RuffRyder

iTrader: (1)

I'm running castrol gtx 10-30. My question is can I top my oil off with castrol gtx 20-50. I have a bunch of quarts of this weight and not 10-30. Both are regular oils. Is there a rule about mixing oil weights?

Please do not turn this into another synthetic vs regular oil thread lol. Just wanna know if topping it off with a diff weight is ok. There shouldn't be a problem right?

adam c

iTrader: (2)

Some people are purists regarding mixing, and will say to never do it.

My Opinion: Pretty much all oils are a blend, so blending them further wont really make much of a difference. Blending even amounts of 10-30 with 20-50 will likely get you to 15-40. Adding small amounts of 20-50 should not have any real effect. Blend away!!

Mahjik

iTrader: (1)

Yes

sittinSideways

No, there's no general rule about mixing oil weights. You should be fine if you're topping it off.

gdub29e

iTrader: (16)

I experienced around with mixing oils for race applications. I spoke to a lot of guys ( Car, motorcycle, and Boat racing ) using different weight blends. Just an fyi the general rule of thumb was to never jump more then one weight when blending oils. This also includes conventional, synthetic, 2 stroke oil, ect. But to just top it off lets say half a quart, i never had any issues.

FD3S2005

iTrader: (11)

why not just use the 20-50? iv been using that weight in my car since iv owned it and never given me any issues

RuffRyder

iTrader: (1)

I will be switching back to 20-50 next oil change. I went with 10-30 because the place didn't have 20-50 in stock.

RuffRyder

iTrader: (1)

Thanks for the advice guys.

mono4lamar

iTrader: (32)

For street cars I recommend 10w40. For any type of racing or harsh driving go 20w50.

Julian

iTrader: (14)

from my dad who was a scientist at Mobil, of course you can mix

1QWIK7

iTrader: (33)

Some say in some brands 10w40 the ingredients aren't the same as the rest 10w30, 20w50 etc.

That true? The only reason why I never ran 10w40 ever.

bajaman

Yeah....I've never understood the voodoo about 10W-40, either....

mono4lamar

iTrader: (32)

Here's in a start to the discussion about the way I go about oils and the rotary engine.

Because of the rotary engine design, these engines can generate very high localized oil temperatures and high overall bulk-oil temperatures. An oil with too low of a viscosity can shear and loose film strength at high temperatures. Now lets not ignore that an oil with too high a viscosity may not pump to the proper parts at low temperatures and the film may tear at high rpm. You have to look at both areas of the batter so there's no one set oil for each person. Someone that putts around with the factory twins and rarely gets into boost I would go with 10w30 as you'll get better fuel economy and quicker warm ups.

Now for the rest of us I look at the "High Temperature/High Shear Viscosity" for the rotary as we get arguably 35-40% of our engines generated heat injected into the oil. Many, many years ago my friends father worked for a VERY well known oil company and at after a few drinks we began to talk about his job and what he's seen in the oil testing department. He actually emailed me some charts that had more information than I could really interpret at the time but I can tell you that the oil engineers are kind of like the automotive engineers at big companies; what they design and say should be "made and sold" eventually gets diluted/changed so that there's the possibility for profit.

Anyway, back to the topic. He said for the most part a lot of the oils are the same and that there's only really 3-4 oil filter manufactures out there too. He said don't get worked up about peoples numbers or additives. He said there's ground rules for oil, you have the mineral (dyno) based oils and you have synthetics; only an idiot buys an synthetic blend. Next stick to the method developed many years ago, the weighting method.

The weights given on oils are arbitrary numbers assigned by the S.A.E. (Society of Automotive Engineers). These numbers correspond to "real" viscosity, as measured by several accepted techniques. These measurements are taken at specific temperatures. Oils that fall into a certain range are designated 5, 10, 20, 30, 40, 50 by the S.A.E. The W means the oil meets specifications for viscosity at various low temperatures depending on weight, and is therefore suitable for Winter use. 5W is tested at -25C, 10W at -20C, 15W at -15C, 20W at -10C, and so on.

Not sure if any of this answered your questions. I sometimes walk into a thread and never really return unless I come back, it's on the font page, and there's an arrow on it. Feel free to add anything I missed or question/correct me. I didn't proofread either so cut me some slack

GoodfellaFD3S

iTrader: (213)

Also remember you can't really compare engine oil suitable for pistons engines vs for our rotaries in part due to the stationary gears and rotor ring gears..... this wreaks havoc on the oil, and makes your choice of oil weight and quality even more important.