Vacuum

[Bob_G]

Anyone had experience of engine rooms operating (at cruising revs) under vacuum? Been told this may be why both engines leak engine oil after a few minutes at 2300 rpm when there is no obvious leak problem. Not enough air getting into the engine room, forcing oil out of the engines?!

Solutions- phone book under the hatch or wider ducting (impossible to instal)

Comments welcome. Cheers

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[boatless]

I'd have thought that if the pressure got that low the engines would stop?

<hr width=100% size=1>my opinion is complete rubbish, probably.

 

[Dave_Snelson]

I'll put good money that vacuum isn't your problem, because it would cut the engines, or make them smoke terribly. A badly ventilated engine room is against all regs anyway. The engines build up internal pressure when running anyway and the faster you go, the greater the pressure. Check all the engine breathers aren't blocked. Also, when the engines get warm, the oil gets thinner, and so they could leak. Are the engines worn out or old? Have your oil checked by an engine surveyor.

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[Bob_G]

Great that's just what I thought! Though 6.6 litres times 2 times 2300 rpm is a hell of a lot of air! Guess with some vacuum they would still suck and run ok cos turbo assisted. Had Finnings on (they're Cat 3116's) who found no leaks.

So no solution guess I'll have to find another engineer..

Thanks for your help

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[Bob_G]

Well I suspect the turbos would still suck the air but.. at some point..

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[jon_bailey]

Difficult to believe that vacuum is significant enough to pull oil out of engine but why not try long length of clear tube dipped into coloured water (used champagne?). Height that liquid pulled up the vertcal tube will indicate size of vacuum. i.e. 33 ft of water is equivalent to 1 ATM. Try to make sure end in engine room is not near moving air, e.g. air intake.

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[Col]

Sounds like cobblers to me.

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[Deleted User YDKXO]

I take it you're talking about your own boat, a Fairline Phantom 40? This is relatively new and popular so I very much doubt that there would be any problems with insufficient air intake volume. If there was, I'm sure it would be well known by now
In any case, I cant see that the engines can create a 'vacuum' as such only a marginal reduction in pressure. There are just too many openings in the engine bay for it to be totally airtight. So, if you can only create a small reduction in pressure than the change in differential pressure across the seals can only be small so unlikely to be reason for leaks IMHO
Have you looked at the boatdiesel. com website on <A target="_blank" HREF=http://boatdiesel.com/index.cfm?CFID=2396276&CFTOKEN=75233331&CFApp=19&&CFIDC=NRU2>http://boatdiesel.com/index.cfm?CFID=2396276&CFTOKEN=75233331&CFApp=19&&CFIDC=NRU2</A>

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[malcolm2]

I would have thought that such a vacuum would be capable of imploding any structural panels, floors or bulkheads in the engine space, long before it would extract oil from the engine.

Do they run OK with any inspection hatches removed.?

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[gonfishing]

Oil Test

Hi Dave
a quick and easy test for fuel dilution can be done by passing a measure of new oil through a filter paper and timing how long it takes to filter through, then take an engine sample at the same temp and same volume etc and pass through the same grade filter paper,again timing how long this takes,any significant differential in the time between the two will indicate fuel dilution or carbonisation of the oil both giving an indication as to the state of the engine ie if it passes through a lot quicker that will indicate fuel dilution a lot slower and that will be oil thickening / carbonisation, another wear indicator.
Julian

Julian

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[jfm]

This is total nonsense. Yes the running engines cause a slight vacuum in the engine room, possibly offset by electric fans on the intakes. But whatever happens here (a) it is only slight and (b) it is a change in the ambient pressure, which means it will have an effect on the atmospheric pressure inside the sump etc, so there will be no differential pressure caused by the partial vacuum

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[itsonlymoney]

One word to say on the vaccum theory.
"Bollocks"
Ian

<hr width=100% size=1>Play the best game you can with the cards you've been dealt ! ! !

 

[Bob_G]

You mean if the ambient pressure reduces so will the sump pressure? What about the effect of the pistons?

Thanks for the response

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[Bob_G]

Next thing to try!

Thanks

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[Bob_G]

Yes got the boat right in one!
It is one of the first and is semi prototype, and does admittedly have small ducting and fans from the side vents.

But you comments noted- thanks

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[Bob_G]

Excellant idea. Would need to be sealed between the engine room and the saloon but I'm prepared to try anything to stop the revolting engine room I get after a two hour run.

Thanks

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[Bob_G]

Thanks! Definately the consensus!

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[jfm]

Yes the pistons etc have an effect, but they will have that effect whether the ambient pressure in the engine room and inside the sump is at a slight vacuum (compared with outside) or not. All I'm saying is that if the ambient engine room pressure is a slight vacuum (as it often is) then that will apply to the ambient inside the engine block too. Any other dynamic efficts like the moving pistons will be overlaid on the background ambient pressure. But the slight lowering of ambient pressure will not itself cause a pressure differential inside/outside the engine so it cannot be causing the oil leak.

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