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i have an old 460, i just replaced the bearings in it and i was gonna run a straight 30 in the summer, is this alot thicker then 10-40 at maybe 70 degrees? i run 10-40 in it now and i have good pressure but i want to keep it lubed good in hotter weather when running it hard. i dont spend alot on synthetic either, its an old beater. SAE 30 goods and bads? how about SAE 40?
Straight 30 may be thicker than 10w40 at 70F, but (assuming the SAE 30 and the 10w30 are both the same viscosity at 100C) if you exceed 210F the 10w30 will be thicker because the VII polymers prevent it from thinning as much. Of course if the VIIs sheer all bets are off and the SAE 30 would be better.
I think by "high detergent oil" you may be referring to heavy duty motor oil, that is diesel rated oils. You should be able to get HD or passenger car SAE 30s. You would have to look up the product data sheets for these oils. Supertech may make a regular and HD version (can't say I ever saw it though) and Superflow would be regular. I am familiar with Valvoline Maxlife and their SAE 30 and 10w30 have the same 100C viscosity and they should have the same detergent levels, which includes a large slug of calcium, but these are not HD oils. Apart from that I know NAPA sells their brand in SAE 30 and SAE 40, which I believe may be HD as the MSDS pulls up from their site as Valvoline All Fleet Plus, but beware they also have an SA/SB version which is not good for car engines after about 1934.
For your application I would use what is called a Universal grade oil. These are the oils that the truckers use in their diesels. Although they are formulated for diesels, they have all the highest certs for gas engines as well. To handle the soot of a diesel, they have lots of extra detergents and will keep your crankcase squeaky clean.
I have used this type oil for about 20 years in everything on my place from diesel tractors, cars and pickups, to gas cars, pickups, lawnmowers, etc. I only recently went to lighter oil for some of the newer engines that require it.
Examples of Universal grade are: Mobil Delvac, Shell Rotella T and Chevron Delo 400. They come most commonly in 15W40, but I know that Delo is available in straight 30 weight. That said, I have used the 15 40 year round in Texas and it takes the summers very well. I have run all these engines to high mileage and hours using this stuff.
shell makes a good 30w that won't shear that bad i was running 20w50 and i could only keep 20 psi warm and the 30 weight kept 35 psi in gear at idle so it helped rotella is also a good choice
Delo 400 and Rotella T are available in 15W-40 or straight 30 here in SoCal. I would go with the Delo 15W-40 because of the group II+ basestocks and moly.
Straight 30 weight is fine as long as the outside temps don't fall below 32 degrees F. I run Chevron straight 30 in my 1969 SS 396 El Camino and my 1970 Dodge Coronet R/T (440).