Castrol Formula R 25w 50. Previously GP50.

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Feb 9, 2004
Hi all, another Castrol question,

Just wondering if anyone has any good or bad comments or experiences with the Aust Castrol Formula R 25w 50. Previously GP50.

My Concern with it is that being a SG rated oil it could lead to a dirty engine over time, but I was told by Castrol that it far exceeds the SG rating, but they only test to SG because of the engines it’s aimed for only require SG and this saves over all costs.

I have also wondered if it was / is used by the V8 Supercars.

The question I asked Castrol is if GTX 2 is SL and Formula R 25w 50 is SG, well then wouldn’t GTX 2 provide a better over all oil? Got no reply.

I would love to hear any thing I can about it.

Thanks all
If you were Larry Perkins, you had a 600HP engine that had to last for a 1000km race and you could use any product in the Castrol inventory, would you use a very basic dino oil or their best synthetic ?

Or, to put it another way, a cousin of mine was doing some business with Castrol last year, and asked one of the reps, as one salesman to another, about their marketing, and how many types of oil they really had.
The answer was something along the lines of how it was great they could market and re-package one of their most basic oils as a V8 oil without telling any real fibs, and charge three times the normal price for it.

It doesn't take too much to work out which one he was talking about.

Cynical, moi ?

Francis Cadstrol are the champions at selling Group III products as a syn. Tech line told me openly Formula R 5W30 synthetic has zero PAO or ester yet still charge like a wounded bull for it.
That's a huge risk on Castrols Behalf.

When there telling guy's to use it in all out Horse Power engines that are using it form street to Comp use and with things like Rolla Cams and rockers, this places a huge responsibility on the Oil.

And should the oil fail because it's a heaper oil rebade, then that could be incredibly damaging to the company name and image.

They claim it has Syn load increasing components in to too.
again on the R 25w 50 is re labeled cheap oil, I at one stage had that thought jump in to my head, and drined it out the next day when I used it once.

But The othe thing I thought is that it is suited to Racing fuels, and to mix with them it must be robust. It also shows a high HTHS. So I just dont know!
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