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I hope that many of you are coming to our Mariposa Rally on September
17 to 22. I am looking forward to again seeing old friends and
making some new ones.
I am still waiting for some suggestions for future Tech Center
articles. I have only had one request in the last six months and
that is for information on building cornering lights. I will cover
that in the next bulletin. Meanwhile, I will cover some topics
that are of interest to me and which I hope you also will find
of value.
LUBRICATION
It is very important to remember to periodically grease you chassis
and replace the motor oil and filter. Also don't forget to repack
the front wheel bearings and change the transmission oil and filter
periodically. The final drive also needs periodic oil changing.
There are normally a total of 17 Zerk fittings for grease. However my original steering relay lever was changed last year and I now have an 18th grease fitting on the rear top of the lever where a ball joint is attached. GM's recommended schedule is every 3,000 miles or 3 months (whichever comes first). Most GMCers recommend that the rear suspension fittings be greased every 1,000 miles and that, to do it right, the side should be jacked up and the air bags deflated so that the wheel can be moved up and down while greasing. This insures getting the grease all the way through and around the pins. You can use a shovel or a pry bar under the elevated tire to move it while greasing. (Probably best to have a helper while doing this.) If on a trip at least grease the fittings at 1,000 miles with the wheels on the ground, and then when you get back from the trip, lift the wheels and do it right.
The change period for engine oil is also at 3,000 miles or 3 months. The oil filter should be changed every second oil change. This is also a good time to lubricate the transmission shift linkage, brake pedal spring, parking brake cable guides and linkage.
The automatic transmission fluid and filter should be changed every 12,000 miles or 12 months, whichever comes first. GM also indicates that if the vehicle is driven under unusual conditions such as heavy traffic (stop and go) during hot weather or where the engine idles for long periods, it should be changed at 6,000 mile intervals.
The rear wheel bearings and the front wheel bearings should be cleaned and repacked every 24,000 miles. Some recommend replacing the front wheel bearings every time instead of repacking them, but at our March 2001 Rally the Timken representative said that if the bearings do not have any scores or pits and have no blue discoloration, they can be reused. Brown staining from the grease is all right, but blue indicates overheating of the bearings.
More and more people are using 100% synthetic oils and greases such as Mobil 1 and Amsoil. Apparently the oil change period can be quite a bit longer with synthetics, as they don't break down in viscosity and don't degrade with heat as easily as regular oils.
OIL INFORMATION
While on the topic of lubrication, I thought it might be a good
time to review some information about oils in general. Choosing
the best motor oil is a topic that comes up frequently in discussions
between GMCers. Oil companies provide data on their oils most
often referred to as "typical inspection data". This
is an average of the actual physical and a few chemical properties
of their oils. This information is available to the public through
their distributors or by writing or calling the company directly.
Below is a list of some popular premium oils so you can make a
comparison. If your favorite oil is not on the list, get the data
from the distributor and use what I have as a database. The information
I am presenting is from data from the manufacturers of oils and
from the Internet including information compiled by Tom Coradeschi
and Ed Hackett.
We are going to look at six of the most important properties of a motor oil readily available to the public: viscosity, viscosity index (VI), flash point, pour point, % sulfated ash, and % zinc.
Viscosity
Viscosity is a measure of the "thickness" or "flowability"
of oil. It is a property of oil to develop and maintain a certain
amount of shearing stress dependent on flow, and then to offer
continued resistance to flow. Thicker oils generally have a higher
viscosity, and thinner oils a lower viscosity. This is the most
important property for an engine. Oil with too low a viscosity
can shear and lose film strength at high temperatures. Oil with
too high a viscosity may not pump to the proper parts at low temperatures
and the film may tear at high rpm. The weight given on a can of
oil is really just an arbitrary number assigned by the S.A.E.
(Society of Automotive Engineers). However, 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, and 50 by the S.A.E. The W designation after the weight
number means the oil is suitable for winter use. So, a 10W weight
oil measured at 0 deg. C would be of much lower viscosity than
a 10 weight oil (without the W designation) also measured at 0
deg. C.
