I run all synthetic in mine as well, makes me sleep better at night. Valvoline syntec in the diffs, amsoil in the transfer case, redline in the ZF5, and Valvoline syn maxlife in the motor.

 

Mine leaks from the rear main as well. It is the only leak I have. It was there before the change to synthetic. I just don't feel like dropping the trans right now...

 

My 1990 has a 3.55 rear end and is starting to leak, so I figured soon I'll change the gasket and fluid. What fluid should I use? Its going to be next year before I can do it so I'm just going to top it off for now and keep driving it. It doesn't drip, the cover is just getting wet with oil.

 

Synthetics are the way to go. I've always used redline in my (granted non truck) vehicles, and have never had an issue. Like everyone else has said, if you run synthetic oil and find a leak, the leak was already there, the synth oil just let you know.

 

80w-90.. And when you change all the fluid just use an rtv as the gasket.. Works better

 

Stock fluids are a pretty good option. They're exactly what the parts are designed to be in use with.
Saying that, fluid technology has advanced and some may be good options to use. Synthetic in the diff may reduce wear and drag. Synthetic in the engine can help reduce wear, just watch for leaks. Don't put anything different in the trans.

 

How long are you going between oil changes when running full synthetic engine oil?

 

Depends on oil.. Me I run Signature Series Amsoil an planning on 15k miles cause how hat I beat the truck.. It's ok'd up to 25k miles..

Most off the shelf synthetics can reach 8-10k miles no problem in a clean engine..

Just depends on engine.. Go 5k do a used oil analysis and go from there.. Get one that includes TBN..

 

Two 87's and when I changed the differential oil in both of them there was zero wear on the ring & pinion. The red & grey truck is at 178,000 and the blue and white is at 138,000 or 238,000 but I think its only 138k. Both trucks ran original Ford "dino" oil for over 20 years.

I'm an Amsoil "dealer" - you pay a nominal fee to purchase at a discount - I do this for my 2011 Tundra. I'm a synthetic oil fan and that's all I put in my new vehicles.

But clearly there is something to be said about the regular "dino" oil doing its job. In both my '87's differentials I went with regular "dino" oil and don't regret the decision one bit.

Dino = slang for natural, not synthetic.
Urban Dictionary: dino oil

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^^^^^^^^^^^^^^^^^
What he said - That is the way to do your oil changes if you want to maximize your investment in synthetic oil.

It has been said that if you refuse to go longer on your oil change interval then you are wasting money on synthetics. Others say synthetics are better, yada yada.

 

I do a UOA on my Subaru, and I use Blackstone Labs. My first one looked great at 4k miles on the oil, so they suggested going 6500 this time. I'll see how this test turns out, and go from there. If I can do at least 7500 or 8k I'd be more than happy. Then again, Rotella T6 is fairly stout oil to begin with.

 

I guess I'll be the lone dissenter here. I don't know a thing about diff fluid or trans fluid, so I have no commentary there.

As far as engine oil goes, my rule is if the engine likes that oil, don't deviate. If it works perfectly fine on regular, stick with regular. If it has synthetic, stick with synthetic. If it likes Castrol, etc etc.

My truck so far seems to be liking the regular Shell Rotella oil in it. It's barely used a drop, so the next change will also be Shell Rotella.

The Lincoln's last oil change was done with the green bottle Castrol High Mileage regular oil. It's ~1500 in maybe and it's eaten between half and 3/4 of a quart. It's going back to regular Castrol next oil change, since it seems to burn less of that.

The 8.1L Chevy eats a bit of regular Castrol, but devours generic Wallyworld oil almost as fast as it devours gas. It's not getting that oil again.


I know synthetic is supposed to lubricate better, last longer, all that jazz. I'm a paranoid person and creature of habit though. I change the oil and filter every 2500-3500 miles, and I'd probably continue to do that even with a modern car with synthetic oil. It's wasteful, sure, and it hurts the pocketbook, but I've never once heard of an engine dying because of oil that was too clean.

I'm no expert, I'm just a paranoid man. I prefer not to provoke the truck gods

 

There's definitely something to be said there. Stuff usually does pretty well with the specific lubricant it was designed to be used with.

 

I use redline in my m5r2. Shifts nice

 

Synthetic oils are good, my personal favorite is Amsoil. It just flows so much better in the cold and it deals really well with heat. Mom's 2012 Escape always had cold start clatter, so I dumped the motorcraft 5w20 and put in Amsoil 5w20 and haven't heard any noise since. I put their 15w40 in my 5.9 Cummins, much smoother and quieter vs the Delo that I had in it. The oil pressure comes up much quicker too.

Their gear oil is good stuff.

As far as regular oil goes Shell Rotella is my favorite.

Sam