I wrote: A friend just bought a yacht with twin Hino diesels. They are started by a key switch but when they you want to shut them off you have to press a stop button until the engines quit, then turn the keys off. I don't have much experience with diesels but years ago when I had a job repairing forklifts I ran into a similar situation. This seems to me to be unnecessarily complicated. After all, most diesel powered cars turn on and off with a key switch. I have asked many people this question but have gotten answers that didn't seem plausible. So now I'm asking the experts. Thoughts?
Some of the replys I got:
< Modern diesel automobiles that I have encountered (and, indeed, modern tractors and whatnot) have fuel solenoids that shut off the flow of diesel to stop the vehicle when you shut the key off. A mechanical diesel (as opposed to an electronic-injection diesel) will run as long as it has fuel, unless something makes it stop. Every diesel will have a kill-switch under the hood in case you lose electrical power - without power you can't move the solenoid to shut off the fuel. If the solenoid is sprung then you might have a situation where without power the spring returns the solenoid and the fuel shuts off. That, to me, is not a good thing. I've made it home in my old diesel truck with a frozen battery and without enough power to run the turning indicators or anything else, but the engine ran fine to get me home. If it had have stopped dead somewhere I would have not been amused. A diesel of an older design may not have a solenoid but rather a spring-return lever that acts both as the emergency kill switch and the usual method of stopping the engine via a cable-pull from the operator's position. In the case of these Hinos, if they're similar to the Hinos that I have dealt with, they will be mechanically injected and definitely of the 'run until they're out of fuel' variety, so they have to be stopped manually. I haven't yet seen a Hino with a compression release, so I would strongly suspect that the button you're pushing is attached to a solenoid that pushes against a spring-return lever on the injector pump to kill the engine. The old Mercedes 240's & 300's start and stop with the ignition key but "off" is not electric. The key off position closes a vacuum valve that is part of the switch assembly, connected by hose to a diaphram-actuated fuel shutoff on the injection pump. So it is not dependent on the electrical system but if there is a major vacuum leak, in addition to the door and gas cap locks and I forget what else stops working, there is a red shutoff lever under the hood. Wait until that diesel runs away by consuming it's own lube oil. You have never been really frightened until you share a bilge with this event. The diesel I have shuts down by cutting off the fuel flow to the injectors. There is a solenoid that, when energized, retracts and lets the fuel cutoff level move to the run position. When de-energized the same solenoid moves the fuel level to the stop position and holds it there. Works nice. For emergency shutdown use a board over the air intake. >>>I appreciated the explanations and stories and I'm not criticizing anyone but I still don't have a definite answer. I liked the jacket story best. A solenoid controlled shutoff makes the engine independant of the electrical system.(for shutoff at least) but some engines die hard. Since there doesn't seem to be any hard and fast reason for a separate shutoff button, I am thinking of converting my friend's boat to keyswitch start and stop for safety reasons,. He's technologically impaired (he had a VCR for 2 years before I pointed out to him that it was one of those that can't be programmed-he was surprised when he found out that he could push the scan button on his car radio to find stations automatically and he has a cellphone but carries phone no's on a piece of paper. I'm thinking of bypassing the stop button with a normally closed relay which when the keyswitch is turned on will open and release the solenoid which is stopping the fuel supply. When the key is turned off the solenoid will be energised and cut off the fuel. Since we don't want to run the batteries dead over a long period we'd have a time delay relay to cut off the power to the solenoid and itself after say, 5 minutes. This I hope is a simple method of accomplishing this purpose with easily obtained materials and not having to make major changes to the system, or is there a loophole in ny logic? Engineman1