Sorry to bring up another oil thread.

This forum and the Mobil 1 website have tons of information on synthetics. I'd like to take the plunge, but I'm not sure what viscosity/weight/grade of Mobil 1 to use. My Toyota takes 10W-30 so I'd use Mobil 1 10W-30. My 91 300SE takes 20W-50 year round. The closest match is 15W-50. Should I use another viscosity/weight/grade in the San Jose, CA area? The 0W sounds intriguing, but will I regret it when the temps hit the hundreds?

Thanks,
Sixto
91 300SE
138K miles
1 qt every 5K miles

You could have asked a question like "can I use 0W-40 synthetic oil for stirfry" which might at least leave you less open to criticism! To answer your question, I would use simple 10W-30 in San Jose.

Kuan

What Does The Manual Say?
 

Use the viscosity that your owner's manual recommends.

If you like the 20W50, I'd use the 15W50. It's getting too damn hot too early around here to be using 10W30...

Thanks for the responses. The question I was skirting is why there isn't a Mobil 1 20W-50 since that's a popular enough viscosity, as in most oil manufacturers/bottlers sell that viscosity.

Thanks,
Sixto
91 300SE
... in for a trreat next oil change

I think I understand what you're asking...
The viscosity numbers indicate the relative viscosity of oil when cold (first number) and when hot (second number). In order to make conventional motor oil behave like 50W when it's hot, they have to start with 20W base stock. It's a long story, but I'll try to give you the "Readers Digest" version...
GM spent a ton of money in the eighties on a study of sludge accumulation that they (and several other manufacturers) were having a problem with. They found that the biggest problem was with 10W40 oil. It just took too much V-1 friction modifyer to bring the 10W oil up to 40W specs when hot. The excess V-1 would vaporize and condense on internal engine parts. The result was that all of the dealers (MB included)in warm climates began to use 15W40. Some manufacturers (like Volvo for example) even went so far as to state that they would not honor engine warranty claims if 10W40 was used. 20W50 oil didn't have the same problem since the "base stock" oil was twice as thick as 10W40 (it takes less V-1 to bring a 20W oil up thirty points than a 10W oil).
So anyway, the point is that they don't have to make a 20W50 synthetic since they can start with a lower weight synthetic and still make it behave like it's much higher weight oil when hot. The best of both worlds; oil that flows well when cold, and protects well when hot.
Is science great or what?
Regards,
Randy D.

Fine.
But I still don't know how comfortable to be with Mobile 1 0w40 with a forty point spread. I live in Texas and use 10W30 synthetic in a E420. I like the idea of having a low cold number to reduce start up wear, so I have not gone to 15w50 and would not use a 20w50. But I may be missing something.

Another Attempt To Answer The Original Question...
 

From: National Oil & Lube News, December 2000

"Synthetic motor oils have a significantly lower pour points and better cold cranking capabilities than petroleum based products. The cold weather performance of synthetic motor oils and lubricants is probably the most recognizable feature of these high tech lubes. Long after petroleum oils have solidified, premium synthetics continue to flow. Some synthetics on the market have a pour point of sixty and seventy below zero."

Does that answer your question? You see, it's not so much intentional, as it is a natural phenomenon. You can't compare a synthetic with petroluem in this regard despite the coincidental fact that they both have motor oils rated at 10W30. And the W isn't for "weight", it's for "winter"...

And as regards apb's comments. Is 10W30 what your owner's manual recommends for the climate in Texas? If I were located in a hot summer climate like Texas has, I would run 15W50. In fact, for the relatively mild climate of Northern California, my owner's manual suggests that 10W30 isn't sufficient for my car, and instead, it specifies using a 15W50 oil.

In fact, the chart that is located in the technical data section in my manual shows 10W30 is for use in temperatures ranging from -4°F to +50°F. 15W50 is used from +23°F to above +86°F. For year-round use, it specifies 10W40 or 10W50. It does not specify a single viscosity oil at all.