I am going to change the oil soon as I suspect it has the wrong oil in it and not a MC filter. It has 87000 miles on it, can i switch to full synthetic or will it leak? I have read that the synthetic oil can leak on higher mileage trucks if it wasnt used from the beginning. If no full synthetic I will use the MC syn blend. What are your thoughts? It's an 04 5.4L

 

I have 196000 on my 04 5.4 and swapped to full synthetic mobil 1 5w30 with a MC filter at 180000. No problems..

 

You should be good to go with making the change to synthetic. If you are worried go with a high mileage like M1 HM but you shouldn't need too.

 

Switching to a full synthetic from dino oil (or synblend) use to be a problem "back in the day". Twenty years ago, it would not be recommended to take your 1985 vehicle and switch to full synthetic after 87000 miles. Back then, most people that I knew that ran full-syn did so after new vehicle break-in period. But as others mention, these days, you should be fine (unless you already have oil leaks, of course).

 

Why synthetic? I run Rotella T....... It's for diesels. It has all the detergents that were taken out of regular automotive oils.

 

I have read that running heavier weight oil can cause problems over time. How long have you been running it? I just don't wanna mess anything up.

 

That's not true!

Synthetic from day one was created to mix with and replace conventional oil at anytime. No such thing as problems arising from switching from conventional to synthetic, even 30 years ago when I was a tech who was part of Mobil 1 testing.

 

I bought my truck mid December last year and my second oil change i switched.... So 6-7k on the Rotella....... I also started using Lucas oil stablizer when i switched. Before the truck had that diesel clack at idle...... Now is wisper quiet except for the injector tick.

 

My 98 5.4 F-150 i ran Valvoline Max life 10w-40+1bottle of Lucas in it for 60k miles before i sold it and never had an issue with it.

 

You might want to reconsider that. While you are right it is great oil and will protect better. I believe it has detergents that can hurt your cats.

Go over to bob is the oil guy and do some searching or ask a question. I could be wrong but I think it is zinc that is the problem one.