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5W-20 Oil?

We recently purchased a slightly used 2008 Honda Accord. Our other cars are 1990’s cars, so I assume technology has changed things since then.

To my surprise, Honda says the Accord uses 5W-20 oil. When manufacturers started recommending 5W-30 for cars some while back, some friends told me this is just an effort to increase the mpg for the car model, and that 10W-40 would still protect the engines better, especially during hot weather.

I generally do what the manufacturer recommends. But I think it’s possible that they are more concerned with fleet mpg than the longevity of a particular unit.

Thoughts on this?

Engineering has bearing tolerances much smaller these days that in years past. A thicker oil can’t get into the eeny-teeny spaces properly and can cause oil starvation and engine damage.

The lighter weight oil moves more rapidly at engine start-up, providing lubrication for critical parts. Your engine doesn’t run hotter in the summer than it does in the winter, so you don’t need heavy weight oil to provide protection during warm weather.

Honda engineers are some of the best on the planet, and the engines they design are some of the most reliable and long-lived. Stop trying to out-think them. Use the recommended oil and follow the recommended change interval. The engineers test their engines under all kinds of horrible conditions. If your engine needed 10w40 in the summer your owner’s manual would tell you so. It doesn’t because you don’t.

In addition to the great replies you’ve received thus far, are you willing to use an oil weight that Honda doesn’t recommend - and perhaps invalidate your warranty?

All excellent posts…I especialy liked Ken’s “eeny-teeny spaces” description.

All of these posts are supported with real world data. Engines today last two to three times as long as the engines of old with far higher reliability. When I was young 100,000 miles was about all you could get out of a car without starting to worry about the cost of a ring job and a valve job. Today engines are routinely going 200,000 to 300,000 miles without wearing out.

I think that the recommendations for thinner oil are the result of at least four things. First, oils are better so a 5W-20 protects better at high temp than it used to. Second, fuel efficiency is better so CAFE numbers go up. Third owner manuals have been dumbed down. You can’t have dealers answering questions from relatively ignorant new car owners about the three or four oils recommended for different temperature ranges. Fourth, with increased oil change service intervals, the decision to change from one oil spec to another with seasonal change is not as easy (see the above comment relatively ignorant car owners).

The other big difference I see in car manuals that indicates that they are being written for relatively ignorant owners is the lack of tire inflation recommendations for loaded vs. light load conditions. It used to be that they discussed increasing inflation with higher loads.

For clarity, my “eeny teeny spaces” is in reference to the main, rod, and cam bearings. An incorrect viscosity here will cause big trouble in the future.

eeny-teeny spaces also include the hydraulic variable valve timing actuator at the end of the camshaft. Oil flows through very small orifices to advance or retard the rotation of the shaft, and so control how soon or how late the valves open and close. Switching to 10W-40 could render this system ineffective or less effective, robbing you of engine power and reducing your gas mileage.

Honda doesn’t use a variable valve timing actuator at the end of the camshaft. The v-tec engine has two different cam lobes for each set of intake valves. The rockers are paired so the the valves follow one or the other lobe depending on load conditions and engine RPM.