I have the 0331 head on my 2000 and I have had a steady loss of coolant for quite some time now and I thought previously it was the OEM radiator that had a slight drip in it. I have replaced the radiator and it is still losing coolant. I fill the reservoir up to the full mark and it loses about a quart or so a week now:/ My oil is clean, exhaust doesnt smell like its burning antifreeze, plugs/compression is good, no visible leaks, runs great, normal mpgs...could it be leaking only when its hot and something (a line?) is expanding, allowing coolant to maybe run onto the block and just evaporate?

Any insight is appreciated

Ever pressure check the system including the cap?

Did you have it tested?

Oil used to turn milky when exposed to water, and it still can in some cases. But generally the detergent packages in oil have gotten a LOT better in recent years, to the point that the detergents bond to the water rather than letting it emulsify. The good result is that the oil handles condensation in the engine much better. The bad result is that if you have coolant in your oil, it's a lot harder to tell by looking at it. When my 0331 went, I was using Mobil 1 synthetic. The color only lightened a little, but not enough for it to be obvious what was happening.

The only way to be certain you do not have coolant in the oil is to send off a sample to a lab like Blackstone. It costs $25, and they'll send you the sample collection kit for free. You'll need to be sure to get the engine up to operating temp for 20 minutes or so before taking the sample to make sure you don't get a false reading from condensation.

Another place where your senses can be unreliable. For around $60 you can buy a combustion leak tester that tests for the presence of exhaust gases in your cooling system. Amazon has them. If you don't want your own kit, a lot of mechanics have them and can test it for you in just a few minutes.

This is the first thing to do and you can rent a pressure checker from several different auto parts stores, just buy a new cap if you didn't with the radiator.

What is the oil pressure at hot idle? Hot idle is after a 15-20 minutes of driving. If its anywhere near 15psi or higher, then you may still have a chance to save the engine by only replacing the cylinder head.

i will pressure check the whole system this week and make sure it holds pressure for an hour(?). Oil pressure is what it should be at hot idle (13-14psi). I did boil this engine over YEARS ago fwiw...but the coolant didnt leak before/after that, its a more recent issue

Your spark plugs will tell the story, pull them.

i did, and they were a-ok! Just a little old, but nothing irregular about them.

Unexplained coolant loss + 0331 head just about guarantees you have been bitten by Chrysler's casting flaw which leads to head cracks between #3 and #4 cylinder.

It is so disappointing these Jeeps do this. After reading this type of post on these engines for over 4 years, I don't think I'd take one even if someone were trying to give me one.

I don't want to spend the $2000-3300 on a 15 year old vehicle to make it right, anymore.

No color variation? None cleaner than the others?

Id even check a new cap. Products are made so cheap these day.

Speaking of caps, how do you check those? Is there an adapter in the test "kit"?

They crack right between the #3 and #4 rocker arms. Pull the oil filler cap and look straight down for coolant, tan lines, milky oil, etc. The longer you drive it with a cracked head the more risk you have of needing to replace the engine. Around 20 psi hot idle at 40+ at 2000 RPM is more normal. Factory minimums are 13 psi at hot idle and 37 psi at 1600RPM.

My coolant leak came from welsh/freeze plug on rear of engine block.
Coolant would pool in bell housing but not drip if I drove it every day, guess it was evaporating or blowing out.
If jeep sat for two days, a green puddle would form under bell housing.

I have inspected the dog **** out of the head and have had motor heads check it out with inspection equipment and we cannot find a crack between those cylinders. Don;t you think it wouldve went way before or perhaps when i boiled it over, some 50,000 miles ago?! I blew a line and had no clue until my temp gauge pinned to 265 or whatever...heh

none. They were all exactly the same. Electrodes were just worn from age.

oil pressure is okay at high/low RPM's. I'd be hearing some kind of knocking or other bottom end issues by now i would think, also, the oil seems to be ok...no discoloration, smell, metal shavings.

I will check this out today