New Castrol oil for the classics! "Castrol GTX Classic" 20W-50

Aug 4, 2020
Forgive me if this is already posted (I checked but didn't see any posts about it). I was at my local Walmart looking for a U1 battery for my new-to-me mower, and of course I had to walk the oil aisle. This caught my eye, and I've never seen it before:



I'll post the text from the rear of the bottle just in case the image gets overly compressed...

"Castrol GTX Classic is a high performance formula for push-rod, flat tappet engines and performance cam applications. Specially formulated for classic/collector cars, muscle cars, hot rods, and race cars. Learn more at

● Specialized additives containing high Zinc and Phosphorus for extreme wear protection
● Formulated to maintain tough and thick oil film even under severe conditions
● Minimal foaming and high resistance to thermal degradation
● Compatible with gasoline and alcohol based fuels


● Meets API SJ"

I think this is fantastic for those who have been struggling to find a high ZDDP oil for their classics. It is ONLY offered in 20W-50. Obviously this isn't for the thin crowd, but what does everyone think?
Thanks very much for bringing this to my attention, I hadn't heard of this and this is my market segment.

Really looks good for my preferences (don't want ZDDP higher than 1400 or so)

From the Castrol GTX Classic 20W-50 PDS (note, 99.99% sure this is the PDS for the USA product. The PDS was searched using USA in the search field for region; the UK classic product doesn't use GTX in the name; and the PDS at the bottom says BP Lubricants USA Inc)

Zinc, % wt 0.13
Phosphorus % wt 0.12

The castrol site also says "buy at local walmart". I wonder if that is just a marketing affinity tie-in, or if it will be a walmart exclusive? Either way, it will be easier to get than Kendall GT-1 Competition which has been my go to for higher ZDDP. Still got to dig my teeth into all the info to see how they compare in other respects.

Castrol's price is nice too compared to what else is in this segment

No branding of this being "conventional" or mineral. I would prefer that being more clear. You'd think if it was a blend or synthetic they'd state such, but in the demographic this is aimed at, highlighting it as a synth may actually be detrimental, as seen by some negative reaction on amazon reviews about VWB becoming (or rather, just labeling its existing formula as) a synblend in some grades like 5w30.

PDS's linked bellow. castrol's site search brings up 4 different PDS links, all posted on the same date and all appear to have same info, but will link all 4 so people can judge for themselves

webpage for Castrol GTX Classic 20W-50

The oil formulator SonofSonof (Joe) recently posted this:

Group I & II base oils come in light, heavy & very heavy varieties & are primarily good for 15W40s & 20W50s. You can make 5W30s, 10W30s & 10W40s with them but only if you're prepared to accept very high Noack.

Group IIIs (& I believe GTL) only come in light varieties (typically 4 to 6 cst). You can make narrow 0W-xx grades & wider 5W-xx grades with them which importantly have lower Noack. You definitely CAN'T make 15W40s & 20W50s from them. Given that the bulk of commercial synthetic oils are Group III based, going synthetic inevitably means a shift to thinner oils.

PAOs come in light, heavy & ultra heavy varieties. The most common varieties are 4 & 6 cst & these find most favour in 0W-xx top-tier oils where they have a small but significant advantage over Group IIIs. However you could conceptually make a full PAO 20W50 from PAO 10 & PAO 40. It would probably be a VII-free mono grade with a zero Noack!! It's commercially reality that rules out such oils rather than any technical reason.
I'm super excited to try this in my air-cooled Honda motorcycle. It's a blast to shift it at high rpms. The higher anti-wear additives in this oil are definitely needed in my application.
If your Honda has a shared sump (wet clutch), I would not use a high Zinc oil.
Maybe enough people will buy it so it stays available. Didn't Quaker State try something like this a few years ago?
If your Honda has a shared sump (wet clutch), I would not use a high Zinc oil.
What ?
I always used high zinc oils in my shared sump motorcycles, never a problem. Clutch worked well even after a decade.

It's friction modifiers I was always told to avoid in motorcycle oil.