I have been using for the last 26 years the same basic oil strategy. A good 30wt detergent motor oil~Chevron~Valvoline~Mobil~etc and I add a pint of STP oil treatment. I have a very steady oil pereassure 15~20 @ idle (700rpm) and 35~40 above 1300 up. I also use a bypass type of oil filter set up from Fram.
My lil beastie is now 40 years old and still ticking although I did do a valve job on her 26 years ago. The only thing not original are a few valve "keepers" and one exhaust valve.
Fights friction to help protect against engine wear by providing a thicker cushion between moving engine parts.
This high-viscosity formula is specially formulated to help fight metal-to-metal friction by providing a thicker cushion between moving engine parts.
Helps
* Protect against engine wear
* Reduce oil consumption
* Protect engine parts
We also tested Slick 50 and STP Engine Treatments and STP Oil Treatment, each in three cabs. (Slick 50 costs $17.79 per container; STP Engine Treatment has been discontinued.) All three boast that they reduce engine friction and wear.
The engine treatments are added with the oil (we used Pennzoil 10W-30). They claim they bond to engine parts and provide protection for 25,000 miles or more. We used each according to instructions.
The STP Oil Treatment is supposed to be added with each oil change. It comes in one formulation (black bottle, $4.32) for cars with up to 36,000 miles, another (blue bottle, $3.17) for cars that have more than 36,000 miles or are more than four years old. We used the first version for the first 36,000 miles, the second for the rest of the test-again, with Pennzoil 10W-30.
When we disassembled the engines and checked for wear and deposits, we found no discernible benefits from any of these products.
The bottom line. We see little reason why anyone using one of today's high-quality motor oils would need these engine/oil treatments. One notable effect of STP Oil Treatment was an increase in oil viscosity; it made our 10W-30 oil act more like a 15W-40, a grade not often recommended. In very cold weather, that might pose a risk of engine damage.
Valvoline 30 weight, natural and detergent. In polling, neglected to check natural and detergent. I'd be tempted to try synthetic if people seem to like it. I use it in my autos.
The water temp in the bayou today is 90 F. So a heavier weight is proper IMO.
Back in the early 70's when I was in marine diesel repair school one of our assignments was to research which oil met most manufacturors and government standards. Chevron Delo 400 met everyone's requirments and I have been using in all of my engines since then except my Chevy Van towing vehicle for boats on trailers, car hauler trailer and my 22' HiLo travel trailer. On the advice of a cousin who worked for GM and the test facility in AZ, I have used Red Line synthetic engine oil and ATF. I am approaching 100,000 miles on the Chevy and she does not use any between changes and the tranny still works perfectly.
Of course, like the Atomic Four, my Chevy was built by Americans in America!
According to the summer newsletter, anything greater than SG is "too slippery" for our wet clutches. Currently I'm using 10 - 40 SL rating and looking for SG rated oil. So far no wet clutch slipping as far as I can tell.
The recommendation to look for SG rated oil (usually only found today at motorcycle shops) was only if you're having trouble with your forward clutch assembly slipping. As long as you can find a comfortable adjustment on your forward latching mechanism, SL or SM oil is OK.
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