2000 Jeep XJ Over heating issue

2000 Jeep XJ Classic 249xxx miles rebuilt 4.0


Hey everyone, I’ve read many issues about overheating with these 4.0 l systems but I have never have seen a solution. I will give a brief run down of what I am seeing, then ask for your input. This motor was rebuilt by a local shop with all stock off the shelf parts. It’s not a Hot rod motor. It has a cold air intake, and an aftermarket aluminum radiator with triple fans on it. It is a FFD EXTREME TRIPLE THREAT COOLING FAN KIT. ( sorry for the caps there it was cut and pasted straight from Ebay where I bought it)


The new build has about 3k miles on it and performs well except for this cooling issue. I filled and burped the cooling system as many suggested here on this site. Front left corner of the jeep high in the air. I let it run and brought the operating temp up 210 where it always runs. I fed it as much coolant as it would take and let it idle there for a while. Once capped I went on with normal use.
Now for the issue I am seeing. While out on the back roads of Wenatchee WA, I started a good service road climb. The temp stayed 210-215 the entire climb, then shot up to 260. I stopped the climb and sat and watched the gauge to see if it would stay pegged at 260 or not. It just sat there, so I put the jeep in Park and the temp dropped back to 215 again. I was stumped at this point. I popped the hood and yes it felt hot, but nothing more that it always feels.

I continued my climb and it shot back up again, this time I kept going to see if the bouncy road might have moved a connector and it would fix itself, but it did not. This time it started to run really poorly, like it would barley run. I thought maybe I hurt it with a true overheat issue. I let the jeep continue to barley idle and revved it a few time to see if it would clear out. About 2 mins later the temp gauge returned to 215 and the engine cleared right out. I knew I had an issue at this point and headed back off the mountain. The jeep did the same issue two more times headed down the hill each time the rough running would be worse and worse. Once back off the trail the jeep seems to be ok and I drove it home and parked it.

Fast forward three weeks, I go out and start it up and pop the rad cap, the water level is at the top, so I cap it back up and let the jeep warm up. Within a few mins it comes up to 210 temp and everything looks great. Then within a couple mins it pegs the 260 number again and starts to run rough.

Any ideas?

thanks !

Is the water pump new also ? Are the radiator hoses collapsing when this happens ?

What temp is the fan controller set for ?

With a stock type radiator, and the stock fans there should be no overheating. I am not familiar with the FFD system, but I would never spend that kind of money on an unnecessary modification.

The XJ cooling system is under 16 lbs of pressure, which raises the boiling point of the coolant. Anything that allows the pressure to drop such as a bad radiator cap, a loose hose, a leaky radiator, a head gasket leak, or anything else, will cause the coolant to instantly flash to steam, and the steam will spike the temp sensor, and it will temporarily block the normal flow of coolant.

The rough starting/running is probably a symptom of the overheating and is likely plain old vapor lock from the excessive heat.

What is the condition of the cylinder head?

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I took the liberty of looking up your fan setup. They sure do mention how much HP and weight loss you get by running it, but there's no mention of how many CFMs the fans pull. I'm going to go out on a limb here and say that these fans aren't pulling enough to properly cool. I'm not going to say that's the only thing though... something else is going on here for sure. Especially if you're flashing steam. I had an aluminum radiator for a long time and it cooled exceptionally well, even with a bad fan clutch my jeep never overheated. When it overheats does the cap relieve the pressure to the catch reservoir?

When it over heats, is the lower radiator hose cold or hot? If cold I would suspect an intermittent tstat problem.

That's the problem, its not really over heating, it is just saying it is. I can grab top and lower hoses and they are not super hot. I guess the next thing I will do is use a IR gun on the radiator,hoses and blocks.

Thanks for the input so far

Cris

Devilfrog said:

What is the condition of the cylinder head?

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Click to expand...

The Head was rebuilt when the motor was rebuilt.

Tim_MN said:

Is the water pump new also ? Are the radiator hoses collapsing when this happens ?

What temp is the fan controller set for ?

