[T3] Stupid question #395 Oil change time?

William Jahn willjahn975 at gmail.com
Thu May 30 16:00:04 PDT 2019

I found out that the STP SAE30 & 40 are made by autozone by calling STP
autozone gets to use their trade mark for a price. STP only deals with

On Thu, May 30, 2019 at 11:08 AM William Jahn <willjahn975 at gmail.com> wrote:

> Jim good write up and it makes sense. I understand how multi grade oils
> work now from calling and doing research. It all has to do with flow rates
> and yes 20W50 does not become thicker as I always thought it is all about
> how long it stays at the bearing do to pressure and flow rates. My only
> fear is going to a SAE 30 rather than a SAE 40. Reason is SEA 40  is what I
> always used and I think I hear some noise even though this engine only has
> at most 35,000 miles on it and could be the result of using the 20W50
> castrol which I used for the last 4 oil changes.   If I deal with autozone
> they do have both in the STP brand for less than Valvoline which they only
> offer in multigrade which I would prefer to say away from. I don't know if
> STP is a good engine oil it's not the thick crap one would add it's just
> oil. Valvoline conventional does have 860 ppm zinc. Trouble is no matter
> what oil company I call or chat with I get a different answer Valvoline
> told me SAE 40 does not thin out yet I know it has to . When I pour in the
> 20W50 it is thin and when I drain it it is thin yet it does cling pretty
> well when trying to empty the drain pan yet by then it's cooled down.
> Bentley does put SAE 30 and SAE 40 in the tropical range class. I need to
> locate the Lucas additive somewhere my thinking is since Valvoline does
> have 830 ppm that's better than none.
> On Thu, May 30, 2019 at 10:06 AM Jim Adney <jadney at vwtype3.org> wrote:
>> Some comments on oil. Some of these are pet peeves, so forgive me if this
>> seems pedantic.
>> 1) There's no such thing as 30W oil. Same for 40W, 30 w, 30w, 30 W, 40 W,
>> 40w or 40 w. Likewise for 10, 20, and 50. These are properly called SAE
>> 30,
>> etc.
>> The W stands for Winter and only appears on multi-viscosity oils, as in
>> 10W-40, etc, or SAE 10W-40 to be complete.
>> I note that the Tractor Supply web site makes this mistake consistently:
>> Although the labels on their bottles all state SAE 30, etc, Tractor
>> Supply
>> consistently describes them as 30W or 30w. This is simply a
>> misunderstanding of what the W means, and is wrong.
>> It's common for people to mention 30-weight oil and this often gets
>> condensed to 30W, because people see that W on the label and confuse the
>> W with weight. I accept this use of "weight" even though there's little
>> difference in mass and what we mean is viscosity. What we mean, and what
>> we should recognize, is that we're talking about SAE 30, SAE 10W-40, etc.
>> (SAE = Society of Automotive Engineers, the group that wrote the
>> specification.)
>> In multi-vicosity oils, the W (winter) viscosity is measured at (I
>> believe) 32 F
>> (0 C) while the hot viscosity is measured (I believe) at 212 F (100 C.)
>> But the
>> 2 measurements are made on different viscosity scales, so this can be
>> misleading. A 30W-30, if such a thing existed, would not have the same
>> viscosity at both 32 F and 212 F. SAE 20W-50 is thinner at 100 F than it
>> is
>> at 32 F, but it hasn't thinned down as much as SAE 20 would have.
>> Note that this means that SAE 20W-50 does NOT get more viscous as it
>> gets warm.
>> I believe the viscosity scales used for gear oils are also different from
>> those
>> used for engine oils, and they also use different scales for hot and
>> cold. So
>> you'll see 80W-90 gear oils. These come in grades like GL-4 and GL-5,
>> where I believe GL stands for Gear Lubricant.
>> 2) I don't see any reason why you could not mix any petro engine oils
>> together for some kind of intermediate outcome, but it's quite possible
>> that
>> mixing synthetic and petro oils might not work. I don't know about that.
>> 3) I bought a 16 oz. bottle of Lucas "Racing ZDDP / TB Zinc-Plus / Engine
>> Break-In Oil Additive" " #0 49807 10063 6 at my FLAPS yesterday for
>> $13.61
>> after tax. The Lucas spec sheet lists this as having 43,000 ppm of zinc,
>> so I
>> ran the numbers to see what this would mean for us.
>> We should get 4000+ ppm additional ZDDP if we add 4 oz (1/4 bottle,
>> $3.40)
>> to one oil change (5.3 pts = 42.4 oz)
>> or 2000+ ppm of additional ZDDP if I add 2 oz (1/8 bottle, $1.70) to each
>> oil
>> change.
>> The bottle states that it is NOT recommended for any vehicle later than
>> 1994
>> or that requires oil meeting API (American Petroleum Institute) spec SG
>> or
>> later. "May cause damage to catalytic converters." I believe the latest
>> spec
>> called out for our cars was SD.
