> Date: Sun, 11 May 2014 11:40:55 -0700
> From: stuartmacm@GMAIL.COM
> Subject: Re: Royal Purple Motor Oil..
> To: vanagon@GERRY.VANAGON.COM
> 
>  .....At high temps an Xw-50 protects like a straight 50w because of
> additives and composition, but is physically much thinner......
> 
Sorry, you need to talk to a lube engineer - this just isn't true.  To get that '50' on the SAE
test, the synthetic oil has to be just as thick as a 'dino oil' 50 - no amount of additives is going 
to make any difference when the SAE tests the thickness of the oil.  50 weight is 50 weight, 
regardless.

It used to be that synthetic oils couldn't get up to the higher SAE numbers, (remember 0W-20 
synthetics when they first came out in the 1980s?) and some makers would use 'weasel words' 
such as 'protects like' - but those oils would vanish quickly when put into 
looser engines, like old VWs, as they would leak through the looser tolerances.  
Synthetic oil chemistryhas improved a lot since then.

James
Ottawa, ON