Oil Recommendation, Cat Converter Protection

Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
My 2008 Wrangler 3.8 has always had a drinking problem, at least since 40k miles.
Sometimes it uses 3/4 quart per 1k miles, sometimes none. Mostly, about 1/2 qt per 1k miles. I had 1 cat replaced at about 100k miles, under warranty. Now both need replaced at 155k. The engine otherwise runs like new.

I've mostly run Mobil 1 oils, 5w20 or 5w30. Occasionally She'll Rotella Gas Truck 5w20, which is in it now. Always 6k OCIs to comply with lifetime power train warranty requirements.

I'm now looking to protect the cats. I'm looking at Mobil 1 ESP oils, particularly 0w/20, 0w/30, or 5w/30.

It is a daily driver (35 min commute) and occasional technical off roader with some lightweight fishing boat towing in the warmer months. (1500-1750lb boat/trailer/gear.)

I'm keeping this Jeep for many many years to come.

I'd be interested in thoughts and opinions on this move and the different weights.
 
Last edited:
Joined
Dec 19, 2019
Messages
2,609
Location
Muncie, Indiana
Ultimately it probably needs new valve seals, you can try to slow the inevitable death of a new cat, but if it's dumping oil right into the cat through a leaking exhaust valve seal any oil is going to kill the new cat sooner or later.
 
Joined
Jul 14, 2020
Messages
60
I don’t understand the info you’ve provided—what’s your oil consumption rate? 3/4qt. every 100 kilometers? Every 100 miles? Every 100,000 miles?
 

JRed

Site Donor 2021
Joined
Jun 1, 2009
Messages
2,592
Location
Virginia
Do you have emissions testing in your part of Indiana? Are you just getting P0420 or is there another issue?
 

IndyFan

Thread starter
Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
Ultimately it probably needs new valve seals, you can try to slow the inevitable death of a new cat, but if it's dumping oil right into the cat through a leaking exhaust valve seal any oil is going to kill the new cat sooner or later.

These engines are well known for using oil, but not for needing valve seals. And I doubt that was an issue at 40k, either, when this started. It also doesn't explain how sometimes it will go several thousand miles without using a drop.

There is all kinds of speculation as to why these burn oil, so that diagnosis is really not what I want to discuss. MANY miles of threads on different forums have produced nothing more than disagreement. The only guy that might have a clue around here about the real story with the 3.8's oil addiction is Kevin @OIL_UDDER but even he might not have the answer.

So I appreciate the input on what might be causing it, but that's a whole other conversation.
 

IndyFan

Thread starter
Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
I don’t understand the info you’ve provided—what’s your oil consumption rate? 3/4qt. every 100 kilometers? Every 100 miles? Every 100,000 miles?
Lol, I'm sorry for the confusion. I typed the original post on my phone and didn't see that I mistakenly put 100k where it should have said 1k, and that I did not say miles. So thanks for helping me clarify. I've corrected the original.

So it is between zero and 3/4 quart every 1k miles. I'd say on average 1/2 per 1k miles. A couple of times over the years it got close to 1 quart per 1k miles, but just not quite, and again, not often. The dealership has said if it gets to 1 quart per 1k miles, they will replace the engine under the lifetime powertrain warranty. But it just hasn't gotten there. For the last few thousand miles, it has been around 1/4 quart per 1k. It really has no rhyme or reason.
 

IndyFan

Thread starter
Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
Do you have emissions testing in your part of Indiana? Are you just getting P0420 or is there another issue?

No, we don't. But it has thrown 2 codes. One was for a catalytic converter (I can't remember the code) and the other was for a lean condition in one of the cylinder banks. It was diagnosed by a highly trusted local shop that knows the Jeep pretty well.

So back to the original question. What are the thoughts on the ESP line of Mobil 1 oils? Everything I read points to Cat protection, which sounds to me to be something that first won't do anymore harm that what I've been running, and second, might actually prolong the life of the cats. I just don't see this thing getting to the point of a warranty engine replacement for a long time. It runs too well and I've been waiting a long, long time to see if it increased and it has not.

I have seen a number of these 3.8's that were oil users that went well beyond 200k miles and were still running well when sold. So I'm not holding my breath on getting to that magical 1 quart per 1k miles threshold for it to be replaced.
 

JRed

Site Donor 2021
Joined
Jun 1, 2009
Messages
2,592
Location
Virginia
It's mainly the phosphorous from ZDDP that kills the cats. Burning 1/2 qt. of M1 ESP is no better than burning any other oil with comparable amounts of P.
 
Joined
Feb 6, 2010
Messages
724
Location
KY, USA
I ran an '88 Escort to 518K miles and the cat was only replaced once in all those miles. If I recall correctly it was replaced right around 200K because of a factory recall but the original wasn't bad then. When I quit driving the car with 518K miles it was using/leaking a quart about every 3-400 miles and as far as I know the cat was still good. I think the car had around 350-400K miles on it when they decided anything older than '96 no longer had to be emissions tested but, the last emissions inspection it had it passed with flying colors and was probably using at least a quart every 1-1.5K miles then. Those were the days of conventional oil with high zinc concentration. With the experience I had with my Escort it makes me wonder if the oil consumption is or isn't what's causing your problem. If so, there must be a difference in the cats themselves. If you're getting a P0420 code it could be that your problem is related to an improper reading from the downstream 02 sensor and it needs to be replaced.
 

