I have been told not to put synthetic oil in a M38A1

Deadguy · Post by **Deadguy** » Wed Jun 15, 2011 10:04 pm

I hear it makes all the gaskets leak. The engine is rebuilt new, the tranny, transfercase, and overdrive are all rebuilt by Novak conversions. So, that probably means the gaskets are a newer, better quality, right?

Post by **wesk** » Wed Jun 15, 2011 10:19 pm

You've been BS'd.

Full synthetics are a lot slicker then semi-synthetics which means they can sneak out through smaller openings then the semi's. The real issue I have with full synthetic oil is it's cost does not justify it's use in a 50 year old engine. It is a great oil in a modern close tolerance engine driven daily. It is pure overkill in any 1950's engine. The touted long oil change periods are useless on these engines that will never make the mileages in 10 years or more that the full synthetic oil is designed for. Generally it is the calender limit of 6 months that forces us to change our oil at least once a year. Any quality semi-synthetic oil is more than adequate for your jeep at 1/3 rd to 1/2 the price.

oilleaker1 · Post by **oilleaker1** » Thu Jun 16, 2011 6:20 am

After considering the input on new production oils, if your motor isn't broken in yet, I'd simply run Rotella T 10-30 or 15-40. They have taken the breakin zinc out of most oils and your cam and lifters go flat. Rotella is supposed to still have it for the diesel truck application. Wallmart sells it in 2.5 and 5 gallon containers at a reasonable price. The racing offroad oils still have it too. If you cover the offroad part with your hand while you pour it in, you are good to go!!!!

John

TomM · Post by **TomM** » Sat Jun 18, 2011 7:11 am

I have run my 89 Chevy S-10 since new to 300k miles using synthetic oil and regular oil changes. Was the oil the reason? Probably no but it was a part of regular maintenance.
For the jeep I run normal oils and I am sure it will never wear out in my lifetime.
I did change my GPW oil once with a Mobil 1 synthetic because it was on the garage shelf at the time. The result was a significant rear-main leak when heated and driven long distances. The oil was slick enough to sneak by the good seal. When I changed back to mineral the leak stopped.
The bigger threat to these old vehicles may not be wear from miles, its more from oil contamination due to moisture, condensation. Changing the oil or driving a lot of fully heated miles is the only way to keep things clean.