I know nothing of flushing engine with kerosene but I have used seafoam with obvious results. I swapped a subaru engine into my Vw Vanagon and after the Subaru engine sat for three months one of the lifters appeared to gummed up due to oil sludge. I fired the engine for the first time in the vanagon and a loud tick could be heard from at least 100' away. I changed the oil 2-3 times in a three week period and no change, tick was still there. I then ran seafoam in the last oil change as directed on the bottle and about 200 miles later tick was gone. That oil was really dark when I drained it at 300 miles. Never had that tick for the rest of the time I owned that van. I agree with all of the other previous posts, check for a bad sender by using a mechanical guage. A friend of mine had a wonky oil guage in a 96' GC with a 4.0 and it was caused by a bad CPS. The guage would fluctuate randomly and after the new CPS was installed it would show normal readings. Gremlins just love electronics especially if it throws your diagnostics in the wrong direction!

 

Wow, reading threads on who like's what oil or oil filter best is like ..well...it they pretty much cover EVERYTHING!

Love Mobile, hate Mobile
Love Penzoil, hate
love etc hat ...

Love K&N filters, hate...
et al

Looking back I don't remember seeing somebody that didn't like NAPA Gold filters, maybe didn't like price but no faults on quality. Must be MAGIC

 

Did u read Motor Oil 101 (and got the facts, not opinions)?.......pop quiz will follow.

 

I run mopar filters.

 

Mineral vs synthetic is much more clear as well as the ratings system ...5W30 etc. Makes me wonder why they even make 10W30 though.

Relative to my original question, it certainly implied the answer is to increase weight/thickness relative to engine wear if need be. At the same time, thinner is better, so error on the thin side.

xj88...this makes me wonder if a that 5W40 may be a bit heavy for you?

 

I can think of a couple explanations. The first is just speculation that people will buy what the manual says - for whatever reasons. A lot of people still believe, erroneously, that 10W30 is thinner than 5W30 at operating temperature. The second is that some 5W30 and 10W30s are made from the same base stocks, with the 5W30 loaded up on additional VIIs and pour-point depressants. People who really beat on their oil observed in UOAs that the additives in 5W30 degraded faster than 10W30. (Maybe because there's more?) Personally I don't see a difference since they'll degrade back to the same goo anyway.

Is this comment towards Motor Oil University or something else? Last time I read it I think the emphasis was on lubricant volume and film strength. Like others have said, pressure is just a cheap way to correlate flow.

Oil weight in the 4.0 I find an interesting subject. Let's start with some history:

- For a given XJ, North American marketed vehicles were specified with xW30
- For that same XJ, export vehicles were specified with both xW30 and xW40
- Renix XJs with the 4.0 were specified with a range of weights from 5w30 through 20W50, in both export and domestic markets

Some possibilities to explain the discrepancies:

- Engine design changes with less tolerance
- Fuel economy or emissions targets
- Increased wear observed by Chrysler at higher weights
- Significant improvements in oil quality and technologies over the past 20 years
- Products consumers are familiar with
- Ease of obtaining a given oil in a given market
- Streamlining dealership stock to keep costs down

In the context of running a heavier weight oil in the 4.0 a few things can be considered:

- The difference between SAE30 and SAE40 weights at operating temperature is very minimal (2-3 centistokes generally, but the specification allows for them to actually be the same)
- Supporting the above, a variety of other engines specify xW30 and xW40 side-by-side, meaning this is not abnormal
- Normal, healthy oil pressure should reflect a balance between 'tightness' in components and sufficient flow. If a xW40 oil on a reasonably worn engine yeilds the same pressure as xW30 on new engine, this could be an acceptable compromise
- Many xW40 oils in North America are API-certified for use in gasoline engines, eg. Shell Rotella T6 bears the API SM mark
- There is more to a modern lubricant than its simple weight. Additive packages should also be considered, which these days is the major difference between brands of a given class (eg. Group IV or high-end dino juice)

Oh and most Jeeps out there on the road probably have such low compression that any oil will thin out to a 10-weight from fuel contamination in a matter of weeks anyway lol

Really just run the oil that makes your Jeep the happiest. At this stage in the game, every engine is different, so unless you perform a TON of testing you can either listen to a bunch of internet nerds or experiment a bit and go with what works best.

