I had the same exact issue, annoying as all hell. I changed out my radiator and used a solvent to flush out the block in case some one before me might have used stop leak in the cooling system. I dropped about 10 degrees on the temp gauge and the Jeep always runs cool with or with out the Ac on. Drove it from Lancaster to Santa Barbra and back with the Ac cranked on a hot day and not a single problem.
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Strange Overheating Issue
- Thread starter Slimer
- Start date
Green XJ Jeep
NAXJA Forum User
- Location
- Spanaway Wa
Might want to do this.
Without a secondariy test either fron an after market guage or ir temp gun going on your explanation i still think its electrical. Either wiring or guage related
A 40 degree drop in temp in 30 seconds is a little extreme
I think the temp is actually changing that much. I am thinking that it actually heats up with a lean fuel condition and as soon as I get out of the throttle it starts to cool off and then the thermostat opens and cools everything off even more. At this point I really don't know, I am just very frustrated. I haven't had time to put the Napier vents on yet and don't really think they will change much. I think I will throw in the towel though and take it to Hopper's Automotive in Tempe and see if they can diagnose the problem. They are Jeep people and have been in business forever. If they can't figure it out I will probably just starting changing stuff out again.
dan1977p
NAXJA Forum User
- Location
- Virginia Beach, VA
That number goes up to about 250 at 15psi and our radiator caps are rated to 16psi. Wouldn't hurt to add coolant to the mix just to raise it a bit but also to help keep corrosion down.
Heater core may be clogged reducing flow, bad water pump or a leak that would drop the pressure down and allow the water to boil early.
It has always had coolant... it is not using any coolant, as in it doesn't need any added or it never gets low...
Boss Cherokee
NAXJA Forum User
- Location
- Riverside Calif.
I've had plenty cooling issues over the years. It started with my 1985 XJ Ford powered V8 swap but I lassoed it in and got it dialed. Then My 95 got crazy. It has 15.50x36 MT's. I did everything but give up. I put vents in and a 6Cyl Grand Cherokee fan clutch and it changed everything. I still heat up a little climbing the mountain roads to Big Bear 8500 elev. but nothing too bad. I am going to replace T-stat with a Mopar one and maybe I will be able to drive later in the day up the mountain. My 99, that is another story. Sold it too many XJ's.
I suggest as one poster said check the sensor and the gauge. Quick erratic gauge movement such as you are experiencing is very odd. Get an IR gun and check both sides of the thermostat then check radiator outlets to start. I have a 4wd Ford van and I made a mistake hooking up the extra battery while I had the ignition on, I know, STUPID, and now my Diesel gauge will sometimes show full when it's not. I shut off the 7.3 motor and start it again and it's fine, go figure????
I suggest as one poster said check the sensor and the gauge. Quick erratic gauge movement such as you are experiencing is very odd. Get an IR gun and check both sides of the thermostat then check radiator outlets to start. I have a 4wd Ford van and I made a mistake hooking up the extra battery while I had the ignition on, I know, STUPID, and now my Diesel gauge will sometimes show full when it's not. I shut off the 7.3 motor and start it again and it's fine, go figure????
Last edited:
burntkat
NAXJA Member #1145
- Location
- Charleston, SC
Perhaps, but not outside the realm of the possible. I've seen it happen.
burntkat
NAXJA Member #1145
- Location
- Charleston, SC
Quit throwing parts at it, and *troubleshoot* it. You have a lot of good advice in this thread, make sure you've checked everything.
burntkat
NAXJA Member #1145
- Location
- Charleston, SC
Adding coolant (glycol) WILL NOT help the motor cool. The best coolant is actually water- but as you said the glycol helps avoid corrosion and also
Really doubt that a plugged or partially constricted heater core is the issue here- it's not in the main flow galley, it's basically parallel to the engine cooling, not in series with it.
Bad water pump could absolutely be an issue. Way to test that is to feel for surging in the hose as you vary the engine RPM at operating speed. Wear gloves (duh).
As for leaks, there is a radiator test kit that will indicate pressure- it's a rental tool at most LAPS. Install, test, and observe.
Concur with the OP, don't think the vents are going to do crap for you except look cool. They will help with underhood temps as well, but they won't be the magic bullet.
dan1977p
NAXJA Forum User
- Location
- Virginia Beach, VA
You are correct that it doesn't help cool, but it does raise the boiling point of water and helps prevent vapor from forming that will significantly decrease the performance of the cooling system in general. In this case, though, it's moot since the OP informed us that he's running 50/50.
