Some diesels don't use glow plugs. Normally they are direct injection and have higher compression than engines that use glow plugs. Requires a more powerful starter, faster crank speed, they are harder to start but easier to get compliance with emissions standards.
Engines with glow plugs are normally indirect injection. Plug heats the air in a pre-combustion passage in the cylinder head and hot air ignites the fuel. Easier starting (as long as the plugs work), lower injection pressures on pump and injectors, harder to get emissions compliance and complete combustion on cold start. There are other systems as well. The new Ultra High pressure common rail Cummins engines (like you find in your pickup truck) have a heating grid in the air intake that heats the air in the intake manifold until the engine is up to temperature. DO NOT DO NOT DO NOT USE STARTING FLUID ON ONE OF THESE BECAUSE IT WILL FLASH BACK IN YOUR FACE. The strangest system I've personally seen is on older Perkins 6-cylinder engines used in construction equipment and larger forklifts. It had a thermostatically controlled solenoid that bled hot fuel into the intake manifold. This enriched the mixture and aided starting. It also smoked like the devil and smelled like a refinery when the solenoid valve leaked - and they all leaked after a relatively short while. Glow plugs or not is an engineering tradeoff made by manufacturers depending on costs, philosophy, and engine application, I don't think any Yanmar marine engine I know of uses glow plugs, but the 65HP 4 cylinder industrial engines do. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of David Risch Sent: Thursday, May 16, 2013 7:58 AM To: CNC CNC Subject: Re: Stus-List Starting a Universal OK...I gotta ask. I have a 1981 3QM30. Purrs like a kitten. No glow plug. Start up cold just fine. Just a few more cranks. Before this engine I thought all diesels had glow plugs. What gives? David F. Risch (401) 419-4650 (cell)
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