I know I've run that oil in the past, but after looking around my garage, I haven't seen a red-capped Mobil1 bottle in a while. I was probably running just the normal 0-30 (IIRC, that's what the normal Mobil1 stuff is...)

Gray cap is 5w30, green is 10w30. Or vice versa? And gold cap is the new extended performance stuff.

Mobil1 synthetic recently changed the bottle design and cap colors.

Old bottles:
0W30 = gray/silver caps
5w30 = blue caps
10w30 = green caps
15w50 = red caps

new bottles:
Caps are all bottle color (silver), but labels still use the same colors as the old caps.

I'm a firm believer in 5-30, maybe Scott, since your car is'nt necessarily a daily driver you could get away with some slippier stuff, but you don't need me to tell you that.
But around here 5-30 seems to be pretty decent.

When the car was daily driven, I ran 0-30 almost all the time. However, when I knew I was going to put the car through higher temps and additional stress (like 2 weekends in a row of autocross in 100deg weather) I would bump up to the 15w50. The heavier weight oil will protect the motor better in the higher temps and additional load, at the cost of horsepower.

For some reason, I thought my last oil change was with 15w50 because that was all that Walbogs had, but I can't specifically remember now, and my confusion was likely due to the new caps as mentioned by Khail.

I'll go look in the garage and try to figure out which of the 15 gallons of used oil is the container from my last change. :lol:

This is what I'm wondering... Is the above statement true? As I understand, oil has two functions:

1. To remove/distribute heat
2. To provide at least a 1 oil molecule seperation between moving metal parts.

OK, and 3 is to carry debris of combustion/wear to the filter.

With today's engines, is heavier oil ever better at 1 or 2?

I would think higher viscosity may offer higher pressures, but at the cost of flow volume. I would think increased flow would offer better 1 & 2...

I guess the question is if thinner oil can do #2 as well? As long as the temperatiures are not such that the oil is breaking down, again, I would think thnner is better to a point.

If I recall correctly I've been using blue cap 5-30 Mobil one.

Well, the 1st number isn't as important as the 2nd IIRC, at least in our application. The first nubmer is the cold weight of the oil. The second is the hot weight. The higher the number, the thicker the oil, the less prone to breaking down it is, as well as the more power it will rob from the motor.

For example, running 15w50 in the winter in your daily driver is probably a bad idea, since it will make the motor work extra hard pushing around all that thick oil. However, on a hot friggen day, when you're racing the motor, a 0w30 might be too light and could break-down reducing lubrication/protection.

At least that's the reasoning behind Mobil 1 selling their 15w50 as "for High Performance Cars".

One thing to note: Subaru's seem to have pretty good cooling systems, so even under extreme loads (racing on a hot day) the motor tends to stay around its normal temps, so the heavier oil probably isn't doing anything but lowering horsepower. Also, the difference between 0w30, 5w30, 10w30, and 15w50 probably isn't that much under normal operating temperatures. The 50 might be a bit thicker, but all the Xw30's are going to be the same at 180deg-220deg.

Anyway, that's my take on it... I certainly don't consider myself an expert on this topic.