[Putershark]

Originally Posted by Zachary

Very good and detailed response. I do have a few questions.

With regards to burning off any deposits, I can understand this with regards to cars because they tend to cruise at, say, 2000 rpm on the highway. I have gunned my cars every so often in order to remove any deposits, and notice that the engine runs better afterwards (although this is not scientific, just my perception). On the other hand, when outboard motors - whether 2 stroke or 4 stroke - cruise around at 4,000 rpm, then that should be way more than enough rpms to burn any deposits. Am I wrong?

With regards to water/humidity in the oil, I understand that revving the engine to WOT helps heat up the oil and thus burn any humity/water. However, wouldn't it be just better to change the oil during shorter intervals?

With regards to making sure than a propeller is the right size/pitch, I also understand that point as well. However, shouldn't the dealer, who sells that brand of boat, with that brand of engine, and thus that size/pitch of propeller, know the proper size/pitch so that you don't need to push your new boat at WOT? Honda and Yamaha, for example, have detailed performance figures for many types of props on the same boats. That way you know exactly what the figures will be with particular props.

Am I wrong on any of these issues?

Thanks,
Zachary

Carbon Deposits mostly form during the engine cool down (burning away) process (like leaving eggs on the skillet too long) and without the correct fuel additives that problem can get very bad and force you to use a higher than normal octane rating fuel due to all the build up (be it your Truck or Outboard). Now many cleaners will remove gum and varnish, carbon though is hard, yet very porous (like a sponge) and very hard to remove. High Speed runs help to remove such deposits as long as you use the correct cleaner like Techron or Yamaha's ring free (which is the same stuff) yet the problem effects 2 and 4 strokes differently.

2 Strokes (mostly older ones) leave a ton of deposits behind due to the burning of oil on every power stroke. If one uses a high quality (synthetic) 2 stroke oil the issue is greatly reduced, but it is still issue for most engines even the newer HDPI models. Over time the rings on the piston's can seize up and the loss of HEAT transfer from the piston to the block for cooling, causes the most failures. And here you thought that rings were only for oil control and compression sealing


4 Strokes suffer carbon build up mostly on the piston crowns and valves slowly forcing the owners to use a higher and higher octane grade of fuel to get the same performance. The carbon deposits on the valves and injectors is a real killer of performance and picture your engine (in human terms) trying to jog with your hand over your mouth... So with the correct fuel additives and higher temps from such runs, you can help knock off these deposits. Now as far as crankcase oil goes, the left over moisture that does not get burned off (really is it boiled off due to the heat) forms a acid that causes the rust that "can" lead to failure. So the thinking that changing the oil more frequent is logical, though does not help if you do not get the engine temps up "High Enough" to "remove" the water and the acid that it forms afterwards in the first place... This no matter how new or "Clean" the oil really is.

So yes the dealer "should" not only know which prop is best for your combo, your combo will change with "your" boat loading for most times, it is just the tech and maybe a few gallons of fuel in the boat for such testing and break in process (if they even do such) when it is on the dealer's lot.

We also have to remember that these engines are design to run at such RPM's for extended periods of time. Now I don't run flat out for miles upon miles upon miles, it is needed during each trip on the water for some amount of time to get rid of the moisture build up and it's possible very corrosive effects.


So like our 60 year old brother in the other comment (like my Father) who was raised (and I can remember some myself) in the era of Big Block, Big Piston, marginal lube qualities the "Thought" of running anything stock above 5 grand makes them shiver... Those old cars could come all unglued if one would to run them at such RPM's for very long. Today though it is a different ball game... We have much smaller engines with different cam shaft profiles, Computer controls, better metals, and better lubes and gaskets, returning the same amount of work and at much better fuel burn rates... Granted, you will not get your best MPG when running that fast (like 4000 to 4500 RPM will) it still does not hurt them at all to run them that fast for 5 to 15 min on the run back to the ramp and can hurt them in the long run, if you do not


Now I do not subscribe to this "Drive it like you Stole it" theory, that does come into play some when it is under warranty cause that is the time you WANT it to come unglued IF it is going to happen to your engine... Engine's can fail at any time I agree, but I would much rather have that failure (after recommend break-in runs) while the factory will cover those repairs and not years later for sure...


Hope this helps answer your questions some? And some of the guys here might say "What does that mouse driver Dave know?" (Fair question) Well many may not know this, but I was first an Engineer in the Coast Guard, Chief Engineer for a private SAR & Salvage firm, then spent 10 years as an Import German and Japan (Porsche, Audi, BMW, Toyota) Automotive Service Director... So you could say, that Dave "may" remember which wrench to grab and when, (though not as good as I did 10 years ago) and did that for quite some time before trading in the 10mm box end for a mouse full time. At lest now the keyboard and mouse don't have grease all over them all the time like they did years ago! Ha-Ha...


Dave