YJ overheating and fueling issues

RooComb

RooComb

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Jul 30, 2025
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Nunya Business
Newly purchased 1990 YJ 4.2 with a Weber carb.

The issue(s):
Everything was fine when I did the test drive before buying it. On the way home the temp gauge slowly crept up all the way to just under the red mark and stayed there. When it got hot, it started sputtering and bucking like a bronco when taking off from a stop light, and would stop sputtering after a few seconds, then keep driving normally. I also noticed it's hard to start hot. Cold starts are easy and fast, but only hot starts are difficult. And also, this thing get's 8mpg on a good day. I know it's not an eco car... but wow that's bad. And it only holds 10gal usable fuel (stock metal gas tank). I looked under the hood, and noticed that someone installed a 2" body lift to clear the 31" tires, but this caused the rad and fan shroud to be misaligned with the engine driven fan. So the bottom of the shroud had been trimmed off since it was obviously interfering with the fan because of the body lift, and the top of the shroud isn't helping much since it's sitting so far up... GRRRRR. I also noticed that for some reason whoever did the Weber carb conversion blocked off the return fuel line to the tank, and got a fuel filter that doesn't have the return outlet on it. Not sure why it was done that way, but I'm wondering if that's causing some of my problems.

What I've already done:
Replaced the fan clutch (standard duty), replaced the thermostat (180*), flushed the cooling system, and refilled with new coolant. That at least is keeping the temp gauge out of the red, but it still runs past 210*, which I'm not comfortable with, and is likely causing vapor lock that then causes the sputtering.

What I'm considering:
I want to install some sort of throttle body fuel injection system, with an electric fuel pump, and get a 20 gallon fuel tank and sending unit from a later model YJ. That should address my fuel capacity and mileage issues. I also want to get rid of that God awful body lift, and get stock height polyurethane body mounts, and either a proper suspension lift (currently considering BDS BDS408H) or just rebuild my stock suspension since I really like the way it rides, and go back to stock wheels/tires. I'm not a hardcore offroader. I mostly run down gravel trails for recreational purposes. Then my rad and engine fan will be in the correct position, and I can replace the fan shroud, which'll get that back in working order. I might also go ahead and replace the rad with a heavy duty aluminum one. I believe that the rad that my Jeep currently has is the original one.

I really love my YJ, and it can definitely be saved. It's a very nice Islander model package, too. I just need to be pointed in the right direction to get the aforementioned issues fixed.
Thanx all :)
 
You can also install a 160 deg. Thermostat. Helped mine a lot. Got mine at Advance auto for about $7.
 
ytradio said:
You can also install a 160 deg. Thermostat. Helped mine a lot. Got mine at Advance auto for about $7.
Click to expand...

I have a 180* t-stat. As the Jeep warms up while driving, the temp gauge briefly stops at 180*, and if I keep up a steady pace at 55mph or better on a level road, it'll stay there. But if I have to wait at a stoplight or heavy traffic for any amount of time, then the temp climbs right up, and is very hard to get back down. I usually end up finding a place to park and shut it down to let it cool off.
 
Definitely need to either drop the radiator or delete the body lift so a new intact shroud can be reinstalled. That would be step one for me if I was in that boat.

Lower temp thermostats can help by prolonging the overheating but when it's hot outside, you will still climb right up to the max temp the radiator can keep you cool to, which ordinarily should be 205-210, but currently that is obviously higher due to whatever is wrong. So I wouldn't rely on a lower temp thermostat to do anything besides give you a bit more margin before overheating. In reality the thermostat just sets the minimum temp and ensures that you reach at least the specified t-stat temp. So I would start by dealing with the body lift and shroud. Is the radiator itself in good shape and fins not clogged up?

Your plans overall are good ones. Just hard to say what is causing the overheating. There is a chance the temp sending unit is bad and reporting false high temps, but that seems unlikely since the temps are scaling pretty consistently based on your description.

If it helps, I just bought this kit and while the title says CJ, that is incorrect and it is all the correct parts for a YJ for stock body bushings. Have to reuse the top inserts from stock though, hopefully yours are in good shape, or you can pick up some from Crown or similar.

Amazon.com: Energy Suspension- 2.4105G CJ BODY MOUNT SET : Automotive

Buy Energy Suspension- 2.4105G CJ BODY MOUNT SET: Body Bushings - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
 
machoheadgames said:
Definitely need to either drop the radiator or delete the body lift so a new intact shroud can be reinstalled. That would be step one for me if I was in that boat.

Lower temp thermostats can help by prolonging the overheating but when it's hot outside, you will still climb right up to the max temp the radiator can keep you cool to, which ordinarily should be 205-210, but currently that is obviously higher due to whatever is wrong. So I wouldn't rely on a lower temp thermostat to do anything besides give you a bit more margin before overheating. In reality the thermostat just sets the minimum temp and ensures that you reach at least the specified t-stat temp. So I would start by dealing with the body lift and shroud. Is the radiator itself in good shape and fins not clogged up?