IndyFan

Thread starter
Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
Diagnosed a lean condition? PCV stuck open (and sucking in oil).

I've always suspected the PCV and have changed it multiple times. The old ones always appear to function normally and the new ones never impact usage. But I can't help but think there is a fault in the design somewhere somehow. I have thought about a catch can but I think I'd better put a Big Gulp cup for a reservior and I don't think there's room, Lol!

I'll replace the PCV again, for good measure, when I get it back.
 

IndyFan

Thread starter
Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
I ran an '88 Escort to 518K miles and the cat was only replaced once in all those miles. If I recall correctly it was replaced right around 200K because of a factory recall but the original wasn't bad then. When I quit driving the car with 518K miles it was using/leaking a quart about every 3-400 miles and as far as I know the cat was still good. I think the car had around 350-400K miles on it when they decided anything older than '96 no longer had to be emissions tested but, the last emissions inspection it had it passed with flying colors and was probably using at least a quart every 1-1.5K miles then. Those were the days of conventional oil with high zinc concentration. With the experience I had with my Escort it makes me wonder if the oil consumption is or isn't what's causing your problem. If so, there must be a difference in the cats themselves. If you're getting a P0420 code it could be that your problem is related to an improper reading from the downstream 02 sensor and it needs to be replaced.

I'll check that, thanks. I've also heard a number of mechanics say Chrysler cats don't have a great reputation, to begin with. Honestly, I've never replaced a cat on any of the many vehicles I've owned over 36 or so years of driving. This is the one and only.
 
Joined
Jul 14, 2020
Messages
115
My 2008 Wrangler 3.8 has always had a drinking problem, at least since 40k miles.
Sometimes it uses 3/4 quart per 1k miles, sometimes none. Mostly, about 1/2 qt per 1k miles. I had 1 cat replaced at about 100k miles, under warranty. Now both need replaced at 155k. The engine otherwise runs like new.

I've mostly run Mobil 1 oils, 5w20 or 5w30. Occasionally She'll Rotella Gas Truck 5w20, which is in it now. Always 6k OCIs to comply with lifetime power train warranty requirements.

I'm now looking to protect the cats. I'm looking at Mobil 1 ESP oils, particularly 0w/20, 0w/30, or 5w/30.

It is a daily driver (35 min commute) and occasional technical off roader with some lightweight fishing boat towing in the warmer months. (1500-1750lb boat/trailer/gear.)

I'm keeping this Jeep for many many years to come.

I'd be interested in thoughts and opinions on this move and the different weights.
try 0w40 ESP

 
Joined
Feb 6, 2021
Messages
768
Check PCV valve and compression.

no motor should burn a drop

If both are good, try going with a 10w30 or 10w40, or even a 20w50 (if its very warm) gasoline rated motor oil.

itd good to check valve seals, you never know.
 

IndyFan

Thread starter
Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
Check PCV valve and compression.

no motor should burn a drop

If both are good, try going with a 10w30 or 10w40, or even a 20w50 (if its very warm) gasoline rated motor oil.

itd good to check valve seals, you never know.

Compression was checked at about 145 to 148k miles and it was good. I will replace the PCV as soon as I get it back. I have a couple of times run heavier oils but they had no impact on consumption, over time. I did several runs of Mobil 1 0w40 Euro and at first thought it reduced it but it came back again, so same pattern. It never produces any soot or smoke from the tailpipe, either. No more than any of my other engines, which never burn a drop.
 
Joined
Feb 6, 2021
Messages
768
Compression was checked at about 145 to 148k miles and it was good. I will replace the PCV as soon as I get it back. I have a couple of times run heavier oils but they had no impact on consumption, over time. I did several runs of Mobil 1 0w40 Euro and at first thought it reduced it but it came back again, so same pattern. It never produces any soot or smoke from the tailpipe, either. No more than any of my other engines, which never burn a drop.
yeah if compression good, and thick oil dont help, try pcv valve, wont hurt it.
 
Joined
May 21, 2018
Messages
2,676
Location
South Carolina
I've always suspected the PCV and have changed it multiple times. The old ones always appear to function normally and the new ones never impact usage. But I can't help but think there is a fault in the design somewhere somehow. I have thought about a catch can but I think I'd better put a Big Gulp cup for a reservior and I don't think there's room, Lol!

I'll replace the PCV again, for good measure, when I get it back.
Maybe try an OEM PCV. And make sure the breather end is OK too. I had a PCV go bad and oil consumption was erratic.
 

IndyFan

Thread starter
Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
Maybe try an OEM PCV. And make sure the breather end is OK too. I had a PCV go bad and oil consumption was erratic.
I've done mostly OEM. The new one I have is aftermarket. Can't hurt to try both. Will do on the breather end.

But I've done these things many times before to no avail. These things are very well known for using oil. Like I said before, lots of speculation but nobody seems to have nailed it down. Some don't use oil, but it is VERY common.
 

IndyFan

Thread starter
Joined
Jun 16, 2005
Messages
2,014
Location
Danville, Indiana
I think whichever weight I choose, I'm going to exclusively run ESP oil. I'm leaning toward 5w30 right now. The engine specifies 5w20. It's not used any more 5w20 than 0w40 in past OCI's. It has 5w20 in it right now and hasn't used much at all the last few thousand miles.

Are there any other oils that are supposed to be easy on the cats?
 
Top