40 or 50 weight for truck

[partsman]

I have a 77 F-250 2 wheel drive 400 engine, thinking of either 10/40 or maybe even going to a 20/50 due to it being an older truck and I do tow in the summer with it.
any advantage of the 40 over the 50 weight?

 

[TallPaul]

Well, I would run a 15w40 HDMO like Valvoline Premium Blue or Shell Rotella in summer. Wouldn't go to a 50 wt unless I had very good reason, say low oil pressure maybe.

 

[Quest]

lol! Poco area? HOw's da weather today? DTown is jus overcast....LOL!

Unless you are having some bearing clearance issues, otherwise, go with some HDEO 10W40.

Q. (yes, I work in DT)

 

[Dad2leia]

Better flow characteristics with a 40 weight as well. I agree with TallPaul on the 15w40 grade, but not necessarily the oil, but I havd used that in the past. Has a robust package, and works well.

 

[partsman]

Okay, oil pressure on start up is 80PSI, dropping to 20-25PSI when hot, blip the throttle and she jumps up to 65, so I feel the pressure is good and where it should be.
Just thought if 40 was good, maybe 50 would be better, so I guess I will pick up 15/40 on the way home tonight.
Weather is overcast, pretty heavy rain at 5:30 this morning, but now it is dry.
Thanks for the feedback.

 

[TallPaul]

Yeah, thats good OP 20-25 idle hot and 65 at speed hot.

You should do better with HDMO as it has more antiwear additives like zddp and the 15W represents a thicker base oil which will do a lot for maintaining viscosity in the bearings.

'77 F250 is a nice looking truck. I had a '77 F150 when I was a kid (20 years old). Kept it 7 years.

 

[partsman]

This is a picture of the old beast.

 

[TimVipond]

Actually, I believe Ford now recommends 5W30 for all temperatures for that vehicle. At least they do as far back as 1980.