"Loose" Jeep 4.0L

[36yrsinTX]

I have this Jeep Cherokee (2001) which I purchased earlier this year. Odo shows approx. 62K miles, CarFax says that is correct mileage. A problem that was not evident when I test-drove it (due to a fairly cool day) is that the oil pressure drops considerably when the engine is fully warmed up. This is not my first 4.0L Jeep, so I know the pressure is abnormally low - on 10w30 idle pressure is as low as about 8 psi, and at 2K rpm, it barely breaks 30 psi. (Verified with mechanical OP gauge.) Jeep shop says it is most likely cam bearings, and says it is not uncommon on this engine/year model, even at low mileage. Given that I'm in Central TX, it is HOT in the summer, so I have gone to Castrol Edge 5W-50. This gives me an idle pressure at about 12 - 15 psi and around 40 psi at 2K rpm. I do realize that this is not a "fix", and most likely it is just making me feel better. I also know that 5 - 8 psi @ idle is not really damaging the engine (according to what I've read on this site), and 30 psi @ 2K rpm is sufficient by the 10 psi/1000 rpm rule of thumb. Question is, am I doing damage by using the 5W-50? The plan is to go to a 10W-40 when the weather cools off. (Normal winter lows here are not much colder than the upper 30's.) What is concerning me is that I'm hearing more internal engine noise at idle with the 5W than I did with 10w30. Is that a problem?

I would just like some informed opinions. This is generally a tough engine, and I'm hoping to get lots of miles out of it in spite of the low OP, so I want to do the right thing now.

Oh, also, the PO said he used Mobil 1 10w30 FWIW.

Thanks for any input!

 

[dave1251]

Internal noises? That is not good at all, if your mechanic says something is mechanically wrong no mickey mouse change in oil grade is going to cure anything. It may allow you to limp your engine along. How long maybe until Monday or until 2020 no way to know for sure. If you do not believe your mechanic find another one and get a second opinion. If you have the money fix it now, if not keep your band aid and save money for a rebuild and keep money on hand for a tow truck.

 

[Chris142]

I'd run 20w50. no thick oil will hurt that one

 

[Kuato]

On my 4.0, the Mobil 1 used oil analysis showed more than twice the iron of any other oil I tested (Amsoil, Super Tech Syn, Valvoline conventional), so I'd steer clear of it for this engine.

It's certainly possible that your oil pump isn't up to snuff; I would have that replaced first.

Did the PO include any maintenance records or did he say what his OCI was?

 

[strongt]

FYI the factory spec from the FSM on oil pressure for the 4.0 is :

Oil Pressure

At Idle Speed 89.6 kPa (13 psi)

At 1600 rpm & Higher 255 to 517 kPa
(37 to 75 psi)

Oil Pressure Relief 517 kPa (75 psi)

If was me, I'd just get her fixed the right way. Not try using a thicker oil to try to get the oil pressure up. Spend alittle more now, save alot later.

 

[3311]

How hard is it to install an oil pump on that engine? Maybe put in a high volume pump and take a look at the a rod and a main bearing since the pan will be off.
I would keep runnig the 5w50 or a hdeo 15w40 if you want to save some coin.

 

[KCJeep]

Highly doubt it's the oil pump, very seldom do they go out on the 4.0 and virtually unheard of at 62k. That year was one of two years that got some bad heads, resulted in a lot of cracked heads and coolant in the oil. It sounds to me like yours may have been run a long time that way.

May be some serious bearing damage but sure I hope not.

Might have it pressure tested it still might have the bad head. If you can find it the bad ones had "331" stamped on them and were made in the 2000 and 2001 model years of the 4.0 Cherokee.

 

[36yrsinTX]

Wow! This is an active forum! Thanks to all for taking time to respond to my question.

