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dockbumdan 11-11-2011 06:13 AM

20 years without knowing, So I thought I'd ask.
Ok, for the past 20 years I've had the same boat, I've put well over 3000 hrs on the engine with several thousand miles under it's belt. So now I have to know.
It's engine is a Yanmar 3GMD. after starting the engine I normally turn off the key, and remove it. Placing it back in its normal location (storage). Now, suddenly I've started to leave the key in the On position, then only remove it after I've choked it off. Any idea if either method is right/wrong? Obviously I havent :confused::confused: caused any damage doing it the first way, start, key off/remove, choke off. but should it be left On during the engine running?

bubb2 11-11-2011 08:07 AM

I know if I remove my key while it's runing it also turns off my hour meter and over temp alarm.

emoney 11-11-2011 08:51 AM

A lot has to do with how your ignition switch is wired. If I turn my key off, it's wired in a way, like bubb's, that my gauges no longer operate. So, how's yours wired?

donradclife 11-11-2011 12:56 PM

Some are wired so that your alternator will not work either.

Jeff_H 11-11-2011 04:18 PM

And some are wired so that turning off the key can damage the alternator coils.

dockbumdan 11-11-2011 04:38 PM

I heard that also, but in 20 years the alternator coils have never suffered, But it does seem to turn off the alarm, at least for the first 2 seconds or so, then the temp goes out (normal). after that first start up alarm, the switch being on or off doesn't seem to matter.
like I said earlier, might be why the engine hour meter never moves. Haha

davidpm 11-11-2011 06:27 PM

This is from the manual:

It does not seem to address your point exactly but the last line indicates that the starter switch is turned off after the engine is stopped with engine kill knob.
But since they don't make a fuss about it either way and it has worked both ways for you maybe it doesn't matter much.

[7-4.] Stopping
1) Stopping procedure
1a) Place the clutch handle in the "neutral" position and
idle the engine for about 5 minutes.
If the engine is stopped suddenly
while at a high temperature, the temperature
of various parts will increase.
This may result in engine trouble.
After five minutes' idling, place the speed control lever
in the "full" position and raise the rpms to about 3600 to
blow out any burnt gas in the cylinder.
Set the engine to the lowest speed (about 850-900 rpm), cut the fuel, and stop the engine.
1. Engine stops if knob is pulled
2. Engine stop cable
Do not stop the engine with the decompression lever. If the decompression
lever used to stop the engine, fuel will spray out and accumulate on top of
the pistons. This will create the danger of an explosion the next time the
engine is started.
2) Be sure to close the kingston **** after stopping.
3) Drain out the cooling water. In winter and in periods of col
d weather when there is the possibility that the cooling water may freeze, the cooling water
should be drained out after use.
Open up the cylinder body side **** located below the intake silencer and drain out the water
in the cylinder.
Open up the **** in the lower part of the exhaust manifold and drain the water from the
manifold. (for 3GMD, 3HM)
Turn the crankshaft 2-3 times by starter motor to remove any water remaining in the cooling
4) While the engine is still warm, wipe off any dirt and grime that has accumulated.
5) Turn off the battery switch.
When stopping the engine with the starter switch "ON", the tube oil pressure warning buzzer
will sound. This does not indicate engine trouble.

Capt Len 11-11-2011 11:08 PM

It's possible your alt gets it's energy thru an oil pressure switch But I think that a good look around should help you understand what you got and that can't be bad.

ggray 11-13-2011 06:05 PM


Originally Posted by dockbumdan (Post 795978)
But it does seem to turn off the alarm, at least for the first 2 seconds or so, then the temp goes out (normal). after that first start up alarm, the switch being on or off doesn't seem to matter.

Unless I misunderstand all what you are saying here, how would you know that being on or off doesn't matter unless you experienced an over heated engine and then tested the switch to see if it mattered? Sounds to me like you have been lucky.

Water temp is the difficult sensor to test. You would need to put it in hot water measured with a thermometer. Oil pressure is easy: it should be silent while running, but sound when the engine is shut down. If your alarm is silent after your engine is shut down, then you have been lucky, so far.

If you have mechanical gauges, not quite so serious, but idiot lights and especially alarms are very helpful.

dabnis 11-13-2011 08:59 PM


What is the downside of leaving the key on?


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