I’ve seen this idea in a number of blogs but no one ever manages to answer it. My new Ford Fusion says to use 5W-20 oil but if you look at the British ford.co.uk website, they suggest 5W-30 over there. The suspicion is that while 5W-20 is adequate to get you through the warranty period and generally past 100k miles, 5W-30 would be better but would cost Ford enough on their Corporate Average Fuel Economy (CAFE) rating that they don’t want to recommend it. Am I being paranoid?
Are you absolutely sure the British Ford uses exactly the same engine?
Oil viscosity does have an effect on fuel economy.
So you’re not shooting in the dark.
Personally, though, I’d stick with the oil called for in your American owner’s manual.
We’ve had this discussion before and Docnik and we had an oil engineer for a while, seemed to provide good answers. Based on tolerances and so on, who knows but you just have to use what the book says.
I agree with the other answers here with one caveat. A lot of owner’s manuals will allow one weight up from the recommended oil. I know my owner’s manual does.
Here is another possibility…
In Europe, due to governmental pressures, car mfrs now specify incredibly long oil change intervals–intervals that most of us in this forum believe to be…just plain looney. Is it possible that car mfrs have found that a higher viscosity oil is more resistant to viscosity breakdown during those ridiculously-extended intervals, as compared to a lower-viscosity oil?
@mffitz You are right, but it is not a conspiracy. North American cars (Canada, USA) are subject to Corporate Average Fuel Economy (CAFE) standards for the fleet of cars they sell. Even the tiniest increase in fuel economy will allow the manufacturer sell more larger cars, which are also more profitable. It also often makes them sell small cars at a loss; Ford never made money on the Escort in North America.
Europen requirements, as stated are entirely different. Their long oil drain intervals are dictated for environmental reasons and instead of fuel standards, they have tailpipe carbon emission is grams per kilometer. So heavy duty oils with a higher viscosity are called for. Many have 5W40 synthetic specs. A normal 5W20 mineral oil as specified here would not meet these 20,000 mile!!! or once a year drain intervals as specified by GM of Europe (OPEL).
I’m looking at the owner’s manual of my wife’s 2012 Mazda3 with the standard 2 liter engine. It calls for 0W20 synthetic as the preferred oil for Canada and the USA. In addition, it says for areas other than US or Canada, use 5W20 oil, and if that is not available (like often in Mexico), use 5W30 oil. Mexico does not have the CAFE standards. In tropical contries many service stations only have 20W50!! oil. I would not recommend anything so thick, however.
For the turbocharged Mazda engine, it calls for 5W30, since the thinner oils would not have enough film strength for the very hot turbo bearings. A Volkswagen turbo calls for 5W40 synthetic with a much tougher European spec.
My son has had a Mazda 3 since 2004 and now has well over 130,000 miles on it. He uses, on my advice, a 0W30 full synthetic which will give easy starting in the morning and good film strength when driving in the SW in the summer.
My advice is to NEVER tow a trailer across the Mojave Desert in July with a cheap 5W20 mineral oil in the engine!! And if you live in a cold region and park outside, NEVER use oil starting with 10W, resulting in considerble enginewear on startup. The valve gear of modern engines uses the oil as a hydraulic fluid, so it has to be thin enough at low temperatures.
A late friend who was a major oil company lube expert, once coached a Corvette racing team to victory, He thinned out all the lubes, and put 0W20 synthetic oil in the engines which have very generous clearances, and normally called for 5W30 synthetic oil. The race was only 500 miles, but the engines went through a lot of oil but they only needed to last 500 miles before being rebuilt. Engine durability was not an issue here. He claimed 5-8% increase in power on the dynamometer.
However, as other say, observe the manufacturer’s recommedations and use what they say until the warranty is up. Always use synthetic and pay a little extra. Then I would switch to a full synthetic 0W30 quality oil, and change it every 5000 to 7000 miles depending on your driving pattern. We are after long engine life here, not saving money on oil changes. Keep all your receipts.
Hope this throws some light on the confusion.