Shell T6 Oil - Let's talk about it

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Ancient

Ancient

Joined
Nov 3, 2025
Threads
7
Messages
20
Location
Atlanta
So, I was doing some research on deciding what oil is best for a high-mileage LC FZJ80, and came across a post saying that Shell T6 15w-40 was the way to go. So I decided to bite the bullet and give it a try, but I opted for 5w-40 due to the climate factor where I live. There are a lot of mixed feelings from all over the place. Particularly, there is a gentleman on YouTube claiming that diesel oil in a gas vehicle is not a good idea due to a bunch of factors, such as the additive in Diesel oil causing damage to your catalytic converter, being one of them. The FJ80 community seem to swear by T6. I'd like to know what you all think and if you could shed some light on whether T6 is the right move.

Thank you.
 
Marvelicious said:
No one tell the cats in most of my vehicles. They apparently don't know they're supposed to be damaged.

Been running the Rotella 5w40 T6 for YEARS in my Tundra and the last couple in my 80.
Click to expand...
How does it compare to regular gas engine oil (i.e oem recommended)?
 
I recommend reading some bobistheoilguy posts on the topic.
 
Honestly, if you're interested in going down the rabbit hole on oil, head over to the "Bob is the oil guy" forum where people post oil analysis, pictures of dissected filters, etc. That's what I did that convinced me to run it in the first place. It has more of a detergent package than many standard gasoline oils, but it has been pretty well proven. Now, take it for what it's worth: I'm not an expert, but I'm also not generating clicks for my youtube channel.
 
What's wrong with regular high-mileage synthetic or synthetic blend? Why the need to go elsewhere? I always figured that changing on a regular basis is the most important thing, but what is your issue with standard oils that make you want to deviate?
 
What I can sum up from reading on this topic over the years is that the 1FZ-FE is not a picky engine when it comes to oil brand, common viscosities and types of oils. Where there is evidence of it mattering is breaking in a newly-rebuilt engine and trying to curb oil consumption.
 
Somehow i'm even more confused now then before I posted this. Gotta love the forums.
 
Is zinc additive not a thing past the 3f?

I’m just along for the ride, I am back here in the dark ages with a 2F and a 3FE and running VR1 in both.
 
In my 1FZ's I have run the same oil that I used in my Duramax for 17 year Mobile 1 Delvac ESP in the 5/40 flavor. They liked it just fine, nothing wrong with a good diesel oil so long as it has the minimum spec for you gas rig on its label
 
I never quite grasped what all the fuss was about when it came to engine oil. I run the Walmart Supertech 10w30. Its cheap and does the trick. I do the blackstone oil analysis every 10k miles or so and results are typically excellent. Some oil is better than no oil.
 
/\ What he said /\
 
Look for a good oil that is speced AECA A3/B4 which is one of the toughest oil tests. It’s high temp, heavy load, high shear, with more detergents, good for cats. It’s literally all the benefits of the old school diesel oils with none of the drawbacks.

Old school Rotella T6 used to be dual purpose. It had API S specs and ratings.

New school Rotella from like 10 years ago stopped being dual purpose.

The 1FZ can kind of get away with it but it’s still not the best option.

Part of the switch was using a 40w oil for gasoline was less common 10 years ago especially for older engines.
 
I’ve recently started using 15w-40 in my stock 80 but plan on only using it during the extreme Texas summer months. Here are just my thoughts..

1. The 1fze will run just fine on it.

2. My only concern is that if you have a high mileage engine with a bunch of crud/sludge sealing the seals… the extra cleaning effect of diesel oil might “cause” leaks.

3. Mpg may decrease by a couple of MPG
 
ZackR said:
FWIW I've been running Mobil 1 10w40 high mileage on mine for the last 10 years with changes every 3-5k miles with no issues.

Diesel engines run at a lower RPM and are much dirtier (soot in the oil from blowby) hence the need for a different oil on those.

I'm not an oil expert but this guy (Lake Speed Jr) seems to know his stuff and this is his take:

Is Diesel Motor Oil the Right Choice for a Gasoline Engine? - https://www.hotrod.com/how-to/diesel-oil-in-gasoline-engine
Click to expand...
Ah yes... our exteremely high RPM 1FZ. 😉 I should point out that lots of people run this stuff in motorcycles. My VFR barely wakes up until you're over 5kRPM and I've never had a lubricity issues due to foaming. I'm sure there are diesel oils that are not good in this respect, but we're talking about Rotella.

There is some confusion about the gasoline rating going back a couple of years, but most of the Rotella family no longer carries an API SN or SM or S[blank] rating... S for "spark" as in gasoline. The key here is that API changed their spec, Rotella didn't change their oil. It has to do with phosphorous content that CAN reduce catalytic converter life. Mostly applies to newer, high efficiency cats. API felt the levels Rotella uses were fine for years, then changed their rules. Rotella still carries the JASO MA-2 rating which JASO states is good for gasoline powered wet clutch motorcycles, WITH catalytic converters.

For the record, going from memory, the Rotella 5w30 grade still carries the SN, or SM rating (and therefore has lower phosphorous).
 
You must log in or register to reply here.

Share this page

Back
Top Bottom