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Oil Grade???

The owners manual for my 98' recommends 10w30. So thats what I use.
Mobil 1 with a Mobil 1 oil filter.
Synthetic all the way.
There are no recommendations or endorsements for synthetic from Jeep, thats just my input.
 
No leak issues. There is a ton of research online about synthetic vs. conventional oil. Or do a search on this forum about "synthetic oil"
There has been much discussion and several threads on this board about it.
All your questions can be answered there.
 
I asked the Jeep dealer what comes in the jeep from the factory and what they use. They told me Mobil 1 synthetic. I have used it for 40K and it works great!
 
Now go order yourself an owner's manual for you XJ. Having the technical data IS REQUIRED, not an option.

You can order a owner's manual form the dealer OR you can do a google search for "techauthority" and you will fill the chrysler publications people. You can order an owner's manual there. I highly recommend you order the maintenance/shop manuals if you plan to keep the XJ. The shop manuals may run you $100 but they will pay for themselves with a repair or two you do yourself.

You need the owner's manual, spend the 10 or 20 bucks for the manual TODAY! You will find maintenance intervals, which oil/lube to use, how much trailer you can tow, and what fuse controls the radio, etc
 
I'm liking Amsoil 0w30 synthetic. The biggest difference I've noticed is that the engine feels a lot less sluggish on cold mornings.
 
jeepguy97 said:
Since when do Jeeps come from the factory with Synthetic???????????
Click to expand...

Never. 10w30 is what they recommend, 10w40 or 15w40 is a MUCH better idea in higher mileage 4.0s.
 
I don't know when the factory recommendation changed, but the owners manual for my 2000 calls for 5W30. The 5W grade provides better flow upon start-up, especially in cold weather (which we still have in New England, at times). For the new ones, I run Castrol Syntec 5W30. For the older ones that need a little help in the oil pressure department, Castrol also offeres a 5W50 and that's what I use. By keeping it to the same brand, in a pinch I can use a bottle of spare oil from one of the other vehicles without worrying that I'm mixing brands and chemical packages.
 
martin said:
You need the owner's manual, spend the 10 or 20 bucks for the manual TODAY! You will find maintenance intervals, which oil/lube to use, how much trailer you can tow, and what fuse controls the radio, etc
Click to expand...


Ha!

That reminds me... I had a grump...

I was doing a bunch of bodywork/paint on the '00 a week or so ago (call it a 5-year overhaul!)... and I had my doors open all afternoon. I finally thought: "Hey, maybe I should pull the fuse to save the battery"....

I popped the fuse panel open, and found, tooled into the cover, the statemenr "See Owners Manual for Fuse Assignments" or somesuch.

So I pop open the glovebox and look up "fuse" in the index of the manual. Page such-and-such. I'm greeted with a picture of the kick panel and door... and the fuse-removal tool... and how to tell if a fuse is good or not. And a
statement that says "Fuse Assignments are on a label inside the fuse compartment".

WTF?

The battery ended up dying... and I had to hook 'er to the charger overnight...
 
DenLip said:
Ha!

That reminds me... I had a grump...

I was doing a bunch of bodywork/paint on the '00 a week or so ago (call it a 5-year overhaul!)... and I had my doors open all afternoon. I finally thought: "Hey, maybe I should pull the fuse to save the battery"....

I popped the fuse panel open, and found, tooled into the cover, the statemenr "See Owners Manual for Fuse Assignments" or somesuch.

So I pop open the glovebox and look up "fuse" in the index of the manual. Page such-and-such. I'm greeted with a picture of the kick panel and door... and the fuse-removal tool... and how to tell if a fuse is good or not. And a
statement that says "Fuse Assignments are on a label inside the fuse compartment".

WTF?

The battery ended up dying... and I had to hook 'er to the charger overnight...
Click to expand...


Thats easy, you got the 'Political owners manual' instead of the 'common sense owners manual'. The difference being the common sense owners manual has useful information in it. The 'Political' owners manual just has finger pointing and no useful information....Must have belonged to a political candidate originally, might be a collector item :D :D :D :D
 
Ha!

That reminds me... I had a grump...

I was doing a bunch of bodywork/paint on the '00 a week or so ago (call it a 5-year overhaul!)... and I had my doors open all afternoon. I finally thought: "Hey, maybe I should pull the fuse to save the battery"....

I popped the fuse panel open, and found, tooled into the cover, the statemenr "See Owners Manual for Fuse Assignments" or somesuch.

So I pop open the glovebox and look up "fuse" in the index of the manual. Page such-and-such. I'm greeted with a picture of the kick panel and door... and the fuse-removal tool... and how to tell if a fuse is good or not. And a
statement that says "Fuse Assignments are on a label inside the fuse compartment".

WTF?

The battery ended up dying... and I had to hook 'er to the charger overnight...
Click to expand...


Uh, just remove the lightbulb. :doh:
 
Eagle said:
I don't know when the factory recommendation changed, but the owners manual for my 2000 calls for 5W30.
Click to expand...

The manual for my '90 says 10w30 or 10w40...I think my '96 just says 5w30. That's not a good choice in the 4.0 at all unless you really need the cold start protection. (and most people don't) 10w anything is good down to ZERO degrees. Since the 4.0 is an antique, hot running, oil blowing pig, thick oils do best. Oils with a large viscosity spread (5w30, and especially 5w50) break down rather fast in an engine like that, and should be changed much more frequently than 10w30 or 15w40. 10w anything will provide better protection from fill to drain than any 5w, unless of course you need the cold start protection.
 
