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Low Oil Pressure and Overtemp Warnings

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Looking for some advice here. Have been tracing the wiring on my boat with a view to replacing the fuse panel and relocating various relays in the engine bay, into a combined fuse and relay panel. This has led to me discovering something, that I am not sure is a good thing. Bear in mind this is an ex hire boat.

The engine has been fitted with a second stop solonoid, the earth return path for this goes through a relay, whose coil is connected to 24V and the output of the 24V alternator. When the engine is not turning and there is no output from the alternator, the relay is pulled in, breaking the earth return for the second stop solonoid, therefore preventing the solonoid from working. Once the engine is turning and the alternator output rises, the relay drops out, providing the earth return for the second solonoid. There are various engine temp and low oil pressure sensors around the engine, which are connected to a second relay. If one of the sensors trigger, then the relay is pulled in, energising the second stop solonoid and stopping the engine, providing the first relay mentioned is not energised. Basically the first relay is there to stop false triggering of the stop solonoid, until the engine has had a chance for the oil pressure to rise, when the engine is first started.

So far so good, except the 24v alternator has now developed a fault, where if you start the engine, the alternator does not give any output until you rev briefly beyond a certain number of revs and then it contimues to give output at any revs. However this means it is possible for the engine to be running and the alternator to be giving no output and therefore because of the actions of the first relay described above, the low oil pressure or temp sensors, could not operate the second stop solonoid.

So on to my concerns. There are a number of things that could go wrong with the first relay circuit that could prevent the stop solonoid from working when it needs to. Secondly and perhaps more importantly, if the sensors do detect a low oil pressure or overtemp condition the engine will cut out immediately. This would not be a good thing if say coming in to moor at Reedham or Yarmouth, where with adaquate warning in the form of a light or buzzer, you might choose to take the decision to run the engine a few seconds more until safely moored up. Maybe I would rather choose to risk damaging the engine, rather than suddenly find I am approaching a mooring and the engine cuts out, or just passing under Vauxhall bridge fighting a strong current.

Any thoughts on the above. Should I keep the system as fitted or modify it? As mentioned the boat is an ex hire boat (Barnes) and I wonder if they have fitted the mod to protect the engine at all costs, to stop hirers who might hear a buzzer, but rather than stop the engine as soon as, just carry on to their next destination, therefore damaging the engine. or is it in fact a good mod? I also wonder how many other private owners are in possesion of ex hire boats with a similar mod.

I was thinking along the lines of taking 24V from the ignition switch to a warning light and buzzer, connected to the output of the alternator. When the engine is stopped they would operate, as the alternator output rose, they would stop, thus indicating the alternator is working, and then replacing the second stop solonoid with a loud buzzer and fault warning light, therefore if they ever operated, I would have the choice of switching the engine off immediately or as soon as it was safe to do so.

All advice welcomed.


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Hi Keith, this setup is clearly designed to stop some numpty who couldn’t care less continuing to operate the engine ignoring the overheat and low oil warnings when it was on the hire fleet. In my opinion it is dangerous, modern engines do have a similar setup that restricts the revs during such conditions, but killing it entirely is beyond belief for the reasons you have already pointed out. If it were my boat I would ditch the lot and replace it with nice loud warning buzzers that test automatically each start up. Safety of the vessel and it’s crew are a far higher priority than the damage you may do the engine by continuing to run carefully in an emergency or close quarter manoeuvring situation which will of course be the only time you would ignore, or rather disregard the warnings.

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but killing it entirely is beyond belief for the reasons you have already pointed out

Imagine that Engine stopping on Braydon or on the river could be very dangers to your boat and others Kieth hope you find the right solution Mate :trophy

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Hi Keith

I totally agree with Antares 9. Controls like you have mentioned can be lethal in the wrong conditions, warning buzzers and lights are a far safer bet and you still have the final decision prior to the engine just stopping unexpectedly.

Mind you, nothing Barnes does surprises me anymore after seeing some of the workmanship completed to the electrical systems on a friends Bayliner recently purchased from them. Just one example of this was the shore power being converted from US to UK Systems. The main 240 volt connections into the inverter changeover relay were left loose. Not only could they have fallen out and touched the grounding on the boat, without doubt if the system had been put under any substantial load it could have also been a fire hazard. two gunstwo guns

Getting 12 & 24volts systems wrong on a boat is bad enough but getting it wrong on mains 240volt systems is inexcusable. In the marine world are engineers restricted to the same certification/qualifications as household and industrial electricians when handling mains systems?


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Well that seems fairly unanimous then. I was pretty sure that I was going to remove and rewire it all, but just wanted to be sure I wasn't being stupid and overlooking some important reason for it being there.. An Easter weekend spent in The Locks and under the dashboard of the boat then. Thanks for all the advice guys.

I wonder how many other ex hire boats are out there with similar wiring?


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