Rebuilt 4.0 question.

TapouT

Well-Known Member
Joined
Oct 5, 2008
Location
Hickory nc
I bought a 1998 Jeep Grand Cherokee today. It has a 4.0 in it. The engine was gone through less than 5,000 miles ago. New pistons/rods, cam, bearings, lifters, gaskets etc...it's time for an oil change. The guy I bought it from said he ran 10w40 Mobil 1 synthetic in it. The engine is exceptionally quiet. It doesn't have the notorious 4.0 tick/rattle at all.

I've owned 14 Jeeps and this is the first one to not make any noise. Holds 40psi cold oil pressure and 30psi warm. Do you think I could make the switch back to regular conventional oil instead of synthetic and go to a different viscosity for the winter like 10w30? I've always had good luck with Castrol GTX High Mileage in my 4.0's but I didn't know if it would be okay in a freshly rebuilt engine. I appreciate any input on this. I'm changing the oil on it soon. Thanks for the help!
 
I don't like running synthetic oil in a fresh rebuild because it can keep rings from seating. It won't hurt anything to switch back and forth between synthetic and conventional.
 
It's not healthy for the engine to switch between oils or viscosities.

Generally speaking, it's better to have higher zddp oil for a flat tappet cam.

^ is correct also though. Not good to break a new/rebuilt engine in with synthetic oil.
 
Cold weather you should be using a 5w3o or 5w40
 
It's a 4.0. As long as there's oil in it, it will run good. Run the best oil you feel like affording, and if you aren't running synthetic then just get what's on sale.
 
for most anywhere in NC, it does not get cold enough in the winter to warrant going to a thinner oil. In cold weather, let it idle for about 30 seconds & get good oil pressure before leaving the driveway & take it easy for the first couple miles. for a 4.0, run 10W-30 in it and it should live a long and healthy life, I'm not a fan of running 5W-whatever in a 4.0
 
TapouT said:
I thought about running 5w30 but I'm not sure. I know it will help with cold starts but the owners manual calls for 10w30 all year round.
Click to expand...
99 owners manual.
141971082396354056388.jpg
 
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Changed the oil in it a little while ago with Castrol 10w40 conventional and a Mopar filter. It's making what sounds like lifter noise now at idle. It doesn't get any louder while driving from what I can tell. Oil pressure is a little better than it was before I changed the oil.
 
hehe....welcome to the 4.0 world there bud... that is the way mine does. The other way sounds more like piston slap till warmed up (another 4.0 problem)
230,000 miles with 190,000 of that on synthetic
engine sounds like a valve is gonna fly out of it for 50,000
I've put in 5w30 valvolene and it is actually a little quieter
don't waste your time with synthetic
 
Thanks for the help guys! I'm not too worried about it either way. It's a 4.0 inline 6. I know how noisy they are. I do hate that the engine was extremely quiet before I changed the oil and now it's not but shit happens I guess.
 
I read an article that tested all the popular oils for additive contents.. Rotella t6 synthetic Is one of the only oils with high zinc to satisfy a flat tappet cam motor. The valvoline and Castrol conventionals had terrible additive packages. My motor has 15k since the rebuild and runs smoother with the diesel oil than anything else I've run, even royal purple. I had a lifter noise that went away after I went to rotella. I will try to find the article and post it up

EDIT: found it http://www.cherokeeforum.com/f2/rot...hair-oil-foot-ointment-salad-dressing-188168/ lots of good info in here
 
I wish all the cars and trucks around here ran as quiet as the flathead/solid lifter engine in my M38

I've tried rotella in 15/40 and made no difference in noise in my application
 
Buddy_Holly said:
I read an article that tested all the popular oils for additive contents.. Rotella t6 synthetic Is one of the only oils with high zinc to satisfy a flat tappet cam motor. The valvoline and Castrol conventionals had terrible additive packages. My motor has 15k since the rebuild and runs smoother with the diesel oil than anything else I've run, even royal purple. I had a lifter noise that went away after I went to rotella. I will try to find the article and post it up

EDIT: found it http://www.cherokeeforum.com/f2/rot...hair-oil-foot-ointment-salad-dressing-188168/ lots of good info in here
Click to expand...

I'm hearing the noise from underneath around the oil pan. Maybe it's not a lifter noise. I can hear it underneath the Jeep and inside the a Jeep but if I'm up top under the hood I can't hear the noise. I wonder why changing the oil would make the Jeep make noise now unless the guy had some really thick oil in it when I looked at it to try to mask the noise.
 
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