Oil question

[Jscott]

Bought a j 2000 with 43k miles. Old full size pickup (1972) . Running rough but low miles. Changed oil to Mobil 1 and didn't help. (valve clatter) idle rough, no power. changed plugs, oil, and played with timing. changed oil to 20/50 racing because of the added zinc (advice from someone else). started smoking like a train after seafoam and noise got worse. changed oil again and still bad. (black oil drained after seafoam) took valve cover off and found a broken rocker. $14 rocker arm and 2 pushrods later it is perfect. Runs like it came off the showroom.. Question: should I go back to Mobil 1 or keep running 20/50 with zinc (offroad)

 

[Jeepergeo]

IMO, Mobile 1 is best when you want extended mileage between oil changes. If you run in the dust and dirt much, you won't want extended mileage because the oil will get dirty whether or not it is conventional or synthetic. So if dirt and dust are in your Jeep's future, I'd go with conventional oil to cut cost and then change the oil and filter regularly.

 

[JohnnyO]

Low-zinc oils are meant to keep from contaminating catalytic converters, which your '72 Jeep would not have anyway. Zinc however is good to run on older flat tappet engines. Mobil 1, in my opinion, is somewhat thin for older engines (yeah, I know oil weight is oil weight but there is a range within it) and I've read where people report more valve noise with Mobil 1 even on newer engines. 20w-50 might be a little too heavy simply because your truck probably isn't going to run at all that high a temperature. If it were me I would use a diesel-rated 10w-30 or 15w-40. Diesel-rated oils have more zinc in them, also high-mileage oils have slightly more zinc than regular oils. At the moment I have Shell Rotella T-5 10w-30 in our '97 Wrangler and will get a used oil analysis when I change it.

In a nutshell, for older vehicles you are better off running either a diesel-rated 15w-30 oil or a high-mileage 10w-30 even if the engine does not have high mileage.