5W-30, 10W-30, but not 10W-40....why not????

Mortgage Paul · January 10, 2003

The manuals state 5W 30 for all seasons. OK thats fine. It also says 10W 30 is Fine in warmer climates, obviously becasue of the cold starting properties, but its says NOT to use 10W-40 under any cicumstances.

Whats the deal?? All I can figure is becasue 10W-40 doesnt have the Energy Conserving Certification(For gas Mileage) becasue of Fluid Drag.

Now Common sense says 10W-30 flows the same at say Freezing, as does 10W-40(W means Winter) so why not have the added Protection of the 10W-40 in just average to high temps??

The difference pouring out of the can is noticable, and have you ever drained 5W-30 (Recommended for all seasons) after a long drive on a 100 degree day? Thinner than water, and that scares me. Even 10W 40 drains easy and very thin when hot. Plus the new motors all run at 195 -210 making matters worse

Are they just stressing the fact for gas mileage, or to satisfy the C.A.R.B. and similar people?

What do you guys run??

bowtie_pasta · January 10, 2003

5W-30 in my 97 Blazer and 10W-40 in my 85 Blazer.

I chose the 10W-40 in based off the recommendation for protection and fuel economy from my Haynes guide.

mdub · January 10, 2003

I think the main reason for this recommendation has to do with the percentage of 'viscosity improvers' included in the oil. Viscosity improvers have a sticky glue-like consistency, and do nothing to lubricate the engine. They're just an additive to the lubricant that keeps the lubricant at the right consistency over the operating temperature range. Of course, an oil with a wider viscosity range has more sticky stuff, and thus less real lubricant. This is why many stay far away from 10W-40 and 20W-50 oil, and stick to an oil with the narrowest viscosity range that still matches the temperature requirements.

Ideally, you would use a straight 30W year around since a straight weight oil is 99%+ lubricant, and 0% non-lubricating viscosity improver. However, most cold weather climates and driving habits (frequent cold engine starts) makes that idea impractical, so you choose the best compromise multi-grade oil. For newer engines with tight build tolerances, the best compromise is likely 10W-30 during spring, summer, and fall, and possibly a quality (synthetic) 5W-30 or 0W-30 only during cold winter months.

-Mdub

BDBWTE · January 11, 2003

I don't know what your talking about I use 15W-40 in the HD...

TxDoc · January 12, 2003

Mobil 1 5W-30 and 10W-30 have no viscosity improvers added. Very few manufactures recommend 10W-40 any more. The polymers.viscosity improvers, can shear and burn, forming deposits that can cause ring sticking and other problems. 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 high polymer content. It is the oil that lubricates, not the additives. Oils that can do their job with the fewest additives are the best.

10W-40 and 20W-50 have the same 30 point spread, but because it (20W-50) starts with a heavier base it requires less viscosity index improvers (polymers) to do the job. Amsoil formulates their 10W-30 and 15W-40 with no viscosity index improvers but uses some in the 10W-40 and 5W-30.

Viscosity Improvers

are temperature sensitive molecules, and progressive in nature. As the oil temperature increases, the VIs begin to bond to each other, or swell (depending upon method used) in a progressive fashion. The hotter the oil gets, the more effect VI brings to the table. Their purpose is only to help counter the natural attributes of base stock oils to thin as they get hotter, witch reduces the ability to protect components. VIs sort of “prop up” the viscosity of base stock oils preventing the “oil” from getting too thin to be of any value as a boundary layer between moving metal components. The only real difference between 10W-30, and 10W-40 oil is the amount of VI needed to attain the higher 40 wt rating at 100 deg C. Recall that VIs provide absolutely NO lubrication, so if a greater volume of VI additive is required for the 40 wt. rating, less base stock 10W oil will be in each quart of “oil”, thereby reducing it’s service life and lubricating abilities. Less base stock is less lubrication ability. A difference of “25” between the winter and summer ratings is generally considered the best trade-off between wide temperature viscosity stabilization, and base stock oil volume (lubricating ability). When the difference is “30” or greater, it is generally considered that too little base stock remains to be effective over the long term for lubricating purposes, even though some benefit may be attained under extreme high ambient loads. It is better to use oil temperature control strategies, than to use oils with higher than “25” point spreads in weight for extreme conditions. This is true because also as the VIs get larger and larger with elevated temps, their resistance to shearing drops, and overall viscosity suddenly drops dramatically, and oil failure occurs shortly afterwards, along with the “protected” components. Remember, VIs provide exactly zero lubrication, they only improve viscosity, or “thickness”.

Another point to consider is that typically, oil temperatures run approximately 20 deg F. cooler than coolant temperatures under most operating conditions. The oil is the last part of the engine to reach full operating temperature, and most often it’s much lower than the coolant temperature. Very high duty cycles can dramatically reduce an oil’s service life, if the oil is maintained at high operating temperatures that are at or above coolant temperature, for extended periods of time. Higher levels of VIs, associated with higher “summer” weight fractions, will only make this problem worse. Oil temperature controls must be employed under these conditions to have acceptable component service life. If adequate temperature controls are implemented, there is no need to increase the “the oil weight”, buy using 10W, or 15W multi viscosity oils. If adequate controls are ineffective, or unavailable, the use of such oils may be advised.

I have seen websites say 10W-40 can void your warranty, but as long as it meets API requirements of the manufacturer, I don't see how that would appy.

http://www.api.org

Mortgage Paul · January 12, 2003

I dunno, I have a Older 4 banger that I ran 20W-50 in the summer when it never gets colder than 50* outside and over 100 during day and 10 W -40 in Winter becasue its never colder than 0 here for the most part.

Im just curious why it says in the manuals for the 8.1 to NOT use 10W-40.

I just cant see how a 5W 30 is good enough when towing in 90+ heat especially with these 195 thermostats and I have a 160 on the way. 195 is just too hot for me.

maybe thats why all these new cars smoke on startup and eat oil like crazy at 40,000 Miles, the motors are wore out from thin oil. its like water.

Plus if they call for a 10W 30 being OK obviously they arent worried about cold start lubrication, just wanting you to use the thin Energy conserving rated Oils.

I could care less about energy conserving when it comes to oil. I want to conserve my motor.