Originally Posted by GI-Jeepin'

Ok, lets get this straight, i am no lilttle punk by any means. I am 39 with 21+ years on active duty in the Army and im still in. Now for 15 of those years i was a turbine mechanic on M1 tanks. I have also been heavily involved in drag racing since i was 9. Lately, i have been wrenching on friends short course off-road racing trucks. I like to think that i know what i am talking about. What i told the OP was that its unwise to mix or go back and forth, not impossible. Ultimately, its the owner's choice, hence your jeep, your engine, your choice. No facts required, it is simply your choice.

Originally Posted by GI-Jeepin'

Synthetic oils are manufactured so that their molecules are of a finer grade and are consistent in size. This is what keeps additives like detergents active for far longer than mineral oils. This is the reason why high reving or ultra high compression or Turbo Charged performance engines require synth oil.

Now, Mineral oils are pumped from the earth and after the refining process, the molecules are inconsistent in size, this can't be helped. This inconsistency is what leads to the breakdown of cohesion between the base oil and the additives. It is this inconsistency that requires users to change their oil at regular intervals. Also, on high mileage engines running with high mileage mineral oils, sludge and dirt deposits will gather at 90 degree corners in the oil galley's and around seals that have areas that hold and trap deposits. When this oil is removed and replaced with Synthetic, it's modern, more effecient oil detergents and other additives will eventually remove and or loosen these deposits. The results "MAY" lead to oil leaks or seepage due to the finer grade of molecules in the synth oil washing away the deposits in and around the seals. Synthetic oils have come a very long way in recent years, but mineral oils have not progressed as far. It is a fossil fuel. You can stuff all day long and it is still a fossil fuel.

Of course, you may get lucky and have no ill effects when you make the change, then again..... It's a gamble we all take when we change something on our vehicles, whether its a jeep or a bicycle.

So, PWB, to answer your question, No there is not any documentation that says you cannot do it. It is your choice. However, you live in Norway. I have never lived anywhere near as cold as what your winters are like. If it were me and I lived in Norway (that would never happen though, I am from Puerto Rico, shopping in the frozen food section is a winter sport where I from!) I would run full synth because of the cold. Synth oil is less effected by the extreme temp change that occurs in an engine in cold climates. Your engine can go from -15 F to 240 F in a matter of 15-30 minutes. But thats just me.

Originally Posted by No4x4Yet

Im sorry if you thought I was calling you out. I WAS NOT! and did not mean to offend you. I was just saying that I dont know you and Im not gonna take a strangers word over the internet on a highly debated issue, with out a lil something to back it up.

I my am a mechanical engineer, I certainly dont have the experience you do but I like to know the facts before blindly taking someones word.



From what your saying here it would be bad to start using synthetic after running mineral oil for years, which I completely agree with for the reason you stated. However that doesnt mean its bad to go from Synthetic oil to mineral. On an older engine this could even help stop leaks. It may even run a lil better with a thicker mineral oil tightening things up.