Sdillon

I have a 2005 fx4 f-150 I bought in February of this year with 138k miles and have already put 10k on her. Bought it from a personal owner that's kept the synthetic blend oil in it. When do you know to go full synthetic?.

PerryB

Personally I run the recommended oil in mine, 5w-20 semi-syn. In the summer I use 5w-30 semi.

Martian

There is no "when to go full synthetic". You either choose to or you choose not to. If there was a set time to, it would be in your manufacturer's maintenance documentation.

grss429

no but it does play a big difference... if you use synthetic at say 140k.. it could cause you all kinds of issues.. I.E all kinds of leaks, and other things due to the other detergents

Martian

The detergents are the same as those in conventional and semi synthetic. You need to use the search function on this forum.

BeerCan

That is some kind of myth that has lived on, but it is not true.

ModelAMike

As said here, it's all a matter of personal preference. IMHO, Mobil1 (full syn) out performs Dino oil or the blends. First a disclaimer, I know nothing and I'm not technically competent at anything. Okay, In June we towed to Maine with a fresh fill of Motorcraft 5w20 synthetic blend. It was a good trip, but I felt that the 5.0 didn't give it's all. So, 1,900 miles later we changed to Mobil1 5w20 full syn. extended performance. On the ride back, we got better mpg and the truck climbed those baby mountains better. In the past, we put 360,000 miles on a 1997 F250 5.4 without a hiccup using synthetic. Maybe, there isn't an iota of difference.

7thSeal

No, full synthetic is compatible with conventional oil. You can change back and forth any time you want. Its just deciding what synthetic oil offers over conventional oil and whether you need it for your particular engine.

kenv47

If the truck went all those miles with synblend, there`s no reason to think that it won`t go another 100k with the same oil.

ModelAMike

Absolutely correct in IMHO....