Along with "flow lubricates" and monograde oils being "horrible" for your engine, cold startup wear is never an issue. Every grade has sufficient viscosity at cold startup to provide more than an adequate MOFT.
Why does my boat engine specify 25w-40
- Thread starter Cousineddy
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Ok, so 90% of engine wear occurs at startup is not true. And, flow is not required for a hydrodynamic journal bearing to create a separation force. You just need viscosity. Got it.
My car specifies 0W-20. This must be the tree huggers trying to give me better fuel economy at the expense of wear. Should I run 25W-40 in my Lexus? I actually do drive this car hard, like a boat.
My car specifies 0W-20. This must be the tree huggers trying to give me better fuel economy at the expense of wear. Should I run 25W-40 in my Lexus? I actually do drive this car hard, like a boat.
MOFT always wins. A 20-grade oil will provide an adequate MOFT under most circumstances in everyday driving in your vehicle.
Flow has never lubricated a bearing but the film thickness always has. HT/HS is your friend here.
And no, 90% of wear does not occur at startup.
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Oh oh, just saw those thick vs thin threads below. Now I am confused again. Here is a quote:
“It is time to introduce the concept of lubrication. Most believe that pressure = lubrication. This is false. Flow = lubrication. If pressure was the thing that somehow lubricated your engine then we would all be using 90 grade oil. Lubrication is used to separate moving parts, to keep them from touching. There is a relationship between flow and separation. The pressure at the bearing entrance is irrelevant”
“It is time to introduce the concept of lubrication. Most believe that pressure = lubrication. This is false. Flow = lubrication. If pressure was the thing that somehow lubricated your engine then we would all be using 90 grade oil. Lubrication is used to separate moving parts, to keep them from touching. There is a relationship between flow and separation. The pressure at the bearing entrance is irrelevant”
Not everything you read on the Internet is correct is it?
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True dat. I wonder why they call journal bearings “hydrodynamic” if they don’t use flow for lubrication. Maybe its cause they spin. And engineers thought it sounds cool. Alrighty then. Thanks everyone!
Boats go their top speeds at high RPM’s unlike a 1997 Chevy Blazer equipped with the 4.3. It might go 70 at 2200 RPM, but that’s about it. A boat may cruise anywhere from 5-8k.
25w40 is a 40 weight oil, but more shear stable. Marine oils also have more “anti water” additives.
25w40 is a 40 weight oil, but more shear stable. Marine oils also have more “anti water” additives.
That’s not at all how hydrodynamic lubrication works. Plenty of information available about how it does work if you want to learn.
Coolant temperature is not oil temperature
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Pretty obvious statement. But let me state what I think you mean...oil temperature is hotter in a boat than a car even though the coolant temperature is 20F cooler. Its because it’s driven at much higher throttle positions for longer periods of time. Therefore, grade 40 is specified instead of grade 30 to achieve the same oil film thickness as the car engine.
Did I say that right?
Did I say that right?
Yes, that's probably why the thermostat is a lower temperature, since the coolant is the only thing helping to cool the oil, since in a passenger car the engine isn't normally subjected to such loads the block really isn't meant to keep the oil cool at WOT for extended periods so in marine applications the compensate by keeping the coolant at a lower temp is my guess, I don't really know that for a fact, kinda like how on the street you'd run 5W30 in a Corvette but on the track you'd run 15W-50 because when you run the engine at WOT for extended periods of time the sump temperature is significantly higher than it would be just driving around the streets.
MolaKule
Staff member
Please do a Reply (which quotes your source) so we can determine the source of your statements and to whom you may be responding.
One source for thinking about lubrication regimes may be these:
Back to Basics III
What is the name of the Graphical Representation that describes the Four (4) lubrication conditions or "Regimes?" as discussed in Back to Basics II? This question is open to all, but let's please allow non-engineers, non-Tribologists and non-chemists time to research the question and to respond...
bobistheoilguy.com
Does Oil Pressure Help Film Strength?
Does high oil pressure help film strength? Thinking of motors like the Ford Coyote V8 that runs on 5w20 and produces oil pressure of 20 to 25 psi per 1000 rpm - - about twice what used to be the norm of 10 psi per 1k rpm.
bobistheoilguy.com
Determining Proper Oil Flow to Journal Bearings
While traveling and teaching lubrication fundamentals courses at various facilities across the country, I am constantly reminded of the misconceptions that are rampant in our industry. Recently, I...
www.machinerylubrication.com
Oil pressure effects on viscosity
Fascinating article: http://www.machinerylubrication.com/Read/29654/journal-bearing-oil A quote from the article, Quote: Fluid pressure is generated in the lubricant film, which is able to support load due to its viscosity. Lubricating oils have a significant pressure-viscosity coefficient...
bobistheoilguy.com
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OVERKILL
$100 Site Donor 2021
We discussed this in a previous thread. Apparently, once-through cooling uses the lower (160F) thermostat temp in case of running in salt water. The salt will accumulate if the coolant gets hotter than that. Engines that are equipped with a heat exchanger run temps more similar to automotive applications.
Mercruiser Horizon (1999) 5.7l heat exchanger equipped engine using Mobil1 15w-50 oil for 22 seasons in salt water on Cape Cod.
Thermostat runs at 170 degrees.
Fresh water flush system installed to flush salt water side of cooling system.
Engine operating range at cruise 2800-3200 RPM.
Zero issues,
Thermostat runs at 170 degrees.
Fresh water flush system installed to flush salt water side of cooling system.
Engine operating range at cruise 2800-3200 RPM.
Zero issues,
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Thats what I run in my boat too. 25w-40 is just stupid. Its pretty obvious that Mercruiser gets a cut for pushing that oil. Mobil 1 is far superior.
Mercury and Volvo buy Chevy blocks and build their own engines with them. It is not a GM engine, only a GM block. So what works in a GM 4.3 engine has nothing to do with what might be appropriate in a Mercury 4.3 engine. I do not run mine hard like many do so I have sometimes use 15w-50 full synthetic. Whether that is a dumb idea or not only time will tell. The engine is only 14 years old. I change the oil once a year since it does not get a lot of hours on it.
No you dont, your car has wheels, your boat doesn't yet the engine still has to move it.
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Considering your off-base comments in this thread about flow and what hydrodynamic lubrication means, I don't think I'd put much stock in your suggestion here.
I have a 4.3 volvo/penta (GM), have always ran Rotella 15/40 in it
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