I've always run valvaline 10w30 in the winter and 10w40 in the hot summer evey 3-4k. I bought 5 cases on sale for $.69 a qt and am about out. (That stuff is normally $1.69/qt) I got 200k out of my 4.9 while driving like a bat out of hell and pulling a trailer frequently. They're good long running engines, so 200k isn't an accomplishment to me but I pulled her still running fine with time left on the clock.

Now that I have my 351 I still expect 150k+ out of the engine, but I noticed Walmart has Mobil 1 fully synthetic 10w30 for $17.88/5qt ($3.57/qt). Seems like a steal to me compared to $5 a qt but is it worth it? I've heard your supposed to stick with synth. once you run it. Any validity to this? Any of you guys run Synth and see an improvement? Is it worth the extra $1.88/qt ($13/oil change)? Seems like it oughta be, but I'm just a tightwad. Anything seems like a lot when Im used to $.69/qt oil, compared to $30/change. I just need somebody give me the OK.

Theres just something about somebody elses approval I guess.

 

Personally...I don't like the stuff. I've tried switching to it and all it did for me was expand the seals and cause oil leaks. I've stuck with Valvoline through the years in my cars and never had an oil-related problem.

 

Full synthetic doesn't really do anything to the seals, but if the seals are starting to dry out and leak anyways the synthetic can leak through easier. I don't think you have to stick with synthetic, i know people who run conventional oil, but buy the synthetic when it's on sale. I think that synthetic is good stuff but it's a little too expensive for me so i run Castrol synthetic blend. I change my oil every 2K anyways so i could probably run anything without having problems.

-Jon

 

I switched to Mobil 1 about a year ago and I noticed my truck running smoother and getting slightly better gas mileage.

 

I've also heard you can go 6k+ on synthetic. The reason given is that on natural oil the molocules vary in size. As the smaller molocules are worn down, the larger molocules that are left cannot lube all the tight fitting areas. Since synth is consistently the same size (smaller) it can remain a viable lubricant longer. Perhaps this is why it can leak easier, although I agree that a properly sealed engine will not.

Any thoughts on this?

 

I've been using Mobile 1 synthetic ever since i dropped my rebuilt 5.0L in.
I wanted to use an oil that wouldn't breakdown as easy as convetional oil.
I need all the protection i can get ....302 pushing 40's