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Old 05-03-2019, 04:58 PM   #1
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Preheating Diesels?

All the diesels I've operated (trucks, tractors, heavy equipment) used glow plugs. Standard procedure is to hold it for between 5 and 10 seconds, then crank the engine. Even my Cummins 6BTAs from the 90's had a preheat (if I recall correctly).

I currently have two 1975 DD 4-71's. There is no preheat ability. The starter buttons are simply press-and-hold-until-it-starts buttons. The engines start instantly - better than any engine I've ever had, marine or vehicle - but it still feels wrong to NOT be "preheating" a glow plug.

Is this a DD "thing"? Or is there supposed to be a glow plug preheat going on?


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Old 05-03-2019, 05:11 PM   #2
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No glow plugs on Detroits. It implies good compression and little wear if your 2 stroke engines start quickly and without much smoke. During the cold season I'd use block heaters. Detroits don't like temps below 40 deg F. Yours should be wired for them. In my last boat I'd just leave the block heaters on during the winter. It prevents corrosion in cylinders open to exhaust or intake.

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Old 05-03-2019, 05:24 PM   #3
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Mr. 15. No glow plugs on any of the 3 Lehmans we've owned. Have always started right up even at 15F.
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Old 05-03-2019, 05:24 PM   #4
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No glow plugs on the Ford Lehman diesels
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Old 05-03-2019, 05:45 PM   #5
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Two kinds of diesels out there: Direct injected (Detroits, Cats, most Cummins, most anything bigger) and pre-combustion chamber aka indirect injection. Most (or lots) of small engines use pre-chambers with glow plugs. Direct has no glow plugs, but some have inlet air preheaters in air passages leading to cylinders (Cummins B and C, some).

Direct shoot the fuel right into the cylinder. Pre-chamber shoot the fuel into a chamber off to the side of the cylinder, with a glow plug stuck in it. Pre chamber diesels most all need some glow to get a good start. Direct needs no glow plug, but even those below a certain temp it simply will not start without help.
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Old 05-03-2019, 05:52 PM   #6
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My Luggers do not preheat. My NL generator does.
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Old 05-03-2019, 06:27 PM   #7
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My small Mitsubishi has chambers and glow plugs.
When I repowered I had glow plugs on my must have list as we were moving to Alaska. But I don’t know if glow plug engines generally start better when cold or not. From what I hear the prechambered w glow plug engines are quieter and smoother. My Mitsu is definitely quiet and smooth compared to other engines.
AusCan has the same engine I wonder if he would agree.

My previous boat had a direct injected Yanmar and it was definitely noisier and w more vibration. It was a 3 cyl though.

North Western Washington State USA
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Old 05-03-2019, 06:37 PM   #8
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Our 855 Cummins has no preheat
Kubota genset does, but is only ever required if the engine room is below 24c/75f
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Old 05-03-2019, 07:45 PM   #9
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Detroit’s in cold and hot climes love block heaters to eliminate smoke on cold starts. They keep the engine room space warm and dry, and these will usually be add on kits separate from your start circuit.
Newer engines benefit as well, some of them circulate hot water in thier cooling circuit to keep them nice and toasty.
If you were to order new engines today for cold climate cruising, the option would be definitely checked.
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Old 05-03-2019, 07:54 PM   #10
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Your Detroits are 2-stroke. They are different than any diesel you've owned before. Ease of starting is one of the differences. Mine also start so quickly it's almost instantaneous.

Block heaters for sub-40 degree weather is a good idea, otherwise they don't need any assistance.
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Old 05-03-2019, 07:56 PM   #11
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My previous boat`s Perkins T6354 needed no preheat. Nor do the Lehmans. But the Onan MDKD 6.5 does, up to 30secs, when cold, and I`m fairly sure the current versions do too.
2005 Integrity 386 "Sojourn"
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Old 05-03-2019, 07:58 PM   #12
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My Cummins do not have glow plugs but I do have Wolverine heaters on my oil pans that keep the blocks (actually the whole thing) warm.
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Old 05-03-2019, 08:07 PM   #13
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Older Detroits had an optional air box heater. It consisted of a hand operated pump and an electric igniter and operated with the starter. It sent flame heated air directly into the cylinders, usually making for quick starts in cold weather.
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Old 05-04-2019, 08:39 AM   #14
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I have a 6-71 and have looked for years to find the air box air heater.

We will be moving LUCY North next spring , to sell her , and I am sure the next owner would be delighted to find one aboard , instead of needing a block heater and power source.

With a dry stack and keel cooling she can ignore the winter ,till iced in.

Ever see the heater for sale?

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