Your plans overall are good ones. Just hard to say what is causing the overheating. There is a chance the temp sending unit is bad and reporting false high temps, but that seems unlikely since the temps are scaling pretty consistently based on your description.

If it helps, I just bought this kit and while the title says CJ, that is incorrect and it is all the correct parts for a YJ for stock body bushings. Have to reuse the top inserts from stock though, hopefully yours are in good shape, or you can pick up some from Crown or similar.

Amazon.com: Energy Suspension- 2.4105G CJ BODY MOUNT SET : Automotive

Buy Energy Suspension- 2.4105G CJ BODY MOUNT SET: Body Bushings - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
Click to expand...

I did a massive parts order last night. Here's what I got:
Champion 3-row aluminum radiator - part #CC2101
Crown Auto replacement fan shroud - part #52004214
Front frame cover - AMC part #8955050158
Prothane master bushing kit - part #12005
And a few other odds and ends that are unrelated to the issues at hand.

My YJ also had a very old Warn 8000 winch on the front that no longer works. I removed it, and purchased the OEM front frame cover. Hopefully this, in conjunction with the body in the correct position on the frame, and a good fan shroud will direct air properly through my new Champion rad. Champ was running a sale, and it was only $40 more to get a 3-row rad than the stock replacement one. As far as the condition of my current rad, I believe it's the original one. Meaning it has 35 years, and 150k miles of bugs, rocks, and dust slapping against its cooling fins, and coolant rushing through its core. It doesn't leak, but with that type of use there's really no telling how much life it really has left in it. When cruising at 60mph or better on a level road when lots of air would be blowing through the rad, my coolant temp still creeps up. It'd be one thing if the temps rose only when standing still, which would definitely just be the lack of a fan shroud. But since it still can't keep cool while driving, I think it's just old and lost its effectiveness. I do plan to keep it as a cool mancave decoration. It's not everyday that you see an all copper radiator.

Now to elaborate more on my fuel system: The previous owners did a Weber carb conversion. For some reason they installed a regular inline fuel filter in place of the stock one that has two outlets, and blocked off the return line to the tank by sticking a bolt in the cut line. I'm going to do my best to reroute the fuel lines away from the engine, and reconnect the stock return line to the tank. I'll also use fuel line insulation to protect the lines. This, combined with my new cooling parts should mitigate my fuel system issues. I think the under-hood temps are so hot that fuel is boiling in the lines, and also evaporating from the carb bowl.

I haven't verified the engine temp with a thermometer, but I can say that when the temp gauge indicates hot and I lift the hood open, the air in the engine bay feels like I'm looking down a volcano. And the last time I remember feeling this was when a Chevy truck overheated on me. It definitely feels way hotter than a normal engine bay at operating temp.
 
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ytradio said:
You can also install a 160 deg. Thermostat. Helped mine a lot. Got mine at Advance auto for about $7.
Click to expand...

Well, what is meant by this is that the thermostat opens a little earlier and gives some more headroom on the temperature. Yes a new radiator is a good idea, but you already had that in the queue. Good luck
 
Has anyone ever done the TeamRush mod on a YJ? I've read about it, and understand it's basically swapping in a distributor cap, rotor, wires, and spark plugs from a Ford 300, and upgrading the coil to an MSD Blaster for stronger and more accurate spark. But I've only heard of anyone doing this on older CJ's.
 
RooComb said:
Has anyone ever done the TeamRush mod on a YJ? I've read about it, and understand it's basically swapping in a distributor cap, rotor, wires, and spark plugs from a Ford 300, and upgrading the coil to an MSD Blaster for stronger and more accurate spark. But I've only heard of anyone doing this on older CJ's.
Click to expand...

I’m not familiar with that mod. But if you want a hotter spark, there are many affordable GM style HEI distributors for the Jeep straight 6 that are drop in ready. One was on my Jeep when I got it, thought that I would need to replace it like everything else that came with it, but I didn’t. Works fine, but I priced new ones and was surprised how inexpensive they were.
 
Update: I have replaced the body bushings, and brought the body back down to stock height. I also replaced the rad with a Champ 3 row, and I replaced the fan shroud with a reproduction unit from Crown, and refilled the cooling system with all fresh coolant. I even added in 10oz of Hypercool Super Coolant. I already had a 180* thermostat with a new gasket installed. I also replaced the plastic inline fuel filter that was on it, with a stock filter that has a return line on it, and reconnected the return line with a new 5/16" hose. The Jeep looks a lot better without the odd body gaps, and the red bushings look great with the red body and black chassis. Hot starts are easier, throttle response is more consistent, and it warms up to 180* and stays there. An odd side effect of lowering the body to stock height is now the shift levers are higher up in the cab. And also sitting closer to the engine means I can now hear every little noise it makes better.

But now I have a new problem. After reconfiguring the filter and return line back to stock, the engine initially started right up and idled very smoothly. But after warming up and driving around for a while, it developed a popping/skip at idle. The popping/skipping sound can be heard the most if you're listening to the muffler. I'm not really sure what to do about that. It drives great, but that new sound is concerning.
 
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