The longer this thread runs, though, the more information we are getting so it's not exactly easy to suggest a test or fix without all the info.
Well, I have done most everything that I can do home in the driveway in 110-120 temps here in Arizona. I am going to do a compression and leak down test tonight. Other than that there is not much else I can do. Sure, I can replace the water pump even though it looks new and the replace the radiator even though it also looks almost new, but I am not going to.
I think I need to have the injectors and the fuel pump tested for correct pressures and flow, but I don't think I can do that myself. Gas mileage is way, way down though, not exactly sure what it is, but I would say less than half of what it was on the way home from Colorado.
I have been hitting the gas tank skid plate bolts with PB Blaster twice a day. I wonder if I will be able to put it back on though, the heavy duty rear bumper appears to be blocking access to the frame rails and I am not sure if I have nutserts or not. It has a Comanche gas tank skid on it.
I will post what the compression and leak down test say, maybe the engine is prematurely shot.
burntkat
NAXJA Member #1145
- Location
- Charleston, SC
I think this is the point I'd be applying a treatment of RMI25 and let it chemically scrub out the entire cooling system. You might be surprised what you get floating in the top of your radiator...
It's VERY good stuff.
It's VERY good stuff.
burntkat
NAXJA Member #1145
- Location
- Charleston, SC
I also think that fuel pressure is going to be a culprit. If you have a fuel filter, replace it. It needs to be done if you haven't already, and it may be blocked- as one poster said earlier, that could well explain your issues- running lean at WOT/high-RPM would make you run hot quite quickly.
burntkat - I will try both of those things, the RMI25 (never heard of it) and replacing my fuel filter/fuel pump (both are in the tank on a '97). I am also thinking of trying some "injector/fuel system cleaner" of some sort but don't know what to use.
Also, while I am trying different stuff, I think I will go ahead and replace my fan clutch. Are there any downsides to the ZJ fan clutch swap if I have the room? My XJ is already noisy with mud tires, lockers and a custom hack job on the top so I am not worried about that. From understanding I should get Napa Part #272310. Does it do anything?
Also, while I am trying different stuff, I think I will go ahead and replace my fan clutch. Are there any downsides to the ZJ fan clutch swap if I have the room? My XJ is already noisy with mud tires, lockers and a custom hack job on the top so I am not worried about that. From understanding I should get Napa Part #272310. Does it do anything?
burntkat
NAXJA Member #1145
- Location
- Charleston, SC
I have no input on the ZJ fan swap, except to say that at the slightest sign of trouble on my son's 97 I will be doing it. (I've had it all of a month now, so I am still learning the later years' peculiarities like no fuel filter outside the tank, which is STUPID!)
I have a 90 I deleted the fan clutch on, and had no overheating issues. That said, I wouldn't do it again after my experience putting a V8 in the S10. I know that sounds unrelated, but I had to go through a lot of testing and trial fitting to get the electrics right in that app, and it has a HUGE radiator. A fan clutch would be a better way to go, but I don't have a shroud to make it effective and can't be bothered to fab one. The XJ radiator presents a much larger fitment issue- so the smart course of action with a 4.0 is to fit the best mechanical fan clutch and fan available... which appears to be the ZJ unit.
RMI25, a good source is Amazon, particularly if you have Prime. It's $16 for 8 ounces, which is enough to do an XJ cooling system.. howefver, for $30 you can get 32 ounces... better deal. I bought a quart, but then I have used it before and it worked for me.
Honestly, I doubt this will fix your problem on its own. I do know it WILL clean your cooling system quite well, though. This removes the concern of sediment or crap in the system causing concern. I'd make sure you have done a coolant flush in the last year, though (think you have).
I think your issue is going to go back to a fueling concern. My opinion, worth all of what you paid for it (nothing)- bet your fuel pump is going out. There is a test gauge available at Oreilly as a rental tool. You will want to test under load (ideally, in a condition that leads to your overheating). If you watch this pressure while the truck is overheating.. well there's your problem.
If it were my vehicle, and given that it's a $100 part, I'd probably go ahead and replace the FP assembly as a matter of PM just so I know it's done.
