Great deals on TJ parts on Amazon!

Looking for parts for your Jeep Wrangler TJ? Checkout the selection of TJ parts Amazon has to offer, many with 2-day Prime shipping!

Click the image below to browse TJ parts on Amazon.

Jeep Wrangler TJ Parts on Amazon

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.

2002 Jeep 4.0 coolant disappearance and oil smells faintly like gas

Lifted straight six

TJ Enthusiast
Joined
Oct 26, 2020
Messages
106
Location
arizona
So I have had these issues for awhile now, but have gotten tired of continuing to top off my coolant resivoir every few weeks.

The issue is, my coolant is disappearing, been like that for awhile(several several oil changes). I do not see any milky residue under my oil cap, or on my dipstick, or even when I change the oil. I use prediluted 50/50 antifreeze.. I recently overhauled my coolant system
New radiator
Cap
Water pump
thermostat
hoses
I do have those stupid worm clamps that you tighten with a flathead screwdriver though.
I also have a crack at the top of my coolant resivoir that i taped up because I have just been too lazy to get a new one.

I am losing coolant out of my resivoir(about an inch down every couple weeks) never overheated, and my coolant does not smell like exhaust gasses, nor is there white smoke coming out of my exhaust. To me, that rules out a cracked head gasket.
My oil on the other hand, smells like fuel, which I believe may be an injector issue. I don’t know if the 2 are related, I don’t have any codes popping up, and even in 110 degree heat my jeep stays between 207-214 degrees.

I am at a complete loss, as I do not see any coolant leaking anywhere, and I obviously don’t see it in my oil, or smell it in my exhaust or even under the hood. Does anybody have any idea where this coolant may be going? Is there a gremlin thats thirsty for antifreeze under the hood?(LOL). Any help would be appreciated
 
OP
Lifted straight six

Lifted straight six

TJ Enthusiast
Joined
Oct 26, 2020
Messages
106
Location
arizona
So I have had these issues for awhile now, but have gotten tired of continuing to top off my coolant resivoir every few weeks.

The issue is, my coolant is disappearing, been like that for awhile(several several oil changes). I do not see any milky residue under my oil cap, or on my dipstick, or even when I change the oil. I use prediluted 50/50 antifreeze.. I recently overhauled my coolant system
New radiator
Cap
Water pump
thermostat
hoses
I do have those stupid worm clamps that you tighten with a flathead screwdriver though.
I also have a crack at the top of my coolant resivoir that i taped up because I have just been too lazy to get a new one.

I am losing coolant out of my resivoir(about an inch down every couple weeks) never overheated, and my coolant does not smell like exhaust gasses, nor is there white smoke coming out of my exhaust. To me, that rules out a cracked head gasket.
My oil on the other hand, smells like fuel, which I believe may be an injector issue. I don’t know if the 2 are related, I don’t have any codes popping up, and even in 110 degree heat my jeep stays between 207-214 degrees.

I am at a complete loss, as I do not see any coolant leaking anywhere, and I obviously don’t see it in my oil, or smell it in my exhaust or even under the hood. Does anybody have any idea where this coolant may be going? Is there a gremlin thats thirsty for antifreeze under the hood?(LOL). Any help would be appreciated

To also add, I had a misfire code one time, after i sprayed the engine down, I unhooked the battery to reset the PCM as I let it sit in the sun and completely let everything dry, no codes of a misfire since, just thinking it was something that got wet that shouldn’t have.
 

Trod286

Member
Joined
Mar 3, 2021
Messages
99
Location
CALIFORNIA
So I have had these issues for awhile now, but have gotten tired of continuing to top off my coolant resivoir every few weeks.

The issue is, my coolant is disappearing, been like that for awhile(several several oil changes). I do not see any milky residue under my oil cap, or on my dipstick, or even when I change the oil. I use prediluted 50/50 antifreeze.. I recently overhauled my coolant system
New radiator
Cap
Water pump
thermostat
hoses
I do have those stupid worm clamps that you tighten with a flathead screwdriver though.
I also have a crack at the top of my coolant resivoir that i taped up because I have just been too lazy to get a new one.

I am losing coolant out of my resivoir(about an inch down every couple weeks) never overheated, and my coolant does not smell like exhaust gasses, nor is there white smoke coming out of my exhaust. To me, that rules out a cracked head gasket.
My oil on the other hand, smells like fuel, which I believe may be an injector issue. I don’t know if the 2 are related, I don’t have any codes popping up, and even in 110 degree heat my jeep stays between 207-214 degrees.

