Here's an interesting write up on why 5W20 is used and also the affect on your warranty etc.. Written by an engineer from an oil company. Sorry for the long post but a good read.
Jim
The 5W-20 recommended is a move on the automakers part to get better CAFE #'s that they can report to the Federal Govt. I am very familar with the reasoning behind this by the auto manufacturers. It basically saves about 0.06
MPG, which is nothing to the consumer but multipled by millions of vehicles it alows them to meet the strict and tightening EPA CAFE regulations and by doing that they can sell more profitable SUV's and have the CAFE #'s offset by the cars and smaller vehicles that get better
fuel economy. It's all a numbers game.
Recently several automotive manufacturers started using 5W-20 or 0W-20 motor oil as a factory fill. Most consumers have many questions about this "new" oil and why after all these years specifying a 5W-30 that they would make the change to 5W-20 or 0W-20. First I must explain that 5W-20 ( or 0W-20) is not a new viscosity motor. 5W-20 has been around since the early 1970's, but not used by consumers or marketed to consumers by manufacturers, until recently.
My research has uncovered the following from a SAE technical paper written by Mobil Research and Development Corp. in 1975 (o): "Research Oil 5 (RO-5) is a conventional 5W-20 viscosity mineral oil product containing an API SE quality additive treatment, but that it may be deficient in some API SE engine performance requirements. RO-6 is also a 5W-20 viscosity and API quality SE but utilizes all-ester (synthetic) base stock components. Adequate wear protection with conventional 5W-20 viscosity mineral oils has been difficult to achieve under moderate and high temperature operating conditions." Mobil's new 5W-20 synthetic formulation, XRN 1669 "has been evaluated in both laboratory and field tests to determine its antiwear performance. In all cases, wear protection equal to or better than premium API SE quality SAE 10W-40 mineral oils has been provided by this experimental formulation"
Now, keep in mind that this is from about 30+ years ago. My intent here is to show that 5W-20 is not a new viscosity of oil. It just never became widely used. The most popular motor oils back in that era for automotive use were typically 10W-40 and in later years 10W-30 and 5W-30. What this data indicated is that a 5W-20 petroleum oil provides adequate engine protection under normal operating conditions, but does not compare to a premium quality 5W-20 synthetic in moderate and high temperature operating conditions. The new 5W-20 oils of today are formulated to meet the latest API SL performance specifications and are perfectly suitable for use in your new vehicle that specifies 5W-20, however my personal opinion is that there are superior oils to use that not only meet the 5W-20 performance specifications, but also exceed them.
Here is a brief discussion of some of the most common questions consumers have regarding the 5W-20 motor oil that is specified for their new vehicle.
Question: Do I really need to use 5W-20 or 0W-20 oil?
Answer: You certainly can if you choose to, however there are also other viscosities you can use such as 5W-30 and 0W-30 that also meet manufacturers and API specifications. One of the main reasons 5W-20 or 0W-20 was specified for your engine is to increase the CAFE (Corporate Average Fuel Economy) reported to the Federal Government. CAFE is the combined average fuel economy of all of a vehicle manufacturers product line. Minimum CAFE levels are specified by the Federal Government. In order for a vehicle manufacturer to continue selling profitable large trucks and SUV's, which typically have poor fuel
mileage ratings, as compared to smaller cars, and still meet mandated CAFE requirements, they must also sell enough of the smaller cars which have much
better fuel economy ratings to offset the poor fuel economy ratings of the larger vehicles. The change to a 5W-20 or 0W-20 oil will allow a manufacturers overall CAFE to increase by a very small amount, typically in the tenths of a mile per gallon range. 5W-20 and 0W-20 oil is a lighter viscosity than a 5W-30 oil and therefore has less internal engine frictional losses, or less drag on the crankshaft, pistons and valve train, which in turn promotes increased fuel economy. This increased fuel economy is *******ly undetectable to the average motorist without the use of specialized engine monitoring and testing equipment under strictly controlled test track driving when compared to a 5W-30, 10W-30 or a 0W-30 viscosity motor oil. Note that certain specific vehicles, such as those with cylinders that selectively cut out to save energy, typically specify a 5W-20 or 0W-20 and for those vehicles it is best to use the viscosity recommended by the manufacturer.
Question: Could using a 5W-30, 10W-30, 0W-30 or even a 10W-40, oil in my vehicle which recommends a 5W-20 oil void my
new car warranty?
Answer: Vehicle manufacturers recommend using motor oils meeting certain viscosity grades and American Petroleum Institute service requirements. Whether a motor oil is a 0W-20, 5W-20, 0W-30, 5W-30, 10W-30 or 10W-40 or even a synthetic vs. a petroleum based oil will not affect warranty coverage. The manufacturer is required by Federal Law to cover all equipment failures it would normally cover as long as the oil meets API service requirements and specifications and was not the cause of failure. In addition, the Federally mandated Magnuson - Moss Act states that a manufacturer may not require a specific brand or type of aftermarket product unless it is provided free of charge. If your dealership continues to tell you that you must use 5W-20 or 0W-20 motor oil and or/ a specific brand of 5W-20 or 0W-20 motor oil (and will not provide it free of charge), then ask them to put it in writing and then contact an attorney. Their position is inaccurate, and, in fact violates existing law.
Additionally, if there is ever a question of whether or not a particular motor oil was the cause of an engine failure make sure to get a sample of the used oil in a clean bottle, typically 6 oz. minimum. The oil can then be sent to an independent ASTM certified testing lab for analysis. This is standard procedure for most commercial vehicles, trucking, construction/excavation and fleet companies and there are many certified test labs all over the country. Remember, a knowledgeable and informed consumer is your best defense against being taken advantage of by a car dealership service center.
Question: My car dealership service center states that I must use 5W-20 or 0W-20 because the oil passages inside my engine are smaller and a higher viscosity oil will not properly flow through them. Is this a true statement?
Answer: That is ridiculous to assume that a manufacturer would purposely make the oil galleys and passages smaller. There is no technical or cost/performance benefit to doing this in reference to recommending a 20W motor oil over a 30W motor oil. My inspection of oil galleys, pistons, bearings, crankshafts, oil pumps and passages from pre-5W-20 and 0W-20 recommended oil engines to the same size and brand of engines that now specify 5W-20 or 0W-20 indicate there are no measurable differences in the oil passages in these components.
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