Hey,

Central FL driving. 90 XJ, 4.0. NAPA fan clutch, bosch injectors, champion plugs (installed 1-3 y ago, mishimoto all aluminum rad, water pumps good, no thermostat, cool hoses are fairly new 1-2 yr, R n R headers a few years ago, cleaned the sin out of the head 6-7 years ago with heavy duty fel-pro gaskets, have run T6 (or is it T5) diesel oil and normal oil PSI in all op conditions, trans fluid always tip top, no visible leaking where I park. Swapped injectors last night (no improvement, even while it was raining outside,), re gapped the plugs (a few were nearly .040 +/-) to .035 (wondering if closing down to .030 would be safe and cool the plug a little? thoughts? also, they look lean, clean looking ceramic, dry, electrodes look good, not worn or melted, a small white dusty buildup on top electrode), I use those funnels that can snap into the fill neck on rad to burp air. I'm always getting air especially if it gets over 210F. (hot spots in cyl?)

I've been running into this issue many a time since I've owned this jeep for nearly 15 years. I get it, "they run hot" but this is absurd. I'm replacing the torque convertor today cause you gotta rev up slightly sometimes on cold to engage. I read here last night that it could cause the motor to overwork trying to engage, but this issue only arose or at least became more obvious last few mo. A few years ago, since the head service, she ran pretty good, kept up w/ fluid changes and occasionally overheated when I taxed the jeep on highways, or on the trail.

The scoop: So for the past several months, anything over 2500 RPMs, like on highway, she'd start to cook nearly redlining. Several occasions she would pop from driving 20-30 min on highway. Its become common practice to always have a jerry can of water with me. City driving seemed to cool it down a little and when I arrived, I would have to idle high in park to cool a bit before shutting down. Idling will catch your attention sometimes, doesn't seem that smooth while in D. In Park she'll idle nice. She shifts alright 90% of the time, sometimes you gotta rev beyond 2500 and flutter the pedal to force a shift. No clunking, the shifts are nice when they happen. For the while I've been blaming the injectors but with such good positive reviews it can't be that. I will be taking them to get cleaned and flowed to just see, but idk, this is too much.

Q. Do any sensors affect pulse on injector? maybe a sensors going? O2 reading bad ? Can't remember but maybe R n R 5+/- y ago.
Q. I believe 90 4.0 fuel pressure is 62 psi? Do I need to adjust FPR with Bosch injectors? I bought an adjustable, but need to weld on AN fitting to get it to work. I won't do this mod until Its running average/normal, but it'll probably go in the Comanche instead.

 

You need a thermostat.

Get a Mopar 8983501426.

 

Agreed. Also, when was the last time you flushed the system? I suggest doing a flush and fill, and replace the rad cap, they do degrade over time, and it's cheap enough.

 

What do you mean pop? As in a rad hose pops off? if so maybe your radiator cap isnt venting off pressure like it should. Also maybe try a heavy duty fan clutch, upgraded facelift e fan and see if your fan shroud is damaged. i noticed my jeep ran alot cooler when the fan shroud still was in good shape lol. Check if the radiator is clogged as well and between the condenser and radiator that could have gotten leaves and crap stuffed between there. Assuming youre in florida youre using ac as well. maybe the ac compressor is putting alot of stress on the engine if its maybe going bad or overcharged. and are you using a 50/50 coolant mix? Also one more tidbit if everything checks out..... maybe do a combustion leak test (the fluid that turns a different color if there is gases leaking into the coolant system) yes i know you had it redone but doesnt hurt to try it as you can rent em cheap at the auto part store.

 

Others have already mentioned the thermostat, rad cap, and possibly water pump. Did you convert to the "open" style radiator? If you still have that crappy plastic football surge tank, the caps are notorious for not holding pressur and causing boil over. Yeah you're gonna boil off steam if you've got the cap off and the engine up to 210*F.

Is the torque converter locking up at highway speeds? That could add a lot of heat to the radiator. Try tapping the brake with your left foot while going steady on the highway and see if the rpm jumps a few hundred rpm. On a 1990 (Renix), the most common of not locking up is the switch at the brake pedal being out of adjustment, causing the trans computer to think you're applying the brakes. It's a separate from the brake light switch, whitish plastic and higher up on the brake pedal, and will have also a vac line attached if you have cruise control. Your shifting issue is almost certainly the throttle position sensor.

