'99 Cherokee Sport Overheating... wtf?
11-08-2014, 10:17 AM
#31
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Year: 1998
Model: Cherokee
Engine: 4.0L HO
Nice post. Sorry, but you are wrong.
The thermostat opens because of temperature, not pressure. Put one in a pan of water, and heat it up on the stove. It is not under flow pressure, yet it will start opening at the rated temperature.
Water pumps in engines do not create pressure. They only create flow.
The pressure in a closed or semi-closed system is caused by the expansion of the coolant due to heating. The radiator cap contains this pressure, up till its rated pressure. Then the spring, which is calibrated, and its associated rubber plug/disk, is forced away from the radiator neck. This opens a path for the coolant to flow out of the radiator neck and onto the ground, or an overflow bottle.
The thermostat opens because of temperature, not pressure. Put one in a pan of water, and heat it up on the stove. It is not under flow pressure, yet it will start opening at the rated temperature.
Water pumps in engines do not create pressure. They only create flow.
The pressure in a closed or semi-closed system is caused by the expansion of the coolant due to heating. The radiator cap contains this pressure, up till its rated pressure. Then the spring, which is calibrated, and its associated rubber plug/disk, is forced away from the radiator neck. This opens a path for the coolant to flow out of the radiator neck and onto the ground, or an overflow bottle.
Here are my recommendations since you have a 99+ model year:
1. Never use synthetic oils (that's all 4.0's)
2. Put a zinc additive in with each oil change
3. NEVER use a FRAM oil filter; they don't have anti-drain-back valves which causes dry engine starting. Metal on metal = no good
4. If you didn't already (I forget) replace the Radiator with a 2-core aluminum. 3 cores actually reduce efficiency of heat dissipation because there's too little space in the grill area for it. NAPA used to have all 3, now they only have 1 for left hand drives. RockAuto.com is the best parts site with unerring accuracy in ensuring you get exactly what is correct for your model year vehicle, and they're the cheapest to boot. They're a whole-sale OEM distributor, with some non-OEM options as well.
5. Don't upgrade the transmission cooler to a larger size. This will put more heat from the transmission onto the engine radiator and the 99+ heads are prone to cracking.
6. Replace the two pre-cat 02 sensors with NTK for optimum AFR ratios to further reduce excessive cylinder heat. As they get older they respond slower so the PCM is constantly adjusting the fuel-trims back and forth more than it needs to going from too-lean to too-rich and back again. This is unnecessary heat and your MPG will improve as well.
7. Consider using a 180 degree thermostat if you don't live in CA or NY. When I upgraded to one on my 4.7 stroker it hovered between 195-205~ on a hot day idling in the city. Yours will be a tad cooler being a 4.0.
On a sidenote, only have work done on your Xj at a shop you know is reputable and you can trust. I had sears change my oil once and when I stopped at a gas station 10 miles down the road there was a giant coolant explosion when the engine shut off. The flow stopped and the backup shot out of the radiator inlet because cap the was sitting elsewhere inside the engine bay it didn't belong. I have never been back there or let anyone else change my oil in it since.
1. Never use synthetic oils (that's all 4.0's)
2. Put a zinc additive in with each oil change
3. NEVER use a FRAM oil filter; they don't have anti-drain-back valves which causes dry engine starting. Metal on metal = no good
4. If you didn't already (I forget) replace the Radiator with a 2-core aluminum. 3 cores actually reduce efficiency of heat dissipation because there's too little space in the grill area for it. NAPA used to have all 3, now they only have 1 for left hand drives. RockAuto.com is the best parts site with unerring accuracy in ensuring you get exactly what is correct for your model year vehicle, and they're the cheapest to boot. They're a whole-sale OEM distributor, with some non-OEM options as well.
5. Don't upgrade the transmission cooler to a larger size. This will put more heat from the transmission onto the engine radiator and the 99+ heads are prone to cracking.
6. Replace the two pre-cat 02 sensors with NTK for optimum AFR ratios to further reduce excessive cylinder heat. As they get older they respond slower so the PCM is constantly adjusting the fuel-trims back and forth more than it needs to going from too-lean to too-rich and back again. This is unnecessary heat and your MPG will improve as well.
