A "0w" oil question...

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Sep 27, 2003
Princeton, TX
I'm sure this has been asked before, but I can't seem to find it by searching.

I have been watching all the UOA's on the GC and would like to give this stuff a try. The only thing is, I live in Dallas, TX. It's pretty hot here in the summer and cold in the winter.

I am currently using M1 10w-30 in one car, and getting ready to run Auto-Rx in the other, and was going to run the M1 after the treatment.

I'm just scared of the "0w" part of this oil. How does this oil hold up in the heat? I noticed that the 40*C and 100*C viscosity’s are thicker than M1 10w-30, and I like that part! Also, the M1 is $1 cheaper than the GC...Is the Castrol worth the extra buck?

Thanks for all your help,
Brian Miller
Do not let the 0w part scare you into thinking it can't be run in the heat. It's the viscosity at operating temperature (100C) which you should be more concerned with, and in the case of GC 0w30 and Amsoil 0w30, they are both thicker 30wt oils than most 10w30s out there. And both of these oils have shown to retain their viscosity well too. Both have excellent HTHS numbers, making them very good candidates for the high stress of summer driving.

And you are correct in looking at the 40C viscosity, because in the hot summer your oil will be close to 40C soon after you start it, so as you can see in both Amsoil and GC 0w30, it is similar in thickness to 10w30 oils on a summertime start. But the beauty of a 0w oil is that when the temps get colder out, they can keep themselves from being too thick. Even if you don't see temps much lower than the freezing point, a 0w oil will still benefit you, as it will flow better than a 5w or 10w at these colder temps. And for anyone who is going to see temps colder than 0F, you'll definitely benefit from having the quick flow of the 0w.

I've been using and selling 0w-30 synthetics for eight years here in Alabama and have never run into any issues. One of the main advantages of 0w-30 over 10w-30 is improved fuel efficiency, particularly if you do lots of short trip driving. I've had numerous customers report gains of about 2%-3%, when switching from the Amsoil 10w-30 to their Series 2000, 0w-30. Many of these local customers are aerospace engineers and they are very AR about their vehicles! I saw similar gains in my personal vehicles when the Amsoil Series 2000 was first released in 1995.

I think the GC, 0w-30 would be excellent for your situation. I"ve been impressed with the wear protection I've seen so far in the oil analyses ....

Dixie Synthetics
Just to try to make it simpler. the 0W-30 oil will get thicker as the temperature drops below 100C. So the only concern is does the GC stay in grade (remain a 30 wt at 100C ) . Since we are now cooler than summer-its a safe time to try the oil. We'll have more experience with this oil before next summer.
I cannot say that GC is worth the extra buck over Mobil1, but I can tell you it's not worth the extra .50$ over Amsoil ATM. But I am biased.

The other guys have nailed it and spiked it as to the 0W part. UOA's are a beautiful thing. 0W's really are 0W's. Leave the summer part to the other number.
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