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IH 706 - Is the over use of glow plugs/chargers really true?

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andy r
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PostPosted: Wed Feb 12, 2020 6:54 am    Post subject: IH 706 - Is the over use of glow plugs/chargers really true? Reply to specific post Reply with quote


This post is about each glow plug being OK while using the boost setting on a big battery charger. I posted last week about my Farmall 706 diesel not starting well at all. I sort of figured the glow plugs weren't working as they should. I found a wire had been hot in the meter and push button switch box. The heat had caused a connection to go bad on the meter, actually causing the plastic housing of the meter to melt. I actually think a corroded connection caused the heat. The tractor sits outside a lot on an auger and has been exposed to its share of rain. I don't think the connection was carrying any current as it just fell apart. Ordered a new meter and will replace some of that wiring. Also, checked each glow plug by disconnecting the wiring harness and using a 12 volt test lamp. Each glow plug carried current. Many, many times in cold weather I have put my Schumacher battery charger with a 200 amp cranking setting on the tractor. Many, many times I have held the glow plug button down for the count of 30 or 45 before cranking and held it there until it clears up after starting. I have read how some recommend holding the glow plug button down for only for a few seconds, then allowing the plugs to cool. Some say a boosting battery charger sends to many volts (14+) to the glow plugs burning them out. What gives??? Why are my glow plugs still working after what would be considered abuse by many?? Thanks.
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PostPosted: Wed Feb 12, 2020 9:10 am    Post subject: Re: IH 706 - Is the over use of glow plugs/chargers really t Reply to specific post Reply with quote

I pretty much do the same thing on my 660. I hold it for 45 -60 seconds before starting. once running I keep holding it till it smoothens out. on my 560 I hold for 30 seconds and it fires right up with no smoke . don't hold after starting. this tractor is original never apart with 5600 hrs. and starts like a champ. my brothers 660 had all glow plugs burn out. the only thing I came up with is once running and holding button is that the generator and regulator is putting out more than 14.8 volts. did not actually check the voltage though. I kind of cycle the plugs on and off once running also as not to burn them out this way. when you check the glow plugs on a battery they get red hot instantly so I don't hold them on it for more than 4-5 seconds testing them.
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pete 23
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PostPosted: Wed Feb 12, 2020 12:14 pm    Post subject: Re: IH 706 - Is the over use of glow plugs/chargers really t Reply to specific post Reply with quote

High voltage definetely burns out those glow plugs. Might take more than a few seconds but it will do it. Replaced a whole lot of glow plugs over the years where operator used a booster of some sort that exceeded normal voltage.

Not all glow plugs are created equal as they change them up over the years. Some more sensitive than others. Some will actually blow the tips right open. Others just pop internally. Then you have the tips that get thin due to leaking injection nozzles so they are more prone to blow easily.

Hard to say how much voltage is sent to the glow plugs because that depends on condition of battery and all wires and connections. If battery is low, putting on high charge the voltage may not even rise to high enough voltage to hurt anything.

Then the other thing. When you start one of those tractors on it's own power, no booster, the normal voltage to glow plugs before you engage starter will be right near 12 volts up to maybe 16.6 if everything is perfect. Keep them held on while cranking and voltage will drop below 11 volts. Keep holding them on after starting, generator starts charging and is limited to about 35 amps. Glow plugs will draw 60 or 70 amps so voltage never even reaches regulated voltage.

Now, if you release the glow plugs for a while with it running, voltage should rise to about 14.5 volts. So, now you again apply glow plugs they will receive higher than normal battery voltage for a period until system stabilizes again to point where the 35 amp generator voltage is closer to normal battery voltage.

So, to be safe, if need to hold them when running, reduce engine speed, maybe even turn on lights to lower voltage, then you will be safe to hold them on . My method.

And as far as testing glow plugs. One other poster recommended the way I also do it. Disconnect all but one and hook one at a time. Good one will show near half way on meter. Two together will show full meter so meter will not tell you if you have one or two burned out.
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PostPosted: Wed Feb 12, 2020 12:52 pm    Post subject: Re: IH 706 - Is the over use of glow plugs/chargers really t Reply to specific post Reply with quote

You said it yourself, the glow plug wiring had problems, most likely a high resistance connection in there somewhere.

That high resistance connection shielded the glow plugs from the boost voltage of the battery charger. Time the juice went through that connection it was down close enough to 12V to not harm the plugs.
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