A little over a year ago I wrote in to see if anybody had experience using a synthetic (like Mobil 1) in these old Willys engines. �As I recall, no one had and a couple of the members advised against it. �Well, not to be deterred, I decided to take on this little experiment after some research. �My main concern was whether or not I would develop new leaks, not whether or not a synthetic would harm the engine. �I have been using Mobil 1 in all of my vehicles and small engines ever since I could afford it which, I guess has been about 35 years or so. �
Prior to the switch, I had a small leak at the rear main - after a long drive I would have maybe 3 drops of oil on the floor overnight. �Also, I had a couple of small drips from the pan gasket. �Other than these drips, all was pretty well sealed up. �
From the Mobil 1 website I saw that their "High Mileage" formulas are what they recommend for older engines as they add "seal conditioners" to them. �These chemicals are meant to "swell" gaskets to some extent. �So, a year ago I put in 5 quarts of 5W30 high mileage Mobil 1 to see what would happen. �I should mention that I started with a pretty sludge-free engine as I had dropped the pan for cleaning and inspection some time prior and had done a couple of frequent oil changes in order to assure that things in the engine were as clean as possible. �
After a couple of weeks the pan leaks had stopped completely, and I still haven't had a drop from them in a year. �The drip at the rear main is still there but only a third of what it was before with conventional oil. �Now after a long drive, I'll go out to the garage the next morning and I have only one drip on the cardboard under the jeep. �Oil consumption is the same as before, using about 1 quart in 1500 miles, but I don't have as much visible smoke on start up, and none at all after warm up. �Compression is also the same as before - 105 psi on each cylinder. �
A couple of weeks ago I changed the oil at 2500 miles or so. �The oil that came out was still relatively clean and had life left in it but I like to change once a year whether needed or not. �It was noticeably cleaner and not as black as oil changes I'd done with conventional oil. �I have to believe I'm getting much less wear of engine parts. �I wanted to see if I could improve on my overall oil consumption so I refilled with Mobil 1 �10W40 high mileage. �Will see in a few months if the thicker formula is of any benefit re:burn off. �I have noticed that cold starts are much smoother with synthetic oil. �And, for those jeeps that run in hot conditions, I think there is less likelihood of the oil breaking down from heat or hard driving.
So this has been my experience switching to synthetic motor oil. �I'm sure there are other brands as good or maybe even better than Mobil 1, but based on what I know now, I would say you want a synthetic with the added "seal conditioners" for an older engine. �Can't vouch for other brands, but in the Mobil 1 "high mileage" formulas, they really do seem to work. �I hope this is useful to those of you who like synthetic but are "on the fence" like I was - a bit nervous trying it in an old 134-L.
