87 yj jeep wrangler IL6 4.2l stick: oil preference

[JoPeter]

Hi everyone,

I am new here. Have some questions about my fav old friend. I bought this jeep in Oct last year. 168,000 odo. Ran fine. Around end of Nov, I changed oil to 5w 10 synthetic Mobil. Shortly after I hear big tapping noises when I start in morning ( later I was informed "lifters"). Then it became worse and started backfiring through intake ( carburetor) and exhaust sometimes and started missing idling and feels like not getting fuel. Not driveable, unless I give clutch too with gas.After new synthetic oil, oil pressure is bet 10 to 15 on the gauge.

Bad winter here and I have another car so never drove it till now. Meanwhile, I have a friend who is handy and we changed one by one many things: ignition coil, Module, fuel pump ( situated on the lt side of motor), EGR valve( which had a busted diaphragm). After all these, Slightly better with misfiring and backfiring, but still not driveable. Spark plugs become dark in a few minutes or hours if we kept on or drive around a bit.
A mechanic came to look and he thinks it is ignition related: one cylinder is misfiring,...
I have to take it his shop.
Looks like I need to take motor to rebuild or a swap.

Now the question:
Just before I do swap engine or something.. the mechanic suggested 5w30 synthetic is not the proper oil for this old engine.He is telling me I am losing compression and plenty of blow by. He said try some heavy oil:

I am not good at these. Please give some good suggestions: I have heard people using Rotella 15 w 40 diesel oil on these old engines with good results.
1) Which is more thick or viscous: Rotella 15 w 40 or Quaker state conventional 20 w 50?
2)In other words, Does diesel engine oil has more viscosity than petrol engine oils only at same viscosity index?
OR
a diesel oil with 15 w 40 viscosity index is less thick than a conventional oil with a higher viscosity index of 20 w 50
3) Does anyone think by using a HEAVIER oil I could be fix lack of compression in one or 2 cylinders? ( which I have to take to a mechanic this week for compression test and check timing with a timing light as my friend do not have one)
4) Since oil pressure is 10-15 . Ideally around 40 if I am correct. How do I know if the oil pump itself is bad. Is there any way to test it? Or by using a heavier oil, oil pressure should arise?

Any advise about oil thickness or about Jeep misfiring will be greatly helpful. Just want to try everything before I spent $$ for rebuild or swap.

Thanks

Joseph

 

[crazyoildude]

joseph Did you do a compression test you could have a piston problem or maybe you broke a rocker arm/stud or a valve spring that could cause a bad missfire also. Take the valve cover off and look to see if they are all intact then start it and watch them and see if they are all doing the same thing at different times of course

 

[Dyusik]

I had a mechanic tell me that vvte will never work unless I use 5w30. This in mind manufacturer recommends 5w20. I run 5w40, and would not hesitate to run 60wt oil if I had to, in the winter. Like always, it's not oil. Carb, bad fuel, loose anything. Oil can mess this engine up if its full of sand...maybe. The things on the 4.0 go bad, the 4.0 itself doesnt. (except 0331 head)

 

[Dyusik]

Oil pressure sending unit comes out, and on you neighbors grass revv the engine. Use a bottle brush if you like. Those passeges are known to clog, and give false low readings. Mine runs just shy if 60, hot at 2k rpm, and 18-19 hot idle running a 5w40.

 

[rjundi]

Use a heavier oil and make sure OCI is 3000 miles max. The carbs were terrible on these engines and the emmissions system a nightmare. The oil is likely getting diluted by all sorts of junk, unburned fuel. I owned a 1986 CJ-7 and it was primitive at best and thankfully my last carb'ed vehicle.

Are there actual lifters in a primitive push rod motor like this? Maybe a different mechanic and an old one!?

 

[SwampSurvivor]

5w-10 oil? Is that even a thing?

I'd run any conventional 5w-30 all the way up to 10-40 in the 258; they aren't a picky oil. I would not run a 20w-40 in a 258 or 4.0 ... many do but it is not ideal. The engines don't lubricate the cam / lifters well unless running at operating speed - that's ahy many of them suffer from sludged / stuck lifters. a 5w-30 is going to treat your cam bearings and lifters a bit better. A 15w-40 is going to be nicer to the top end than 20w-50.

