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post #1 of 13 Old 08-05-2010 Thread Starter
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Glow plugs

Here's a question.. Why do some marine diesels have glow plugs (and need them to get going) and others don't??

It'd be wonderful to get out there and simply crank the engine - I see others doing that, but with my Volvo I have to wait 15 seconds first...

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post #2 of 13 Old 08-06-2010
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A lot depends on the size of the engine and such. Some designs, with higher compression ratios, don't require glow plugs, since the higher compression ratio causes the diesel to ignite without assistance.

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post #3 of 13 Old 08-06-2010
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In the case of the popular Kubota-based diesels, their head design is totally different than the non-glow designs like the Yanmar.
I do not know of any substantive compression difference, but am not an engineer...

In cold weather when you might have to crank a Yanmar quite a bit to get 'er to fire, you can heat up the glow plugs on a Universal or Beta for about 20 seconds and get an immediate start, in my experience.

In hot weather the Kubota-based engines will normally start without glow plugging, or only a little bit.

I live in a colder climate and kinda prefer the glow plug design, but all the other types work just fine too, as long as they are in good condition.

L
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post #4 of 13 Old 08-06-2010
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One day I tried starting mine without the glow plugs. it actually started! but it had to crank a bit. (kubota based universal 5416)

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post #5 of 13 Old 08-06-2010
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If the water/weather is warmer or the engine is still warm, it will start right up the first time with no glow. When water/weather is colder, I'll hit the glow plugs for a few seconds before starting.
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post #6 of 13 Old 08-06-2010
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Quote:
Originally Posted by olson34 View Post
In the case of the popular Kubota-based diesels, their head design is totally different than the non-glow designs like the Yanmar.
I do not know of any substantive compression difference, but am not an engineer...

In cold weather when you might have to crank a Yanmar quite a bit to get 'er to fire, you can heat up the glow plugs on a Universal or Beta for about 20 seconds and get an immediate start, in my experience.

In hot weather the Kubota-based engines will normally start without glow plugging, or only a little bit.

I live in a colder climate and kinda prefer the glow plug design, but all the other types work just fine too, as long as they are in good condition.

L
I'm with you on that one, i.e. preference for glow plugs.

Yanmar actually does use glow plugs on their small diesel tractor engines. Most folks think of Kubota as the "tractor engine", but Yanmar is too -- in a very big way. Just take a look in the engine compartments of all John Deere's compact utility tractors and many of the GTs, or the Yanmar/Cub Cadet utility tractors, or loads of other small tractor manufacturers. Little Yanmar diesel engines, everywhere! They have so many more models than we ever see over on the marine side -- only a small fraction get marinized.

My understanding is that when Yanmar went after the marine market with their small diesels, they felt few people would be out recreational sailing/boating in weather cold enough to need glow plugs. So they dispensed with them and the engines do start fine in moderate to warm temps.

That said, we do a lot of "shoulder season" sailing where temps drop down in the 30's (F) at night, and even below freezing. I wish we had glow plugs on those mornings. Hartley, consider yourself lucky, in my book!

Of course, the big Yanmar marine engines do have glow plugs.


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post #7 of 13 Old 08-08-2010 Thread Starter
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I guess the reason I ask is that the Manual for our Volvo (hey, I didn't have a choice - it came with the boat; anyway, it's stamped "Perkins" on the side so some part of it must be okay?) states pretty strongly:

Quote:
IMPORTANT! Always pre-heat the engine (even when it is at operating temperature
Are they correct or not?

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post #8 of 13 Old 08-08-2010
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Quote:
Originally Posted by Hartley18 View Post
I guess the reason I ask is that the Manual for our Volvo (hey, I didn't have a choice - it came with the boat; anyway, it's stamped "Perkins" on the side so some part of it must be okay?) states pretty strongly:



Are they correct or not?
Cameron, In your case, I would just follow the owner's manual. Even if it's overkill, there's really no harm in it. And it could be that the design of your Volvo needs the plugs at start-up for some reason.

Or you could get a Yanmar.


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post #9 of 13 Old 08-08-2010 Thread Starter
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Quote:
Originally Posted by JohnRPollard View Post
Cameron, In your case, I would just follow the owner's manual. Even if it's overkill, there's really no harm in it. And it could be that the design of your Volvo needs the plugs at start-up for some reason.
And I'd be very interested to know what that reason might be..

Quote:
Originally Posted by JohnRPollard View Post
Or you could get a Yanmar.
Funny you should mention that. In talking to the mechanic it seems the PO had a choice of spending $9,000 on a new Yanmar or $7,500 on a 2nd-hand Volvo..

Hey, the guy was an architect. No prizes for guessing which option he took.

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"Honestly, I don't know why seamen persist in getting wrecked in some of the outlandish places they do, when they can do it in a nice place like Fiji." -- John Caldwell, "Desperate Voyage"

Last edited by Classic30; 08-08-2010 at 11:42 PM.
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post #10 of 13 Old 08-09-2010
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Try starting without the pre-heat. If it works, you didn't need to pre-heat. It won't hurt anything as long as the motor starts right away.
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