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post #21 of 53 Old 07-27-2014
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Re: Universal M25 Knock?

Here is another possibility - you inadvertently added diesel with low cetane. You could try a cetane additive to determine if it makes any difference. Did you buy the fuel from a different source than you normally do?
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post #22 of 53 Old 07-27-2014 Thread Starter
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Re: Universal M25 Knock?

This O'day 35 has the original 1986 Florida Marine Tanks 35 gallon tank;


I use about 20 gallons of diesel per year, and always top it off from my marina before winter layup, so it has never been fully drained. I tape the vent closed, and close the fuel shutoff during winter layup.
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post #23 of 53 Old 07-27-2014
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Re: Universal M25 Knock?

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Originally Posted by eherlihy View Post
I installed new injectors last winter, replaced the valve cover gasket (not needed), and upgraded the heat exchanger from the 2" to the 3"... nothing that should have mussed up the timing though.
The more I think about the intermittent nature of the problem the more I think it may be an injector problem. When knocking and putting out excess smoke one of the injectors may not be producing a proper spray pattern, due to debris or water?

If it was fuel starvation I think you would just lose power. Kind of sounds like fuel may be puddling up? Are there any indications that excessive blow by vapors can be collecting in or near the intake tract?

Having the injectors checked by a shop would be easier than pulling the head?

James' comment about cetane additives would be an easy try. Or maybe a heavy duty "cleaner" additive? I used to use this in my VW diesels & never had any fuel related problems:

DIESEL KLEEN® +Cetane Boost®: Max HP Formula ? use during non-winter months for the ultimate in performance.

I am sure there are lots of different additives that may be as good or better?

Paul T.

Edit: Just saw your picture, the tanlk has been around for a while.

I did some tests with the Power Service additive a long time ago. Put some diesel in a coffee can, added a little water to it, then added the additive & the water was no longer visible. A tank that old may very well have some water in it. However, a good filter/separator should catch it. Some units have a clear bowl on the unit allowing you to see water or debris.

Paul T

Last edited by dabnis; 07-27-2014 at 04:29 PM.
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post #24 of 53 Old 07-27-2014
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Re: Universal M25 Knock?

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The more I think about the intermittent nature of the problem the more I think it may be an injector problem. When knocking and putting out excess smoke one of the injectors may not be producing a proper spray pattern, due to debris or water?

If it was fuel starvation I think you would just lose power. Kind of sounds like fuel may be puddling up? Are there any indications that excessive blow by vapors can be collecting in or near the intake tract?

Having the injectors checked by a shop would be easier than pulling the head?

James' comment about cetane additives would be an easy try. Or maybe a heavy duty "cleaner" additive? I used to use this in my VW diesels & never had any fuel related problems:

DIESEL KLEEN® +Cetane Boost®: Max HP Formula ? use during non-winter months for the ultimate in performance.

I am sure there are lots of different additives that may be as good or better?

Paul T.

Edit: Just saw your picture, the tanlk has been around for a while.

I did some tests with the Power Service additive a long time ago. Put some diesel in a coffee can, added a little water to it, then added the additive & the water was no longer visible. A tank that old may very well have some water in it. However, a good filter/separator should catch it. Some units have a clear bowl on the unit allowing you to see water or debris.

Paul T
Thought maybe you might have missed the edit.

Paul T
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post #25 of 53 Old 07-27-2014
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Re: Universal M25 Knock?

Molecules of water going thru the injector tip tear helll out of the tiny holes Bad spray pattern can blow holes in the piston top. Sounds like knocking until the serious blowby starts. Some fuel additives can carry the water to places it's not meant to be .Catch it early.
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post #26 of 53 Old 07-27-2014
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Re: Universal M25 Knock?

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Molecules of water going thru the injector tip tear helll out of the tiny holes Bad spray pattern can blow holes in the piston top. Sounds like knocking until the serious blowby starts. Some fuel additives can carry the water to places it's not meant to be .Catch it early.
I have read about but never had the water/injector problem, that I know of. If there is water in the tank It would be good to get it out before it goes into/thru your filter/separator. From the picture it looks like there is a port cover/cap that may be able to remove on the left side. If so, maybe put a piece of hose into the forward left corner & use a pump to pull it out. Suggest you not try to siphon it by mouth. I swallowed a LARGE mouthful of gasoline doing that.

Perhaps you could weight the boat so that the forward left corner of the tank the lowest. I think most pick up tubes are not right on the bottom of the tank. So if you are picking up water, there may be a fair amount of water in the tank. After removing the tank cap, you may be able to see any water rolling around in there?

A good filter/separator should catch any water or debris? "Should" is the key word.

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post #27 of 53 Old 07-27-2014
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Re: Universal M25 Knock?

[QUOTE=eherlihy;2045465]This O'day 35 has the original 1986 Florida Marine Tanks 35 gallon tank;


E! isn't that steering cable a bit on the loose side of tight?

Me's dunno nutin bout no molly cues meself

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post #28 of 53 Old 07-27-2014
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Re: Universal M25 Knock?

I think that's one of them Tadslack steering systems.
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post #29 of 53 Old 07-29-2014
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Re: Universal M25 Knock?

remove oil filter cut open look for metal,nometal pull injectors,they will knock like a rod.When it knocks open injector lines one at time if noise stopes that cylinder is where the problem is.
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post #30 of 53 Old 07-30-2014
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Re: Universal M25 Knock?

Quote:
Originally Posted by eherlihy View Post
Yes the decreasing oil pressure has been a long running mystery. It starts out at 50 PSI, the gradually drops, but never so low as to sound the alarm. It has done this for the past 2 years, possibly longer.
It's probably not as much of a mystery as you would think.

IMHO it is probably nothing more than a failing oil pressure sender unit. This is quite common - I have had it on my own boat and recently had exactly the same thing on the wife's car. On the boat it went on for a few years getting gradually worse. On the car it went from normal to "no pressure" in about a month.

As the engine warms up the resistance in the sender changes and indicates lower and lower pressure but never sets off the buzzer. That's because the buzzer has its own sender and doesn't use the signal from the gauge sender so is sensing the "real" pressure which is probably normal.

For the cost of a new sender unit, the peace of mind is worth it.
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