To clean or not to clean(high mileage 4.0l)

[Demonoid369]

So I've acquired a 91' 4.0l xj with 334,000 miles awhile back and up to this point, except for the hiss of a cracked exhaust header, this thing has ran quiet as a mouse, no ticks, no chatter, nothing.
Well I removed the exhaust and intake manifold to weld up the header and found this

Looking under the oil fill cap also determined that there is a ton of sludge build up under the valve cover also.
My question is with a engine this old, dirty, quiet. Should I try and clean it? A part of me say yes as that can help the longevity of the engine but another part is telling me that if I try and clean it, I might open a can of worms lol any thoughts or opinions? I was planning on using rotella T3 as it's got a good amount of detergent/scrubber additives to it.

 

[Tim_MN]

Remove and clean the intake, and give it regular oil changes. No other cleaning is required.

 

[Demonoid369]

I don't know if you understood what I meant and I apologize if you didn't. What I mean is should I do nothing and let the sludge build up stay because it's a old engine and it's running quiet and smooth or should I take the chance of using things like seafoam or marvel mystery oil or rotella t3 to try and clean up the sludge build up in the engine but run the risk of getting lifter chatter or similar? Because under the valve cover the lifters and such look exactly like what's in the intake manifold, bunch of oil sludge build up.

 

[Tim_MN]

Do nothing is the correct choice. Regular oil changes with high detergent oil will remove a good deal of the sludge, and if you have good oil pressure and no strange noises, there is no problem.

 

[cruiser54]

5 quarts of Rotella T3 and 1 quart of Marvel Mystery Oil. Watch it melt away.

 

[Digger87xj]

tread with caution. Depending on the consistency of the sludge, i.e. dry and chunky or smooth and creamy, can determine what you want to do. The creamy style can be easily cleaned away with a good oil filter and a quality additive like BG MOA or marvel mystery oil and several successive oil changes.
If it's the dry-ish chunky sludge, cross your finders and just drive it. Attempting to chemically clean out this type usually results in the sludge breaking off, dropping to the pan and subsequently plugging the pick-up tube screen.

 

[cruiser54]

I did a dry and crusty one with the T3 and MMO. Worked great.

 

[techno1154]

5 quarts of Rotella T3 and 1 quart of Marvel Mystery Oil. Watch it melt away.

Along with several oil filter changes between oil change.

Digger87xj have a valid point. Tread with caution.

 

[Waynerd]

Maybe an oil catch on the ccv. If the intake is that nasty. And if you were to do a top end cleaner or something similar I would do it with the cat disconnected as not to clog it. Maybe mchanically clean the intake ports while holding a shop vac nozzle to suck it all out when it falls off so it doesn't fall in around the valves.

 

[Green Mesa XJ]

Doing anything (for gunk in the engine) can come back to bite. But at least the 4.0 oil pan is accessible.
Whatever you do, do not run a "motor flush" through it.

Safest is a oil with mild detergent. But if you really want do be proactive.
You've got great advice on the rotella, I run rotella T6 it's a synthetic Diesel oil with a lot of detergent many 4.0 owners and Subaru WRX STI owners use. I run it in a 300k 4,0, it was never very dirty that I can see and always has great oil pressure.
I'm also doing a test I'm trying to save my brother-in-law's car, (expletives deleted) didn't change the oil for over a year maybe more (thought his wife did it, I asked when between 3 kids does she have time to worry about your car? ) 10k later and two oil changes I can see it's making a difference. The car has filter incerts rather than traditional oil filters, tiny flakes of crud are visible in the filter eminent.
If you do run something like Rotella t3 or T6 change the filter ever 1k or do at first. If you have a gauge and you see the pressure drop off some just go ahead and change it.




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[Demonoid369]

Thank you guys, ya that's what I was thinking and wanted to get your guys opinions. Just wants to tread with caution as its my moms old jeep that got me into the jeeps so I want to keep it going for as long as I can for a daily driver.

 

[Ecomike]

If it ain't broke don't fix it!!!!

If it starts to have problems use MMO with a good cheap dyno oil and change the oil and filters very frequently.

 

[Saudade]

Nuttin' but Castrol GTX and MMO in my 88 since I bought it in 2000. I seafomed it back in 2009 (doesn't seem that long ago). Discovered an exh leak. A few months later, I replaced the manifold. Here's the link back to my post with a pic of the intakes.

http://www.naxja.org/forum/showpost.php?p=244438902&postcount=3

Please don't post to the old thread.

 

[XJonAZ]

5 quarts high mileage oil, and a quart of ATF with a new filter. Auto tranny fluid is a high detergent oil

 

[cruiser54]

Rotella T3 and MMO with a Wix filter.

Watch the sludge melt away.

 

[Johnnie Walker]

For Renix if you want a larger oil filter. Wix 51182, also Cq 85182. Before I switched to a larget filter I ran 5 qt of oil + 1 of MMO.
With taller filter my XJ cap. Is about 6.5