Best time to swap to Synthetic

Bro I work in a shop repairing diesel and gas engines. I see people come in and tell me everything you just said. "I used heavier oil for my internals cause a buddy said it would be okay". If you are using heavier oils for your internals, I am pretty sure your seals are all ready bad, and yes it will cover plugs. If heavier oil was okay for all cars and applications then can some one explain why dragster, street cars and diesels all use different weight oils? Why stop at 10W40? Use 80-90. Yes heavier oil does cause sludge because it's thicker and leaves residue in your engine and that oil inturns sits there breaks down, collects dirt and becomes sludge. Which is also why there is engine flush. I am in Hawai'i so we don't have offical winter months. I do know the lower the "W" rating the easy the motor cranks in colder weather.
2005 Consumer Reports article discovered that some engines from Audi, Chrysler, Saab, Toyota, and Volkswagen appear prone to sludge almost no matter how often the oil is changed.

 

I worked as a mechanic for a few years myself after getting out of the Navy. Granted this was awhile back before the high mileage oils and synthetics started to get into everyday use. At that time with regular dino oil even if no seal leaks the rule of thumb was to bump up to a higher weight oil, usually the next one up on high mileage vehicles. Low mileage didn't need to unless seal leaks were present. Keep in mind heavier weight oil can get you by until you can afford to have them fixed. Where I worked wasn't a very affluent area so we had to come up with ideas to help people out.

We're not talking about running diesel oil such as Rotella 20w50 or heavier and especially not 80-90 which are gear oils that'd blow a gas engine all to hell. Never worked on diesels other than oil changes so can't speak about them. You're right about the lower weights flowing easier in colder temps.

Different applications require different oils. High rpm i.e, dragsters produce more heat so you'd need a different oil. Diesels work harder than gas engines so I guess that's why they run a heavier oil you'd know more about that than I do since you specialize in them. Just to throw one in, motorcyles use a different oil than cars also. Something to do with the additives in car oil causing slippage with the clutches and transmission of the bikes since the oil lubricates both the tranny and engine. At least with the jap bikes. I don't claim to know everything. This is only what I've been taught and it's served me well. If some of it's wrong then show me and I'll learn it and move on.

Your right about build up on spark plugs I didn't even think about the electrode side. Read over the report you mentioned. I learn something new everyday. I've been out that line of work for almost nine years now and since your still in it and up to date I'll shut up and listen like a good boy. Have fun in Hawaii. Had some buddies based in Pearl, they loved it. Maybe I'll get out that way someday.

 

I have a 08 v6 with 55000 on it that I just switched over to Mobil 1 Exended Performance, The only reason I waited so long, had free oil changes to 40000, I did two after that myself with dino, then just switched.

 

If you make out this way, drop me a line.
As I mentioned earlier different applications do require different oils. Again which brings me back to what I mentioned earlier, about using 10W40, 80-90. If heavier oils were okay there would only be one,and oil companies would be screwed. And yes I know 80-90 is gear oil. The reason is all oils are not created equal. All engines have different demands which uses different minerals, additives, viscosity and so forth.
I don't know everything myself, and like you, we are all learning. It's human nature. Some myths do need to be put to rest. Jerry rigging is one thing, but it will only get you so far till either it gets worse or you fix it, or breaks.
My little brother was in the Navy. U.S.S Abe Lincoln. Coolness bro.