Is this a change from past performance?

 

Been doing this since last summer, October. Not sure I remember any part changes that went with the change in behavior except going to 35s.

Been throwing parts at it, replaced the thermo and sensor couple months ago, waterpump last week, NAPA parts replaced with MOPAR parts, no changes.

 

I say fan clutch.

 

I am leaning away from that since the problem is at high speeds and I thought the fan would be more likely to be a problem at low speeds.

 

did you clean out the radiator with a garden hose? i've thought mine was clean in the past and then took a hose to it as i had the shroud off and couldnt believe how much crap came out. that would be my first step, then probably a radiator flush and verify the thermostat isnt defective.

i agree with it likely not being the clutch or the fan as they arent as important at highway speeds

 

did you clean out the radiator with a garden hose? i've thought mine was clean in the past and then took a hose to it as i had the shroud off and couldnt believe how much crap came out. that would be my first step, then probably a radiator flush and verify the thermostat isnt defective.

i agree with it likely not being the clutch or the fan as they arent as important at highway speeds

I replaced a NAPA thermo recently with a MOPAR thermo with no change. I was also thinking about cleaning the radiator, difficult to do with the AC condenser packed right in front of it. I'll take a hose and start spraying from engine side first then shoot it from the condenser side see if that helps. Maybe do a flush after I get back from a wheeling trip this weekend. Jeep will be on a trailer for this trip.

Thanks for the input.

 

Fan clutch has been suggested as not being the cause, but I am not sure I would rule it out yet.

If the fan is not spinning at the speed it should (or stops spinning all together) driving at highway speed, the slow or stopped fan could be blocking the air flow enough for the temp to rise. Maybe the clutch is experiencing slippage at the higher RPMs on the highway, slowing or stopping the fan...

I would still see if the fan clutch can be checked a little further before ruling that one out for this case.

If it is the original with 150k miles... It may be hinting that it is on the way out.

I hope you find something quick and cheap to fix this!

Keep us posted.

 

I would suggest taking a conservative approach given the manufacturer doesn't have a warning chime come on until the engine reaching 261 degrees per FSM (Section 8J-26). If you were running right on the edge of the fan engaging (165-185 at the shroud) I wonder if when the clutch kicked in, it would have brought the temperature back down. Either way the fan is testable so you can see whether it is working (section 7-32 is where I find in my manual). It does take a lot for the fan to engage. I have been down this road before, although not with Jeeps, and cleaning the radiator with a hose resolved the issue. Hope it works for you here.

Steve

 

I'll give her a cleaning tonight, and will check my service manual for those sections, thanks for the info. If I am on the road, I keep my OBDII going on my phone so I know the exact temp. If I go over 230° I kill the AC and slow down.

 

Engine oil can normally sustain 250 degrees in the sump according to online, although I am not suggesting you purposely run hot. If fan kicks in you should be able to hear and feel it.

Steve

 

Doesn't a viscous fan run all the time, just faster when it engages? At cold start, mine is spinning. How do I tell if it is fully engaged? Never noticed a difference in sound in the fan.

 

How old is the NAPA radiator? Sounds like it's clogged or just not performing up to Mopar standards.

 

Possible, only about 3 or 4 years old. I've been using a infrared thermal thermometer to test the upper vs lower hose, if working properly at operating temp, what kind of temp drop should I see?

Maybe better to test metal neck on the thermo housing and input neck on the water pump.

 

Start with the free solutions, tonight, I will thoroughly clean the radiator and condenser. Can this be done with a hose and sprayer, or should I go to the car wash for higher pressure?

 

Don't go to car wash.... Use a "Shower" or "Fan" pattern. High pressure will bend fins if you aren't 100% dead straight on.

Start by blowing compressed air (low pressure!!! like a little harder than you could blow through a straw) to get loose dust before soaking it with water. Then spray with water. Might need top loosen condenser or rad to get a little space in there to rinse off front face.

 

x2, do not use high pressure water, just a regular garden hose, no end is needed but if desired, use low pressure settings.

