Question:

[Destroyer]

Originally Posted by phatdaddy

i am glad that you need to change it annually, that insures you can get the lower unit off when you need to.

Now there's an argument that I can agree with 100%.

[Destroyer]

And lets take this a step further... WHY is it necessary to regulate the water flow pressure? I mean, think about it.. does it really matter what the pressure is, as long as the volume is sufficient to cool the engine? We're talking about metal engines, and I seriously doubt that additional water pressure will cause any harm. So you build up a higher head pressure with a centrifugal pump. Who cares???? The temperature of the engine will still be regulated by the thermostat, regardless of what the water pressure is. Automotive applications (like your car) have used centrifugal pumps forever, and they seem to run just fine with them. So why the big whup over higher pressure in an outboard? What would it hurt?

[smokeonthewater]

Higher head pressure is higher parasitic drag, less mpg and less power to the water.

[THEFERMANATOR]

Contrary to what you might think, higher head pressures CAN cause problems inside the engine. The gaskets and such for the cooling system would have to be completely re engineered to handle pressures in excess of 20 PSI. The only sealing surfaces meant to hold higher pressures are the sealing ring for the head gasket in the cylinder area only. Also higher pressures can have a negative effect on cylinder liners not only from abrasion, theres also cavitation, and micro bubbling at the cylinder liners from the engines combustion process. You are going to get micro hot spots which form tiny air bubbles along the cylinders in the cooling jackets, and these air bubbles under pressure can act like a snad blaster when a combustion event occurs. It is like a hammering action when the cylinder fires, and that hammering action acts upon the cylinder wall in the cooling jacket. As pressures increase, this event is worsened. Believe me, there have been attempts at finding something better, but if it existed don't you think somebody would have come out with it by now. The engines you are talking about with hard impellers osund more like tender engines used on non planing hulls where ingesting air at speed, high RPM useage, and other factors are not a concern, hence why they can use what they use.

And engineers have come up with a pump that can do multiple applications, it just so happens to be the rubber impeller that has proven itself for over a century now.

[Destroyer]

Originally Posted by THEFERMANATOR

Contrary to what you might think, higher head pressures CAN cause problems inside the engine. The gaskets and such for the cooling system would have to be completely re engineered to handle pressures in excess of 20 PSI. The only sealing surfaces meant to hold higher pressures are the sealing ring for the head gasket in the cylinder area only. Also higher pressures can have a negative effect on cylinder liners not only from abrasion, theres also cavitation, and micro bubbling at the cylinder liners from the engines combustion process. You are going to get micro hot spots which form tiny air bubbles along the cylinders in the cooling jackets, and these air bubbles under pressure can act like a snad blaster when a combustion event occurs. It is like a hammering action when the cylinder fires, and that hammering action acts upon the cylinder wall in the cooling jacket. As pressures increase, this event is worsened. Believe me, there have been attempts at finding something better, but if it existed don't you think somebody would have come out with it by now. The engines you are talking about with hard impellers osund more like tender engines used on non planing hulls where ingesting air at speed, high RPM useage, and other factors are not a concern, hence why they can use what they use.

And engineers have come up with a pump that can do multiple applications, it just so happens to be the rubber impeller that has proven itself for over a century now.

Ok, I'll go along with what you say as far as the re-engineering of various gaskets to take a higher pressure. So you'd have to use an automotive type of gasket. (Or some kind of pressure regulator elsewhere in the engine) But the cavitation and micro bubbling you speak of I have my doubts about. After all, you would have the same effects in a car, and I don't recall ever reading about it in and of my shop manuals.

You are spot on about the seagulls.. they are low speed engines for sailboats and other non-planing hulls. Still not convinced about the rubber impeller though.

[THEFERMANATOR]

Originally Posted by Destroyer

Ok, I'll go along with what you say as far as the re-engineering of various gaskets to take a higher pressure. So you'd have to use an automotive type of gasket. (Or some kind of pressure regulator elsewhere in the engine) But the cavitation and micro bubbling you speak of I have my doubts about. After all, you would have the same effects in a car, and I don't recall ever reading about it in and of my shop manuals.

You are spot on about the seagulls.. they are low speed engines for sailboats and other non-planing hulls. Still not convinced about the rubber impeller though.

The micro bubbling is more an issue with diesels due to the higher cylinder pressures, but it is present in gas engines as well. Do a search on INTERNATIONAL 7.3's(not the powerstroke, but the IDI version), and you will find plenty of problems with cavitation and cylinder erosion due to the micro bubbling and it's effects. As pressure increases, the effects are normally worsened. Outboards already use automotive grade gaskets or better. Most automotive engines rarely see more than 16-18 PSI whereas in an outboard that is common pressures, and 20-25 can be seen. I understand your thinking, but your over thinking it. I know many think they can build a better mouse trap, but i nthe end the tried and proven design normally wins out. This is one of those situations.

[Destroyer]

Originally Posted by THEFERMANATOR

The micro bubbling is more an issue with diesels due to the higher cylinder pressures, but it is present in gas engines as well. Do a search on INTERNATIONAL 7.3's(not the powerstroke, but the IDI version), and you will find plenty of problems with cavitation and cylinder erosion due to the micro bubbling and it's effects. As pressure increases, the effects are normally worsened. Outboards already use automotive grade gaskets or better. Most automotive engines rarely see more than 16-18 PSI whereas in an outboard that is common pressures, and 20-25 can be seen. I understand your thinking, but your over thinking it. I know many think they can build a better mouse trap, but i nthe end the tried and proven design normally wins out. This is one of those situations.

Not looking to build a better mousetrap, just wondering if one has already been built but they want to sell us new impellers instead.