Diesel engine query

BrianM

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Does it do any harm to the engine if you don't wait until the glow plug symbol on the dash goes out before you start the engine?
I'm in the habit of inserting the ignition key and immediately turning it fully to start the engine ..... and the engine always fires up straight way .... but I've noticed that if you put in the key and part turn it then the glow plug icon lights up for a few seconds then goes out.
According to the handbook you should wait until this happens before turning the key further to start the engine. Can it do any harm not waiting or, by virtue of the engine starting, is everything still OK?
 

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As long as the car starts,thats OK, as the weather gets colder you may have to wait, if it does not start instantly when the temperture drops, you wear the starter motor,thats all.

Malcolm
 

Chazchuzzlewitt

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I think it's always best to wait for the glow plugs to warm before starting, in fact I often leave them to warm longer in the winter for easier starts. Remember a diesel engine has no spark to ignite the fuel/air, just using compression and it's very cold on that first start of the day this time of year... mine won't start without major grumbles if I don't warm her up first, it may be less important with more modern ignition systems...
 

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If the weather and or your engine are warm just turn the key and go always waiting for the light to go out just cuts down the working life of the glow plugs. The very worst that could happen is your engine won't start, in which case try again and wait for the light to extinguish, but all things being equal if the engine and or weather are warm your it should start ;)
 

Parrot of Doom

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I always think about the unburnt fuel entering the catalyst.
 

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I always think about the unburnt fuel entering the catalyst.

And getting past the rings into the sump oil. With such long intervals between oil changes nowadays, I wouldn't want even the slightest risk of diluting the oil.

For the sake of 5 seconds, let the glowplugs do their work!
 

Ultymate

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Sorry guys can't agree your paranoia is emptying your pockets into the dealers for no good reason, and from what I've read on other threads some of the glow plugs are far from easy to change (sometimes resulting in head removal) so why shorten their working life unnecessarily plus they don't come cheap to buy:???: Get to know your motor when it will and won't start without glow plugs, I'm not advocating sitting there for ages cranking away on the starter, if it won't go right away stop cranking light up the plugs and away you go. Another thing to remember is that every time you use the plugs you are pulling lumps out of your battery!
 
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ba9rn

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I cannot believe that (electrically) heating the plugs makes a jot of difference to their life. They get just as hot (probably hotter) when the engine is running. :confused:
 

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I wouldn't agree about shortening the glow plug life- they typcially have a long life anyway, much longer than spark plugs of course. By design a diesel engine uses heat to run, and needs that help on the first start of the day to start efficently. By ignoring this you'll just end up putting more strain on other components, and it's lazy... on the other hand, once the engine's warm then you don't have to worry about pre-glow (even says this in the manual).
 

Ultymate

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I never said ignore it on the first start of the day but many people use them on every start that is what I was advising against you have just said the handbook advises just the same thing :confused: The diesel engine uses heat generated by compression as it's source of ignition and does'nt rely on any outside source of ignition, the glowplugs are only there as a cold starting aid your engine once warm would perform just as well without the plugs at all. Many of the old diesels in trucks had to be sarted in cold weather by inserting a lit fuel soaked rag into the inlet air. some of the "modern diesels" don't have a heater device at all, the Ford Tansit being one that has a waxstat device that physically advances the timing to aid cold starts and that seems to be equally as good if not better than glow plugs.
 
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Parrot of Doom

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The glowplugs are on for 60 seconds when you start the engine anyway.

I don't see how another 3-4 seconds on a cold morning is going to make a huge difference to their life.
 
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BrianM

BrianM

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  • Thread Starter
  • Thread starter
  • #12
Does it do any harm to the engine if you don't wait until the glow plug symbol on the dash goes out before you start the engine?
I'm in the habit of inserting the ignition key and immediately turning it fully to start the engine ..... and the engine always fires up straight way .... but I've noticed that if you put in the key and part turn it then the glow plug icon lights up for a few seconds then goes out.
According to the handbook you should wait until this happens before turning the key further to start the engine. Can it do any harm not waiting or, by virtue of the engine starting, is everything still OK?

Thanks for all the discussion and debate my original post has generated! On balance it seems like it's better to let the glowplugs 'glow' before starting the engine so thats what I'll do in the future.
 

