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Discussion Starter #1
I've used Castrol 10W-40 for years and years, but recently changed to 20W-50 based on something I read. I'm in central Texas, and man, it's HOT! The weight change was recomended because of the extreme heat here. I gotta admit though, I'm not exactly sure why it benefits me...

Can someone give me a brief explanation of the different weights, and why one may be better than the other?

Also, brands: seems like everything I read says that Amsoil is the best. Can anybody back this up from personal experience? Is it worth the extra money, and why?

And lastly, should I consider switching to synthetic; and how long could I go between oil changes? How many VMFers use synthetic, and what brand?

There...those oughta keep you busy!

Thanks!
 

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Basically the higher the number the thicker, or more viscous, the oil is. Multi viscosity oils such as 10W 40 act like a 10 weight oil at low temperatures so that it flows nicely and like a 40 weight oil at higher temps to keep everything protected. Keep in mind that a single weight oil such as straight 40 weight are considerably thicker at low temperatures than at high temps. Thus in the "old" days it was typical to run a different oil in winter than summer in northern states.

Higher viscosity can be used as a band-aid for low oil pressure caused by excessive bearing clearances.

Consumer Reports in a test on oils a while back. Basically they concluded that the closer the spread in a multi viscosity oil the better the oil held up. For example, 10W-30 held up better than 10W-40.

I think synthetics did hold up better but there was not a great difference.

I stick to conventional Valvoline or Castrol. A mechanic friend has seen too many cars come in that mainly used Pennsoil that were all gummed up. For that reason, I stay away from Pennsoil.
 

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One more thing, from Consumer Reports, the oil change frequency with synthetics was the same as for regular oil, every 3000 miles.
 
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Synthetics are only recommended for cars with some miles on them, I personally do the switch after 10,000 miles. (5 Regular oil changes, 500, 1000, then every 3,000) You have to run a Synthetic filter with Synthetic oil. The filters are specially designed for the oil and has a higher filtration rate. Mobil 1 is and excellent product, Amsoil is excellent as well. I believe amsoil recommends with there oil and filter, 10,000 miles can be run between changes with normal driving. Currently I run regular oil in my Clev. because I only have break in time on it and it holds 12 qts., can't wait to buy Synthetic for that. I run Mobil 1 in my Cherokee, Jeep recommends 7500 miles between changes, With regular oil I did 3000, with the synthetic and filter I do the 7500, and the oil is cleaner than the regular oil was after 3,000.
 
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10W30
First # 10 is the weight of the oil
The W tells you it is tested for winter use
Second # 30 is the properties at 212deg with no anti thinning ingredients.
The wider the viscosity range the faster the oil will breakdown under heat.10w50 has a wider range than 10W30 but will begin to break down under stress faster. In the old motors I dont use synthetics,finds its way past the old style seals too easily. I do use it in all my late model stuff and it is worth the extra cost,but I put alot of miles on my cars (30k plus per year) so the extended range between changes helps.
As far as Amsoil goes I would not waste my money
 

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Discussion Starter #6
So basically, we all know that motor oil thins with heat. And since I'm in such a warm climate (pretty close to 100 for two or three months), it makes sense for me to start with a thicker grade...that's the logic, right?

It never really gets terribly cold here either...maybe a few freezes each year. Does it make sense to continue something as thick as 20/50 year round?

I guess synthetics aren't necessary for me. I've never had any problems with good ol' Castrol - and I change it religiously. So, if it ain't broke...

Thanks for all the replies so far.
 

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I would bet money that your engine runs hotter than even the hottest Texas summer so I don't see any advantage for you to switch to a heavy weight oil.

Stick to 10W30 or 10W40.
 

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My basic rules regarding oil:

Oil weight : use the lowest weight possible to keep the oil pressure acceptable. New Mustangs use 0W-20 for example.

Oil pressure when using standard oil pump: anything over 30psi (20psi when hot) at idle and 50psi at 5000rpm is fine.

Oil pump: use standard for street

The brand and synth: if you change oil often enough, it doesn't matter for normal motoring.
 
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