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Then back to my point…why dont we run 25w-40 in our cars in the summer? Its only at 25 for an instant ya know. You would have your MOFT in your car too.

Referring to a cold start. Doesn’t matter what temp. A 10W will be thinner than a 25W. If quick silver is a straight 40 weight, then this is not the best oil for your boat. This is basically an oil with a crappy viscosity index. Its 50s oil technology. Oil companies invested tons of engineering...

The viscosity units of measure are different at the W than the high number. Oil is always thicker when its cold despite the lower number. The question is, why would you ever want it that thick cold?

Why would you use a 25w and not a 5w or 10W in a boat engine? The W is the cold viscosity, the 40 is the hot viscosity. Everyone says its because boats work harder, and oil temp runs hotter. Everyone knows that. But when you start and idle a boat cold, its just like any other car engine. So, why...

Okay then. We should all run 25W in our cars when its warm out. Not the 0W or the 5W. Thanks wpod! I knew that the automakers just want our cars to wear out fast so we buy new ones. I just knew it! Not my car! So grateful Quick Silver followed the science and developed this oil grade and gave...

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.

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...

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!

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...

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...

Ok, if I sum up what you all are saying is that the oil type is designated based on how the engine is used, not based on the design of the crank and journal bearings or other internal parts. Im guessing the engineers felt the extra protection needed at constant WOT and 3/4 throttle justified the...

So, the logic is that since marine engines are pushed much harder than a car engine, and operated above freezing, it needs a much thicker oil for protection. But, why wouldn’t you run 25w-40 in your car engine, which is basically the same, to give it more protection?. Wouldn’t it last longer if...

Isn’t monograde horrible for engines at cold start? Wouldn’t any engine be better off with a synthetic 10w-40? Or even 5w-40? Not a 25W.

Hi Bob, My 4.3 L mercruiser specifies 25W-40. But, the 4.3L Vortec in a GM car specifies 5W-30. I assume the Marine version has the same crank and bearings. It actually runs a lower coolant operating temperature than a car. So why the big change in the viscosity requirement?