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Oil pressure JS3M


Nds123

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Hi

Can one please help. I have the above engine ( JS3M )

The problem is when I start and cruise the oil is 15/20psi however after say 2 hrs the oil will drop to around 5/8 psi.

There is no black smoke the sounds good

You help in this this little matter would be appreciated.

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I would start by checking the oil pressure relief valve is clean inside, undamaged and seating properly. Is the engine fitted with a separate oil tank? the location of this differs depending on if it has one or not.

 

Secondly anything above 5psi to 20 ish is fine for a JP/JS or JK if below 5 its a problem and needs looking into.

 

Kind Regards

 

Martyn

 

P.S what oil are you running it on?

Edited by martyn 1
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Hi

Can one please help. I have the above engine ( JS3M )

The problem is when I start and cruise the oil is 15/20psi however after say 2 hrs the oil will drop to around 5/8 psi.

There is no black smoke the sounds good

You help in this this little matter would be appreciated.

Has the [hot] oil pressure suddenly dropped to the 5-8 psi, or has it run at around that figure since you've had the engine.

 

I think you're probably the gentleman I saw in Trevethick's dock in early Summer this year with the ex fishing boat engine, but I can't remember if it had the standard Lister dry sump tank or a different type.

Edited by Tony Dunkley
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Hi to every one who has gave me some very helpful information.

Yes I was that gentleman we meet at Trevethick ( ian&colin)

It has a dry sump with a sep oil tank to one side with a 30 oil

It does not suddenly drop down it will slowly drop down to around 5-8 psi

I hope am worrying about noughting at all.

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Hi to every one who has gave me some very helpful information.

Yes I was that gentleman we meet at Trevethick ( ian&colin)

It has a dry sump with a sep oil tank to one side with a 30 oil

It does not suddenly drop down it will slowly drop down to around 5-8 psi

I hope am worrying about noughting at all.

 

You've misunderstood what I was asking. Has it always run at 5-8 psi after a couple of hours when the oil has warmed up, or is this something new that it's doing?

Do you know if the oil tank is a Lister type with two built in circular gauze screens to filter the return oil, and if it is, when were the gauze strainers in the oil tank last cleaned?

Edited by Tony Dunkley
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Hi to every one who has gave me some very helpful information.

Yes I was that gentleman we meet at Trevethick ( ian&colin)

It has a dry sump with a sep oil tank to one side with a 30 oil

It does not suddenly drop down it will slowly drop down to around 5-8 psi

I hope am worrying about noughting at all.

At what revs do you only get the 5-8 psi when warm?

 

I get something similar with my JP2M, which could be over 25 psi when cold in winter at around 450 rpm, but dropping slowly over three hours or more to as low as 10 psi at same revs in summer. Having just fitted a tachometer though, I realise that you really need to get the revs up to say 800 rpm or more to get a true and meaningful pressure reading, bearing in mind Lister suggest idle speed between 400 and 500 rpm. Pressure rises noticeably at the higher speeds although they may not be practical on shallow canals.

 

Note also a roof mounted pressure gauge may read 1-2 psi lower than one at engine level.

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We have an old JP3M in our barge that does exactly the same thing, starts at 25 psi plus and then will drop to 10 or below when hot. Our engine is a bit worn, so this is what I'd expect. Also our idle speed is about 300 rpm which is too low really. In short, I think your pressures are pretty normal for these old engines.

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