>> I'm going to start using ~2 oz with each oil change. I agree with Brian
>> that
>> the fancy, high-priced oils are probably not worth it for us, but I think
>> the
>> ZDDP probably is. I would use twice as much for break-in of a new engine.
>> 3) Because it gets quite cold around here, and I have engines that get
>> driven
>> occasionally in that cold, I think I'll continue to use the cheap Diesel
>> SAE
>> 15W-40 year round but with the addition of the Lucas ZDDP additive. This
>> is
>> a cheap, effective solution for year round use in climates that see temps
>> well
>> below freezing. If I lived in a warm climate, I'd find SAE 30, add 2 oz
>> of the
>> Lucas ZDDP additive and use that year round.
>> 4) It may also have been Brian who mentioned how it was more important to
>> value flow to the bearings over pressure in the oil passages. I agree
>> with
>> this. The only pressure that counts is the pressure that's developed
>> between
>> the rotating shaft and the bearing. I'll try to explain why oil pressure
>> isn't as
>> important as oil volume.
>> If you don't already understand this, it may be helpful to draw yourself
>> a
>> picture of a rotating circle within another circle. The rotation of the
>> center
>> circle drags the oil around it.
>> Now draw another set of circles with the center circle a bit off-center.
>> This
>> creates a "wedge" where the dragged-along oil gets pushed into a tighter
>> and tighter space. This is where the rotation of the center circle
>> creates
>> pressure, and that's the pressure that keeps the 2 parts from touching.
>> The pressure developed depends on the speed of rotation, the viscosity of
>> the oil, the width of the bearing, and how tight the wedge gets. It gets
>> higher
>> as the shaft gets closer to touching the bearing. If the clearance gets
>> close,
>> the pressure can get extremely high: much higher than the oil delivery
>> pressure. This is what keeps the two parts from ever actually touching,
>> and
>> this is why plain journal bearings work so well.
>> Note that this all depends on the oil being virtually incompressible, so
>> if
>> you're delivering air or foam to the bearing there will be almost no
>> pressure
>> developed in the wedge and the shaft is likely to rub against the
>> bearing.
>> This may happen each time we start, but there is likely to be a thin
>> layer of
>> oil still there to prevent actual metal to metal contact.
>> Note that this explains why the oil entry points in a bearing may seem to
>> be
>> in odd places. The people who design engines have found that they need to
>> inject oil at the low pressure areas so that the rotation of the shaft
>> can put
>> the most pressure where it's most needed. The worst possible place to try
>> to
>> inject oil would be where the wedge effect is trying to build pressure;
>> that
>> would just give the pressurized wedge of oil a path to escape, allowing
>> the
>> parts to touch.
>> This may help you understand why it is not necessarily a good idea to
>> choose a higher viscosity oil. The higher viscosity will make it harder
>> to
>> pump, especially during warmup, and may be slower getting to the places
>> where it's needed. It takes more engine power to pump, so it will cause
>> more
>> wear on the pump and the parts that drive the pump. If you have a filter,
>> it
>> will be harder to pump thru the filter and that puts even more load on
>> the
>> pump, its drive, and the engine. While the higher viscosity will increase
>> the
>> wedge pressure in the bearing, that's probably not as useful as being
>> of plenty of flow into the bearing.
>> 5) Note that in 1970 VW increased the size of the oil passages, but
>> didn't
>> change the size of the oil pump. If that was all they did, this would
>> have
>> meant the same flow, but with reduced oil delivery pressure. However, VW
>> also changed the pressure relief system, so this muddies the picture.
>> They
>> didn't change the oil pressure switch, so it seems likely that the
>> pressure
>> relief system changed to keep the oil galley pressures pretty much the
>> same.
>> However, in 1972, they increased the size of the oil pump without
>> changing
>> anything else. This clearly increased flow and should have increased
>> pressure, too, but we don't see the pressure increase, probably because
>> the
>> pressure relief valve works well and because of where we measure the
>> pressure, unless we use oils with higher viscosities than VW ever
>> recommended. These late engines seem to have better longevity than the
>> earlier ones.
>> Thanks for reading. I hope it wasn't too painful.
>> --
>> *******************************
>> Jim Adney, jadney at vwtype3.org
>> Madison, Wisconsin, USA
>> *******************************
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