I can't imagine the oil would cause backfiring.

 

[JoPeter]

@Miller88:
Thanks for bringing up the typo, typing half asleep @ midnight: originally posted 5w 10 synthetic Mobil. I am wrong.
It is 5w 30 for sure.

Lessons learning..old 258s tend to not like synthetic oil, may be too less viscous compared to conventional.
1) I am sure u heard lot of folks run Rotella 15 w 40(which is a diesel oil) on these oldies. Is this thicker than a conventional petrol engine oil with same viscosity index?
2)or a diesel engine oil like Rotella with comparatively more ZDDP can cause more sludge and probable cat damage, at least in theory?
3)Could a thin oil can cause low compression in cylinders? guess thin oil can help with loss of compression with in and ex valve problems?

Thanks

 

[kschachn]

So are you saying a synthetic oil of the same grade is thinner than a conventional oil?

Originally Posted By: JoPeter
Lessons learning..old 258s tend to not like synthetic oil, may be too less viscous compared to conventional.
1) I am sure u heard lot of folks run Rotella 15 w 40(which is a diesel oil) on these oldies. Is this thicker than a conventional petrol engine oil with same viscosity index?
2)or a diesel engine oil like Rotella with comparatively more ZDDP can cause more sludge and probable cat damage, at least in theory?
3)Could a thin oil can cause low compression in cylinders? guess thin oil can help with loss of compression with in and ex valve problems?

Thanks

 

[SwampSurvivor]

A 5w-10 would definitely cause some issues in an old 258!

Rotella 15w40 is going to be the same at operating temp as a 10w-40 motor oil or 5w-40 motor oil. The difference is, the diesel oils (it's really dual use gas/diesel) have a bit better add pack and addtivies that are specifically better in these older, flat tappet cam engines.

 

[JoPeter]

@RJUNDI:

Thanks for taking time to help me out.
I am hearing from many use thick oil:

which one : conventional 15 w 40 (no synthetic, too thin for this old) or diesel oil Rotella 15 w 40
U probably gave me a great advice.. old mechanic who also know a bit about carbureator too.
The one or 2 i went are new guys familiar w sensors and OBD diagno.
Also I am thinking and hoping change to a thicker oil asap...but should I wait till compression test and timing check w a light ? thinking if i need to take off head then drain oil and all again.

 

[JoPeter]

@ kschachn:
Thanks for bringing this up.
I did not want to type and guide anyone to wrong conclusions.

At same viscosity, I am advised synthetic do not have "shear" capabilities like conventional ones or diesel oils.

Please correct if I am wrong?
If iam wrong, then I dont need to worry about conventional & I can just goes with my eyes closed to synthetic on my oldie which has more OCI?

 

[JoPeter]

@Miller88:
Thanks and convincing answer for Rotella which I am leaning to. Good objective reason which I was looking for diesel vs conventional at same rating.
If you heard anywhere or have any experience with Rotella causing cat damage because of ZDDP and other additives ? Many have vouched no problems , though in theory it says with diesel oil use.

 

[JoPeter]

Originally Posted By: rjundi
Use a heavier oil and make sure OCI is 3000 miles max. The carbs were terrible on these engines and the emmissions system a nightmare. The oil is likely getting diluted by all sorts of junk, unburned fuel. I owned a 1986 CJ-7 and it was primitive at best and thankfully my last carb'ed vehicle.

Are there actual lifters in a primitive push rod motor like this? Maybe a different mechanic and an old one!?


my mechanic said 4.2 has flat tappet lifters

 

[SwampSurvivor]

Originally Posted By: JoPeter
@Miller88:
Thanks and convincing answer for Rotella which I am leaning to. Good objective reason which I was looking for diesel vs conventional at same rating.
If you heard anywhere or have any experience with Rotella causing cat damage because of ZDDP and other additives ? Many have vouched no problems , though in theory it says with diesel oil use.


