Oil Question

[454cid]

Rotella T6 is not an SAE S (automotive) rated oil. It is only SAE C rated for diesel engines. T4 and T5 the same. If you want the advantages of diesel rated oil in a gasoline engine, it should also be S rated. There are several available.

Rumor is that the formula didn't actually change, just the labeling. It used to be gasoline rated. Another rumor is that it foams at high rpms, but I think that is in motorcycles that run much higher than what an automotive engine turns.

 

[Road Trip]

Thanks for all the comments. I'll switch to the 5W30 synthetic. But I'm still wondering about the rear differential and using the 75W140. My RPO codes from the vin say G80-Rear Axle - positraction-limited slip, G75-4:10 ratio with a MT1- 4sp auto tranny THM R2(4L80E). I'll attach some photos of the differential in hopes of getting some confirmation of what I have there. Also, I see a leak around the Diff/Axle area. I found a TSB# 99-04-20-001 suggesting 88-99 C/K model testing has shown that synthetic lubricant will attack RTV sealant and to use only non-synthetic. Not sure if I have a gasket or RTV and if that is related to the leak I'm seeing. Looking forward to additional comments and an education
Thanks

Greetings Islandwhiteknight,

I happen to have the same 14-bolt under my '99 C2500, so your photos are visual confirmation.

For what it's worth, here's a drawing of the Dana taken from the C/K Factory Service Manual:

You must be registered for see images attach

Once you see a Dana, there's no confusing it with the 14-bolt you got.

Note: Back when your truck was made, synthetic gear oil was new/spendy. Interestingly,
there's a note at the bottom of this page concerning the Dana diff under 'extreme use'
where the recommendation is either changing the conventional oil every 3K miles (not a typo)
or, if you used the 75W-140 GM synthetic, you could extend the oil change intervals to 30K miles:

You must be registered for see images attach

Obviously synthetic gear oils can handle the high heat from sending big power through a 90° turn better than
the conventional 90 wt. NOTE: In a previous life I used to maintain night-vision (IR) Litening Pods
as part of our Avionics package, and after a successful repair/Ops check at night I'd take a look across
the airfield at all the Civilian trucks servicing their airplanes, and I was always amazed at just how clear
and bright the ring & pinion gears would be visibly 'glowing' under the trucks. I don't know exactly
what percentage of hp/torque is left behind at the 90° turn in the diff, but the resulting heat is the
real deal. I wouldn't have believed it if I hadn't seen it for myself. :0)

****

And if you are ever having trouble falling asleep, you can check out what Gale Banks has come up
with to keep differential lube cooler during heavy use:

xc_hide_links_from_guests_guests_error_hide_media

BTW, nice rig. Always cool to see a GMT400 busy earning it's keep like yours obviously is.

And welcome to the GMT400 forum.

 

[OutlawDrifter]

Rotella T6 is not an SAE S (automotive) rated oil. It is only SAE C rated for diesel engines. T4 and T5 the same. If you want the advantages of diesel rated oil in a gasoline engine, it should also be S rated. There are several available.

Rotella produces some of the best oil out there. I've run Rotella in gas engines for almost 4 decades...it will be fine.

 

[Erik the Awful]

And if you are ever having trouble falling asleep, you can check out what Gale Banks has come up
with to keep differential lube cooler during heavy use:

These trucks typically go 200k on the original gear oil. Unless you're burning your fluid up towing insane loads or desert racing, his fancy diff covers are only going to lighten your wallet. I plan on running the stock diff cover on Roscoe.

 

[Road Trip]

These trucks typically go 200k on the original gear oil. Unless you're burning your fluid up towing insane loads or desert racing, his fancy diff covers are only going to lighten your wallet. I plan on running the stock diff cover on Roscoe.

Yup, we're on the same common sense page. (See attached. Taken from here.)

Whenever I'm trying to come up to speed on a potential issue, I like to explore &
study all possible solutions on offer. And then try to figure where the best ROI is.
(What the old timers used to refer to as "The best bang for the buck.")

And given the robust nature of the FF in the chore truck vs how I'm tasking it,
I figured that a fresh fill of synthetic gear oil and a full-strength stock cover
was just what the doctor ordered.

Q: Has anyone in here pointed an IR thermometer at a pumpkin after a hard workout?
I'd be interested in whatever folks have observed.

 

[Rock Hard Concrete]

Running a heavier gear oil will not hurt anything.

Use any multi weight engine oil that ends in 30 or 40. Synthetics last longer between changes. Your truck won't particularly care what it has as long at its clean.

Rotella T6 is god's spit in the motorcycle world, it is an excellent "synthetic" for the price. It does not foam at high rpm, at least once it is warm. I have used it in many types of engines.

Approx. 9% of power transmitted through a 90* split converts to heat. I can believe a poorly maintained diff would glow. Poor, or low fluid cannot pull heat away as effectively.

 

[618 Syndicate]

I can confirm that Rotella T6 15-40 does not foam at motorcycle RPM. Used it for years.

 

[Islandwhiteknight]

Greetings Islandwhiteknight,

I happen to have the same 14-bolt under my '99 C2500, so your photos are visual confirmation.

For what it's worth, here's a drawing of the Dana taken from the C/K Factory Service Manual:

You must be registered for see images attach

Once you see a Dana, there's no confusing it with the 14-bolt you got.

Note: Back when your truck was made, synthetic gear oil was new/spendy. Interestingly,
there's a note at the bottom of this page concerning the Dana diff under 'extreme use'
where the recommendation is either changing the conventional oil every 3K miles (not a typo)
or, if you used the 75W-140 GM synthetic, you could extend the oil change intervals to 30K miles:

You must be registered for see images attach

Obviously synthetic gear oils can handle the high heat from sending big power through a 90° turn better than
the conventional 90 wt. NOTE: In a previous life I used to maintain night-vision (IR) Litening Pods
as part of our Avionics package, and after a successful repair/Ops check at night I'd take a look across
the airfield at all the Civilian trucks servicing the airplanes, and I was always amazed at just how clear
and bright the ring & pinion gears would be visibly 'glowing' under the trucks. I don't know exactly
what percentage of hp/torque is left behind at the 90° turn in the diff, but the resulting heat is the
real deal. I wouldn't have believed it if I hadn't seen it for myself. :0)

****

And if you are ever having trouble falling asleep, you can check out what Gale Banks has come up
with to keep differential lube cooler during heavy use:

xc_hide_links_from_guests_guests_error_hide_media

BTW, nice rig. Always cool to see a GMT400 busy earning it's keep like yours obviously is.

And welcome to the GMT400 forum.

Thank you for the very informative post. The video was very interesting.

 

[Islandwhiteknight]

Thanks to everyone for sharing their insights. It's a privilege to be a part of this Forum.