I am at a complete loss, as I do not see any coolant leaking anywhere, and I obviously don’t see it in my oil, or smell it in my exhaust or even under the hood. Does anybody have any idea where this coolant may be going? Is there a gremlin thats thirsty for antifreeze under the hood?(LOL). Any help would be appreciated

I'm waiting to see what to do as well. I just had my system flushed and replaced thermostat and lower hose. My resivoir doesn't have a crack but is almost empty every 2 weeks. No leaks or cracked head or anything. I do regular changes but my coolant is always low in the resivoir.
 
  • Like
Reactions: Lifted straight six

Jerry Bransford

TJ Guru Moderator
Staff Member
Supporting Member
Joined
Nov 9, 2015
Messages
24,963
Location
Fleming Island Florida
My bet is either a blown head gasket or a cracked head. 2002 was the last year for the infamous 0331 head problem that was more prone in the 2000-2002 model years to crack than other model years. It was replaced by the TUPY version of the 0331 head which can be identified by looking down through the oil fill cap opening in the valve cover. If it says TUPY it's the improved head.

Here's a thread on the 0331 head issue... https://wranglertjforum.com/threads/how-to-identify-0331-or-tupy-head.8112/

Hopefully yours is nothing more than a blown head gasket, though there's no assurance that either of the above are guaranteed to be the cause of your lost coolant but my money's on one of them being the cause.

TUPY 331.JPG
 
  • Like
Reactions: Lifted straight six

mattyice2

TJ Enthusiast
Joined
Jan 21, 2018
Messages
209
Location
York County, PA, United States
What Jerry said. If it's the head gasket or cylinder head, it's just going to keep wiping out all your cooling systems until you fix the real issue. I recently had to get my head gasket replaced. The 4.0 can go 300,000 miles, but sometimes the head gasket will not. Def can be the cylinder head crack too.
 
  • Like
Reactions: Lifted straight six

Trevlaw

Sketchy Machinist
Supporting Member
Joined
Jan 8, 2021
Messages
623
Location
Corvallis, OR
You need to do a leak down test. I had the same issues you were having, slow unexplained loss of coolant. During the leak down test I was able to hear air coming up out of the radiator with the cap removed.

I was also getting a misfire code every so often, always on the same cylinder. You might be able to pull your plugs and see if there's a visual difference between one or two of them and the rest that could indicate it's burning coolant.
 
  • Like
Reactions: Lifted straight six

KingCarGuyZ

TJ Addict
Supporting Member
Joined
Feb 26, 2020
Messages
1,236
Location
Dallas, TX
Im not 100% convinced the head/gasket is toast, though it does seem likely. I would swap out the worm clamps, even though I don't think they would account for that much of a leak, I would also see if you can find any coolant residue indicating a leak, especially around the coolant tank itself. If not you must be burning it which has to be head/gasket. (or IG it could be a pinhole in the block, if god really dosent like you)

Gas in the fuel.... I would bet injectors (do you ever have cold start prime problems?) or Rings. If it's rings, I would just keep running it until it blows and start looking around for whatever you want to put in it when it does.
 
  • Like
Reactions: Lifted straight six
OP
Lifted straight six

Lifted straight six

TJ Enthusiast
Joined
Oct 26, 2020
Messages
106
Location
arizona
My bet is either a blown head gasket or a cracked head. 2002 was the last year for the infamous 0331 head problem that was more prone in the 2000-2002 model years to crack than other model years. It was replaced by the TUPY version of the 0331 head which can be identified by looking down through the oil fill cap opening in the valve cover. If it says TUPY it's the improved head.

Here's a thread on the 0331 head issue... https://wranglertjforum.com/threads/how-to-identify-0331-or-tupy-head.8112/

Hopefully yours is nothing more than a blown head gasket, though there's no assurance that either of the above are guaranteed to be the cause of your lost coolant but my money's on one of them being the cause.

View attachment 343782

I have a tupy head. I think the smell I am getting is just the different oil I used, as my buddy who used the same oil has the same smell in his 98.
 
