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Old 20-12-2017, 22:11   #1
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What does the glow switch do on my Yanmar 3JH5E and when do I use it?

My Jeanneau Sun Odyssey 409 has a glow switch, as seen on: https://www.yanmar.com/media/global/...tasheet-LR.pdf

I was wondering when I would use it and how do I properly use it. Normally, to turn on the engine, I press the ON/OFF SWITCH briefly and then press and hold the START SWITCH until the engine is running. That's what I did in the Caribbean waters when the weather was warm. Ironically, that's where I purchased the vessel and was never told otherwise.

Now, I'm in Jersey City, New Jersey. It's cold, but the engine starts fine in 40-50 degree Fahrenheit weather. But, what if the weather drops to below 30... what's the best/safest way to start my engine?

My "Anywhere" is my first sailboat and I put my life savings into her and she's my pride and joy... I want to make sure I take care of her for myself, for my family, and... if I ever do decide to sell, which I hopefully won't, then I want to make sure any future owner also has a well-kept engine.

Thank you in advance to all the experienced sailors/mechanics!!

-Lukas
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Old 20-12-2017, 22:17   #2
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

10 to 15 seconds of using the glow plugs should warm the upper cylinders of the engine, ready for easy start. Depending on how your glow plugs are connected, either press the button or hold the key in the "glow" position while you count 15 seconds. Then activate the engine start (press the start button or turn the key to the "start" position).
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Old 20-12-2017, 22:22   #3
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

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Originally Posted by Alan Mighty View Post
10 to 15 seconds of using the glow plugs should warm the upper cylinders of the engine, ready for easy start. Depending on how your glow plugs are connected, either press the button or hold the key in the "glow" position while you count 15 seconds. Then activate the engine start (press the start button or turn the key to the "start" position).
Thank you for the quick reply, Alan Mighty!! Will I hurt the engine if I don't need the glow? I'm hesitant to use the button, but would be willing to try it while the weather is still semi-warm in New Jersey.

I'm trying to figure out if I press it before or after the ON button and when I do press it, should I press and release or press and hold.

The 3JH5E is 40HP and helped me on my solo-sail from BVI to St. Croix to Bahamas to Florida and finally to NJ. The engine has been impeccable!
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Old 20-12-2017, 22:23   #4
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

Well the best bet would be to use it in accordance with the engine operation manual which I sure can be downloaded from the web - somewhere...

The next thing would be to ensure the glow plugs are actually fitted - the presence of a switch does not ensure they are fitted fitted - they may be an optional extra.

Lastly, glow plugs are typically used for as aid for cold weather starting and a rule of thumb would be to switch them on for around 10 to 20 seconds before attempting to start.

They preheat the combustion chamber to ensure faster starting. They are turned off once engine fires and idles smoothly.
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Old 20-12-2017, 22:27   #5
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

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Originally Posted by Cool Hand Luke View Post
Thank you for the quick reply, Alan Mighty!! Will I hurt the engine if I don't need the glow? ......
No, if the engine is starting quickly (a second or two) without the glow plugs, then they are not needed - at that ambient temperature. No damage will occur.
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Old 20-12-2017, 22:31   #6
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

Here you go:
http://www.yanmarmarine.com/theme/ya...JHM-EN0023.pdf

Page 53 - Staring in cold weather - push and hold glow switch for 15 seconds and then crank engine.
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Old 20-12-2017, 22:34   #7
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

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Originally Posted by Wotname View Post
Well the best bet would be to use it in accordance with the engine operation manual which I sure can be downloaded from the web - somewhere...

The next thing would be to ensure the glow plugs are actually fitted - the presence of a switch does not ensure they are fitted fitted - they may be an optional extra.

Lastly, glow plugs are typically used for as aid for cold weather starting and a rule of thumb would be to switch them on for around 10 to 20 seconds before attempting to start.

They preheat the combustion chamber to ensure faster starting. They are turned off once engine fires and idles smoothly.
Point well made... thank you, Wotname!! I'll look for the manual and I'll try to contact Yanmar and see if they can help me out.

It was a big assumption that the glow plugs were installed, but you never know... you're right, just because the switch is there, doesn't mean the glow plugs were installed. I'll look for the manual and try contacting Yanmar and see if they could give me some input.

