Synthetic after Long Use of Dyno?
 

My Road King has about 70K miles on it. I bought it new, and have done every oil change with HD MoCo Dyno oil. At first I changed at 150, 500, 1000, 2500, and ever since I never have gone over 2500 miles between changes. With that said, I read a few threads in various places that said 15W50W Mobil 1 was good, and that a lot of folks are using it. I can buy it in a 5 qt container at WalMart for $26, and that's less than HD Dyno Oil. I'm thinking about switching over to Synthetic. Anyone got any reasons not to? I haven't had any kind of oil leaks or problems with the current MoCo Dyno oil, and some folks tell me I have to worry about leaks with the synthetic. Why? Please PM me if more convenient. I already posted this in the Touring Section, but thought I'd try here as well, to get as many comments as possible.

Personally, after 70k I would not switch to a synthetic. The seals in your engine are used to dino oil chemistry. Besides the HD 360 20w50 is more shear stable than Mobil1 15w50 which will shear to a 40w very quickly. HD Syn3 is a GroupIII synthetic which is made from a dino base oil and would be a better bet but is expensive. Brad Penn oil is a dino oil that you can get by the case for about $5-6/qt. It has a high amount of anti-wear additives and would be a good choice for you as well. Look them up at www.bradpennracing.com and call them to find a local distributor.

Seals in modern engines don`t get "used to" any type oil.
These seals are fully compatable to Dino or Synthetic oil, you won`t have any problem if you change to synthetic oil.

Shear is something that happens to lubes that are used in gear systems, it is what happens to the polymers used in making the oil multi-weight. There are less of these polymers used in synthetic oil, which would make them more shear stable.

Any modern oil with the correct weight will be fine, don`t beat yourself to death over oil, no matter what you use, the engine will look the same after 100,000 miles when you tear it down.

Thanks for the input guys, much appreciated.

I have 3 clients in my business that are all major tier one automotive gasket & seal manufacturers. The engineers there have advised me to stick with whatever oil you are using (synthetic or dino) after you have used it about 30,000 miles. While all oils are compatible with seals the materials chemists have told me that in fact your engine seals do get some effect from oil chemistry over time. So, I'll take their word for it.

The Used Oil Analysis done by some of the members here have shown the Mobil1 15w50 sheared to a 40w within 1-2000 miles. Oil shearing does happen in your engine as well.

Good info, thanks.

I was always under the impression that if you switch to synthetic oil after using Dino oil it would start to pull the carbon particles away from the motor seals and cause it to leak. I'm not a mechanic, I just ride the sob.

If it isn't broke don't fix it. 70k why change now, just continue doing what you do, seems to be working. Maybe send in some oil to blackstone for a UOA.