 

I was chasing an intermittant overheating for a year. It would not overheat around town and I could idle for a hour and temps were normal. I burped it dozens of times. My engine is rebuilt and everything is new except the clutch so I changed it. Gauge dropped and stayed at 180 for about a year and then started again. I was stumped, then noticed a black oil on my shroud and fan. The new clutch failed. I changed it with a cheap Oreilly fan clutch and problem solved.

 

I was chasing an intermittant overheating for a year. It would not overheat around town and I could idle for a hour and temps were normal. I burped it dozens of times. My engine is rebuilt and everything is new except the clutch so I changed it. Gauge dropped and stayed at 180 for about a year and then started again. I was stumped, then noticed a black oil on my shroud and fan. The new clutch failed. I changed it with a cheap Oreilly fan clutch and problem solved.

View attachment 4516201

I'll pick one up tomorrow, easy enuff to replace.

 

I ordered a Hayden fan clutch from RockAuto.com, but I would not have a problem with NAPA fan clutch either.
Hayden was the most popular and on RockAuto and had a good reputation from what I was able to find on the interweb.

Here is the NAPA fan clutch.

https://www.napaonline.com/en/search?input-q=4.0+L+242+CID+L6&q=N%3D2500012%2B2601208%2B2800898%2B10200500%2B5003800%2B200380360%2B403800700%2B599999900%26Nty%3D1%26Score%3D1&text=fan%2Bclutch&keywordInput=fan+clutch&referer=nol-veh-conds

 

Update:

Cleaned the radiator, started with compressed air followed with enough water that animals were approaching the Jeep in pairs.

Replaced the fan clutch and reassembled.

Test drive was inconclusive since the temp was in the low 80s. Took about an hour drive, after getting it to about 200° I headed for I-80, ran it at about 80MPH for about 20 miles with nice long uphill grades hit 210° several times, when I came off the interstate it showed a mix temp of 212°. I think it hit the 212° when on the exit, not sure, must not have been there long.

Tomorrow I will make a similar run when it is warmer out, supposed to be in great upper 80s tomorrow.

Just for fun this morning, on the way to work, the Jeep just died, tried to restart, starter wouldn't even kick in. Found the ASD relay took a crap, easy fix.

 

Just Empty Every Pocket.

My "Toy" turned out to be very expensive

 

The part that puzzles me, is where you say you "hit" 210 under load on the long grade. Engine should already be at 210 shortly after leaving your driveway and stay there...
You did not even reach 210 until the long grade?

210 (+/- a couple) is about where it should be. I haven't read live OBDII data, but my gauge is always on (or close to) the 210 mark all the time after initial warm-up, which is only a couple of minutes or about a mile of driving. Doesn't matter if it is 99F or -5F. Once it is warmed, it stays rock steady where it should and really doesn't move up or down.

If you now see 210-212 and stay steady under all conditions, I would say you are good. But, if it takes heavy load just to get you to touch 210 mark... You would want to follow up a little more to find out why.

 

The gauge on the dash is pretty crude, mine will drop to 204° on the OBDII, and it is on the low side of the 210° dot, 212° is on the high side of the dot.

 

Update, replaced fan clutch, slight improvement, may be my imagination.

Ordered a new OEM radiator, should be here Wednesday. Will flush the system while I'm at it.

 

Didn't even think of that, good point.

 

Replaced the radiator tonight, took the same drive on I80 as I described earlier, max temp 206. It was only about 72 degrees out, ran AC full blast anyway, but looks better. Will be in the low 80s tomorrow, and upper 80s by Tuesday, will continue to test. If this isn't it, I'm not sure what to do next.

 

Another test drive today, outside temp 81 and sunny, same trip down I80, max temp 204.8, starting to think that I got it.

 

Good decision going with the Mopar radiator.

 

It's been in the low 90s this week, still no issues. Occassionally uo to 208°, once, my max reading read 210°, but havent been able to reproduce that.

Thanks for all of the input, Jeep is happy, I am happy.

John