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Old 01-08-2011, 05:50 PM   #1
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cycling preheaters

i was doing some research on cold weather starting of diesel class a's.
one of the posts said you might want to "cycle the preheaters in the motor several times" before starting.
what does this mean and how do you do it.
thanks
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Old 01-08-2011, 06:05 PM   #2
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Not all diesel motors have preheaters. If they do and it was a benefit it would say to do it in the motor's operators manual. I say it is a urban legend.
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Old 01-08-2011, 06:27 PM   #3
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All modern diesel motorhomes have some sort of pre-heat when you start the engine. Note, this does NOT mean an engine block heater. It means some sort of heating coil in the air intake system which preheats the air going into the cylinders. Some engines have 'glow plugs'; most actually have intake heater coils.

Turn your ignition key to the 'on' position. Note the 'wait to start' light. Wait until the light goes out. This is the preheat cycle.

In cold weather, simply perform this cycle 2 or 3 times. Once the 'wait to start' light goes out, simply turn off the ignition key, and turn it on again, repeating the cycle. Your diesel should start.

For us folks who live in the frigid climates, the use of the engine block heater is recommended at or around freezing temperatures. Preheat your engine for an hour or two before starting. The switch for my engine block heater is in the 'One Place' panel in my Winnie. Must have 110V to operate the engine block heater.
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Old 01-08-2011, 06:27 PM   #4
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Quote:
Originally Posted by bandmbrown View Post
i was doing some research on cold weather starting of diesel class a's.
one of the posts said you might want to "cycle the preheaters in the motor several times" before starting.
what does this mean and how do you do it.
thanks

The pre-heaters, when present, warm the air before it goes into the engine. When you turn on the ignition you would see a red or orange message sayiing something like "Do not start engine yet". When it goes off it has cycled. To re-cycle you turn the ignition off then back on.

I generally cycle it three or four times in cold weather. Engine will start easier, and in my case, no smoke at start.

If you aren't sure whether you have a pre-heater or not, get your engine serial number and call the tech support for your engine make. They will have that information on file.
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Old 01-08-2011, 06:48 PM   #5
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That is not a true state that all MHs have preheaters or glow plugs. My Detroit Series 60 has no glow plugs or preheaters and my previous MH with a Cummins engine had no preheaters or glow plugs. My Detroit has no "wait to start" and starts just fine in cold weather. The preheaters in other motors come up to a preset temp when you turn the key on. Turning the key on and off will not change this preset temp of the preheaters so it doesn't make any difference on how many times you do it after the required first time.
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Old 01-08-2011, 07:51 PM   #6
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Mike, I have never owned a Detroit engine, and what I read is that they don't have engine preheat. They do have optional ether systems for cold start.

I have owned both Cummins and CAT engines, and both have engine preheat. They do add more heat if you cycle the ignition key.
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Old 01-08-2011, 09:19 PM   #7
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I think the key words in Pushermans statement in his previous post are "modern diesel motorhomes". It is true that older diesels did not have a means of pre-heating the intake air, either inside the cylinder with a glow plug, or along the path of air entry into the engine with heating coils or gridwork like most modern day diesels do. Repeating the glow or pre-heat cycle will warm cold winter air more than a single cycle will, thus making for an easier cold start of the engine. I am not familar with the Series 60, but evidently a heater is not necessary for cold starts.

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Old 01-08-2011, 09:30 PM   #8
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Glow plugs have been used in some diesels for years. I worked on some in the 1960's that had glow plugs and even then they had been around for a while. I have not had the Detroit in any cold weather that I have not had it start right up but I have always used the Aqua Hot to warm it up to get the oil flowing easier for better startup lubrication.
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Old 01-09-2011, 12:03 AM   #9
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Theres no benefit to cycling the heater, any time its off, its producing no heat. It might be a little easier on the battery or wiring. I hear snippets of urban legend here..
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Old 01-09-2011, 04:46 PM   #10
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Theres no benefit to cycling the heater, any time its off, its producing no heat. It might be a little easier on the battery or wiring. I hear snippets of urban legend here..

Dave, the reason for recycling the pre-heat system for the engine is to re-set it to cycle on again. Most if not all pre-heat system have a timed cycle, (when the light goes off, engage the starter). By recycling it a couple of times without engaging the starter, warmer air is produced for the engine to start on.

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Old 01-09-2011, 04:54 PM   #11
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My old 1998.5 Dodge / Cummins p.u. with the ISB motor said in the owners manual to cycle the preheater one extra time if temp was I think below 32
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Old 01-09-2011, 04:57 PM   #12
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Glow plugs have been used in some diesels for years. I worked on some in the 1960's that had glow plugs and even then they had been around for a while. I have not had the Detroit in any cold weather that I have not had it start right up but I have always used the Aqua Hot to warm it up to get the oil flowing easier for better startup lubrication.
Mike, the Aqua Hot system definitly works in your favor when it comes to start up time for the engine. Keeping the coolant and engine warm is a good thing all the way around.

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Old 01-09-2011, 05:03 PM   #13
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My Cummins ECU keeps cycling the preheater after engine start until the engine is warm enough.
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Old 01-09-2011, 05:29 PM   #14
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My Cummins ECU keeps cycling the preheater after engine start until the engine is warm enough.

Dirk, I have an old 76 Mercedes 240D that has manually engaged electrical connnection for the glow plugs. No ECU here, but I can keep the plugs going for awhile after the engine starts on those cold mornings ,till she gets her breath, so to speak

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