7. Consider using a 180 degree thermostat if you don't live in CA or NY. When I upgraded to one on my 4.7 stroker it hovered between 195-205~ on a hot day idling in the city. Yours will be a tad cooler being a 4.0.
On a sidenote, only have work done on your Xj at a shop you know is reputable and you can trust. I had sears change my oil once and when I stopped at a gas station 10 miles down the road there was a giant coolant explosion when the engine shut off. The flow stopped and the backup shot out of the radiator inlet because cap the was sitting elsewhere inside the engine bay it didn't belong. I have never been back there or let anyone else change my oil in it since.
Last edited by djb383; 11-08-2014 at 10:19 AM.
11-08-2014, 10:56 AM
#32
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Year: 2015, 2012
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Engine: 3.6L
But due to conduction, the temperature will not stay boiling hot in the engine, and ambient temperature in the radiator for long. The heat can get to the radiator via the lower hose, which is an open passage from the block to the radiator.
Just expanding on the topic.
11-08-2014, 10:58 AM
#33
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Engine: 3.6L
Yeah, I wondered why no synthetic oil, among other things. I use synthetic in just about everything I have, including lawnmower engines.
11-08-2014, 02:48 PM
#34
CF Veteran
I put that tidbit in there because that's what I do and I don't want leaking gaskets 20-40,000 miles down the road. Everyone and their mother with a stroker that has had a failed camshaft knows, or should know, that synthetic oils are missing all the zinc additive that is what kept flat tappet camshafts from wearing down over time. OHC have far less lob stress than the cam-in-block (jeep 4.0) style so they have a lot more wiggle room; hence the reason that design came about so they could run zinc'less oils to reduce emissions and increase catalytic converter efficiency. Synthetic is a known cause of distributor/cam gear wear. I've worn out 4 in the first 3-4 months of my new stroker requiring a whole new camshaft so I'm a solid believer, because I only ran synthetic because that's what EVERYONE tells you to do with a new engine. WRONG. This is a recommendation directly from HESCO. Never use synthetic on the 4.0 engine. You can call them and ask them yourself. The phone number is on their web-site. No, it won't cause the engine to wipe out a lobe and blow a head gasket 5 minutes after you run it; but once it's in there it's in there for life. Stop using synthetic oils down the road and see if you start getting small oil leaks. They've been building jeep stroker engines for over a decade now and I will take their recommendation over JoeSchmoeStorm500 every day of the week.
OP, apply logic and common sense where it fits. Everyone and their mother will post that something is wrong because either they think it or someone else told them it is so because either they thought it, or someone else who thought it told it to them. There's a perpetual cycle of misinformation spreading that occurs on this particular forum for reasons I have yet to figure out. I'm guilty of it in the past as I would also apply my mechanical know how from other vehicles only to find out in the end the Jeep 4.0 is it's own entity outside the realm of common mechanics in different areas. Commonly correct advice is not always correct advice. Be careful and do your own research. When you find things out for yourself you can rarely go wrong.
I don't repeat what I hear from others on CherokeeForum. I only give advice from personal experience, experiences from other experienced AMC/Chrysler technicians, or from referencing numerous articles I have read. If they just say it's wrong and have no way to back it up then take it with a huge grain of salt; then take that huge grain of salt and throw it in the trashcan after you find out the real answer. There is only 2 people on this forum I will take advice from directly anymore. Anything else gets ran through the Google BS sniffer.
If you do everything I've told you you will have a much longer head life on your engine.
Last edited by CoffeeCommando; 11-08-2014 at 02:53 PM.
11-08-2014, 02:59 PM
#35
CF Veteran
But due to conduction, the temperature will not stay boiling hot in the engine, and ambient temperature in the radiator for long. The heat can get to the radiator via the lower hose, which is an open passage from the block to the radiator.
Just expanding on the topic.
Just expanding on the topic.
