Carabinerx

I recently bought this 2001 xj, maybe a month ago. I've been slowly working on it and bringing it up to snuff (plugs, coils, injectors, battery, sensors, etc.) And have put a few hundred miles on it.

When I bought it, original owner knows next to nothing about it’s history, but I saw the coolant was over filled. Now, a month and a few hundred miles later, the coolant looks to be down to the "full" line.

A mechanic did an engine flush and oil change the day after I bought it (the rest was done by and me) and didnt mention any issue of bad oil, and there is no oil in the coolant or milky stuff in the oil that I can see. The oil pressure does drop to around 18psi when hot Idle.

But I'm worried about a crack now, and I just cant see into the valve cover's oil port...how else can I check this? Also, the coolant doesnt have anything to do with with the ac lines does it? There's no ac compressor (previous owner didn’t want to replace it, so had it removed) and one day I saw what looked like coolant on the aluminum head that would connect the two lines to the compressor.

Also, I dont have a garage, I've been doing all of this street side in my neighborhood.

Thanks for any responses.

dave1123

Check your oil first thing in the morning. It you see the level rising, that's a sure sign of coolant in the oil. You can also take a sample from the oil drain plug by catching a little bit and quickly putting it back in. Do it after it's been sitting overnight. The coolant will be the first thing out. Losing a little coolant over time is not unusual for a jeep. The water pump has a "weep" hole on the impeller shaft bearing that will drip a tiny bit, then evaporate. The newer pumps actually have a weep chamber that holds about a teaspoon full of coolant that is allowed to evaporate without you even seeing it. If you start going thru a quart a week, then you can start to worry. When my jeep's head cracked, I got lucky. It only cracked into an exhaust port, so I had lots of steam and coolant dripping out the tailpipe. Another point of coolant loss is a leaking heater core. That coolant you saw on the compressor mount may be from a heater hose or loose clamp.

It's not unusual for an XJ or ZJ to have low oil pressure at hot idle because of the low oil flow and restriction of the oil filter adapter's banjo bolt. As long as it increases above 1000 or 1500 rpm, it's okay. My 2000 XJ had 15 psi at idle hot with only 125K miles on it. I switched to a Mopar pressure sensor and Rotella T6 5W-40 Synthetic Diesel oil and now have 55 lbs at cold startup, 30 lbs at hot idle, and 40-45 at anything over 1000 rpm. Jeep 4.0s need oil with high levels of zinc in it. ZDDP is necessary for lubrication of the flat tappet valve lifters. They have removed zinc from modern oils because most engines today either have roller lifters or overhead camshafts with roller followers.

Another good modification you can make is an upgraded headlight harness. The factory setup puts all the current for the headlights thru the switch, resulting in dim lights and burned out switches. The upgrade harness lets the switch just activate a pair of relays which draw the current for the lights directly from the battery. It's just a simple plug&play installation with only a couple of connections and a bolt to mount the relay pack. The difference will astound you! I put Sylvania Silverstar bulbs in mine as well.

What part of NYC are you from? My wife grow up in Flatbush. Kings Highway and 13th st.

Dave51

Flat tappet engines only need high levels of zinc during cam and tappet break in. ZDDP was reduced because once zinc and phosphorous coat the catalytic converter it is rendered ineffective.

In a new vehicle you can get away with it for a while but the thing everybody seems to forget is these are 18+ year old engines and cats without a lot of wiggle room.

puredrive

I would monitor the coolant level and in doubt get the oil analyzed. That's how I confirmed my suspicion of the cracked cylinder head.

dave1123

Whay! No picking apart the headlight harness?

PatHenry

The 4.0 likes the Zinc. You can get zinc additives if you're not using a diesel oil.

It's bad for the cat if you are both
- burning oil
AND
- Live in a state where you have to pass emissions.

Shockingly, in MA once you're past 15 years you're exempt from the emissions and then there's LOTS of wiggle room on the cat.

Carabinerx

Thank you @dave1123 that was incredibly helpful. I have been planning on doing an oil change with some heavier stuff I'll look for the one you mentioned.

On a positive note, there is definitely coolant dripping from one of the lines that would have gone into the ac compressor, so that would explain the loss! Hopefully no crack then. I guess I'll know for certain when I flush the oil.

Thanks for everyone's help

Dave51

But it's not like there's NO zinc in oil. Current oils are ~800 ppm. It would seem that after the asperites are filled in you don't need 1600+ ppm zinc any more. How much zinc does a flat tappet engine that has been properly broken in, under normal driving conditions, and routine oil changes, actually need?

PatHenry

How much does it NEED - I couldn't tell you. However, under normal driving conditions, routine oil changes, etc.. the engine is designed to run for X amount of miles. If I want to get twice or three times X, I'd choose to reduce any possible wear over preserving a catalytic converter that I only "need" because federal/state law says I need one...

Dave51

And diesel oil is gonna do that?

https://zddplus.com/wp-content/uploa...ne-Engines.pdf

Kinda makes ya wonder why they increased the level of ZDDP in diesel oils...

PatHenry

Sounds like that's exactly why they increased the levels.

I don't know about using the diesel oils - lots of guys on here swear by it - I personally use Mobil 1 and will throw in a half bottle of the ZDDP additive for the aforementioned trade-off. My feeling on it is that I watched my Dad get 400k on his 94 with zero issues and a perfectly running engine on it's retirement day, he used Mobil 1 throughout. Then I put 302k on my 00 TJ and that engine still runs smooth as silk, I used Mobil 1 throughout and I think it was CoffeeCommando that presented evidence of the reduction in Zinc in all oils in recent years so my feeling is I'm basically restoring the Mobil 1 to the same formula it was 15 years ago. Maybe it's helpful, maybe not, but if I don't give a hoot about the cat, it's definitely not going to hurt.

Edit -- O.P. Getting back to the original topic here - I had an 0331 head on my 00 TJ, I bought it brand new, so I can confidently say that it got all that mileage (and as far as I know still runs - I sold the Jeep to a buddy) without ever having the head crack and despite at least 1 major overheating incident that occurred around the 220k mark.

Dave51

I suppose.

Still, it seems like the 4.0 crowd is so out of place with this zinc thing. The "flat tappet" problem really isn't a big deal in these engines. If we can all agree that it is spring pressure that is the determining factor in zinc requirements, if we look at stock (trusting internet sources)

Spring Tension --
Valve Closed ……………71 to 79 lbf. @ 1.64 in.
Spring Tension --
Valve Opened ……………202 to 218 lbf. @ 1.216 in.

Now compare that with the gearhead engines. Those are the guys who had (have) the most to lose (I had a solid lifter cam. Gotta look that up to see if that's the same problem. Certainly spring pressure closed is zero...).

Anyway, what's spring pressure now in these 4.0s, 20 years later?

If we look at a graph from the zddplus website:




https://zddplus.com/wp-content/uploa...e-Oil-Myth.pdf

0.06% provides a more than adequate concentration.

Zinc behavior is a little odd. According to the graph, having no zinc is adequate (assuming it was broken in.correctly).

But like you say, can't hurt...

Dave51

Oh.

I thought it was about oil.

NM.

5-Speed

Carabinerx

Just bought some rotella and a wix filter, hopefully I’ll see what all the buzz is about!