Oil failure

"My Volvo Penta 5.0 OSI-E was

"My Volvo Penta 5.0 OSI-E was backfiring at cruising speed and above, after 1-2 hours of running. After sitting all night the problem would go away and repeat the next day. Replaced plug wires and plugs (did not fix problem), but problem was eventually determined to be oil which had lost it's viscosity, causing oil starvation after engine was hot at cruising speed and above (could hear tap, tap, tap). Got oil changed (both old and new were Amsoil synthetic), and backfire probelm has disappeared. Does this make sense that I really have solved the problem.... I am skeptical."

"Was that a backfire or a misf

"Was that a backfire or a misfire? How long was the old oil in there before you changed it? What viscosity are you using? What type of ignition system does it have? Distributor? If so, is it points and condenser or is it breakerless electrnic?

Stay away from the ----- who recommended Amsoil!!!!"

It was a backfire. Not sure o

It was a backfire. Not sure of viscocity put in at the shop. Electronic ignition/Fuel injected. No points and condener. Most boat shops around here use Amsoil.

"I suspect you may have tempor

"I suspect you may have temporarily fixed your problem.

How often do you change your oil/filter?

What was your temperature readings during the times when it was experiencing problems?

Are you running your boat for a long period of time past your 'cruising rpms' near WOT?

Have you examined/replaced your impeller lately?

Your oil will break down(even synthetic) when it's temperature exceeds it's viscosity rating.
Did you have your centistokes tested in the old/bad oil?

This could come from a number of factors including limited flow of your cooling system(most likely), over or underfilled oil capacity to your motor, obstruction of your engine's lubrication system(including filter), operation for a long period of time at high rpms at excessive temperature, your boat being over loaded(excessive load on engine) or a combination of all of the above.

At any rate, there's lots of opinions on what to run in our boats and ultimately is up to you. We all use our boats differently in most cases to being a fishing boat/ski boat/cruiser/etc... in different parts of the world.

Personally, I use conventional in my boat due to the frequency of oil changes and the cost difference. I use synthetic in all of my vehicles(Mobile 1). And everything I own gets a dose of Lucas Oil Treatment... tractors, atv, skid loader, snow blower. I like the stuff alot.

Perhaps oilguy will find his way back to the boards and give his

Also, El Pesc has some keen insight on why he runs a little heavier oil in his craft than factory rec... something I personally do, finding validity in his observation."

"Tom, I just went from 15W-40

"Tom, I just went from 15W-40 to 20W-50 in my 5.7 (ex AQ311). The original engine came with an oil cooler (which I got rid of) and with the oil cooler installed the oil specification was 10W-30. However, the same base engine run by Mercruiser uses 25W-40 and does not have an oil cooler; and newer Volvo Penta 5.7 also do not have oil coolers, but now the factory recommended oil is 20W-50.

The reason I went to a higher oil grade (again) is that, after running the engine at cruising speed for 1/2 hour or more and with good pressure (50-60 psi), once I reduced the speed and idled the engine, I could hear the valves tapping and the oil pressure would drop to below 20 psi. As you suggested, this is clearly a viscosity related problem. In my case, the symptoms can be clearly explained because at idle there is less flow (the oil pump turns at lower RPM) and the oil was too thin due to the viscosity range and being too hot. In your case, however, I would look at why did the oil become thinner at cruising RPM or why was there oil starvation. I am not sure which viscosity range is your oil (I hope you are using the right one for your application) and you did not say what was the oil pressure when you had the problem. In any case, I think that the symptoms you experienced and that were "cured" by the oil change could have been caused by fuel dilution in the oil lowering its viscosity (this can happen when you idle the engine for long periods of time), or by a glogged oil filter, or by the oil bypass valve opening too soon, or by one or more lifters in bad condition.

PS. I forgot to add that my 5.7 has installed a FW cooling kit and the coolant temperature is 180º, which is higher than in many raw water cooled engines. This is why the oil gets hotter (and thinner) during operation than in comparable engines that are raw water cooled."

"El, he did list some numbers

"El, he did list some numbers here...
http://www.marineengine.com/discus/messages/12487/86665.shtml"

"Engine temp never got our of

"Engine temp never got our of normal range (175 or less). Recently boat was loaded up for a long trip and had to run in the ocean, keeping up with bigger boats with twin engines. Wondering if running above 4000rpm in 2-3 seas for a while, ruined the oil? Could I have gotten a bad batch of oil on my last oil change (was at 95 hours - I am now at 130 hours).

Right before the backfire when the tech was on the boat and he recognized the oil starvation, the oil pressure dropped to 20."

"Tom, I still think it could h

"Tom, I still think it could have been fuel dilution or a clogged filter. If you always ran in calm water and all of a sudden you went in the open seas and ran over swells, don't be surprised if some sediment that otherwise would remain at the bottom of the oil pan became stirred and ended clogging the oil filter."

Any other causes for fuel dilu

Any other causes for fuel dilution besides extended idle?

"A faulty fuel injector, or to

"A faulty fuel injector, or too much fuel being injected at idle."

"Sticking valves can happen wh

"Sticking valves can happen when sludge builds up in the oil. Detergents that are a part of the additive package put into modern oil helps deal with that but eventually the detergents start to break down and are overwhelmed. Over the years those detergents have been improved to a great degree but there is a limit.

I can tell you right off the bat that any mechanic pushing Amsoil does not have your best interests in mind. Keep you oil changed at regular intervals. You should come up with an interval of months as well as engine hours, which ever comes first. Trust the recommended viscosity of the engine manufacturer.

In light of the apparent low pressure running at temperature I'd try the recommended straight weight oil, should be straight 30 or even straight 40 weight. If your oil was really dirty the last change, you might want to do a couple of changes close together to help clean it up."