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Old 10-27-2006
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Cold Weather Engine Start

What is the recommended glow plug "push" time to start after a week long downtime in cold fall time NE weather? Is there a time period which you do not want to pass as it may cause damage?

How does the glow plug actually work?

Thanks!
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Old 10-27-2006
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Yes, glowplugs do work, a twenty count (~20 seconds) is usual for most engines.
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IIRC, the Glowplugs are just that... metal plugs with an internal heating element that allow them to heat up to the point where they are hot enough to ignite the Diesel fuel sprayed into the cylinders by the fuel injectors. Effectively, they act as a spark plug until the diesel engine has heated up enough to provide its own ignition source.
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Old 10-27-2006
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http://en.wikipedia.org/wiki/Glow_plug

Not all "glowplugs" are the same. In my Perkins 4.108, the cold start device consists of a small heating element that plugs into the air intake manifold. Diesel dribbles onto the red-hot coil and ignites, and is then drawn into the combustion chamber. This device stopped functioning one time when it was cold, so I got a can of WD40 and a cigarette lighter and made a torch, directing the flame into the breather while the engine was turned over. Worked fine.

My cold-start device takes about 4 seconds to do its job.

Last edited by jr438234606; 10-27-2006 at 10:50 AM.
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usually there is a relay/timer that provides power to the glow plugs for a pre-determined time. You don't want to burn them out.
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Quote:
Originally Posted by sailingdog
Effectively, they act as a spark plug until the diesel engine has heated up enough to provide its own ignition source.
Sorry, SD, I don't think that's quite right - The glow plugs "preheat" the combustions chamber and/or a pre-combustion chamber to facilitate the compressive firing of the fuel. No fuel is injected or "bled into" the engine during the preheat time, and I've never held the glow plugs on during cranking to start, so the spark plug analogy doesn't really apply. I doubt there's actually enough heat there to fire the fuel anyway.

There are "quick acting" and "slow acting" glow plugs available for various engines, and the required preheat time varies with each type. For the slower ones I'd agree with a max count of 20 for a cold start. In milder weather you will likely need less time.

Should you find yourself "needing" excessive preheat time, check the condition and function of the glow plugs. If they check out it's quite likely that your compression is beginning to suffer, making starting difficult.

Last edited by Faster; 10-27-2006 at 02:04 PM.
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Faster-

Actually, they do act as an ignition source when the engine is first starting. Along with heating the combustion chamber, the glow plugs are hot enough to ignite the vaporized diesel droplets. After a few combustion cycles, the engine has generated enough heat to not need the assistance of the glow plugs. Granted, the spark plug analogy isn't 100% accurate, but it is a simplified analogy, to allow people who have a better understanding of gasoline-powered internal combustion engines than the less common Diesel cycle used in many marine auxiliary engines.

Much of the heat required for the ignition process is actually provided by the high compression levels found in a diesel engine, but in a cold marine diesel, too much heat is lost to heating the cold metal parts.

You might want to do a bit of research before writing. If you look at this page or this page, you'll see that the tip of the glow plug is often at 900+ degrees....which is sufficient to ignite vaporized diesel fuel and is used to ignite the fuel when the engine is being started cold.

My analogy was based on a description of glow plug function by a former SAE section chairman, who is an automotive engineer with over 40 years of experience in the industry.
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Old 10-27-2006
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Quote:
Originally Posted by Faster
No fuel is injected or "bled into" the engine during the preheat time, and I've never held the glow plugs on during cranking to start, so the spark plug analogy doesn't really apply. I doubt there's actually enough heat there to fire the fuel anyway.
My cold-start device incorporates a valve in the fuel line that opens when the heating element reaches the critical temperature (it takes about 4-5 seconds). Fuel then dribbles over the element and ignites. If you take the breather cap off, a large flame will actually leap out of the air intake. This is BEFORE you even turn the engine over. It's VERY effective.

I wonder what type of cold start device the original poster's engine uses?
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How does one check glow plugs

How does one check glow plugs, if they seem to be working (to ensure they keep working)? Do they wear out gradually, or burn out suddenly like a fuse/lightbulb? How can one tell if they are still good or need to be replaced? Is there a normal replacement cycle, or can they last many years?

For someone not mechanically inclined, is there a quick check, or does one need to dismantle things to get at them?

I'm hoping it's like checking spark plugs on a car--unscrew, look, clean, re-install....

Thanks for any replies.
Frank.
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Old 10-27-2006
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On the 2 cylinder Universal diesels that I am familair with you cannot crank the engine over unless the glow plug button is pushed at the same time as t eh starter button. Therefore I would assume the plugs are on on when diesel is being injected into the cylinders.
In cold weather of course you hold the button in for 20 or so seconds but even in warm weather you must use them.
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