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I was under the impression that the glow plugs act differently in the CDI engines; in that they only come on if they are required. In previous non high pressure diesels the car would not start until the glow plug light went out. With my CDI I just turn the key all the way and release, when it's really cold I may turn the ignition to position 2 until the glow plug light goes out.
 

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And getting past the rings into the sump oil. With such long intervals between oil changes nowadays, I wouldn't want even the slightest risk of diluting the oil.

For the sake of 5 seconds, let the glowplugs do their work!

please explain HOW...............................IF the rings/bores were worn to that extent - not even having glow plugs would allow the engine to start from cold - this as you know is a CI engine - if there was enough 'blow by' the rings to let a fluid past (diesel) then you would not be able to compress the air enough to start combustion.
 

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I thought that ALL diesels are 'high' pressure this high pressure being needed to vaporise the diesel as it is injected into the engine - what do you mean by a non high pressure diesel?
I was referring to non common rail diesel engines.
 

Ultymate

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All diesels are indeed high pressure but in the new breed cdi common rail engines the high pressure is present in more parts of the system ie from the pump or pumps usually in the tank all the way up through the pipework through the fuel filter to the common rail which connects to the electronically controlled (via the ecu) injectors. All this means you have to be far more careful about opening any connections in the system when it's charged with pressure as the pressure involved is sufficient to push the fuel through your skin and into your bloodstream with extreme consequences. Believe it or not you can actually feel the fuel filter expand when the fuel pump fires up and this is an extremely good and safe way of finding out if you have pump pressure in the system.Another thing to note is that if you disconnect an injector(electronically) while the engines running you will hydraulic lock that cylinder as the injector will go to full open:???:
 
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Hibbo

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please explain HOW...............................IF the rings/bores were worn to that extent - not even having glow plugs would allow the engine to start from cold - this as you know is a CI engine - if there was enough 'blow by' the rings to let a fluid past (diesel) then you would not be able to compress the air enough to start combustion.

David, I will answer you by quoting two specific words from my post.

slightest risk
 

Flying Scot

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All diesels are indeed high pressure but in the new breed cdi common rail engines the high pressure is present in more parts of the system ie from the pump or pumps usually in the tank all the way up through the pipework through the fuel filter to the common rail which connects to the electronically controlled (via the ecu) injectors. All this means you have to be far more careful about opening any connections in the system when it's charged with pressure as the pressure involved is sufficient to push the fuel through your skin and into your bloodstream with extreme consequences. Believe it or not you can actually feel the fuel filter expand when the fuel pump fires up and this is an extremely good and safe way of finding out if you have pump pressure in the system.Another thing to note is that if you disconnect an injector(electronically) while the engines running you will hydraulic lock that cylinder as the injector will go to full open:???:

Sorry but that is is just RUBBISH Bosch Common Rail uses an engine driven high pressure pump - yes driven by the engine not sitting in the fuel tank. This pump then supplies the common rail accumulator at the pressures listed below. The pump in the tank is not supplying any diesel at high pressure it is just a simple lift pump to supply and feed the Common Rail High Pressure Pump. Bosch Common Rail generations are characterized by the injection pressure – 1,350 bar in the 1st generation, 1,600 bar in the 2nd generation. With the 3rd generation more technological sophistication was the change the pressure remained at 1,600 bar. Bosch is planning another leap in innovative development for the Common Rail in 2006. They are currently analyzing concepts to increase the pressure in the Common Rail to more than 2,000 bar at the injector by means of a booster without having to increase the system pressure as such. In a parallel approach, they are studying injectors with variable nozzle geometry.

There exists only these high pressures in 'one short pipe' from the engine driven high pressure pump to the common rail these sort of pressures listed above dont exist in the lines from the tank to the engine bay and through fuel filters.

Come on guys lets be logical here - just think about it - you have a pump taking diesel fuel and raising it to pressures of around 1,500 bar therefore this is a very very finely made pump very very small tolerances. Your going to put that in the tank where it will ingest all the crud that enters the tank - i think not. Then we need fuel lines and filters that can resist this pressure and meet safety regulations. Then we have to drive this pump at various speeds in relation to engine RPM and power output - nope not a good idea. Lets take the easy route and hang it on the engine and drive it by the engine and use an ECU to control it and the injectors.
 


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