Answers to questions asked:
- "Internal noises"- Not sure if it is piston slap or bearing noise. Occurs cold and hot, no change. I tend to think it is rod bearing noise. Although I've rebuilt a few engines, I'm not an expert mech/diagnostician. Sounds faintly like a diesel at idle ("clacking") but much quieter. As mentioned, with 10W idle was quiet. I presume the increased noise is due to the lower viscosity properties of the 5W (true?)
- As stated in the orig post, I understand using 5-50 won't cure any ills and it isn't intended to.
- I accept the diagnosis that cam bearings are at fault. I have found this problem documented on other forums, and given the Jeep shop works on lots of 4.0L engines, he probably knows of what he speaks.
- Using 20W-50, per Motor Oil University on this site, is a bad idea, due to start-up lube issues. Ideally, I'd wanted 10W-50, but no such thing exists as far as I know.
- I'm not a big fan of M1, so I don't use it. As stated, I am currently using Castrol Edge, also not ideal but the most commonly available 5-50 synthetic. PO did not give any maintenance records but told me he changed 1X per year. Given the truck only racked up an average 5K miles/year, that is not as bad as it sounds. Not what I'd do, but by itself should not have caused the accelerated wear.
-Most all knowledgeable folks say the pump is probably not at fault. Pump install is realtively easy, but using a high volume pump would not be my choice due to history of twisted pump drive shafts, plus it really would not accomplish anything more than what heavier weight oil accomplishes.
-I was aware of the factory spec on OP, but this engine is below those figures.
-No evidence of any coolant in the oil, and this does not have the 331 head.

A little more background: This is not a critical vehicle in my household. It is mostly a daily beater with a little light off-road use, and will accumulate 5 - 6k miles/year. As such, while I could afford a rebuild, I suspect that with good choices in oil at this point, this engine (which is a low-tech "tractor" engine) will last a long time. Simply fixing the cam bearings on this engine requires major disassembly, so just doing that is kind of pointless without a complete rebuild. It would not be a small effort/expenditure to replace cam bearings at this point.

No question I will need a rebuild at some point, but my question is, am I doing unnecessary damage by using the 5W-50? Would I be better off in the long run using the factory recommended 10-30 and ignoring the low OP?

Thanks again.

 

[tstep]

I had a 94 GC 4.0. I gave it up after 264k miles and 12 years of service still running just not inspectable without getting alot fixed. At somewhere around 150k I thought the engine was shot. Loud, diesel-like, low oil pressure, burned a quart every couple of hundred miles, etc. It was my work beater at this point. I did little to nothing as far as real service. Changed the oil once in a long while since it burned so much. 100k later it was still running. take it for what its worth.

 

[caravanmike]

use the multi grade 50 weight. and report back how much hot oil pressure went up!

 

[KCJeep]

Originally Posted By: 36yrsinTX

Answers to questions asked:
- "Internal noises"- Not sure if it is piston slap or bearing noise. Occurs cold and hot, no change. I tend to think it is rod bearing noise. Although I've rebuilt a few engines, I'm not an expert mech/diagnostician. Sounds faintly like a diesel at idle ("clacking") but much quieter. As mentioned, with 10W idle was quiet. I presume the increased noise is due to the lower viscosity properties of the 5W (true?)

-No evidence of any coolant in the oil, and this does not have the 331 head.


No question I will need a rebuild at some point, but my question is, am I doing unnecessary damage by using the 5W-50? Would I be better off in the long run using the factory recommended 10-30 and ignoring the low OP?

Thanks again.


My take:

1) The diesel like sound of this engine at idle can vary from engine to engine and different oils will make some difference but for all intensive purposes consider it normal and "justforgetaboutit". Yes many of them will be notably louder on lighter oils, particularly the year/version you have many Jeep owners of similar Jeeps like HDEO's or 10w40's and those are "healthy" 4.0's.

2) If it doesn't have the 331 head it's apparently already been replaced

but it sounds like the damage was done.

3) Since it's really too late for this engine I'd try a high HTHS 15w40 or even a 20w50 for the oil pressure I see no point in start up protection concerns now I'd want the oil pressure. About 30-40 psi at hot idle on 10w30 is considered "normal" for this engine. Good chance with very thick oils you can continue to drive this Jeep quite a while yet.

Hope this helps, Tim

 

[mechtech2]

Thicker oil for worn parts is the oldest trick in the book.
Your 50 [or 40] should help .
Rebuilding an engine or replacing it is not an easy option.

