Question on the 0331 head
07-26-2015, 11:46 PM
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Year: 2000
Model: Cherokee(XJ)
Engine: Golen 4.6L
The milky oil is no longer a reliable method of detection of water in your oil. What used to happen is that the water would get mixed with the oil and emulsify. It wasn't really bonded to the oil. It was just like putting some oil and water into a bottle and shaking it. Eventually it'll separate again, but meanwhile it's a white mess. You could see an obvious color change as a result.
Over the past few decades the detergent packages have gotten increasingly better. Normally when an engine sits, water condenses out of the air in the engine and causes oxidation of metal parts. Detergents are added to oil to combat this wear from condensation. The detergent molecules attach to the oil on one end and water on the other end so that they're chemically bonded until the engine heats up enough to burn off the water. The detergent is intended to protect your engine while it's warming up.
That's meant for small amounts of condensation, however, not coolant from a cracked head. The detergent can't protect the engine from that much water. But the detergent still tries, and as a result the oil may never turn milky like oil used to. Now you have a lot of shade tree mechanics who look at the oil and don't see any milky look to it, and they assume there's no coolant in it. Even so, the oil doesn't lubricate properly with water bonded to it, so you still get damage, just not as fast as you would 20 years ago.
Don't panic. Not all of them crack. There was a guy who posted on here a few weeks ago that had 400K miles on his original 0331.
If I were you, I'd do one of two things. Either:
Run it like it is for now, but monitor the cooling system like a hawk and send off oil samples every oil change to detect any coolant in the oil. I use Blackstone Labs, who charges $25 per oil analysis. They'll send you the test collection kit for free. Personally, I do this anyway on both my cars, because the oil analysis tells a lot about how the engine is wearing. It's cheap peace of mind. But it can also act as an early warning for a cracked head so you can swap it out before it trashes your bearings.
Or:
Preemptively swap the head with a known good replacement. As I said above, you can get a new head from Clearwater Cylinder Heads for around $450 that will be set up for the coil rail on the '00 and '01. You can swap in the older 0630 head, but you'll have to do a little more work. Or you can try to find a TUPY head, which will swap right in but may require a trip to the machine shop.
If it were me, I'd do the preemptive swap to a Clearwater head when it was convenient for me, just to be able to have confidence that it wasn't going to decide to crack when it's less convenient.
The OEM head does a pretty good job on its own. Edelbrock now makes a performance head for the 4.0L, but that thing runs about $1700. Unless you're planning to race, it doesn't look like the gains are really worth the money.
Over the past few decades the detergent packages have gotten increasingly better. Normally when an engine sits, water condenses out of the air in the engine and causes oxidation of metal parts. Detergents are added to oil to combat this wear from condensation. The detergent molecules attach to the oil on one end and water on the other end so that they're chemically bonded until the engine heats up enough to burn off the water. The detergent is intended to protect your engine while it's warming up.
That's meant for small amounts of condensation, however, not coolant from a cracked head. The detergent can't protect the engine from that much water. But the detergent still tries, and as a result the oil may never turn milky like oil used to. Now you have a lot of shade tree mechanics who look at the oil and don't see any milky look to it, and they assume there's no coolant in it. Even so, the oil doesn't lubricate properly with water bonded to it, so you still get damage, just not as fast as you would 20 years ago.
If I were you, I'd do one of two things. Either:
Run it like it is for now, but monitor the cooling system like a hawk and send off oil samples every oil change to detect any coolant in the oil. I use Blackstone Labs, who charges $25 per oil analysis. They'll send you the test collection kit for free. Personally, I do this anyway on both my cars, because the oil analysis tells a lot about how the engine is wearing. It's cheap peace of mind. But it can also act as an early warning for a cracked head so you can swap it out before it trashes your bearings.
Or:
Preemptively swap the head with a known good replacement. As I said above, you can get a new head from Clearwater Cylinder Heads for around $450 that will be set up for the coil rail on the '00 and '01. You can swap in the older 0630 head, but you'll have to do a little more work. Or you can try to find a TUPY head, which will swap right in but may require a trip to the machine shop.
If it were me, I'd do the preemptive swap to a Clearwater head when it was convenient for me, just to be able to have confidence that it wasn't going to decide to crack when it's less convenient.
The OEM head does a pretty good job on its own. Edelbrock now makes a performance head for the 4.0L, but that thing runs about $1700. Unless you're planning to race, it doesn't look like the gains are really worth the money.
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