I have a 90 I deleted the fan clutch on, and had no overheating issues. That said, I wouldn't do it again after my experience putting a V8 in the S10. I know that sounds unrelated, but I had to go through a lot of testing and trial fitting to get the electrics right in that app, and it has a HUGE radiator. A fan clutch would be a better way to go, but I don't have a shroud to make it effective and can't be bothered to fab one. The XJ radiator presents a much larger fitment issue- so the smart course of action with a 4.0 is to fit the best mechanical fan clutch and fan available... which appears to be the ZJ unit.
RMI25, a good source is Amazon, particularly if you have Prime. It's $16 for 8 ounces, which is enough to do an XJ cooling system.. howefver, for $30 you can get 32 ounces... better deal. I bought a quart, but then I have used it before and it worked for me.
Honestly, I doubt this will fix your problem on its own. I do know it WILL clean your cooling system quite well, though. This removes the concern of sediment or crap in the system causing concern. I'd make sure you have done a coolant flush in the last year, though (think you have).
I think your issue is going to go back to a fueling concern. My opinion, worth all of what you paid for it (nothing)- bet your fuel pump is going out. There is a test gauge available at Oreilly as a rental tool. You will want to test under load (ideally, in a condition that leads to your overheating). If you watch this pressure while the truck is overheating.. well there's your problem.
If it were my vehicle, and given that it's a $100 part, I'd probably go ahead and replace the FP assembly as a matter of PM just so I know it's done.
burntkat
NAXJA Member #1145
- Location
- Charleston, SC
Another thought (bear with me as I think out loud here):
Can you get an IR thermometer ("temp gun") and check the radiator temp top to bottom? I can't remember if this is a bottom-up or top-down feed on the factory radiator, but you should see a steady gradiant one way or another.
If you don't, your radiator may well be full of "oysters"... calcium carbonate. This would block some of the tubes, resulting in inefficient cooling, especially under load. FYI, RMI25 will eat that out of the system. I'm beginning to sound like a commercial, I know- I have no holdings with them, just a happy customer.
If you REALLY wanted to go nuts and "nuke from orbit" any crap in your cooling system like I did (the coolant was brown when I got my 97)- install a Prestone flush kit (the Tee in the heater hose), drain the radiator (I removed the lower hose and let it drain into a bucket), then refill with water. Run the engine to heat-cycle it, then follow the instructions in the prestone kit- repeat as necessary till you see clean water coming out. Then here's where I get crazy:
Go to the grocery store (Lowes, AA Hardware, whatever). Buy a couple bottles of CLR. Pour ONE of them in your radiator, top off with pure water (We are going to assume you don't have freezing temperatures to worry about- I'm unfamiliar with your region of AZ at this time of year). If you have freezing concerns, by all means add a little glycol to protect against it. Don't worry about rusting- yes it will happen but we will address that chemically) Run that for a few hours of runtime, whether a long trip or commute to work over a few days. Just don't leave it in for more than a couple weeks (you've got an iron block here, and not running a super concentrated solution- so don't have to worry about eating the radiator (this is why we are only running one bottle). Drain and see what you get- bet it's not the clear water you got last time you drained it- this tells you there's blockage/buildup somewhere in the system and you are chemically eating it out of there. Repeat till you get clean water out. It may take a few bottles of CLR, but you know you have a clean system when you're done.
Some folks run a box of baking soda to neutralize the CLR, I've never bothered with it- because by the time I do the final straight-water, no CLR and then flush/fill with coolant mix iteration, the acid content is trivial... and will be neutralized when I add my 8 ounces of RMI25 anyway.
So, as I just said- after you get that final heat-cycle and few hours of running with CLR and get clean water out on the flush- refill with straight water. Run that through a heat cycle (doesn't need to be a few days, a run to the store and back is fine), drain the water and refill with a proper water/coolant mix. 50/50 is a good baseline, I think I run 25/75 glycol/water simply because we don't know what sub-zero temps are where I live
. Top off with 8 ounces of RMI25, and then follow the instructions on that bottle (basically, leave it in for ever and ever amen, and periodically open the radiator cap and coolant tank bottle, if you see anything but green, add water till the gunk floats out. RMI25 will float all the crap to the top of the tank.
Parenthetically, have you checked your coolant recovery tank? Is it clean? If not, take it out, take a hose and spray it out. Get some Dawn (or dishwashing soap of choice), shake it around and get all the muck out of it. You don't need that junk in your engine.
Naysayers can send their complaints to /dev/null. I have been there, do this, all the time, on iron blocks without issues. I'd be slightly concerned with AL blocks/heads- but in that case I'd just heat cycle it for an hour or so and get it out of the engine that same day. I literally did the above on my 97 just like yours and it's been just fine.