The following chart shows the relationship of "real" viscosity (numbers 2 through 42) to their S.A.E. assigned numbers at 100 deg. C. The relationship of gear oils to engine oils is also shown. Many people are not aware that gear oils and motor oils are rated differently for viscosity. Looking at this chart you can see that 90 "weight" gear oil has about the same viscosity as 40 to 50 "weight" motor oil (at 100 deg. C)
SAE Gear Viscosity Number
SAE Crankcase Viscosity Number
Real Viscosity in centistokes
@ 100 degrees C. |
Multi-viscosity
Multi viscosity oils work like this: Polymers, called VI (viscosity
index) Improvers, are added to a light base oil (5W, 10W, 20W),
which prevent the oil from thinning as much as it warms up. At
cold temperatures the polymers are coiled up and allow the oil
to flow as their low numbers indicate. As the oil warms up the
polymers begin to unwind into long chains that prevent the oil
from thinning as much as it normally would. I often suggest the
image of trying to pour a can of peas and a can of spaghetti.
The result is that at 100 degrees C the oil has thinned only as
much as the higher viscosity number indicates. Another way of
looking at multi-vis oils is to think of a 20W-50 as a 20 weight
oil that will not thin more than a 50 weight would when hot.
Multi viscosity oils are one of the great improvements in oils, but they should be chosen wisely. Always use a multi grade with the narrowest span of viscosity that is appropriate for the temperatures you are going to encounter. In the winter base your decision on the lowest temperature you will encounter and in the summer the highest temperature you expect. The polymers can shear and burn and form deposits that can cause ring sticking and other problems. 10W-40 and 5W-30 require a lot of polymers (synthetics excluded) to achieve that range. This has caused problems in diesel engines, but fewer polymers are better for all engines. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the higher polymer content. It is the oil that lubricates not the additives. Oils that can do their job with the fewest additives are the best. One of the problems with multi viscosity oils is that, over time, the polymers can shear and your oil will thin down. This is another reason to change your oil at regular intervals.
Very few manufactures recommend 10W-40 any more, and some threaten to void warranties if it is used. 20W-50 has the same 30 point spread, but because it starts with a heavier base, it requires less VI improvers (polymers) to do the job. AMSOIL can formulate their 10W-30 and 15W-40 with no viscosity index improvers but uses some in their 10W-40 and 5W-30. Mobil 1 uses no viscosity improvers in their 5W-30 and in their 10W-30. I believe they use a small amount in the 15W-50 oil. Follow your manufacturer's recommendations as to which weights are appropriate for your vehicle.
Viscosity Index (VI)
Viscosity Index is an empirical number indicating the rate of
change in viscosity of an oil within a given temperature range.
Higher numbers indicate a low change; lower numbers indicate a
relatively large change. The higher the number the better. This
is one major property of an oil that keeps your bearings happy.
These numbers can only be compared within a viscosity range. It
is not an indication of how well the oil resists thermal breakdown.
Flash Point
Flash point is the temperature at which an oil gives off vapors
that can be ignited with a flame held over the oil. The lower
the flash point the greater tendency for the oil to suffer vaporization
loss at high temperatures and to burn off on hot cylinder walls
and pistons. The flash point can be an indicator of the quality
of the base stock used. The higher the flash point the better.
400 F is the minimum to prevent possible high consumption. Flash
point is in degrees F.
Pour Point
Pour point is 5 degrees F above the point at which a chilled oil
shows no movement at the surface for 5 seconds when inclined.
This measurement is especially important for oils used in the
winter. Some manufacturers give a borderline pumping temperature.
This is the temperature at which the oil will pump and maintain
adequate oil pressure. This was not given by a lot of the manufacturers,
but seems to be about 20 degrees F above the pour point. The lower
the pour point the better. Pour point is in deg. F.
Sulfated ash
Sulfated ash is how much solid material is left when the oil burns.