I'll post results as soon as I try it out... I'll be on the sailboat this Friday.


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Originally Posted by Wotname View Post
No, if the engine is starting quickly (a second or two) without the glow plugs, then they are not needed - at that ambient temperature. No damage will occur.
Great! Thanks for the reinforcement of knowledge. Means a lot to me! Will try this Friday and let you know.

Hope you guys have a Happy, Healthy, and Merry Christmas!!!
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Old 20-12-2017, 22:39   #8
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

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Originally Posted by Wotname View Post
Here you go:
http://www.yanmarmarine.com/theme/ya...JHM-EN0023.pdf

Page 53 - Staring in cold weather - push and hold glow switch for 15 seconds and then crank engine.
Got it! Thank you! Printing it out, as I write this. I'm printing it out double sided (duplex) and going to hole punch it and put it in a binder and keep it on the vessel
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Old 20-12-2017, 22:42   #9
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

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Originally Posted by Cool Hand Luke View Post
Got it! Thank you! Printing it out, as I write this. I'm printing it out double sided (duplex) and going to hole punch it and put it in a binder and keep it on the vessel
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Old 21-12-2017, 01:37   #10
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

It may not actually be glow plugs, - despite the fact the switch/button is labeled 'glow' I think it's actually an air heater on the intake manifold, I've only seen it installed once before.
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Old 21-12-2017, 01:58   #11
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

As long as the engine is starting in just a few seconds, there is no need for them. If you are cranking for 30-60 seconds, there is a problem and you may have to shut off the water intake or risk pulling water into the engine (immediately open once started or you cause another problem).

Diesel engines take advantage of the fact that when you compress a gaseous mixture, it heats up. If that mixture includes a fuel and oxygen and you compress it enough, it will reach ignition temperature and auto-ignite (as opposed to a gas engine that uses a spark plug to create a small hot spark to set off the mixture).
- In warm weather or once the engine is running, this isn't a problem.
- In cold weather it can be a problem because it doesn't heat up enough to set the fuel off.

This can be made worse thru a couple of common issues:
- If the starter/battery is weak, the compression occurs too slowly and the surrounding cold metal absorbs the heat as it's generated and you don't get enough of a temperature rise.
- If the engine has poor compression, the gas escapes rather than compresses so you don't get enough of a temperature rise.

A glow plug is just a specialized heating coil inside the cylinder head. It creates a warm spot so that during compression, the fuel adjacent can hit the flash point. It may run rough for a few seconds but then the block starts warming up and idle RPM is usually faster than the starter can generate so it quickly smooths out and runs fine.
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Old 21-12-2017, 08:31   #12
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

As far as I know, there is nothing wrong in running the glow plugs for 10-15 seconds, even if not strictly needed to start the engine. It may even be good practice when the temperature is below 45.
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Old 21-12-2017, 08:53   #13
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

Some of my engines had glow plugs, some didn't. I never needed them in either case though here in the PNW, even winter. (Perkins, Volvo, Yanmar)
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Old 21-12-2017, 10:34   #14
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

First thing I would do it check to see if your engine even has glow plugs. I've yet to see a Yanmar that actually had any glow plugs. I've seen a few panels with the option on the key ( mine included) but it doesn't actually have glow plugs.

The only engines I've seen glow plugs on were Universal/westerbeke and BMW engines.
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Old 21-12-2017, 12:07   #15
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Re: What does the glow switch do on my Yanmar 3JH5E and when do I use it?

If the engine starts without preheat, then you do not need preheat.

The temperature at which preheat becomes necessary varies depending on the age and condition of the engine. With an engine that is in good condition preheat shouldn't become necessary until temperatures fall below freezing.

As posted upthread the button may not connect to anything. It is also common for these systems to fail, so you would want to confirm that everything is present and actually working if you anticipate needing to start in extremely cold weather.

If you have shore power you may find it more helpful to warm the engine compartment or the water jacket than to use glow plugs or a manifold heater. Below about -10 F those are the only things that work.

Quote:
Originally Posted by sailabroad View Post
It may not actually be glow plugs, - despite the fact the switch/button is labeled 'glow' I think it's actually an air heater on the intake manifold, I've only seen it installed once before.
Typically the air heaters require less time with the switch depressed than glow plugs.
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