I'm not saying this will fix your problem- but I AM saying it WILL scrub the heck out of your cooling system, thus removing another point of uncertainty in fixing the issue.
Sorry, got long.
Can you get an IR thermometer ("temp gun") and check the radiator temp top to bottom? I can't remember if this is a bottom-up or top-down feed on the factory radiator, but you should see a steady gradiant one way or another.
If you don't, your radiator may well be full of "oysters"... calcium carbonate. This would block some of the tubes, resulting in inefficient cooling, especially under load. FYI, RMI25 will eat that out of the system. I'm beginning to sound like a commercial, I know- I have no holdings with them, just a happy customer.
If you REALLY wanted to go nuts and "nuke from orbit" any crap in your cooling system like I did (the coolant was brown when I got my 97)- install a Prestone flush kit (the Tee in the heater hose), drain the radiator (I removed the lower hose and let it drain into a bucket), then refill with water. Run the engine to heat-cycle it, then follow the instructions in the prestone kit- repeat as necessary till you see clean water coming out. Then here's where I get crazy:
Go to the grocery store (Lowes, AA Hardware, whatever). Buy a couple bottles of CLR. Pour ONE of them in your radiator, top off with pure water (We are going to assume you don't have freezing temperatures to worry about- I'm unfamiliar with your region of AZ at this time of year). If you have freezing concerns, by all means add a little glycol to protect against it. Don't worry about rusting- yes it will happen but we will address that chemically) Run that for a few hours of runtime, whether a long trip or commute to work over a few days. Just don't leave it in for more than a couple weeks (you've got an iron block here, and not running a super concentrated solution- so don't have to worry about eating the radiator (this is why we are only running one bottle). Drain and see what you get- bet it's not the clear water you got last time you drained it- this tells you there's blockage/buildup somewhere in the system and you are chemically eating it out of there. Repeat till you get clean water out. It may take a few bottles of CLR, but you know you have a clean system when you're done.
Some folks run a box of baking soda to neutralize the CLR, I've never bothered with it- because by the time I do the final straight-water, no CLR and then flush/fill with coolant mix iteration, the acid content is trivial... and will be neutralized when I add my 8 ounces of RMI25 anyway.
So, as I just said- after you get that final heat-cycle and few hours of running with CLR and get clean water out on the flush- refill with straight water. Run that through a heat cycle (doesn't need to be a few days, a run to the store and back is fine), drain the water and refill with a proper water/coolant mix. 50/50 is a good baseline, I think I run 25/75 glycol/water simply because we don't know what sub-zero temps are where I live
. Top off with 8 ounces of RMI25, and then follow the instructions on that bottle (basically, leave it in for ever and ever amen, and periodically open the radiator cap and coolant tank bottle, if you see anything but green, add water till the gunk floats out. RMI25 will float all the crap to the top of the tank. Parenthetically, have you checked your coolant recovery tank? Is it clean? If not, take it out, take a hose and spray it out. Get some Dawn (or dishwashing soap of choice), shake it around and get all the muck out of it. You don't need that junk in your engine.
Naysayers can send their complaints to /dev/null. I have been there, do this, all the time, on iron blocks without issues. I'd be slightly concerned with AL blocks/heads- but in that case I'd just heat cycle it for an hour or so and get it out of the engine that same day. I literally did the above on my 97 just like yours and it's been just fine.
I'm not saying this will fix your problem- but I AM saying it WILL scrub the heck out of your cooling system, thus removing another point of uncertainty in fixing the issue.
Sorry, got long.
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dan1977p
NAXJA Forum User
- Location
- Virginia Beach, VA
Aside from noise, your mpg may take a hit. Could be as much as 2-3 mpg. If it offsets your fan blades at all and your motor/trans mounts are weak, flex of the engine may smash it into your radiator or shroud. Something to keep an eye on.
FWIW, I run an almost stock cooling system (heater control valve delete is only change) on 33's, geared to 4.88 with an aux AT cooler and never get overheated on slow crawling days or fast interstate days going through mountain passes. Biggest change to my temps was adding the aux AT cooler but replacing old worn parts and cleaning the block and heater core out were also big helps.
I am running 33's with 4.56's, an aux AT cooler, but am in Arizona where the average summer temperature is about 110 degrees!
Thanks for the replies everyone!!