Overheating final boss

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StimitheJoop

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Okay 1993 cherokee, 4.0, manual, electric fan converted, turbocharged, edelbrock head are the main modifications to keep in mind with the following.

My headgasket was leaking so I replaced it and my head covering my bases. I measured and triple checked my deck was flat prior to assembly. Got it all together and did the first run heat cycle and this thing got hot fast. I let ot get up to 220 indicated on the gauge and shut it down. Let it cool off and did my retorque. Got all the air out of the system but still couldnt keep it cool for longer than probably 4 minutes before shutting it down.
It has an entire new cooling system; new water pump flowcooler high volume of the correct rotation orientation for xjs, mishimoto radiator, new hoses, new thermostat, new sending units for temps.
So after that. Fed up with stimi the unquenchable, I removed my upper and lower rad hoses and flowed water through the radiator and it was good. Then attached the lower rad hose and let it flow through the entire block, up and out the water neck and the flow was severly reduced. I then took off the thermostat housing and watched the water flow through the head and it was fine.
Okay bad thermostat? Changed it again and ran it with the hose still feeding the cooling system and same exact issue. Disconnected the bypass hose that feeds the heater core and that allowed coolant to flow enough to not overheat!?
So im at a loss as to what to think with any certainty. I have vauge guess of a lack of flow to the rear of the block?? I have verified that rear sensor is correct with a temp gun and having a boiling occure.
Or somehow could it be still a water pump pressure issue? I have no frame of reference to know if what i have for pressure is good or not but it was equal to a lazy faucet at idle and some good distance at rpm!

Super weird, cant wait for some good input as im so lost
 
It's that radiator. Everyone has problems with them. I'd try a stock one just to see what the difference is. Last time we had someone with a hot build like yours they ended up having to have it re tuned before it would run proper temp. I don't recall what radiator they ended up with, it wasn't mishimoto though.
 
So I considered my tune being the issue as I did it myself. Its essentially a stock xj tune with timing bumped up by 2 degrees after 1500 across the board and then boost tune stuff for in boost conditions. Because of it overheating at even just idling, I checked with a timing light that it didnt have some absurd advance. Its ranging from 10-14 but mostly 11 degrees which is exactly what my tune wants.

I read tons of mixed reviews on that rad but went with it because of it not having crimped tanks and a 2 row. I will feed the waterpump cold hose water and see if it helps. Id be so thankful for a resolution so i hope it does.

I do believe I have coolant not circulating correctly through the entire block. For the thermostat to not open and the ecu temp sensor to read cold. Yet at the same time, having the rear of the block at scary temps is so weird and I feel a clue?

Maybe there is something blocking the main 2 coolant flow ports in the block that flow into the head. The ones that if you look at a headgasket are in the back of the block. The water pump will come off this weekend for a water jacket inspection with a borescope as a last resort.
 
Unclewolverine said:
It's that radiator. Everyone has problems with them.
Click to expand...

I've got a Mishimoto and while moving my engine temp (as reported by REM) is consistently at 182-189F at 70F ambient with e-fan off. If idling for 15+m it'll rise, but with the e-fan on it comes right back down.

All that just to say I wouldn't write off the radiator, although I don't know enough to say if they are commonly a problem. Just giving another data point.

Stimi - you mentioned disconnecting, but if you just pinch off the heater core (reduce flow, don't remove), do you see an improvement?

Edit: to be more clear, pinch (decrease to a significant degree, I'd say you're shooting for 25% flow or less) off the feed from the thermostat to the heater core and valve if you still have one
 
Last edited:
Ill try that tomorrow and get back to you!

I have had the radiator for a year now and it has worked well. I didnt see much cooling gains from it but i have been dealing with lesser variants of this overheating issue for over a year. Slowly putting on better parts to replace OEM style ones to stave off the overheating until now where i have the big radiator, high flow water pump, tripple e fans and its undrivable.
 
Okay so I did a few things.

