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Posted: Tue May 05, 2009 1:28pm

Post Subject: electrical

About 2yrs ago I fitted a Durite electric pressure gauge to my Lister Canalstar engine. On initial startup it gave a full scale deflection (FSD), the fault was traced to a poor eath connection. Since then it has been ok, until about 2 weeks ago. On startup it goes to FSD so I diagnosed a faulty earth but, not having the time to faultfind immediately, I didnt investigate However, later in my cruise I noticed that the gauge was reading normally --"intermittant fault" was my first thought. This happened on several following cruises but 2 days ago I noticed that when I raised the engine speed from tickover (800rpm) to approx 1200rpm, the gauge flicked from normal to FSD. On reducing RPM it dropped back to normal. Over a period of time I played with RPM settings and observed voltmeter, ammeter readings and charging rate at the time-- none have shown any variation at the flickover stage. Today, on a cold, morning start, RPM at 700, gauge still gave FSD. Ammeter reads 45amps, 1x40amp charger on and 4kva genny in circuit. 15mins later, engine at correct temp, RPM now 850, gauge is slowly flicking between 20-80psi. Increasing to 1200RPM gives FSD, back on tickover the reading is normal for a few seconds then resumes the slow flick 20-80. Additional info--the charging system comprises 35amp alternater plus 4kva generator, charging via split diode, Stirling battery management , 2x40amp Stirling chargers. Engine battery 1x110amphr, service 5x140amphr. I would appreciate your help with this problem. Peter Bishop


Posted: Tue May 05, 2009 4:28pm

Post Subject: electrical

Dear Peter, the first thing to check with any gauge giving full scale deflection is the condition and continuity of the negative lead (earth) one the gauge. The easiest way to do this may be to run a temporary cable direct to the gauge from the battery negative. Also make sure the engine battery to domestic bank negative link lead is in good condition with tight, clean connections. If this is OK then the most likely suspect is the gauge sender unit. I have never found electrical oil pressure gauge senders to be particularly reliable and the choice of a non-marine manufacturer may well have appeared to be cost effective at the time of purchase but may not be now. From the symptoms i am suspicious that the sender is a hot, bi-metallic strip type (the least reliable in my experience) and would suggest that you try another Durite sender if you can get one and if not this time choose a gauge using a piezo sender - how you find out is the hard part. Tony Brooks

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