ZmOz said:
The manual for my '90 says 10w30 or 10w40...I think my '96 just says 5w30. That's not a good choice in the 4.0 at all unless you really need the cold start protection. (and most people don't) 10w anything is good down to ZERO degrees. Since the 4.0 is an antique, hot running, oil blowing pig, thick oils do best. Oils with a large viscosity spread (5w30, and especially 5w50) break down rather fast in an engine like that, and should be changed much more frequently than 10w30 or 15w40. 10w anything will provide better protection from fill to drain than any 5w, unless of course you need the cold start protection.
Click to expand...

Not really true, as time passes the manufacturing equipment gets better and the tolerances get closer. Somewhere in 99 the specs called for 5w in the cold weather and 10w summer then it was changed to 5w all year. Part of the change was an increase in milage for federal purposes. My wifes Oldsmobile calls for 5w30 in her 3.something engine so thats what we use. My 98XJ and both 97TJ's call for 10W30 and thats whats in there. My biggest pressure variation expiriences running the same oil, Mobil-1, have been with filters, there have been some pretty big spreads there between Mopar, K&N, Mobil-1 and Purolators. I currently run either Mobil-1 or K&N filters on them all.
 
RichP said:
Not really true, as time passes the manufacturing equipment gets better and the tolerances get closer. Somewhere in 99 the specs called for 5w in the cold weather and 10w summer then it was changed to 5w all year. Part of the change was an increase in milage for federal purposes.
Click to expand...

Exactly. It's for mileage reasons. Has nothing to do with if it's good for the engine or not, because they don't care. 5w30 is a bad choice in the 4.0, period. (unless it's synthetic or you need the cold start protection) The only time you need better cold start protection is when it's below ZERO degrees. Not many places get that cold. A '91 engine is almost exactly the same internally as an '04 engine. In '91 the EPA wasn't bitching about every little thing, in '04 they are. That's why newer vehicles tell you to use thinner oil, even though it's the same engine. When the KJ came out the 3.7L called for 10w30. Now it's 5w20. Same exact engine. Worse EPA restrictions.

Also, the majority of XJs are 1) old, and 2) high mileage. Both of those things mean you need a thicker oil, regardless of what the manual says. Same goes for just about every engine ever made.
 
Last edited:
ZmOz said:
Exactly. It's for mileage reasons. Has nothing to do with if it's good for the engine or not, because they don't care. 5w30 is a bad choice in the 4.0, period. (unless it's synthetic or you need the cold start protection) The only time you need better cold start protection is when it's below ZERO degrees. Not many places get that cold. A '91 engine is almost exactly the same internally as an '04 engine. In '91 the EPA wasn't bitching about every little thing, in '04 they are. That's why newer vehicles tell you to use thinner oil, even though it's the same engine. When the KJ came out the 3.7L called for 10w30. Now it's 5w20. Same exact engine. Worse EPA restrictions.

Also, the majority of XJs are 1) old, and 2) high mileage. Both of those things mean you need a thicker oil, regardless of what the manual says. Same goes for just about every engine ever made.
Click to expand...

I don't think milage has anything to do with having to run thinner or thicker oil. My 98 at 235,000+ miles runs 10W30 just fine as do the two well maintained 2.5L TJ's with over 100,000 mi each [or thereabouts]. Granted, if you do some bearing damage thru poor maintenance or drowining it or whatever you *may* be able to compensate with a 20W but thats just a band aid trying to hide the problem. Everytime I have read about a teardown on a synthetic run motor and measurements are taken I'm always amazed there there is no measureable wear on parts and that they fall within factory specs.
We had to replace the engine in our oldsmobile 2 summers ago when an overheat warped the heads [I just $#%$# LOVE cast iron blocks and aluminum heads :puke:], when the stuff had to come off to go on the new Jasper motor we looked and that engine was immaculate inside as in looked like new but it had only ever been run on mobil-1. Just for laughs we/he pulled two main bearing caps, and two piston caps, no visible wear.
I hope I'm still saying the same thing at 500K..... I'm almost halfway there.
 
Thanks for all my replies. My first post and I start a debate.
PS The owner's manual was in the black glove box in a black cover. Kinda like a black stealth airplane at night. I'll be ordering a factory service manual before venturing into any repairs.
 
RichP said:
I don't think milage has anything to do with having to run thinner or thicker oil.
Click to expand...

That couldn't be farther from the truth. High mileage engines have wider clearances - everywhere. Thicker oil means better protection. That's a fact. The 4.0 isn't a tight engine to begin with. The inside is almost exactly the same as it was in the '60s. There are plenty of used oil analysis results to provide scientific proof that 40 weights do extremely well in the 4.0. Sure, 30 weights will WORK, but 40 weights work better, and cost the same.

Also, the first number has nothing to do with engine protection past warmup. The larger the number spread, however, means that an oil will break down faster - meaning a 5w30 isn't 30 weight for nearly as long as a 10w30.
 
Oil pressure is mostly the result of the volume of oil pumped, the viscosity of the oil, and the resistance to flow that the bearings present. As an engine ages and the bearings open up, the pressure will drop. It's just like the pressure in a garden hose as you put your thumb over the end. I had a high-mileage beater where the oil light would flicker at idle, not because the pump was bad but because the bearings were shot. Using a higher viscosity oil will bring the pressure back up.

FWIW I have been running 5w-40 Amsoil this summer, switching to 0w-30 Castrol in a few weeks for the winter. The Castrol 0w-30 is very thick for a 30, almost a 40 and with excellent cold start characteristics.

I see no reason in this particular engine to listen to what the manufacturer says. They are catering to the government.

BTW, Mobil 1 xw-30 is ALMOST a 20 weight. EEEK!!
 
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