 

Mishimoto rad with fill cap, so open. It aint the water pump, the rad is not clogged. I flush at least once a week cause after running so hot, I gotta fill. I have a fill T on the lines that used to go to heater core. My plugs look very lean I would like to mention again. Even after a flush and fill and burp, It won't stay around 210, but slightly higher and will climb if I left it running 20+ min. in park. Driving seems to keep it cool a short spell until I come down gears or park or sit in traffic. But running 20+ on the highway, the gauge will be around the 3/4 mark just before redline. I've also ordered a new temp sensor, but still, I'm still scratching my head. Just fin. lunch so I'm going back out to finish dropping the trans and swap out the torque convertor.

Cruiser-

"You need a thermostat.

Get a Mopar 8983501426." -

Q. How would a T stat keep me running cooler?
I'll throw one in there just for giggles, but I was having this overheating issue when I had one in there 3-4 oil changes ago. I pulled it with the thinking that it would circulate the coolant a little faster to the rad.

EEVEE-
"Pop" like when you finger-banged Mary-Jane Rottencrotch back in the day. Like a boil over. I'm thinking maybe the mishimoto rad cap could be to strong a PSI, but ideally there shouldn't be any air whatsoever.
I have no a/c. The plastic grill has been removed for years. and the radiator is only a few years old. I'll give the leak tester a shot. However, wouldn't there be discoloration in the coolant or oil? They've always looked typical. But with the amount of times I've overheated, I wouldn't doubt there are fractures in the block or head :/

Lawsoncl-

I'm not too sure about it not locking up at highway speeds but i've no real complaints about it shifting once warm or on the freeway. Like I mentioned initially, on a cold start It takes several seconds to shift into reverse, then again into drive when I'm trying to pull away. I'll hit a high idle and it will eventually go from a slow roll to 1st.

 

Could be such a minute leak that its only leaking gasses into the coolant jackets. But yeah i totally forgot about the closed loop system on those lol my bad. Also you are a mad man with no ac in florida lol. Also the plugs look like your running lean? Pictures maybe just to be sure but if so that can contribute to the issue.

 

thermostat helps keep coolant in the radiator longer to get it to cool.

Otherwise, your cooling system works like a tea kettle. Crappy cap doesn't hold pressure allowing it to boil. Don't use a lever style cap.

 

Solid! Maybe the gaps were bad then and with clogged injectors cause my overheating then... in other news... I'm hung up on the pass side upper trans bolt. I spent a few hours with a ratchet trying to spin a striped bolt head. I gotta pull the dash now so I have room to cut into the floor board so I can take a cut wheel to the MMFFkkNK#**#U(!*#&$(*@#&$(*&%*$%(#$(*%&(*$&%&(#&$& %*&!(*@&#(*!&#@(*.... I promise, It was striped to begin with. I pray I'll have a new torque convertor in by tomorrow evening and I'm curious if that would drop the temp a little. But I'm throwing a t-stat in immediately after sending the last bolt from wrapping up this god awful nightmare. Thanks for the thinking gents!

 

I've been used to no A/C for a long time. I have been trying to get my plan B and C running so I can tear this XJ done to the bone and do her right. It just happens to be my daily unfortunately. I wana put a diesel in it so it could finally be a true work truck to tow a small trailer rig, boats and trailers for side work.

 

Public Service Announcement regarding the top trans to engine bolts.:
Alway break those 2 bolts loose before any others.

 

Dully noted. Dully.

 

I just got home and with the new torque converter, its running noticeably cooler (installed sunday) Still running warm, but waiting to cool more before I put a t-stat in to see if that would do the trick.


Tried hacking away with an air chisel. The bolt extractor in the following photo wouldn't grab the bolt prior to the condition you see here. Mashing the **** out of it open it up a little

It looked better, but still very rounded out when I tried to pull it. Upper-pass trans bolt. "Pull them first ********!" -some guy in Prescott

 

LOL. Thanks. I needed that.