MPETE said:
I think this got missed so I am posting again.
so kaiserjeep, are you saying I SHOULD NOT run the 10w40 because of the additives, or should I just make sure I run seafoam a lil more often to clean out those deposits ?
thanks in advance
I actually think that you can run any grade of oil authorized in the TJ Owner's Manual, which is any multigrade oil with A specified SAE viscosity rating and an API Quality Classification. MOPAR specifies that 5w-30 is "preferred" for 32 degrees F and below, and 10w-30 is "preferred" for 0 degrees F and above. "Preferred" in this case means that these are the grades that maximize fuel economy.
10w-40 is a non-preferred grade that will cost you a bit of fuel economy because it will be thicker than 10w-30 when the engine is hot. It will also make more carbon when your engine is mildly ill and burning a bit of oil, because of the higher amount of multi-viscosity clay additives.
I pretty much follow the MOPAR reccomendations for the first 100,000 miles. In California's mild climate, I run 10w-30 all year. Where I depart from the MOPAR reccomendation is when the engine goes above 100,000 miles. Then I switch to 20w-50 because I think it restores some lost oil pressure and clings to worn bearing surfaces better. Just something my old man taught me - he started running the AMC I-6 engines in the 1960's in Rambler automobiles.
As for Sea Foam, I DO NOT run it or any other additive intended to loosen or remove carbon. Firstly because I believe that any such additive is totally useless for the stated purpose. Secondly, if the additive were to ever start to work as described, then both the pre-cats in the manifold and the rear catalytic converter would be destroyed by the loose carbon. I believe the only way to remove carbon is to remove the cylinder head and use scrapers and abrasives. I also believe that such is only necessary when carbon has built up to the point where pinging happens and the engine diesels after shutoff.
The dieselling only happens on carbureted engines, so that symptom is only found on older Jeeps. But if your engine pings and you can't stop it by buying the next higher grade of fuel, time to disassemble the head and remove the carbon, in a safe procedure that will not destroy the converters.