Straight Grade Oils

Merkava_4 · May 19, 2007

What are your thoughts on straight grade oils?

From what I understand, a straight grade SAE30 is much thicker at start up than its multi-grade counterpart, but it's more durable for extended periods of time because it contains no viscosity index improvers.

Also, a 10w30 is actually a 10 weight oil that is built up to become a 30 weight oil at operating temperatures. This will reduce start up wear and improve fuel economy during the warm up period.

A straight 30 weight will maintain it's viscosity better over extended periods of operation because it will never shear back in grade with the absence viscosity index improvers.

The ideal multi-grade oil would have viscosity index improvers that never wear out.

wileyE · May 19, 2007

Correct me if I'm wrong, but a 10w30 might also be a 20w with vi improvers and point depressants, or any other combination of start weights and additive. To assume a 10w30 is loaded with vii's and to be avoided is just more internet dribble IMO. Also a 10w30 made with a very high index base, like some synthetics and grp 3 may have little or no vii.

So say a 10w30 was heavey with vii, and after some time they sheared down leaving the oil a 20w. So is it the end of the world? I dunno, many engines are being run on 20w these day, and 20w are being run in 30w engines by the thinner is better crowds (including manufactures that have jumped aboard). Also are the dead vii hurting anything? Guess they used to add to sludge but have been improved where thats not a problem anymore. There is even research that shows chewed up vii can act as anti-wear additive.

Guess the big question is whether the benefits of cold start pump ability of the 10w30 out weighs the 30w ability to hold grade slightly better(even the 30w will shear) In my mind the answer is application specific, not whether one oil is better than the other.

Dominic · May 19, 2007

This is the same misunderstanding everyone has before they learn at BITOG. It might be true that a SAE30 is more durable in keeping its viscosity than a 10W30 or 5W30, especially in years past, however today's xW30 motor oils pretty much stay in grade for even 15000+ miles.

If you look at the spec sheet of a SAE30 versus a 10W30, you'll notice that as the oil temperature passes 40C (100F) the SAE30 is nearly 100cSt in weight, while the 10W30 is about 60. This massive difference accounts for lower wear and lower oil drag on all the parts in the engine. In this respect the multigrade oil wins.

To try and debunk the 10W30 what weight is it myth... think of it this way: 10W30 = An oil that acts like a SAE30 when at 100C, but when cooler it thickens at a slower rate. This gives it the benefit of working better over large temperature gradients, something car engines need since they're not run at a constant temperature 24/7.

However it is my understanding that when crossing the 100C barrier where the SAE final weight of an oil is spec'd, the 10w30 will be thinner than an SAE30, something undesireable. This is one reason to run a xw40 or xw50 oil on the track.

All oils shear though, when abused.

Auto-Union · May 20, 2007

I use the Delo 30 and the cooler viscs are similar to a 15w40. Not exactly engine-siezing.

G-MAN · May 20, 2007

Quote:

If you look at the spec sheet of a SAE30 versus a 10W30, you'll notice that as the oil temperature passes 40C (100F) the SAE30 is nearly 100cSt in weight, while the 10W30 is about 60. This massive difference accounts for lower wear and lower oil drag on all the parts in the engine. In this respect the multigrade oil wins.

Actually, 60 at 40C is more like a 5w30. 10w30s are typically in the 70-80 range at 40C. But even 60 is not "massively" different from 100. A 10w40 is typically about 100 at 40C. Should we conclude that catastrophic start up wear is taking place if you use 10w40? During the summer months where the coldest start up temp will typically be >50F there is really nothing wrong with using a straight 30 in any engine spec'd for 5w30 or 10w30.

All things being equal, a straight 30 will be more shear stable than even the best modern 5w30 or 10w30. Under HT/HS conditions we can't forget that the shear strength of a multigrade oil is almost solely a function of the VI improver. But for a straight grade it's the base oil.

wileyE · May 20, 2007

Used to have some valve covers with the tops cut out to service and inspect valve train with the engine running, or be able to warm the engine and check again. These motors were small bock fords that we raced with straight 50w race oil. Even with the 50w stone cold, as soon as you jumped the starter the oil instantly flooded the rockers and was all over the place. This was back when the talk of thin multi's "getting oil to the parts" quicker was starting. Had to laugh, having witnessed how quickly 50w pumped. On the other side of thick-thin story, I have driven oil pumps with my cordless drill motor to prime, test or flush, and the is a noticable difference in how hard the drill has to work depending on the thickness of the fluid. Anywhere from solvent tank fluid which will hit the ceiling if your not careful (don't ask), to 50 or 60w that just bubbles out the tube.

Eddie · May 20, 2007

Straight 30 weight is recomended for my 12 HP lawn mower. No reason to abuse my car engine which I must start cold 2X times per day.

TallPaul · May 20, 2007

I think you can still get straight 30 Maxlife. Won't abuse your car engine if you live in a warm climate or only run it in summer. But Maxlife multigrades are so good I don't see much point. You could put a couple quarts of straight 30 in with the multigrade to beef up the base oil. Maybe get a 15w30 or something.

