0331 cracked?

ok i did a search and a lot of reading. also has been posted on jeepforum.

2001 XJ 4.0L 95k on the clock. very well maintained, not hard on the skinny pedal. offroad maybe once a month.

here's my symptoms:

unexplained coolant loss (about an inch a day)
no visible dripping
doesn't run hot
no smell from the exhaust
very little milky residue on the oil cap (i only have a 12 mile commute, could be condensation)
no milky residue on the dipstick.
looked inside the oil fill hole with a flashlight, not residue in the from what i can see.

i already had it int he shop once.
did an oil change, no water or coolant present
checked for exhaust in the coolant, none found
pressure tested the cooling system, came back good

no leak down or compression test
no engine codes, no misfires

i'm dropping it off at a friend radiator shop to see if they can find a leak or source this problem.

what do you guys over here think? my brain is pretty much fried

BMXxXJ said:

ok i did a search and a lot of reading. also has been posted on jeepforum.

2001 XJ 4.0L 95k on the clock. very well maintained, not hard on the skinny pedal. offroad maybe once a month.

here's my symptoms:

unexplained coolant loss (about an inch a day)
no visible dripping
doesn't run hot
no smell from the exhaust
very little milky residue on the oil cap (i only have a 12 mile commute, could be condensation)
no milky residue on the dipstick.
looked inside the oil fill hole with a flashlight, not residue in the from what i can see.

i already had it int he shop once.
did an oil change, no water or coolant present
checked for exhaust in the coolant, none found
pressure tested the cooling system, came back good

no leak down or compression test
no engine codes, no misfires

i'm dropping it off at a friend radiator shop to see if they can find a leak or source this problem.

what do you guys over here think? my brain is pretty much fried

Click to expand...

Do a leakdown. If you lose more than 7-10% or so on any one cylinder, check for escaping air at all likely points (intake/exhaust/oil cap/bubbles in coolant/head gasket edge.) If you lose it between two cylinders, you have a burn-through on the head gasket (this is why you pull all plugs when you do a leakdown test.)

0331 cracks are typically between #3 & #4, and could be either a crack allowing coolant to enter the oil, or coolant to enter the chamber. If you can get a light in through the spark plug hole and look in there, you might notice that one cylinder is awfully clean - this would explain your coolant loss as well (it's going into a cylinder and steam-cleaning it.)

I know you said that you pressure-checked the cooling system (how high was the test pressure?) but cracks can be funny things. Also, a leakdown would reverse the pressure, and use a rather higher level (typically 100psig, vice 12-20psig for the typical cooling system test.)

i didnt personally do the pressure test, i dont know the pressure it was at. if coolant was goign into the chamber, would i smell it out the exhaust? and what about the lack of coolant in the oil when the oil was changed and inspected?


also, would i experience any drivability issues??? like weird noises or something or no?

Not necessarily any noises or drivability issues. I'm kind of chasing the same thing right now. The coolant has to be going somewhere, right? Into the air (external leak), into the oil, or out the exhaust. If it's going into the oil, the oil level should go up on the dipstick and look milky in the head. Mine's a little milky on the bottom of the oil filler cap, but I'm hoping the recent oil change will make it go away (lol).

BMXxXJ said:

i didnt personally do the pressure test, i dont know the pressure it was at. if coolant was goign into the chamber, would i smell it out the exhaust? and what about the lack of coolant in the oil when the oil was changed and inspected?


also, would i experience any drivability issues??? like weird noises or something or no?

Click to expand...

Theoretically, yes. Practically? Not so much. Depends on the rate of loss, concentration of antifreeze in your coolant, and the like.

water pump

just replaced my 00's a month ago, was leaking from the shaft seal
and there was no dripping or puddling to tip me off
found a cake of dirty, black coolant sludge under the shaft

i was losing coolant about as fast as you
replaced all the hoses while I was at it

i'll be fixing this myself no matter what it is. would i rather do the head or the water pump? i almost want to do the head. so i know it's gunna be a-ok

If you fix the head and the water pump is leaking, you'll end up doing that too. Easiest way to find water pump or other external leak is to pressurize the system. Buy, rent or borrow the pump/gage setup and pressurize your system to the pressure cap PSI or a little above. Check the weep hole on the water pump. Then start vehicle up. If needle bounces, it's a sign of head gasket or head issues. (Compression getting into cooling system on compression stroke)

well, i'm goignt o be away on business for the next week, so i'm dropping it off at my friends father radiator shop for the week. hopefully he will be able to diagnose exactly what's happening here.

if need be i can get my hands on a 02 head for 150

5-90 said:

Do a leakdown.

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As the man said, do a leakdown.

It gives you the most definitive testing BANG for your buck. If you're on the early side of a head gasket lead or a head crack, it's very likely you won't have any symptoms or check engine light.

i leave a note with the mechanic on what i want done. i friends with his son so hopefully he'll help me out. he'll have it for a week so hopefully when i get back i'll have a much better idea on what this is going to cost me. till then i have the RWD work van it's goign to snow tonight! yay....

just popped the oil cap again. it milky as XXXX. dipstick is clean tho. dropping it off in the morning

if you have an automatic tranny possibly the internal tranny cooling that is inside the rad is cracked or something and allowing the pressurized coolant to flow into it and mix w/ the tranny fluid. just a random guess. also you could try hooking up one of those radiator test kits that screw onto where the rad cap goes. you pump it up until you hit max pressure that the rad cap should vent at (16psi i think).

this is what i'm thinking....

hook up that pressure tester and pump it up to the max. then remove all spark plugs and disconnect the fuel pump fuse. leave the system pressurized at max over night. then have a buddy crank the car over the next morning while you look. if there is any coolant in the combustion chamber you should see it spray out.

also if its leaking into the combustion chamber if at all possible take a look at the piston tops. any combustion chamber that is notably cleaner and new looking than the others is suspect since burning coolant acts like a steam cleaning.

also after it sits over night you could slowly unthread the oil plug... water being denser/heavier than oil will be the first to drain out. so if there is any sort of quantity of coolant in the oil you should see that clear as day leak out first.

and of course the heavy 'mayo' built up on the oil fill cap is a sure sign. but as you said can be condensation. however a 12 mile trip should be plenty to get the oil warm enough to vaporize off any condensation. unless you idle the car for extended periods all the time. or have a faulty thermosat

BMXxXJ said:

If coolant was goign into the chamber, would i smell it out the exhaust?

Click to expand...

In some cases the cat can burn off any evidence of a coolant leak while its in the early stages. 5-90 is right on the money with how you should go about it.

yeah, milky oil under the cap is sure sign the head has cracked.
hopefully the main and cam bearings are intact.

well it's at the shop now, my gut is telling me it's the head. i found a JY head out of an 02 TJ for 150 completely assembled. aboput 30k on it. i hear its the revised casting.