1976 GMC SIERRA

[RHALL]

I’m going to make the oil change with Delvac 1300 15w40. What OCI should I do on this 350?

 

[Fabulous50s]

I’m going to make the oil change with Delvac 1300 15w40. What OCI should I do on this 350?

What did they put in it when it was serviced recently? You said 40psi oil pressure.

15w40 may be a bit on the thick side if this is a decent engine, which it sounds like it is. I have a 79 C-30 with a pathetically worn out 350 that is a dually with PTO hydraulic dump. I put Rotella T4 in it, change it whenever I feel like it...maybe every 2 years. Gets about 500 miles a year put on it hauling trash to the dump and firewood to the house.

 

[ripcord]

I’m going to make the oil change with Delvac 1300 15w40. What OCI should I do on this 350?

A carburated motor tends to be a bit harder on the oil. I wouldn't go over 5k miles on it were mine.

 

[RHALL]

What did they put in it when it was serviced recently? You said 40psi oil pressure.

15w40 may be a bit on the thick side if this is a decent engine, which it sounds like it is. I have a 79 C-30 with a pathetically worn out 350 that is a dually with PTO hydraulic dump. I put Rotella T4 in it, change it whenever I feel like it...maybe every 2 years. Gets about 500 miles a year put on it hauling trash to the dump and firewood to the house.

I noticed 40 psi on my drive home around 55 mph. What’s frustrating is that everyone that knew anything about this truck is dead! I’m pretty much on my own with this one. I have no idea what oil was used. What I can tell you is there is no exhaust smoke whatsoever on startup.

 

[ripcord]

I noticed 40 psi on my drive home around 55 mph. What’s frustrating is that everyone that knew anything about this truck is dead! I’m pretty much on my own with this one. I have no idea what oil was used. What I can tell you is there is no exhaust smoke whatsoever on startup.

I wouldn't worry about what oil was used in the past. Any kind of oil you can buy today is superior in every way to what was available back then. I would just change all the fluids, give it as good a tune up as you know how and drive it with a smile on your face.

 

[CleanSump]

1974 Chevrolet Light Duty Truck Manual
http://www.mediafire.com/file/dcbsu...Chevrolet_Light_Truck_Service_Manual.pdf/file
You are welcome.

 

[blufeb95]

1974 Chevrolet Light Duty Truck Manual
http://www.mediafire.com/file/dcbsu...Chevrolet_Light_Truck_Service_Manual.pdf/file
You are welcome.

View attachment 149472

Old viscosity charts that date before the early 90s or so though, aren't the most useful thing since the meaning of the W rating has changed so radically over the years. Nowadays there's not a whole lot of difference between 10w30 and 5w30, back then 5w30 was only recommended at cold temperatures because they were using a very poor quality solvent refined based oil loaded with pour point depressants and VIIs that were not shear stable and probably had an HTHS viscosity that would fail to meet in 20 grade by the todays standards that were adopted in the early 90s.

 

[Egg_Head]

This group is a great source for do-dads that need replacing, enjoy!

https://www.lmctruck.com/chevy-gmc-truck-1973-1987

 

[cheesepuffs2]

OCI depends on how much you'll be driving it in my opinion. If it's going to mostly sit and be driven on the occasional Sunday when the weather is nice, then I would only change it once a year.

 

[UNC054]

Drove a ‘79 GMC Jimmy 350SB throughout highschool, put 10w40 in it and AC Delco or Napa Gold filters.