comment ... but I work on 60,000 miles ... same as the fanclutch.

Something else to consider is the coolant mix ... whilst not likely to be your issue - simply lowering the ethyl-glycol percentage will result in a cooling benefit. What percentage you use is dependant on your climate conditions. Im using an off the shelf, corrosion inhibitor premix that has next to no anti-freeze in it ... but I can where I live.

Additionally - a high anti-freeze concentrate, does need a fully functioning waterpump to facilitate heat transfer ... so checking the condition of your waterpump could well be beneficial.

The electric aux fan should be fine ... but its certainly possible that its turning at less revs than it should.

Radiator fins ... didnt get flattened over with all the washing prior to shipping O/S did it ???.

The other thing to consider about your radiator is .... what sort is it ???

Is it just the factory type single core, ideal for canada, radiator ... that is struggling with Hawaii temps ???

carves said:

As joe_peters has been highlighting .... Your main issue would appear to be airflow.

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That's what I thought too, especially given the high intake air temp.

A thermostat doesnt cool an engine ... It sets a predetermined, minimum hot temp for the engine to run at ... a faulty one not opening fully will contribute to higher running temps.

Click to expand...

They tested the original tstat at Sears and said it was opening fine but I had them replace it anyway because they're so cheap.

The factory skidplate/bashplate wont cause airflow issues .... Have had mine off and on with no differences in temps. In fact, having it fitted should reduce turbulence effects behind the radiator and allow the fan to perform as best it can.

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I always figured the skid plate would help at highway speed, because behind it is a vacuum that would help suck air out of the engine bay. Without the skid plate, airflow would hit the axle and create a high pressure zone. At low speed though I wasn't sure.

The fanshroud ... poor as it is, it needs to be in place - for the small diameter fan to have any chance of operating with any real effect. If yours has been modified it might be wise to replace it.

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I'll take a pic of mine and post it. I don't know why anyone would mod it rather than just remove it if it was in the way.

Clutchfans ... I hate the things ... and replace them at the first hint of an overheating issue on any vehicle ...

Fanclutches are also meant to be stored vertically as far as I know .... Yet how many parts places have them laying on their backs on the shelf ??? ...

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DOH! So a bad new clutch is a possibility.....

I agree with the point that your waterpump is probably not at fault, in regard to your low speed / high temp issue .... but its only a coupla bolts, a gasket, and some RTV to inspect the thing and see if the impellor is corroded ... or the circular area below the impellor has been corroded to an egg shape or similiar. 4yrs lifespan as per joe_peters comment ... but I work on 60,000 miles ... same as the fanclutch.

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But don't you also have to drain the coolant, at least partially? I'd have to take it to a shop, and in that case if I was paying for labor I'd have them replace it.

Something else to consider is the coolant mix ... whilst not likely to be your issue - simply lowering the ethyl-glycol percentage will result in a cooling benefit. What percentage you use is dependant on your climate conditions. Im using an off the shelf, corrosion inhibitor premix that has next to no anti-freeze in it ... but I can where I live.

Click to expand...

I didn't know products like that existed. I don't think they are even sold in the USA. That would be perfect because it doesn't get to freezing temperatures here except at really high elevation.

Additionally - a high anti-freeze concentrate, does need a fully functioning waterpump to facilitate heat transfer ... so checking the condition of your waterpump could well be beneficial.

Click to expand...

If only I could check it without removing it.

The electric aux fan should be fine ... but its certainly possible that its turning at less revs than it should.

Click to expand...

I don't think it's the aux fan. AFAIK it's not supposed to be necessary except with high stress conditions right? My coolant hits 230F even in 75F weather.

Radiator fins ... didnt get flattened over with all the washing prior to shipping O/S did it ???.

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They look fine

The other thing to consider about your radiator is .... what sort is it ???

Is it just the factory type single core, ideal for canada, radiator ... that is struggling with Hawaii temps ???

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It's an OEM but it was fine in Texas summer last year, which was 90-95F. The highest temp I've seen here is maybe 85F.

BTW, if the pump needs replacing can I get one of these high flow Hesco ones without changing the thermostat also?

http://www.jeep-xj.info/HowtoWaterpump.htm

Edit: Forget that.. $150 vs $50

For only $50 I should have had them just replace the pump when they did the coolant drain. I was thinking it was a somewhat separate job which would mean an extra hour of labor but it doesn't look that way from reading that howto.

Last night I checked the fan clutch again when it was hot. Still easy to turn. Is it really supposed to be stiff when it's hot, or just give some resistance? It feels like the clutch is full of honey.

Then I noticed the electric fan wasn't spinning!! It's supposed to be triggered by temperature right? Even if it was triggered by A/C, the A/C was running.

I tried to take out the fuse but it was stuck in the socket so I left it alone. Then when I checked again once I got home, the electric fan was spinning. So either there is something wrong with whatever runs the efan, or the fuse wasn't seated properly.
But at this point, even though the efan was working, the coolant temp was 227F.

hook a switch to your electric fan. or check the temp sensor.