Oh no not another oil thread...Merc 25/40 Vis Delo 40

[Lou C]

Agreed, Rick, I for sure will do it. Now if you're willing to disclose your oil choice (lol) why not post up an oil analysis of yours, Blackstone makes it easy because they sell a nice vaccum pump that you can use to pull a sample out without contaminating it with other oil from the vaccum pump you use all the time. We could create a database like Bob is the oil guy and put an end to speculation and say once and for all, this oil is fine, or you really need something beyond 10w-30, or whatever the results tell us.
Even just looking at the difference in cruise RPMs from automotive to marine use, you're circulating that oil through the system 2x as fast, given that rpms are roughly double.
Thinking back, I had a Toyota Corolla GTS (1989) with the Toyota 1600 twin cam engine. These engines were set up to produce peak power at 6600 rpm and redlined at 7500. Cruise RPMS at 70 were about 4100 and it did have an engine oil cooler... I used 20/50 in hot weather....

 

[HT32BSX115]

You know, Consumers Reports did an article on Motor oil back in the mid 90's or so and Consumers Digest did one in 2010 I think............

They used a taxi-cab company and ran the oil 3000 miles, 6000 miles and more. They were trying to dispel some "conventional truths" like changing oil at 3000 miles and that some brands were "better" than others.

After all the testing on the engines (10 months and about 60,000 miles) , they tore them down and inspected.

They also used the GM 4.3L engine in the tests...... this might be of interest to the people here that have it installed in their boat. They also had flat tappets. So they could test the wear "bug-a-boo" that everybody here and elsewhere worries about in older boat engines!

For consistency, we used only 1992-93 Chevrolet Caprice cabs. Each received a precisely rebuilt 4.3-liter V6 at the beginning of its 60,000-mile test. We started with six rebuilt engines; after each engine was installed in a cab, the six engines that were removed were rebuilt and installed in six other cabs-and so on. Using that rotation, we monitored 75 cabs over 4-1/2 million miles of driving in New York City and its environs. Each oil was tested in three engines. A local shop completely machined each engine block and crankshaft, rebuilt the cylinder heads, and installed new bearings, pistons, rings, seals, gaskets, and oil pump. Though the engines originally had roller lifters and camshafts, a design that reduces friction, we installed conventional sliding lifters and camshafts to accelerate wear.

I would encourage everybody to read that article. Here's the Consumers Digest article: http://www.consumersdigest.com/print/article/motor-oil

Forget what Dad, Big Brother, Uncle, Pet Mechanic, big truck driver, marine mechanic or Briggs & Stratton store tells you.............It simply doesn't seem to matter what oil you put in your engine if you use the recommended grade and change it when you should................

And no. I won't tell.......my oil is classified.!!

 

[Lou C]

I do recall reading that way back when....but I can tell you having been someone who used cabs in NYC for a period of time back then and I still do from time to time...in typical NYC traffic, they rarely get over 30 mph. These engines ran around the clock, but I doubt they were ever run at the high revs that boat engines see. More typical use is they are idling, creeping forward, they might hit 35 mph tops between traffic lights.

 

[HT32BSX115]

These engines ran around the clock, but I doubt they were ever run at the high revs that boat engines see. More typical use is they are idling, creeping forward, they might hit 35 mph tops between traffic lights.

But in general, oil doesn't "age" from being used at constant RPM and/or load anywhere near like it does in frequently cycled engines.

Frequent cycles (cold-soaked starts, and shutdowns) put far more "stress" and wear on an engine (and oil) compared to an engine that is run at constant power settings with more or less constant temps........which is probably why stationary engines, over the road trucks and other vehicles can go many hours and thousands of miles between oil changes....... (and why oil analysis can be used to extend oil change intervals)
[The newest Detroit Diesels can go as far as 50,000 miles (or 1200hrs) between oil and filter changes]
https://www.demanddetroit.com/parts-service/supportbymodel/engines/dd15.aspx

4-stroke marine engines are a lot more like stationary engines than they are like automotive engines because they run more at constant power settings (although they also are run at MUCH higher continuous power settings)