what weight oil to run?

[cp2295]

I got a 98 4.0 ohv. pulls 19.5" Hg at idle with 155k on the motor. I currently am running 5w-30 mobil 1 full synthetic and according to the dipstick i have not lost any oil in 2,500 miles. I got all new seals and gaskets on the motor (even the heads). So this is not a concern of running thicker oil to stop leaks, just want to know whats better. Summer is coming and i just wanted to know if running 10w-40 would be better since i go mudding and trail riding too, so the engine will be revving up high sometimes to get me out of situations. Again i will be running Mobil 1 full synthetic with a motorcraft filter.

How long between oil changes also? i was told with full synthetic i can go 10k between changes.

 

[veefer800canuck]

For summer use, 10w40 would work fine.

Here in Alberta, I use 0w30 in the winter when the temps are consistently below freezing.

In the summer, I usually use 10w30, our summers rarely get above 90f

 

[cp2295]

Yeah here in the pacific nw winter stays at about freezing every morning for dec-jan. I just run 5w-30 then. That 5w-30 full synthetic just seems to slippery in the summer though.

 

[adsm08]

5-30 is what these engines were designed to have. It should be just fine for summer use.

Ford says 5-30 is good in the 4.0 from about -20 through 110F.

 

[SenorNoob]

5-30 is what these engines were designed to have. It should be just fine for summer use.

Ford says 5-30 is good in the 4.0 from about -20 through 110F.

This.^

I made the mistake of trying 10-30 in a 2.3 during the winter and ended up changing the oil again in like 100 miles. Sooner if it hadn't been for work. Sounded like someone had thrown bb's into every cylinder for the first minute or 2.

 

[bmerr98]

Yeah, I just keep the 5w30 in it year 'round. Seems like changing weights = changing the amount of "cushion" your moving parts get from your oil. Sure the ambient temperature varies greatly from summer to winter, but normal operating temperature for your engine is pretty consistent no matter what season, providing the cooling system etc is working properly.

 

[Dune Runner]

Stick to the 5w30 and you could go 10w30 in the summer. No reason to go 10w40. Your engine was not designed for thicker oil. Stick to what Ford recommended for it.

 

[hilltopfarm]

^Second that, stick to what Ford recommends...