11-08-2014, 05:36 PM
#36
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Year: 1998
Model: Cherokee
Engine: 4.0L HO
Once you use synthetic oil you're supposed to continue using it for the rest of the engine life because it permeates the seals and gaskets of the engine. Normal oils, which are thicker, will not get in there and you will accumulate old-gummy synthetic oil settling into various gaskets that will eventually start leaking require replacement. Good on you if you have a steel head and exhaust manifold gasket that you put in there yourself like me, but all of the other ones are some sort of paper material or rubber.
I put that tidbit in there because that's what I do and I don't want leaking gaskets 20-40,000 miles down the road. Everyone and their mother with a stroker that has had a failed camshaft knows, or should know, that synthetic oils are missing all the zinc additive that is what kept flat tappet camshafts from wearing down over time. OHC have far less lob stress than the cam-in-block (jeep 4.0) style so they have a lot more wiggle room; hence the reason that design came about so they could run zinc'less oils to reduce emissions and increase catalytic converter efficiency. Synthetic is a known cause of distributor/cam gear wear. I've worn out 4 in the first 3-4 months of my new stroker requiring a whole new camshaft so I'm a solid believer, because I only ran synthetic because that's what EVERYONE tells you to do with a new engine. WRONG. This is a recommendation directly from HESCO. Never use synthetic on the 4.0 engine. You can call them and ask them yourself. The phone number is on their web-site. No, it won't cause the engine to wipe out a lobe and blow a head gasket 5 minutes after you run it; but once it's in there it's in there for life. Stop using synthetic oils down the road and see if you start getting small oil leaks. They've been building jeep stroker engines for over a decade now and I will take their recommendation over JoeSchmoeStorm500 every day of the week.
OP, apply logic and common sense where it fits. Everyone and their mother will post that something is wrong because either they think it or someone else told them it is so because either they thought it, or someone else who thought it told it to them. There's a perpetual cycle of misinformation spreading that occurs on this particular forum for reasons I have yet to figure out. I'm guilty of it in the past as I would also apply my mechanical know how from other vehicles only to find out in the end the Jeep 4.0 is it's own entity outside the realm of common mechanics in different areas. Commonly correct advice is not always correct advice. Be careful and do your own research. When you find things out for yourself you can rarely go wrong.
I don't repeat what I hear from others on CherokeeForum. I only give advice from personal experience, experiences from other experienced AMC/Chrysler technicians, or from referencing numerous articles I have read. If they just say it's wrong and have no way to back it up then take it with a huge grain of salt; then take that huge grain of salt and throw it in the trashcan after you find out the real answer. There is only 2 people on this forum I will take advice from directly anymore. Anything else gets ran through the Google BS sniffer.
If you do everything I've told you you will have a much longer head life on your engine.
I put that tidbit in there because that's what I do and I don't want leaking gaskets 20-40,000 miles down the road. Everyone and their mother with a stroker that has had a failed camshaft knows, or should know, that synthetic oils are missing all the zinc additive that is what kept flat tappet camshafts from wearing down over time. OHC have far less lob stress than the cam-in-block (jeep 4.0) style so they have a lot more wiggle room; hence the reason that design came about so they could run zinc'less oils to reduce emissions and increase catalytic converter efficiency. Synthetic is a known cause of distributor/cam gear wear. I've worn out 4 in the first 3-4 months of my new stroker requiring a whole new camshaft so I'm a solid believer, because I only ran synthetic because that's what EVERYONE tells you to do with a new engine. WRONG. This is a recommendation directly from HESCO. Never use synthetic on the 4.0 engine. You can call them and ask them yourself. The phone number is on their web-site. No, it won't cause the engine to wipe out a lobe and blow a head gasket 5 minutes after you run it; but once it's in there it's in there for life. Stop using synthetic oils down the road and see if you start getting small oil leaks. They've been building jeep stroker engines for over a decade now and I will take their recommendation over JoeSchmoeStorm500 every day of the week.
OP, apply logic and common sense where it fits. Everyone and their mother will post that something is wrong because either they think it or someone else told them it is so because either they thought it, or someone else who thought it told it to them. There's a perpetual cycle of misinformation spreading that occurs on this particular forum for reasons I have yet to figure out. I'm guilty of it in the past as I would also apply my mechanical know how from other vehicles only to find out in the end the Jeep 4.0 is it's own entity outside the realm of common mechanics in different areas. Commonly correct advice is not always correct advice. Be careful and do your own research. When you find things out for yourself you can rarely go wrong.