 

[TFB1]

The "Diesel" sound is generally piston(s) slap, a rod will ALWAYS be more prominent at operating temp when oil is thin... If it's audible cold, it would be raising [censored] at normal temp, even with a 50W oil...

Unless it has broken skirts, piston slap will generally be less at operating temp, loose wrist pins make approx same noise cold or hot...

 

[36yrsinTX]

Originally Posted By: tstep
I had a 94 GC 4.0. I gave it up after 264k miles and 12 years of service still running just not inspectable without getting alot fixed. At somewhere around 150k I thought the engine was shot. Loud, diesel-like, low oil pressure, burned a quart every couple of hundred miles, etc. It was my work beater at this point. I did little to nothing as far as real service. Changed the oil once in a long while since it burned so much. 100k later it was still running. take it for what its worth.
Yep, I've heard several similar stories. Tough ol' engine, for sure, and one of the primary reasons I looked for a Cherokee. Also they are EZ to work on and relatively low cost for parts. Just too bad this one has accelerated wear.

 

[36yrsinTX]

Originally Posted By: caravanmike
use the multi grade 50 weight. and report back how much hot oil pressure went up!
Per orig post, hot idle was ~8psi, now ~13, 2K rpm was 30+, now 40 psi hot.

 

[36yrsinTX]

Thank you to all, esp. Tim - you have given great feedback. Believe I'll be sticking with the 5W-50 through the hot weather, but I'll get an oil analysis done @ the next oil change to see if there's evidence of the abnormal internal wear continuing. If so, then a rebuild sooner rather than later!

 

[crazy8]

Originally Posted By: 36yrsinTX
Wow! This is an active forum! Thanks to all for taking time to respond to my question.

Answers to questions asked:

- As stated in the orig post, I understand using 5-50 won't cure any ills and it isn't intended to.
-
- Using 20W-50, per Motor Oil University on this site, is a bad idea, due to start-up lube issues. Ideally, I'd wanted 10W-50, but no such thing exists as far as I know.

I see no problem running 20w50 high 30 deg temps are not a problem for 20w50.

- I'm not a big fan of Mobil 1, so I don't use it. As stated, I am currently using Castrol Edge, also not ideal but the most commonly available 5-50 synthetic. PO did not give any maintenance records but told me he changed 1X per year. Given the truck only racked up an average 5K miles/year, that is not as bad as it sounds. Not what I'd do, but by itself should not have caused the accelerated wear.

I understand your not a Mobil 1 fan, however if you can stand for it there is a Mobil 1 15w50

A little more background: This is not a critical vehicle in my household. It is mostly a daily beater with a little light off-road use, and will accumulate 5 - 6k miles/year. As such, while I could afford a rebuild, I suspect that with good choices in oil at this point, this engine (which is a low-tech "tractor" engine) will last a long time. Simply fixing the cam bearings on this engine requires major disassembly, so just doing that is kind of pointless without a complete rebuild. It would not be a small effort/expenditure to replace cam bearings at this point.

No question I will need a rebuild at some point, but my question is, am I doing unnecessary damage by using the 5W-50? Would I be better off in the long run using the factory recommended 10-30 and ignoring the low OP?

I would not be using a 5w50 , the 5w seems to be a little light to me.

Thanks again.

 

[caravanmike]

keep in mind some 5w-50 will shear early. so keep an eye on the pressure guage.

 

[wyrmrider]

Former Chry service manager here
lots of good info
5-50 Edge good choice
given TX temps and low usage
It will not thicken much over time as a conventional oil would
Once a year should work unless you get a lot of fuel dilution
you are injected so that should not be a problem (keep pcv clean)
oil pump easy to change and there should be a HV pump= best option
This engine does not need a lot of oil pressure
bearings are nice and wide
some replacement cam bearings are too tight- you must check after installation and, as you say, a major project
I've built lots of these with 258 crank and rods and one turbo that made over 1000 HP- but that's another story

 

[1345]

What kind of oil filter are you useing? Try a napa platinum 41515 filter and rotella t6 oil. My cherokee 4.0 idles at 21 psi hot. Before this filter it would idle at 12 psi hot. I live in south central Texas. rotella t6 even made my dipstick slide out smoother.