 

Motor oils and motor/vehicle happiness......never have quite understood the correlation.

 

Its no coincidence many vehicles are considered female! Another of life's great mysteries

 

......and when mama's happy, everybody's happy.

 

Thanks for the in-depth Salad.

I take it 4.0s are not nearly as picky about good even compression as my Sea Doo is lol

 

Is your Seadoo a 2 stroke?.....if so, then it's probably a lower compression ratio than the XJ. Just because a motor has a somewhat low compression ratio doesn't mean the cylinders don't seal well. A cylinders sealing condition has little/nothing to do with its compression ratio. Carbon build-up can increase cylinder pressures but it's not figured into compression ratio. Likewise, worn rings/cylinder walls and leaky valves will reduce cylinder pressures and increase oil dilution but have no effect on the motors designed compression ratio.

 

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Geeky, Excellent analogy with the hole in the upstream tube. Yes if a bearing was worn the flow would increase at the worn bearing and flow would decrease to the rockers. However, the bad bearing is where flow is needed the most. Thicker oil would be restricted more at the points of close tolerances starving them of oil especially on cold starts. Reduced flow to rockers is an unavoidable consequence but rockers do not need high flow. Also since 10 weight or 40 weight have close to the same viscosity at 210 degrees nothing has really changed except for the fact that vital lubrication points are being starved until the engine warms up.

Not sure about the head issue but I do suspect that as a possibility by a PO. I have been driving it for 14 months and over 10k. Service records from my Jeep dealer reports this condition existed over 2-1/2 years and 27,000 miles ago.

 

As tired as a subject is it's always fun to have a little serious discussion!

The 4.0's compression spec is 120 PSI with no more than 30 PSI variation across all cylinders. (Test as performed by the FSM method of thottle blocked open, take measurement on 3rd stroke.) There are a few people on here running in the 80s and 90s across all six. It's a beastly engine, some of them survive one oil change per 60,000 miles, quite a few of them keep on ticking (hah) after inhaling a bunch of water. Not exactly good for them but they do still work afterwards...

 

Wow, sounds like these engine can take a lickin' and keep on tickin'. Matter of fact I read they like to tick a lot. lol.

My SeaDoo is a 787 2stroke but it likes 115PSI in both. While it is still happy at say 110 in one and 103 in the other it starts getting picky not far from there. But then there are only two cylinders...

 

While I said I wasn't really here to talk about diagnosing my issue several of you have been kind enough to offer help in that arena so I figure I may as well post my intentions for tomorrow.

Oil does not look so good so I intend on changing and putting in a synth for cleaning as much as anything else. So I think I will try the shell that xj88 is looking at along with a napa gold /wix filter (oversize?). This jeep will be my wife's and she puts very few miles on a vehicle. I also will use it to tow my 2000 lb boat/trailer. This will be low mileage for us so I figure one change in spring/one in fall will likely be plenty so price of synth will not be so much and I like the engine cleaning benefits as well.

As a side note she is having to give up her Wrangler, that I nearly forced upon her 11 years ago, so that I can have a vehicle to tow my boat. Her fee for this is not only the Cherokee but also a motorcycle (the Wrangler spend a good deal of most summers topless and doorless). My arm still hurts from the twisting. I have a great wife!!!!

While changing oil i will remove oil pressure sensor (looks very recently replaced) and check for sludge and such both there and in the pan.

I have already requested one of the oil analysis kits be sent to me and will save at least 4 oz of the middle flow oil as it drains to send in when the kit arrives.

After the oil change if pressure does not return, I will once again remove ops and check with mechanical gauge. If good with mechanical, I will replace with new napa ops. If still bad I will remove oil fill cap and make certain I'm getting some oil flying around up there. If so, let my wife drive and wait for oil analysis to come back.

I've removed the oil cap and peaked in through the valve cover to the cylinder head passenger side and did not see anything odd. I did this with engine cold thinking that would be the best time to see a fluid difference look. I will do again with engine hot.

Also intend on taking the trans in for a flush, I've read the filter doesn't needs changed unless the fluid looks bad, this one's doesn't. I guess if I read more I'm sure I'd read always change the filter too... so hard to know. Thoughts?

If I'm missing something or need guidance .... please, type away!