I don't repeat what I hear from others on CherokeeForum. I only give advice from personal experience, experiences from other experienced AMC/Chrysler technicians, or from referencing numerous articles I have read. If they just say it's wrong and have no way to back it up then take it with a huge grain of salt; then take that huge grain of salt and throw it in the trashcan after you find out the real answer. There is only 2 people on this forum I will take advice from directly anymore. Anything else gets ran through the Google BS sniffer.
If you do everything I've told you you will have a much longer head life on your engine.
Although there is a clear path to the radiator via the hose, if there is a blockage in the path, IE the thermostat closed, it won't flow. It has no where to go because the coolant in front of it is roadblocked. Hence the reason it goes from ambient temperatures to CEL-overheating in within 15 miles.
Do a little research before posting/perpetuating false info in this form and on the Internet.
Last edited by djb383; 11-08-2014 at 05:52 PM.
11-10-2014, 06:47 PM
#39
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Year: 1999
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Engine: 4.0 I-6
Good evening gentlemen,
I found that I have a defective owner's manual which stated fuse slots 10 and 18 were open, which was 100% bu**$**t. #18 controls the power mirrors and #10... the NSS, backup lights, radiator cooling fan, o2 sensors... etc. What I've come to believe is that because I was missing those fuses, and since I added those fuses, the temperature is under control (I haven't broken 210 degrees since... no boilover... flow is all good. the electrical fan engages on its own (it's a bit sticky... could use some WD40) I still have a P1491 code, but I know the where and how is on that (pwm relay)... it's the only possible remaining option. Everything else related to my overheating issue has been solved. Thank you all for your insights, suggestions, thoughts and comments. I'm on to jumpin' all over Chrysler for releasing a screwed up Owner's Manual, and the possible consequences that "by the book" type of people (like me) may/will incur.
I found that I have a defective owner's manual which stated fuse slots 10 and 18 were open, which was 100% bu**$**t. #18 controls the power mirrors and #10... the NSS, backup lights, radiator cooling fan, o2 sensors... etc. What I've come to believe is that because I was missing those fuses, and since I added those fuses, the temperature is under control (I haven't broken 210 degrees since... no boilover... flow is all good. the electrical fan engages on its own (it's a bit sticky... could use some WD40) I still have a P1491 code, but I know the where and how is on that (pwm relay)... it's the only possible remaining option. Everything else related to my overheating issue has been solved. Thank you all for your insights, suggestions, thoughts and comments. I'm on to jumpin' all over Chrysler for releasing a screwed up Owner's Manual, and the possible consequences that "by the book" type of people (like me) may/will incur.
11-11-2014, 12:18 AM
#40
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Good.
But WD-40 is not a lubricant. WD stands for "water displacement". It was originally used to dry distributor caps. It is designed to evaporate.
Use PB Blaster instead.
But WD-40 is not a lubricant. WD stands for "water displacement". It was originally used to dry distributor caps. It is designed to evaporate.
Use PB Blaster instead.
11-11-2014, 01:53 AM
#41
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11-11-2014, 02:09 AM
#42
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Update:
I drove to school tonight with no issues, drove to the grocery store on the way home... came out, started the Jeep... and that CEL was gone!!! No more annoying orange words... no more overheat... no more leaky a$$ transmission... o2 sensor codes are gone along with range sensor code. My power mirrors work, and I have backup lights!!! All because of info I found right freakin' here on this forum.
Now it's onto stuff I want to do with my XJ as opposed to stuff I have to do... I've also decided to call my XJ "Nightmare" Thanks again to all.
I drove to school tonight with no issues, drove to the grocery store on the way home... came out, started the Jeep... and that CEL was gone!!! No more annoying orange words... no more overheat... no more leaky a$$ transmission... o2 sensor codes are gone along with range sensor code. My power mirrors work, and I have backup lights!!! All because of info I found right freakin' here on this forum.
Now it's onto stuff I want to do with my XJ as opposed to stuff I have to do... I've also decided to call my XJ "Nightmare" Thanks again to all.
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