OP
Lifted straight six

Lifted straight six

TJ Enthusiast
Joined
Oct 26, 2020
Messages
106
Location
arizona
Im not 100% convinced the head/gasket is toast, though it does seem likely. I would swap out the worm clamps, even though I don't think they would account for that much of a leak, I would also see if you can find any coolant residue indicating a leak, especially around the coolant tank itself. If not you must be burning it which has to be head/gasket. (or IG it could be a pinhole in the block, if god really dosent like you)

Gas in the fuel.... I would bet injectors (do you ever have cold start prime problems?) or Rings. If it's rings, I would just keep running it until it blows and start looking around for whatever you want to put in it when it does.

I do have long cranking issues, that seems like an injector issue, as I have not replaced those. That is on the list of things to do when it’s not 120 outside 😡
 
OP
Lifted straight six

Lifted straight six

TJ Enthusiast
Joined
Oct 26, 2020
Messages
106
Location
arizona
You need to do a leak down test. I had the same issues you were having, slow unexplained loss of coolant. During the leak down test I was able to hear air coming up out of the radiator with the cap removed.

I was also getting a misfire code every so often, always on the same cylinder. You might be able to pull your plugs and see if there's a visual difference between one or two of them and the rest that could indicate it's burning coolant.

Waiting to do a leak down test soon as well, so when that gets done I will let you guys know the results. She runs strong still, and haven’t had any misfire codes since I got something wet that shouldn’t have gotten wet.
 
OP
Lifted straight six

Lifted straight six

TJ Enthusiast
Joined
Oct 26, 2020
Messages
106
Location
arizona
My bet is either a blown head gasket or a cracked head. 2002 was the last year for the infamous 0331 head problem that was more prone in the 2000-2002 model years to crack than other model years. It was replaced by the TUPY version of the 0331 head which can be identified by looking down through the oil fill cap opening in the valve cover. If it says TUPY it's the improved head.

Here's a thread on the 0331 head issue... https://wranglertjforum.com/threads/how-to-identify-0331-or-tupy-head.8112/

Hopefully yours is nothing more than a blown head gasket, though there's no assurance that either of the above are guaranteed to be the cause of your lost coolant but my money's on one of them being the cause.

View attachment 343782

I'm waiting to see what to do as well. I just had my system flushed and replaced thermostat and lower hose. My resivoir doesn't have a crack but is almost empty every 2 weeks. No leaks or cracked head or anything. I do regular changes but my coolant is always low in the resivoir.

Mine is only about an inch down every 2 weeks, but I think the source of my issue is within my cracked resivoir, and I have a small amount of coolant that I recently noticed on the bottom of my thermostat housing, it definitely isn’t enough coolant to explain the loss of what I am losing, but it is definitely a factor. I have done everything visually that I possibly can, going to do a leak down test eventually, but it’s so dang hot out it’s hard to do anything on my days off without feeling like I might overheat myself!
 
  • Like
Reactions: Trod286
OP
Lifted straight six

Lifted straight six

TJ Enthusiast
Joined
Oct 26, 2020
Messages
106
Location
arizona
What Jerry said. If it's the head gasket or cylinder head, it's just going to keep wiping out all your cooling systems until you fix the real issue. I recently had to get my head gasket replaced. The 4.0 can go 300,000 miles, but sometimes the head gasket will not. Def can be the cylinder head crack too.

I know for a fact it’s not a cylinder head crack, a head gasket may be possible.. but still feel it’s unlikely as I have 0 other symptoms other than my coolant just going down slowly overtime. I refill, she runs, never overheats, never skips a beat. It’s probably a small leak that is exaggerated when the engine is hot and running.
 

Gilaguy23

TJ Enthusiast
Joined
Sep 21, 2021
Messages
392
Location
A'holeville
Not to argue but what make you know for a fact you dont have a cracked head? I say this after owning a couple V10 engines who use coolant like you are seeing. Pressure tests can come back clean,no leaks spotted,no green crusties at connections ect but the problem exists. I hauled a camper and stock trailer all over,never overheated,never a glitch,just keept adding several ounces of coolant every few weeks or so. Maybe Im getting lazy but it would suck to tear things down and do a HG only to find there was a cracked head. Just sayin.
 

CODE5

Member
Supporting Member
Joined
Apr 28, 2022
Messages
43
Location
Alabama
I do have long cranking issues, that seems like an injector issue, as I have not replaced those. That is on the list of things to do when it’s not 120 outside 😡

Are you able to remedy the long crank by cycling the key a few times and then cranking? That is what I've been doing until it cools off this fall and I can drop my gas tank to fix the problem.

BTW, my Jeep is having the same trouble. So keep us posted. Hoping to get my engine pressure tested soon.