Ok, so I've been searching and searching and I haven't found my exact answer, but here goes. I've replaced my radiator, thermostat, fan clutch (installed a ZJ FC), flushed the system, and reverse flushed my heater core. My coolant warms up to a little over the 210 mark (probably about 212), then falls to 200-210 and stays there (I assume a slow-reacting thermostat). I don't have any/much heat though, so I'm thinking the HC is clogged up a bit again. My oil pressure is good (50psi on cold start, ~32-40psi at HOT idle, and about 48-52psi at HOT cruise) and the power is about what it should be. Now, with all the horror stories about the infamous 0331 head (I have a '00), I took off the oil cap and had a look: the cap looks a little "milky", however the oil on the dip stick is clean and the oil on the rockers looks clean as well. I took a look into the valvetrain and I don't see any visible cracks. I even revved it up a bit while looking in there and I didn't see anything bubble up or the likes of a crack. Am I safe to assume it's just a little condensation under the oil cap from it getting cold? I plan on reverse flushing the HC again to get my heat back, but otherwise the rig is running great. Only other "issue" is some super *****ty gas mileage, but this isn't a Honda either. LOL Any advice would be welcomed!

 

The #1 symptom of a cracked 0331 head is coolant consumption.

Keep an eye on your coolant reservoir like a HAWK.

Do you take a lot of short trips? That can lead to a bit of condensation on the oil filler cap.

How often do you change your oil?

Engine ever overheated? Overheating is a surefire recipe for cracking an 0331 head.

Some things to consider......

 

If you consider short trips under 10 miles, then yes...every morning/evening to/from work. And my coolant consumption is minimal (my rad. cap is leaking slightly, so I just top off the jug every 3-4 weeks...I check it every fill up. And by top off, I fill it from just above the low line to the max line). I have only had the rig long enough to change the oil when I first bought it, so I'm coming up on my next oil change now actually. Engine has overheated once, but it was about 215 when it got hot, wouldn't cool down on the highway, I shut it off and just watched to see if it'd go down. It then said "Check Gauges" and the needle pegged. I did NOT turn the car on until it cooled and at that point I replaced the radiator, thermostat, fan clutch, and flushed all the crap out. Apparently the PO used stop leak and that crap is a BEAST to get completely out. I was also told my block is rusting (I think they're full of s**t), so I'm continually fighting to keep the coolant clean. Other than my 12-13mpg, I'm happy w/ the rig and it idles and drives great otherwise.

 

Just went out to check it again now that it's cooled off, and the reservoir tank is down to the min line (when it was warm and running, it was about 1/2 way). I popped the oil cap again and it's still milky looking on the bottom of the cap; I also shined a flashlight into the valve cover, but I can't see any visible crack (it is quite dirty so who knows). Any other suggestions?

 

I'd strongly recommend a new rad....$5, 5 min (COLD ENGINE). Any cast iron block/head is going to rust......they rust less when the coolant is properly maintained.

 

Clean the head and check for the crack.

 

That's the key: proper coolant mix. When I got my XJ, apparently the PO used stop leak and, as we all know, that stuff gets EVERYWHERE. I replaced the radiator, thermostat, clutch fan, and flushed it multiple times, and it's STILL brown coolant. It'll stay green for a few days, then be rusty (not milky). However...she doesn't overheat and the temp needle is rock solid just below the 210 mark...I just have no heat...again. LOL I can fix that part easy though.

 

Since we're on the coolant subject, do you guys use 50/50 or just pure antifreeze? because i replaced my upper rad. hose and my coolant was very low, and i had like 6 gallons of pure antifreeze. So i just used pure, its probably like 90% or more pure coolant, very little water

Coolant is straight up lime green

 

Never use pure antifreeze. You lose efficiency. This is one of those situations where MORE IS NOT BETTER.

50-50 will give you great coverage down to -34f and on high end as well.

 

OP, are you trying to figure out if you have a cracked head or just a blown head gasket?

xj_maniac_newb - not a good idea to use pure antifreeze, it doesn't cool the engine very well.

 

I would use 50/50 antifreeze, that is what the Manufacturer recommends and it actually works better than straight, cheaper too.

On the over heat issue - the standard thermostat is rated a 195 degrees and the Rad. cap at 16-18 lbs.

195 is when the t-stat starts to open, it takes another 10 - 15 degrees to open fully. Thats why you see a rise then fall on the guage. BUT 210 or 215 isn't over heating. This is the optimal temp designed by the engineers.

FOR EVERY POUND OF CAP PRESSURE YOU ADD 4 DEGREES TO THE BOILING POINT. 16 x 4 = 64 degrees + 212 (boiling point) is 276 degrees. You should NEVER see this temp but I don't get worried till about 250 degrees. When I see a long uphill I switch on the E-fan over-ride way before thing start to get sweaty, usually solves the problem.

 

It must be in the air. My buddy told me he hardly ever hears of a 4.0 having head issues. Mine is screwed, new motor time.

Sorry to hear your having problems too. These guys can help you out. They have been great to me.

 

water pump impellar

 

Just cracked head. I know the headgasket is fine. I think all my worries are me over-thinking stuff. I'll keep an eye on it and report back if I have more info. I'm going to do an oil change soon so when I do, I'm going to inspect the old oil for coolant traces.

 

also use a block tester on radiator to check for combustion leak into cooling system