Mixing grades
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Fleet Mechanic
Joined: Feb 2003
Posts: 1,314
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Mixing grades
I got some Castrol GTX 5w30. Then I realized I wanted 10w30 in my climate (90-100F summer). I have some 20W50 Castrol GTX oil. How can I mix them to get 10W30?
I also have some generic 10w30
I also have some generic 10w30
Posting Guru
Joined: May 2002
Posts: 1,673
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From: Chicago Area
Mixing grades
I am not an expert on this and I have heard some say that you shouldn't mix different viscosities, but I think it is pretty much a weighted average. I would feel better if the oils were the same brand, but even if not I wouldn't expect a problem (But then it's your truck, not mine!).
In other words, take the lower number times the number of quarts of that viscosity, add the lower number of the second component times the number of its quarts, and divide by the total number of quarts. Do the same thing for the number after the "W" and you have the approximate overall viscosity.
Its not ideal, but I don't think you will cause any harm if the resulting numbers are within 5 and maybe 10 points of recommended viscosity.
Personally, I'd return it or use it up in the lawn mower, but then I'm overly protective of my truck.
In other words, take the lower number times the number of quarts of that viscosity, add the lower number of the second component times the number of its quarts, and divide by the total number of quarts. Do the same thing for the number after the "W" and you have the approximate overall viscosity.
Its not ideal, but I don't think you will cause any harm if the resulting numbers are within 5 and maybe 10 points of recommended viscosity.
Personally, I'd return it or use it up in the lawn mower, but then I'm overly protective of my truck.
Last edited by MrBSS; Jun 6, 2003 at 11:37 AM.
Elder User
Joined: Oct 2001
Posts: 724
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From: Cypress, CA
Mixing grades
I read somewhere in the not-too-far-distant past about the multi-viscosity oils and will look again for the site. Basically what it said is that all oils were manufactured to the same standard for VISCOSITY however the additives in the different oils is another whole story. The article went on to state that for instance 10 W 30 is basically a 30-weight oil with additives to thin the viscosity under cool/cold conditions to 10-weight.
Again, I will look around for that article and post it.
Russ
Again, I will look around for that article and post it.
Russ
Elder User
Joined: Oct 2001
Posts: 724
Likes: 0
From: Cypress, CA
Mixing grades
I rummaged through all of this paper on my desk and found the site. It is called the Vintage Triumph Register. The website is:
www.vtr.org/maintain/oil-overview.html. They advertise this as more than you ever wanted to know. Obviously they are not referring to the FTE crowd.
Good Luck
Russ
www.vtr.org/maintain/oil-overview.html. They advertise this as more than you ever wanted to know. Obviously they are not referring to the FTE crowd.
Good Luck
Russ
