FordSeriesF

I have a '98 F250 LD 5.4 with 100K.. just had my PCV valve changed out and Marvel Mystery Oil added to my last oil change with 5W 30 weight oil.. I was getting about 14-14.5 mpg and now I am getting 15.77 mpg! I need to get the plugs changed soon...hoping to break 16 before long.

Jacob.P93

Dang man I don't get it you have a f250 w/5.4 and getting 15 MPG. I have a single cab short bed 4x4 f150 w/5.4 and I'm getting 14.5

otto457

Sounds like there was some sludge/varnish in the motor, plus you made the oil into a 20 wt so little better mileage there too. IMO I would have just used Kreen instead of MMO but that's just me. Just remember mileage has several factors so citing one source of the gain isn't always the best.

FordSeriesF

We'll see on next fill up but so far the needle is about where it was last time based on the number of miles I have driven. I also try not to drive above 75mph on the highway.

FordSeriesF

Probably because I have a 2WD? Don't know. All depends on driving habits I guess.

Jacob.P93

Its just crazy the dif in wieght and you're doing better than me. And I don't get on the highway hardly ever. I really never get about 65.

FordSeriesF

Well my highway/city driving is about 50/50 I'd say. The 98 F250 LD looks like an F150. It is slightly heavier I'm sure but don't believe there to be much of a difference in fuel consumption.

Jacob.P93

Is yours extended cab or 4 door? Long or short bed? I have the lightest f150 there is only thing I have that does take power is 4x4. My friend had an f250 single cab long bed 2wd w/5.4 my truck just long bed and f250 and he can't even think about keeping up with me. Does that mean he is way heavier than me? And what is the pcv valve is it costly to change? did it go bad then you changed it? Or did you just change it? Do you run marvel mystery in all oil changes or just one every so many miles? Sorry for all the questions man I want my rig forever would you recommended switching to 5w 30?

FordSeriesF

I have an extra cab and I have owned it since December... I used 5w 30 oil because I thought that's what the manual said to use. I have also heard 5W 20 is ok to use. Since Marvel Mystery Oil is thin I figured it better to use the 5W 30 anyway. I put a full quart of MMO into my last oil change. The PCV valve is very cheap and easy to replace. Under $10.

Jacob.P93

Thank you for the help sir.