Removed the rad from the picture by inserting a garden hose into the lower rad hose propped up so it would be vertical. I pinched the heater core hose to 25 % and no noticable change to the immediate overheating.

I then un attached the other side of the loop at the waterpump hardline that screws in and it actually stayed cool exhausting all the water onto the ground. Then i pinched that to 25% and that took a few minutes to get hot. Water temps were like 120 or so id estimate but the coolant gauge was more like 160 unrestricted and climbed to eventually 230 restricted.

Weirdly enough the hardline going to the waterpump did not suck air in and infact leaked some water out during this process and I had thought it should be drawing water in from that hose?

I also measured the amount of water being circulated by the pump by taking the heatercore hose circuit and letting it exhaust the water into a bucket instead of the ground and it was a little less that 5 gallons per minute. This number seems really low? Atleast compared to the very few sources of comparison i found online

The water temperature never reached a high enough temp to open the thermostat.

Just to see if it would work i connected the lower rad hose to the radiator, left the upper off and ran the water neck heater core feed hose to the radiator and let that run. It overheated but the engine actually came up to temp at a normal rate but eventually overheated.
 
My experience with my 90 over 33 years is that it takes multiple burps to get the air out. It's now a 4.1, with a 11-1 compression ported HO head, Hesco cam, Hesco water pump, bored T-body, Mopar headers, 2.5 inch exhaust pushing a heavy beast on 35's at 6k feet and above. The only time I needed the e-fan was crawling uphill at 11k feet in 4-lo. Hesco water pumps are amazing.
 

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I don't think water pump is the solution to your problem unless your current water pump is toast.

Pinching off the heater core circuit will divert more water through the radiator.

Air bubble or some kind of blockage sounds more likely to me if there really is a big difference in temp at the rear of the block. Or blown HG.
 
Hard to use the word assume, but assuming that the head gasket is correct and all water ports were lined up/matched on installation....
Go back to the basics and just make sure that all components are working properly. Thermostats are lousy these days, even the Robertshaw junk that everyone praises. Test it in a pot of water on the stove.
Dont forget the radiator cap, they are also all junk, because having that pressure raises your boiling point.
If you want a good radiator that holds more coolant, Ive got 2 XJ's that both have the CSF 2671's, never had a problem and work well. Stock mechanical fan, stock aux fan.
Even with a modified engine, which mine are, the standard cooling system is just fine if everything is in good shape and working correctly, and Im dealing with the Arizona sun.
 
So i took the water pump off and did a visual inspection with a borescope down into the cooling jackets, remarkably clean. No obstructions or anything. I decided to put it all back together and start at square 1. Let it run and still saw the gauge peg itself in the red really fast. Decided to reverify that sensor. I took an ohm meter and measured the ohms coming out of the pin at the sensor and got 380 ohms. According to the ohm charts I could find this indicated cold despite the gauge saying hot. Okay? So i take the gauge cluster out and see how many ohms i have at the cluster thinking it might have a short to ground somewhere and its perfectly the same, i even check for continuty to ground in the disconnected wire and there is none. I check power and ground to the gauge cluster and have 18 ohm on the ground. I repair that and retest to the same issue. My gauges have battery power and good ground and nothing wrong for the wire to the sensor. Do i have an internal coolant temp gauge fault all along?
 
380 Ohms is right around 170F
 
Just to give a conclusion. I plugged in an aftermarket coolant temp gauge into the factory harness and let it warm up while using a scan tool to monitor the other temp sensor. They were within 10 degrees of eachother all the way up till the coolant temp leveled off at 200. I then proceeded to remove the factory defective gauge and replace it with the aftermarket one. Just incase anyone ever wonders. A 2 inch aftermarket gauge fits well with some modification to the cluster back plate. Almost factory looking! I utilized all the factory wiring and sensor for the gauge. Just put screws to attach eyelets to the wire to the gauge cluster ribbon circuit board.
 