Zaedock · May 20, 2007

I run Delo400 SAE30 in my '92 Jeep Wrangler trail rig. With the gearing in my SM420 transmission and axle gears, it sees consistant revs throughout the trail ride. My last UOA was pretty good for the abuse this thing sees (having to idle on it's side, etc). It has a nice 12.1cSt@100*C viscosity for the 2.5L/4.0L crowd too.

While todays 10WXX's have come a long way, I think the straight grades have too and still have their place. I run GTX 5W30 in winter and haven't noticed a difference on my oil gauges (I have the factory elec. and a mechanical).

Take it easy.

G-MAN · May 20, 2007

If you look at a VOA of a typical 30 wt vs that of a typical 5w30 or 10w30 it's a real eye opener. You'll see just how much the multigrade Xw30 oils are relying on their additive packs compared to the straight 30, which is relying on its base oil.

Even a VOA of 30-year-old straight 30 would show much less ZDDP than its contemporary 10w30.

Ignatz · May 20, 2007

My 93 MB 190 2.3 does well with straight 30 in the summer months. I tried putting it in my 92 Escort wagon and the engine sounded auful on start-up. I took it out after a couple days. Now I just add some of my 30wt along with other weight oil to use it up. 20-50 starts up better than straight 30 and will have better oil pressure at idle on hot summer days. I'm a sucker for $0.59 oil!

Steve S · May 20, 2007

Quote:

Straight 30 weight is recomended for my 12 HP lawn mower. No reason to abuse my car engine which I must start cold 2X times per day.

What?

ewetho · May 20, 2007

You ought to see them try and change that 100 (SAE 50) aviation oil ot of small planes and have to run the engine if they can get it warm enough to start to change the oil otherwise two hours later and 20 OZ of oil later you realize it is not coming out.

it gets places quicker that is for sure. After seeing my used oil analysis of10W-30 Havoline from last winter though, I will probably go back to 10w30 year round as my car was MAD happy with it.

Take my time warm it up and drive slowly and all was VERY well. That and I like the lower Noack volatility, not sure it help much but seems to me like it would be less likely to leave any sludge from breaking down.

Curious Kid · May 20, 2007

I thought that the viscosity of a straight weight once past the oerating temp of 100 deg.c, thinned at a higher rate than the multi-grade that was assisted with it's still expanding VII's? Any benefit thought they thought not as stable? Espesically in HDEO's, it has been said around here that the VII's are shear stable, being of a higher cost than others and so in the end, adding to the formulated oil's cost.

Interesting.

Craig in Canada · May 20, 2007

Quote:

Also, a 10w30 is actually a 10 weight oil that is built up to become a 30 weight oil at operating temperatures. This will reduce start up wear and improve fuel economy during the warm up period.
A straight 30 weight will maintain it's viscosity better over extended periods of operation because it will never shear back in grade with the absence viscosity index improvers.

The ideal multi-grade oil would have viscosity index improvers that never wear out.

Whether VIIs are necessary or not depends on the base stock. Amsoil ASE, for instance, is an SAE30 intended for small engine use and has no VIIs. It also meets 10W30 because of the PAO basestock used.

Many other PAO based 10W30s may have no VIIs as well. I often see the recommendation for 10W30 synthetic or SAE30 in various kinds of power equipment. If regular consumer name-brand oils started marking them like ASE (SAE30/10W30) the average consumer would be confused and never buy it.

That might be an interesting question to various manufacturer tech lines... Do their 10W30 synthetics have VIIs or not?

Craig.

TallPaul · May 20, 2007

Yes, given a 10w30 and a SAE 30 of the same 100C viscosity, the 10w30 will be thicker above 100C, but the SAE 30 will be thicker below 100C.

Quote:

Also, a 10w30 is actually a 10 weight oil that is built up to become a 30 weight oil at operating temperatures. This will reduce start up wear and improve fuel economy during the warm up period.

I don't think this is quite true. The API classification does not have a 10 weight, just a 10w which is merely a test for cold properties. A 10w30 could be built with a 11 cSt (At 100C) ester and meet the 10w properties without any other additives. Other oils may need pour point depressants. Most typical 10w30s will be built off roughly a 6 cSt (at 100C) base, using VIIs to get the 10.5 cSt at 100C. Then they may need to add pour point depressants to meet the 10W, or maybe not if they use a good base oil like PAO. I suspect the PAO in Maxlife helps meet the "w" rating while allowing more robust (thicker) base oil and less VIIs.

Fordiesel69 · May 22, 2007

One thing I will say that I noticed about SAE 30, is that it does not burn off like a multiweight oil will. I can run all summer and part of the next summer on 30wt on my lawnmower. If I use 10w30 or 5w30, it does not smoke, but the oil level will go down very quickly. All my air cooled engines seem to burn multiweights quicker than straight weights.

G-MAN · May 22, 2007

Quote:

One thing I will say that I noticed about SAE 30, is that it does not burn off like a multiweight oil will. I can run all summer and part of the next summer on 30wt on my lawnmower. If I use 10w30 or 5w30, it does not smoke, but the oil level will go down very quickly. All my air cooled engines seem to burn multiweights quicker than straight weights.

The lighter base stocks used to blend 5w30 and 10w30 are more volatile than the heavier stock used to blend a straight 30.

Straight Grade Oils

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