Does it even have a converter? Unless it's burning massive quantities of oil the ZDDP will likely never affect it. Plus, it's carbureted, I'm sure it will burn out the cat from overfueling long before it burns it out from ZDDP

 

[JoPeter]

Originally Posted By: Dyusik
I had a mechanic tell me that vvte will never work unless I use 5w30. This in mind manufacturer recommends 5w20. I run 5w40, and would not hesitate to run 60wt oil if I had to, in the winter. Like always, it's not oil. Carb, bad fuel, loose anything. Oil can mess this engine up if its full of sand...maybe. The things on the 4.0 go bad, the 4.0 itself doesnt. (except 0331 head)

Hey Dyusik,

Thanks for replying.
The PO used to "play in the mud" in his own words. He never knew when he changed oil or what type. "just grab whatever cheap on the shelf. Its old". But no sand inside hood and most likely in engine. It was running fine.
I am guessing 5w30 was not a smart choice to begin with for me. But a lot of guess working makes me think it has something to do with cylinders, so looking to get a compression test done.
Will get back to you after that.
I don't have that 0331 head?? Is n't it for newer. U mean prone to cracking.

 

[JoPeter]

@Miller88:

Cool.
I have to go down and look at it in evening. I am new and learning..
I think yes, but will confirm if there is a Cat right before muffler.
Even if to replace myself is not that is expensive compared to a engine probs
Thanks
Rotella I am going to get today

 

[JoPeter]

Originally Posted By: Dyusik
Oil pressure sending unit comes out, and on you neighbors grass revv the engine. Use a bottle brush if you like. Those passeges are known to clog, and give false low readings. Mine runs just shy if 60, hot at 2k rpm, and 18-19 hot idle running a 5w40.

Thanks!
This one I am going to come to u again after getting to the bottom of that idling and missing problem.
I am new to mechanical.. But a good physical therapist lol Never thought i could change oil and take off valve cover or spark plugs..lol
Before changing oil pump, i will def be at sending unit. I am glad I came to this forum with helpful people. Either my friend & myself could do with sound advices from experienced folks here or even if I go to a mechanic, I am well armed with knowledge so I wouldn't be taken for a ride)

 

[JoPeter]

@Miller88:

How you edit ?
How to get this forum on iphone . i am on laptop & iphone will come handy
Thanks

 

[JoPeter]

Originally Posted By: crazyoildude
joseph Did you do a compression test you could have a piston problem or maybe you broke a rocker arm/stud or a valve spring that could cause a bad missfire also. Take the valve cover off and look to see if they are all intact then start it and watch them and see if they are all doing the same thing at different times of course


Thank You crazyoildude.
All this time, it is mostly shooting in the dark. change this or that.I really want to get to the bottom of this problems and fix for good. All these advises help a novice like me who is not mechanically skilled or not exposed.

Very sound advice. My friend is away and I have never done a compression test.
1)How much a compression tester cost or any decent brand to suggest?
2) If I go to a decent mechanic( many hawks in Brooklyn), any idea the price for compression testing
I am going to ask around with friends , Iam sure someone might be able to help me w this.

Also going to get a timing light from Harbor Frieght, Have a friend who could check that.

3) Would be best to hold off with putting a thicker oil until i do compression test, just in case if i need work w pistons or valves, this is a waste?

I did open valve cover and looked at those things on top(rocker arms) they are moving good like in a pattern of waves up down. nothing is stuck.

Well .. let me get that compression test and go from there

4) Also a bad muffler can get this idling issues.. ?

Thanks

 

[Dyusik]

Mo the bad head was early 2k 4.0, and most jeeps I see run sale oil to 300k+.

Here is food for thought,10w30 is thicker only at colder temps, and is usually 1cst thinner than 5w30 @ 100celsius.
If you want add pack delo is the way to go with boron out the ahem. I never buy into the whole oil ruined my engine stuff, because there are a lot of people running 30 40 wts with lucas hdos thickening it to beyond 60 and 70 wt oils. Cars dont blow up, just become sluggish and sooper quiet