1979 F-150 What Oil?

[Popple]

Hello, I have just acquired a 1979 F-150 4x4 with a 351M, I found documents in the glovebox that the motor was rebuilt in 1990 at 90,000 miles. The truck now reads 32,000 miles so I don't know how many miles on the rebuild. I bought the truck from a local who bought it at a dealer auction about 5 years ago, he has not driven it much at all in the past 5 years, he used 10w40 but didn't drive it in winter. I have searched the posts here but still am not sure what I should do as my situation is a bit unique. I will only be driving the truck about 3000 miles a year, mostly hauling firewood and going to the hunting shack. Most of these miles will be on dirt roads, and our weather here runs from 90+ in the summer down to -50 in the winter, I won't be driving the truck if it's that cold though

My questions are:

What weight(s) oil should I be running in the truck? I assume I should change the oil in the fall and spring to get the best weight for the seasons. I know that I won't have many miles on each oil change but that's fine with me, I don't mind doing it.

Should I be using dino, blend or synthetic? The truck leaks a bit of oil, will need to add some often.

What brands do you guys recommend, does anyone else with a similiar climate have anything that works good for them?

I am also going to change the differentials and NP205 transfer case fluids (tcase is leaking a bit), any suggestions there?

This is a great truck in very good shape, I want to keep it running as good as possible. I also am not very concerned with oil costs as I will not be changing it often, just want to use whats best.

This is my first post, I also posted this question on the FTE (Ford truck) forum, I figured the more opinions the better though!

Thanks in advance!

 

[JohnnyO]

The motor ought to have 42,000 miles on it then. I would use Havoline or Pennzoil 5w-30 in winter and 10w-30 in the summer, or any blend would be fine. Mobil 1 if you ARE going to drive it when it's that cold.

I'd use synthetics in the diffs and t-case, either Valvoline or Mobil 1 but only because of the cold and you won't change them often, if at all again.

 

[TallPaul]

Synthetics in the differential, t-case, and transmission are a great idea and, since these stay in for a long, long time, might as well go all out and use Redline. Some of the Redline ATF has better antiwear (GL-4 level) than Mobil 1 ATF (I called and their tech said they are not rated by GL but if they were, at best it would maybe be GL-3, which is about half the antiwear of GL-4).

 

[OffOrWFO]

I have a similar truck and I run Rotella 5w-40 syn in it. It's a group III syn not a real POA. I buy it at walmart for $3.89 a quart I think. Also has more ZDDP antiwear additives because it is a diesel rated oil -something that non-roller cams really like. It's the cheapest 5w-40 that I could find because I couldn't justify running a $5 oil when it gets burned up in 1000mi. I live in Co and it gets cold but not like in Mn. So maybe 5w-30 might be better as long as you only run it in the winter. I have UOAs to back up the fact that M series engines don't like 30weight oils in anything more that 60deg weather.
I run redline all up and down the driveline in my trucks. 75w-90 in Tcase and front axle. 80w-140 in rear axle because I pull hard in the summer. Any leaks in the NP205 should be easy to fix. If you dunk your running gear in creeks regularly I would skip on the syn cause you'll need to change it alot more often. Also any syn like redline will cause small seeps to get bigger.
FTE is has a lot of good info over there but I have seen a lot of misinformation about oil there.FWIW

 

[JHZR2]

do as OffOrWFO suggests... That was going to be what I posted as a suggestion.

JMH

 

[Popple]

Thanks for the info. Would you recommend running the Rotella 5w40 year round? Also what temps is this oil good for? I am sure I won't be driving the truck under -20. Do I need to worry about the engine leak problem getting worse with the synthetic oil? Thanks again, I really appreciate the input, with so many options out there for oil it gets kind of overwhelming.

 

[OffOrWFO]

5w-40 would be fine at -20. I run 5w-40 year around and chose the oil for that reason. You could run 5w-30 in the winter and 10w-40 the rest of the year if you don't mine changing it more. Your leaks could get slightly worse with a group III syn, but nothing like a groupIV+. Group III is basically a highly prosessed dino oil with some real syn added with the additive package so it doesn't have as much of a tendency to leak. I had a slight rear main leak, you know the kind that never hits the ground, and it didn't get any worse with the rotela syn but yours may react different.