redghost wrote:
Gump gets hers red hot for long times. Then we go again, just for good measure. At this point I feel it is warm enough inside the car to start the engine.
With parallel glow plugs, the plugs reach 1000 deg C after ~12 sec and their MAXIMUM temperature after about 30 second. Further heating will NOT increase their temperature beyond this temperature (which will be about 1180 deg. C.). Series (loop) plugs do not get that hot - their max is about 1050 deg. C after about 40 seconds and it takes 28 sec to reach 1000 deg. C. There is virtually no point in heating the plugs more than 5-10 sec past the point where they reach their maximum temperature. Further heating results in little improvement in starting and may result in poorer starting.
Fuel is being sprayed right at the glow plug element and the ball pin (adjacent to the heating element and which is most effectively heated by it) where the heat is maximal and where combustion will commence. Once these reach their maximum temperature, continued application of current will NOT increase temperature further so combustion will NOT be further enhanced. Longer application will not detectably improve combustion if the engine is in optimal operating condition (valves adjusted, injector spray pattern and pressures optimized) and even when these other factors are less than optimal, the benefits of additional glow plug heating almost always is negated by the drop in energy available for the starter (and thus the starter turns more slowly and less compression is developed).
For optimal winter starting, the two biggest improvements you can make to an series glow plug engine in good adjustment is to replace the plugs with parallel plugs AND to use a diesel rated group IV/V oil (all the Mobil synthetics are group IV/V - none of the other major oil company synthetics sold in the US that i know of are) which will boost below zero starter cranking speed by 40+% (that's measured in MY cars - I can't guaranty yours will be quite that good) and that REALLY improves cold weather starting. Those two things together will reduce the minimum start temp by 10-15 deg (everything else being equal).
In very cold weather (much below freezing), cars with parallel plugs will benefit from allowing the plugs to glow for an additional 10-20 seconds AFTER the dash lamp goes out (yes the plugs continue to glow for 15-30 sec AFTER the dash light goes off) but this seldom exceeds about 30-40 seconds total - never more than 10 seconds longer than it takes the plugs to reach their maximum temperature of 1180 deg. C.
Marshall -- Marshall Booth Ph.D. Ass't Prof. (ret.) Univ of Pittsburgh School of Medicine Department of Pharmacology 1300 BST Pittsburgh PA 15261 USA [EMAIL PROTECTED]