I chased overheating for probably a year, new 2 row all aluminum radiator, thermostat, fan clutch. Nothing stopped it getting hot on longer highway runs. The aluminum radiator sprung a leak, so I put back a stock one from NAPA. Last of all, I mixed 50/50 coolant and distilled water, and it's been fine ever since, so in my case, there was too high a concentration of glycol. Even that little plastic shroud is important on these, mine's missing a chunk and now it gets a little hot running around town with the A/C on.
 
StimitheJoop said:
Okay so I did a few things.

Removed the rad from the picture by inserting a garden hose into the lower rad hose propped up so it would be vertical. I pinched the heater core hose to 25 % and no noticable change to the immediate overheating.

I then un attached the other side of the loop at the waterpump hardline that screws in and it actually stayed cool exhausting all the water onto the ground. Then i pinched that to 25% and that took a few minutes to get hot. Water temps were like 120 or so id estimate but the coolant gauge was more like 160 unrestricted and climbed to eventually 230 restricted.

Weirdly enough the hardline going to the waterpump did not suck air in and infact leaked some water out during this process and I had thought it should be drawing water in from that hose?

I also measured the amount of water being circulated by the pump by taking the heatercore hose circuit and letting it exhaust the water into a bucket instead of the ground and it was a little less that 5 gallons per minute. This number seems really low? Atleast compared to the very few sources of comparison i found online

The water temperature never reached a high enough temp to open the thermostat.

Just to see if it would work i connected the lower rad hose to the radiator, left the upper off and ran the water neck heater core feed hose to the radiator and let that run. It overheated but the engine actually came up to temp at a normal rate but eventually overheated.


Man, this whole saga reminds me of the kind of troubleshooting work companies like FSG Inspections do but for houses. The way you're chasing down flow issues, using borescopes, and questioning sensor accuracy? That’s exactly what they do with airflow, water leaks, and thermal problems in buildings.
Click to expand...
That ~5 GPM output is low for a high-volume pump, which makes me suspect your pump isn’t moving coolant efficiently could be cavitation, an internal casting flaw, or even a mismatch in impeller design. The fact that the heater return line isn't under suction is another red flag.

Combine that with the thermostat never opening and the rear of the block getting hot, and it really points to either a blockage or poor circulation from back to front possibly due to the Edelbrock head and gasket combo.
Is the head gasket you're running specifically made for the Edelbrock head + XJ block combo?

Can you try running it without a thermostat briefly, just to see if coolant circulates properly front to back?
 
I am having issues with my Edelbrock head too. After reading I'll check my head gasket direction. By the way I used a high flow thermostat

Mr. Gasket 4364 High Performance Thermostat​

and it had bottomed out and bent the housing since Edelbrock heads have a smaller space and it stuck closed. I am now using a high flow Edelbrock thermostat and that fits
 
jeepxjdan said:
I am having issues with my Edelbrock head too. After reading I'll check my head gasket direction. By the way I used a high flow thermostat

Mr. Gasket 4364 High Performance Thermostat​

and it had bottomed out and bent the housing since Edelbrock heads have smaller space and it stuck closed. I am now using a high flow Edelbrock thermostat and that fits
Click to expand...
photos.app.goo.gl

New item by Danny c

photos.app.goo.gl photos.app.goo.gl
 
cedricw01 said:
That ~5 GPM output is low for a high-volume pump, which makes me suspect your pump isn’t moving coolant efficiently could be cavitation, an internal casting flaw, or even a mismatch in impeller design. The fact that the heater return line isn't under suction is another red flag.

Combine that with the thermostat never opening and the rear of the block getting hot, and it really points to either a blockage or poor circulation from back to front possibly due to the Edelbrock head and gasket combo.
Is the head gasket you're running specifically made for the Edelbrock head + XJ block combo?

Can you try running it without a thermostat briefly, just to see if coolant circulates properly front to back?
Click to expand...
He tracked it down to a faulty temperature sensor.
 
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