With a stock type radiator, and the stock fans there should be no overheating. I am not familiar with the FFD system, but I would never spend that kind of money on an unnecessary modification.

The XJ cooling system is under 16 lbs of pressure, which raises the boiling point of the coolant. Anything that allows the pressure to drop such as a bad radiator cap, a loose hose, a leaky radiator, a head gasket leak, or anything else, will cause the coolant to instantly flash to steam, and the steam will spike the temp sensor, and it will temporarily block the normal flow of coolant.

The rough starting/running is probably a symptom of the overheating and is likely plain old vapor lock from the excessive heat.

Click to expand...

Tim

The hoses are not collapsing, The fans controller is preset,and I did not change it. It kicks in at 210 and off again around 195. thanks for your editorially comment on if you would buy this or not. It was not needed , nor helpful, but its part of the Forms so I'll take it.

I refuse to believe it can flash to steam , then be fine moments later. This seems more like a sensor/ computer issue. as for the cutting out, I'm looking for information if there is a limp mode that kicks in.
again I will use a IR gun tonight and post temps I'm seeing in real time.

thanks again Tim


Cris

If you're saying it isn't overheating but it is vapor locking (the chugging part after it says 160) then it's possible you're connection to the sender on the water pump is loose. Pull it, clean it, put some dielectric grease in it. Chase your ground for that sensor too and make sure it's clean.
Based on other symptoms, you are overheating but maybe it gets angry loosing your connection to the sensor too.

If the indicated temperatures are steady at about the normal 195*-215* and then it instantly jumps to 260*, you are very likely forming steam. I too wonder about the CFM's of the FFD fans. Simple fact, a well maintained stock XJ cooling system can handling just about any climate and trail conditions. Old Farts with lots and lots of practical experience can give unasked for opinions; there is a rule in my AARP handbook that says that is so.

Tim_MN said:

If the indicated temperatures are steady at about the normal 195*-215* and then it instantly jumps to 260*, you are very likely forming steam. I too wonder about the CFM's of the FFD fans. Simple fact, a well maintained stock XJ cooling system can handling just about any climate and trail conditions. Old Farts with lots and lots of practical experience can give unasked for opinions; there is a rule in my AARP handbook that says that is so.

Click to expand...

Tim


I'd venture to say we are about the same old age The reason I am questioning the steam flash is it would not flash, then be instantly OK. I grabbed my Flir thermal gun and will try ot answer the story tonight. I wonder if cutting in a Tee into the highest host might be helpful to fill and burb the system of any air pockets.

Thanks again for the reply

Cris

I run just that on my 2000 XJ ... Used a sensor adapter in the upper hose with a petcock in it. Fill, burp, fill, burp, done.

With a 180 thermostat and a fully functional stock cooling system (with a Hayden 2737 fan clutch). I run at 210* in traffic and on the trail in the summer (late July to mid Sept) and dead on 180 for the rest of the year.
When it was stock, one tick over from straight up was normal for slow speed driving. The lack of a shroud will increase Temps as the fans have less ability to pull air through the rad. They pull around it more.
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I thought post 91s with the open cooling system were "self-burping." I've had 4 XJs since 1989 and the only one I had to "burp" was the closed system 89. Only cooling system issue I've had (other than a blown head gasket and two water pumps) was a spiffy 3 row copper/brass all metal radiator I put in a year ago. Problem went away when I went back to OEM aluminum 2 row with plastic tanks.

Tim


So I took your advice in a round about way. I went at this as if it were flashing to steam. I stopped and purchased a funnel that fits perfectly in the radiators mouth and was 6 inches tall. this gave me more than 8 inches of level over any other part of the cooling system. I started the jeep and started to pour in coolant. it burped a lot and allowed me to add another gallon on coolant to the system.

Once capped I climbed back into the cab and the temp gauge is resting at 195. It has never sat that low warmed up. Its always been a 210 jeep. that other thing to note is the heater is putting out a ton of heat now.

I drove it for 20 mins in a 89 outside temp. I'm happy to say it never got above 200. thank you Tim for taking this conversation back to basics.

Cris