I have been using 5w-20 mobile 1 in my s2k for the last 2 oil changes. Is there any downside to this? I heard the thinner oil will help with fuel efficiency and engine protection in the mild California weather.

 

So...... you think you know better than the Honda engineers who designed the whole car and decided/recommended that it's best to use 10w-30? hmm...

 

I would think you would use a lot of oil.

Mobil 1 is 10W30 is something less than 30W and it literally seeps out of my AP1.

 

You're going the wrong way if you drive in So Cal, the thinner 5W characteristic is supposed to help in very cold temps. I don't think you'll get much benefit (or problems for that matter) in a street driven car.

 

Only one way to know for sure, sample it for oil analysis. You might be fine, you might have the potential for more wear. You may increase fuel efficiency slightly and perhaps grab a bit of extra power, but at what cost? Without analyzing it you really don't know and the safe bet is the factory recommendations.

As far as thinner providing better protection, no. Not unless you were running fluid that was too thick for the car/conditions. Southern California is ideal as far as weather conditions and when would it ever be cold enough to justify the 5w?

 

i always used 10w30 castrol full synthetic but since i've been boosted i've used 10w40

 

These motors tend to shear various oil ,brands, many 30 weights end up being in the high 20 range by the end of their oil change interval. If you run a 20 weight it could end up being in the 10 range if it shears. You'll notice that all of Honda's high revving (8k+) motors are spec'd with 30 weight oils, the non-high revving variants of those engines are spec'd with 20 weights, there has to be a good reason for that.

Run a good 5w30 if you want some better oil flow characteristics at start-up and in cooler temps, I run Amsoil 5w30 spring/summer/and fall. I run 20 weights in my daily driver that is designed to run it, but I wouldn't use it in my s2k.

The best built 5w20 oil based on specs is Redline 5w20, it is one oil that can offer you some added protection if you want to do your own testing on 5w20 oil. One member on here ran it and posted up some used oil analysis data on it, the results were okay if I remember correctly, but I think a good sythetic 5w30 offers the best of both worlds and will outperform a 5w20 in this engine. Just my two pennies.

 

30 weight typically shears down to 20 as its in the S2000's engine; I'm not sure I'd want to start at 20 weight and let it shear from there. Will a 20 shear down or is that the happy point for oil in the engine? 30 weights shear to 20 and other UOAs i've seen show no wear problems, so maybe 20 new is okay, but if it were me I'd want some proof.

Only way to know for sure is to get a used oil analysis and see. www.blackstonelabs.com

Let us know what the results are.

 

Its common for Mobil1 to seep in the S2k's engine; try a different oil and it will stop or be less.

 

I myself use 5w40 for the track, Eneos ftw!