Nds123 Posted December 23, 2014 Report Share Posted December 23, 2014 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. Link to comment Share on other sites More sharing options...
martyn 1 Posted December 23, 2014 Report Share Posted December 23, 2014 (edited) 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 December 23, 2014 by martyn 1 Link to comment Share on other sites More sharing options...
Stilllearning Posted December 23, 2014 Report Share Posted December 23, 2014 I would echo what Martyn has said. A different engine, but a friend of mine used to worry about the oil pressure on his Lister HA till he checked the gauge! Link to comment Share on other sites More sharing options...
Tony Dunkley Posted December 23, 2014 Report Share Posted December 23, 2014 (edited) 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 December 23, 2014 by Tony Dunkley Link to comment Share on other sites More sharing options...
Nds123 Posted December 23, 2014 Author Report Share Posted December 23, 2014 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. Link to comment Share on other sites More sharing options...
MtB Posted December 23, 2014 Report Share Posted December 23, 2014 I think what Tony was seeking clarification on was whether the engine has always dropped to 5/8psi after two hours of running, or whether it used to stay high and this dropping after two hours is new behaviour. MtB Link to comment Share on other sites More sharing options...
Tony Dunkley Posted December 23, 2014 Report Share Posted December 23, 2014 (edited) 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 December 23, 2014 by Tony Dunkley Link to comment Share on other sites More sharing options...
by'eck Posted December 24, 2014 Report Share Posted December 24, 2014 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. Link to comment Share on other sites More sharing options...
flatplane8 Posted December 24, 2014 Report Share Posted December 24, 2014 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. Link to comment Share on other sites More sharing options...
Nds123 Posted January 1, 2015 Author Report Share Posted January 1, 2015 Thank you all fellow boaters for all the information you have shared with me and hopefully other boaters Thank you Link to comment Share on other sites More sharing options...
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