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Use of 0W40 oil in engine that calls for 5W30 -Bad or good idea?

I know oil is like religion and politics. Everyone has an opinion...

I know several people who are running a Mobil 1 synthetic 0W40 in all their vehicles. This is a European spec oil which I understand are made to better standards than most API oils. People are running this in engines that call for 10W30, 5W30, 10W40, etc. and just buy this quality oil in bulk at a low price. I wouldn't be worried about the 0W in the spec for cold weather starts but was wondering if a 40W oil is too thick for driving down the road with the engine warmed up. Is this a bad idea? I know you might take a small hit in mileage which is one of the reasons everyone has started using thinner oils but would it be harmful or helpful with regards to engine wear and operation. The vehicles in question are a 2000 S-10 with the 4.3L and a 1997 Ford with the 4.6L The 4.6L is the 2 valve model and I don't think there are any issues with cam timing, etc. on these. I know some of the newer models used cam phasers and needed exactly the right oil to operate correctly. Both of the engines I mention call for 5W30.

I know that running an oil slightly out of spec would be better in a pinch than running it low but I am curious as to what opinions are here about this. I also know people who run the Rotella T6 5W40 synthetic "fleet" oil in a variety of vehicles and applications without issues. This is what I run in all my outdoor lawn equipment as it isn't much different in price than a quality conventional oil.


  • 0w40 full synthetic is pretty expensive, and total overkill for both of your trucks, I would say

    If you want to go one step better than the factory recommendations, why not run full synthetic 5w30 in your trucks?

    There are more choices for 5w30 full synthetic. Napa even has a 5w30 full synthetic, which is considerably cheaper than Mobil 1 full synthetic oil. But I haven't heard any opinions about it yet
  • Expensive ?
    $26 for 5 quarts at Wally World ain't expensive !
  • edited November 2013
    I agree that it is over kill. Sure, $26 for 5 quarts at Wally World may be cheap, but what do you think the least expensive API certified 5w30 oil which is more then adaquate for your trucks, will cost ? Like, $14 for 5 quarts !
    I would like to save $12 for every oil change for no appreciable difference IMHO in performance. Too much thinking a buck or twelve and go with mineral 5w30.
  • Oil serves three functions. it lubricates, cleans, and removes heat.

    If you use a thicker oil when the engine is hot the oil flows slower. This means the oil spends more residence time in critical engine components and doesn't remove the heat as quickly as the thinner oil because it flows faster.

  • For those 2 vehicles I would not go with 0W40 synthetic (European spec) from Mobil. As others point out, the cars don't call for any special oil. If you live in a very cold region and have to park outside, a 0W30 US spec synthetic would be a good choice. If you live in an area with a normal climate, a generic synthetic 5W30 will add additional life to the engine, which becomes important if you want to get more than 300,000 miles out of it.
  • Actually, the reason I was looking at this oil is because it is CHEAP compared to other oils of its quality. I am sure it is way overkill as I know this stuff is designed to hold up for the long haul in turbo diesel Audis and such. I can get this oil for between $20-25 on sale in 5 quart jugs. Check your local Wal-Mart for deals on this. I have read it is a much better oil than most of the other Mobil 1 products yet it goes on sale for exactly the same price. Sometimes the parts stores will have 5 individual quarts with a filter for around $30. If the filter of the day is decent, I sometimes go this route.

    The reason against me running the Mobil 1 5W30 is that I understand those who have run oil analyses on it suggest it is a Group 3 base oil as is the 10W30. Europeans wouldn't allow this to be labeled as a synthetic by their standards. The 0W40 appears to mostly be Group 4 base oils which are considered "true" synthetic oils by some. Mobil considers their exact oil formulation to be proprietary information and will not release the ingredients list so individuals have figured out some of the details by submitting unused oil for analysis.

    Any of the 5W30 oils meeting the European specs of the 0W40 above would cost at least 2.5-3x that of this Mobil 1 product so this is why I am attracted to this one. I also drive a 1994 Geo Metro as my daily driver/beater/work car due to the mileage and these tiny engines are very hard on oil. All the enthusiasts of these little cars suggest European spec oils to help prevent stuck rings and such that these engines are subject to if oil is neglected. The 0W40 is on the "approved" list of oils for these engines even though a 5W30 is specified in the manual. The engines were developed 30 years ago and oils have advanced a long way since then. I use this oil in the Metro and was thinking about just using it in everything so I only have to buy one kind of oil.
  • I don't know why my messages sometimes take so long to appear. Anyway, it looks like any decent synthetic is oil for other of these engines if you want to go the extra step in protecting the engines. I currently have just shy of 300,000 miles on the Ford and it doesn't use a drop of oil between changes. I am sure the body is likely to rust away before anything serious goes wrong with these engines so this is likely overkill as others have suggested.
  • These sound like older vehicles with a lot of miles..They are a lot looser that when they left the factory, so 0-40 isn't going to hurt anything except your wallet....
  • Yeah, they are all older but still run well. Although I haven't taken apart any of these engines to measure clearances, etc. they do not use oil between changes and the engines sound smooth without clattering or knocking sounds. I am sure some wear has occurred but cannot tell. The Ford has many more miles than the Chevy which has around 110k. I have had that once since it was new and have always been a stickler about oil changes and other routine maintenance. I know people who have gone up a grade or two in viscosity to maintain oil pressure and prolong the life of really worn engines but these still have like new oil pressure on the gage.

    Some engines, especially the valve trains, are picky about oil viscosity. For example, using too thick of an oil in the 3 cyl Geo Metro I have, especially the cold/startup viscosity, will result in the lifters overpumping and burned exhaust valves rather quickly. Most run a 0W or 5W oil in these little engines. A 10W is bad news unless you live in a warm climate and mainly drive on long trips where startup wear becomes minimal as a percentage of miles traveled. I know other engines, especially those with some type of variable valve timing, are not forgiving to using other than the specified oil weight.
  • Your assuming the 0-40 is much better than 0-30 based on test results of others. Perhaps the euro oil stock IS actually better. I would not assume the US stock, sold at Walmart is for sure the same. There is a reason stuff is cheap at Walmart.
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