10-30

5W-30 is what I use for my 305 TBI. I've always used that and I've just hit 108,000 on my car the other day. Engine is running stronger than ever. The motor oil that is used for higher mileage engines really doesn't do much unless you're experiencing some problems. I hear from the commercials that these oils can actually replenish the seals in your engine but I think that's a bunch of doo-doo. Just stick with the 5W-30 and you should be fine.

i'd use heavier in heat and thinner in cold

I agree with ede. I use 10w30 in my GTA in the summer. Don't drive it in the winter so that really doesn't change.

5w will never hurt anything. For warmer climates on higher mileage motors, I'd us 10w30

Run 5-30 when less then 60 degrees outside. Otherwise run 10-30 the rest of the time.

What they say - "0W-30 Enhanced Fuel Economy Formula". Thinner oil takes less power to pump through the engine. Since that is the "W" number, it applies when the oil is cold (or, at least, not hot).

I'm using AMSOIL 0W-30 in most of my vehicles. The difference between mileage with it and 5W-30 or 10W-30 is small, but when multiplied by all the vehicles on the road, becomes more significant (but still a small percentage of total consumption).

I run it year round.

10W-30 should be just fine.

Another tidbit of information: Why 5W-x oils exist. 20 years ago, North America went through a prolonged cold snap, with temps at -20 F for a couple of weeks over a large part of the country. People using 10W-30 and 10W-40 petroleum oils, whose cars sat outside all night, would go out in the morning, start them up, and drive off. Problem was, the oil was too thick for the pump to pick it up, and the car companies paid for a whole bunch of warranty engines with wiped out bearings. They went to the oil companies and said they wanted a pour point of -20 F. The compromise was to impose the -20 F pour point on 5W oils, but not 10W on up weights. Notice that I included the "W" in each statement above, because the "W" is the cold temp rating.

FWIW, none of the car companies paid for a single engine that had Mobil 1 or AMSOIL in it that winter (for that reason, at least).

Any of the Mobil 1 oils you mentioned in your original post would be fine to use year round. The only one that is at all marginal is the 15W-50, and only because it really isn't needed and the extra thickness would cause unnecessary and completely avoidable drag. There wouldn't be any other harm, though.

whats the matter with 20-50 don't you want the heaver oil in the summer for better lubrication?

Doesn't necessarily work that way. With synthetics, it's typically a waste (although you're still getting better lubrication and efficiency than you would with any petroleum oil).

so what everyone i ssaying is that the higher milage engines should not go out and buy the higher milage formula unless problems are arizing?

what if you valve seals need changing? would that be enough to get 10w-30 highermilage formula mobil 1 synthetic?

Vavoline says they add seal softening agents to their high mileage oil. That won't fix seal wear or cracking, though, only hardened seals (and most likely won't help SBC valve stem seals in any way at all).

Mobil 1 Higher-Mileage Vehicle Formula is a synthetic/petroleum blend with seal conditioners. It costs less than full synthetic, so it won't cost you as much to add oil as the older engine burns it. It also isn't a bad choice for synthetic change-over, as it will help clean up deposits left by petroleum-based lubes. Just change it sooner than you normally would.

WOW! Ive been using 15/50 mobil1 syn for the last 3 years, is that bad?

The "weight" that is assigned to a particular oil means that viscosity falls within a certain range. The "W" number represents the viscosity range at low temperature, and the number w/o the "W" represents the viscosity range at high temperature.

In general, a 30 weight oil will be thicker at high temperature than a 40 weight oil. But, since the ranges overlap a little, it is possible that the 30 and 40 weights are exactly the same thickness at high temperature.

Your change-over plan would be okay. If deposits aren't particularly heavy, though, you could run it for whatever drain interval you chose right from the beginning.

Having used the 15W-50 oil isn't "bad", it's just been taking more power to pump it around than necessary without any extra protection benefit.

"In general, a 30 weight oil will be thicker at high temperature than a 40 weight oil"

You sure about that? It'd seem to me the 40 weight oil would be thicker...temp for temp?

Oops, change "thicker" to "thinner". I was going to say the 40 was thicker than 30.

Sorry about that. Good catch.

Ok this is really starting to get out of control!!!! Is anyone paying attention here???

Its like this:

1. Synthetic provides greater protection and longer change intervals.

2. If the outside temp is over 60 degrees run 10-30 syn.

3. If the outside temp is under 60 degrees run 5-30 syn.

4. Anything over 10-30 syn is overkill unless you spend most of your driving time at WOT, but as hot as factory 3rd gen runs 10-40 aint gonna rob much power at all if any, 15-50 is well beyond the requirement of any street car no matter what your mods are.

5. You folks dont own race cars, you own low compression smogger TPI motors, the factory fill is fine to run as well all year round.

6. If you are having a hard time understanding what "viscosity" means, use the damn search button indtead of keeping this thread alive.

Hope this helps!

Just go with the 5w-30 year round. If you dont feel comfortable with an oil that thin then just use the 10w-30 year round. Either will work good, and as others have stated anything heavier than that isn't necessary. I run 5w-30 mobil 1 in my LS1, my LT1, and my L03.

If you want to keep one grade all year round that is fine, there is more then enough info here for you to be able to make that choice.

If you want further info on 0-30 you need to cal Mercedes Benz and talk with one of their engineers about bearing clearance and oil pump pressure, LOL!!! Right now I cant think of any American cars that have 0-30 as a factory fill.

I personally think it's a little too thin, but I seriously doubt you would hurt anything.

I don't know, evidently mercedes uses 0w-30 as a factory fill and they must have a reason for it. Most chevy's use 5w-30 as factory fill. They most likely also have a reason for it.

What oil would be good for 0 degrees to 90?

5-30 syn I assume

Hmm - interesting. I live in Colorado where it gets into the 90's in the summer and the -20's in the winter. (sometimes it can do all that in one day, well, almost!) I have an 87 350TPI with 125k on the engine, in the winter I run 10w-30 and in the summer I run 20w-50. When I am running the 20w, oil pressure is 60+ PSI cold and 45-50 PSI hot idle. 10w-30 will get me 50-60 PSI cold and 30 PSI hot idle. Isn't more PSI ( up to a point of course) better? I would think you'd want to run the oil that your car is happiest with, and that's gonna vary depending on your car, and the driving conditions.

ok so 10-30 is good for the stock engine what if you're running a high performance engine 500hp+ say a 383 or a 400 and you're at WOT alot?

When the throttle is wide open

I run 15-50 in My Formula, Lumina, and Maxima , and 10-30 in my grand Prix