A high ash content will tend to form more sludge and deposits
in the engine. Low ash content also seems to promote long valve
life. Look for oils with a low ash content.
Zinc
Zinc is the amount of zinc used as an extreme pressure anti-wear
additive. The zinc is only used when there is actual metal-to-metal
contact in the engine. Hopefully the oil will do its job and this
will rarely occur, but if it does, the zinc compounds react with
the metal to prevent scuffing and wear. A level of .11% is enough
to protect an automobile engine for the extended oil drain interval
under normal use. More doesn't give you better protection; it
gives you longer protection if the rate of metal-to-metal contact
is abnormally high. But note that high zinc content can lead to
deposit formation and plug fouling.
The Data
Listed alphabetically. --- indicates the data was not available
(or does not apply to synthetics).
Brand | VI | Flash | Pour | %ash | %zinc |
20W-50 | |||||
AMSOIL | 157 | 507 | -44 | --- | --- |
Castrol GTX | 122 | 440 | -15 | .85 | .12 |
Exxon High Performance | 119 | 419 | -13 | .70 | .11 |
Havoline Formula 3 | 125 | 465 | -30 | 1.0 | --- |
Kendall GT-1 | 129 | 390 | -25 | 1.0 | .16 |
Pennzoil GT Perf. | 120 | 460 | -10 | .90 | --- |
Quaker State Dlx | 155 | 430 | -25 | .90 | --- |
Shell Truck Guard | 130 | 450 | -15 | 1.0 | .15 |
Unocal | 121 | 432 | -11 | .74 | .12 |
Valvoline All Climate | 125 | 430 | -10 | 1.0 | .11 |
Valvoline Race | 140 | 425 | -10 | 1.2 | .20 |
20W-40 | |||||
AMSOIL | 124 | 500 | -49 | --- | --- |
Castrol Multi-Grade | 110 | 440 | -15 | .85 | .12 |
Quaker State | 121 | 415 | -15 | .90 | --- |
15W-50 | |||||
Chevron | 204 | 415 | -18 | .96 | .11 |
Mobil 1 | 170 | 470 | -55 | --- | --- |
5W-50 | |||||
Castrol Syntec | 180 | 437 | -45 | 1.2 | .10 |
Quaker State Synquest | 173 | 457 | -76 | --- | --- |
Pennzoil Performax | 176 | --- | -69 | --- | --- |
15W-40 | |||||
AMSOIL | 164 | 462 | -49 | --- | --- |
Castrol | 134 | 415 | -15 | 1.3 | .14 |
Chevron Delo 400 | 136 | 421 | -27 | 1.0 | --- |
Exxon XD3 Extra | 135 | 399 | -11 | .95 | .13 |
Kendall GT-1 | 135 | 410 | -25 | 1.0 | .16 |
Shell Rotella w/XLA | 146 | 410 | -25 | 1.0 | .13 |
Valvoline Turbo | 140 | 420 | -10 | .99 | .13 |
10W-30 | |||||
AMSOIL | 162 | 520 | -76 | --- | --- |
Castrol GTX | 140 | 415 | -33 | .85 | .12 |
Chevron Supreme | 150 | 401 | -26 | .96 | .11 |
Exxon Superflo Hi Perf | 135 | 392 | -22 | .70 | .11 |
Kendall GT-1 | 139 | 390 | -25 | 1.0 | .16 |
Mobil 1 | 160 | 450 | -65 | --- | --- |
Pennzoil PLZ Turbo | 140 | 410 | -27 | 1.0 | --- |
Quaker State | 156 | 410 | -30 | .90 | --- |
Shell Truck Guard | 155 | 405 | -35 | 1.0 | .15 |
Unocal Super | 153 | 428 | -33 | .92 | .12 |
Valvoline All Climate | 130 | 410 | -26 | 1.0 | .11 |
Valvoline Synthetic | 140 | 450 | -40 | <1.5 | .12 |
5W-30 | |||||
AMSOIL | 186 | 464 | -76 | --- | --- |
Castrol GTX | 156 | 400 | -35 | .80 | .12 |
Chevron Supreme | 202 | 354 | -46 | .96 | .11 |
Chevron Supreme Synt. | 165 | 446 | -72 | 1.1 | .12 |
Exxon Superflow HP | 148 | 392 | -22 | .70 | .11 |
Havoline Formula 3 | 158 | 420 | -40 | 1.0 | --- |
Mobil 1 | 165 | 445 | -65 | --- | --- |
Quaker State | 165 | 405 | -35 | .90 | --- |
Shell Fire and Ice | 167 | 405 | -35 | .90 | .12 |
Unocal | 151 | 414 | -33 | .81 | .12 |
Valvoline All Climate | 135 | 405 | -40 | 1.0 | .11 |
Valvoline Synthetic | 160 | 435 | -40 | <1.5 | .12 |
10W-40 is not listed as today many manufacturers indicate that you should not use it. |
All of the oils above meet current SG/CD ratings and all vehicle
manufactures' warranty requirements in the proper viscosity. All
are "good enough", but those with the better numbers
exceed the auto manufacturers' minimum specs.
