Taliska Posted July 27, 2004 Report Posted July 27, 2004 Someone said... "Diesels always use their glow-plugs to start."Because, they said... "You need both heat and compression to start the engine."Well I'm not convinced! There's a light on the dash that says "Hold on - wait for the glow-plugs to warm a bit, then start the engine", but that only comes on in the deep winter. Clearly I could take the glow-plug power connector(s) off and try to start the engine, but I don't fancy tinkering under the hood. So what's the low-down? Taliska Quote
seatkid Posted July 27, 2004 Report Posted July 27, 2004 Glow plugs are used to warm the air intake and so aid cold starting of diesels. When a diesel engine is cold, sometimes the slow cranking speed and air temperature is insufficient for the air in the cylinder to reach the minimum required during the compression stroke for ignition. Back in the days of indirect diesels (which was the norm a few years ago), the prewarming period was considerable even during summer months, the culprit being their pre combustion chambers. However modern direct injection diesels are higher compression and suffer less from heat loss and most will start during summer without the aid of glow plugs. However dont think they don't come on just because the light didn't come on. On most vehicles, the glow plugs are activated during the starting period and continue for several seconds after it starts, in order to lower pollution and noise during this phase. The dashboard light doesnt light because we would all be confused by what was really going on. The light is only on when the ECU thinks there is a chance you won't start and kindly request that you wait. Quote
Denis Posted July 27, 2004 Report Posted July 27, 2004 I thought the glow plugs protruded into the cyclinder, like a spark plug, to make a kind of 'hot spot' and encourage ignition when the cylinder was cold. Am I wrong or have I misunderstood your explanation seatkid? Quote
seatkid Posted July 28, 2004 Report Posted July 28, 2004 Yes you're right, sorry my explation was perhaps too general. The hotspot created ensures that the air charge in the cylinder reaches the minimum ignition temperature when the air is compressed on the compression (ignition) stroke, as in the case of slow cranking, low air intake temperature and cold piston/sleeves. Note, on some vehicles - dont think this applies to VAG Tdi models - the glowplugs are activated "silently" when you unlock/open the drivers door, just in anticipation of a start.. Quote
Denis Posted July 28, 2004 Report Posted July 28, 2004 Thanks seatkid. The idea of 'anticipating' a start when someone opens the door seems a really neat idea. Quote
Guest fredt Posted August 5, 2004 Report Posted August 5, 2004 Note, on some vehicles - dont think this applies to VAG Tdi models - the glowplugs are activated "silently" when you unlock/open the drivers door, just in anticipation of a start.. This does apply to the early Galaxy's and I would imagine the later ones as well the activation of the glow plugs is triggered by the drivers door courtesy light switch and does away with the delay needed for pre heating when starting a cold engine Quote
rwtomkins Posted August 9, 2004 Report Posted August 9, 2004 Just for the record, my experience isn't the same as Taliska's - my glow plug indicator comes on briefly whatever the outside temperature, at least on the first start of the day. This also suggests that there's no intelligent device telling the glow plugs to warm up when I unlock the door. Quote
Guest TOPDECS Posted August 10, 2004 Report Posted August 10, 2004 When i start my "X" the glow light comes on after first start and sometimes stays on for a while even in this heat,when i start it revs up then dies down after a while. If i leave start up for a while after the glow light has gone out it seems togo ok. :lol: Quote
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