The synthetics offer the only truly significant differences due to their superior high temperature oxidation resistance, high film strength, very low tendency to form deposits, stable viscosity base, and low temperature flow characteristics. Synthetics are superior lubricants compared to traditional petroleum oils. You will have to decide if their higher cost is justified.
The extended oil drain intervals given by the vehicle manufacturers (typically 7500 miles) and synthetic oil companies (up to 25,000 miles) are for what is called normal service. Normal service is defined as the engine at normal operating temperature, at highway speeds, and in a dust free environment. Stop and go, city driving, trips of less than 10 miles, or extreme heat or cold puts the oil change interval into the severe service category, which is 3000 miles for most vehicles. GM considered the GMC service as being extreme so they recommended 3000 mile changes. Synthetics can be run two to three times the mileage of petroleum oils with no problems. They do not react to combustion and combustion by-products to the extent that regular oils do. The longer possible drain intervals help take the bite out of the higher cost of the synthetics. The recommended drain intervals of the manufacturer are set for petroleum oils, and the manufacturers make no official allowance for the use of synthetics.
The numbers above are not, by any means, all there is to determining what makes top quality oil. The exact base stock used, the type, quality, and quantity of additives used are very important. The given data combined with the manufacturer's claims, your personal experience, and the reputation of the oil among others who use it should help you make an informed choice.
OIL ADDITIVES
In my personal opinion, oil additives should not be used. The
oil companies have gone to great lengths to develop an additive
package that meets the vehicle's requirements. Among other things
they add VI improvers, antifoam agents, corrosion inhibitors,
extreme pressure additives, detergents, and dispersant agents.
Some of these additives are synergistic, that is the effect of
two additives together is greater than the effect of each acting
separately. If you add anything to the oil you may upset this
balance and prevent the oil from performing to specification.
When you really think about it, the major oil companies are some of the richest, most powerful and aggressive corporations in the world. They own multi-million dollar research facilities manned by some of the best chemists and engineers money can hire. It is probably safe to say that any one of them has the capabilities and resources at hand in marketing, distribution, advertising, research and product development equal to 100 times that of any of the independent additive companies. It therefore stands to reason that if any of these additive products were actually capable of improving the capabilities of engine lubricants, the major oil companies would have been able to determine that and to find some way to cash in on it. Yet of all the oil additives I have seen, none carried the name or endorsement of any of the major oil producers. In fact, I have seen many directives from oil companies warning not to add any additives to their products.
This material is based on my personal experience and the personal experience of other club members. It is our viewpoint and does not represent authorized data pertaining to the GMC Motorhome. It is the responsibility of the readers to make their own judgment as to the validity of this material in relation to any repairs and/or modifications to their own vehicles. |
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Emery Stora, Technical Vice President, 3128 Vista Sandia, Santa Fe, NM 87501-8526 Phone: (505) 989-8157 E-mail: emerystora@mac.com |
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