coffeeman said:
Summer starting? I guess a diesel engine should warm up before running full rpm. Of course winter needs lots of warm up time. Question; is it ok to start up and run tractor to hook up a machine or run a little distance to do some work, keeping the rpm below 2000. If not, how long should a warm up take?
Cheers Coffeeman
Yes, you should allow a short warmup period before putting the engine under full load (not the same as full rpm, btw...). 3-5 minutes of running at half-throttle or less should be ample, especially in the summer. If it's extremely cold, a little longer warmup may be required, but remember that diesels don't warm up very well at all by just idling... they're too efficient... they need to be doing some work to really get warmed up.
Glow plugs themselves don't "warm up" the engine. Instead, they work in one of 2 ways:
- They create a "hot spot" inside the cylinder which ignites the fuel that is injected into the cylinder when the engine/ambient air temperature is too cold for compression alone to raise the air temperature in the cylinder to the fuel's ignition temperature at the top of the compression stroke. The fuel is injected into the cylinder, hits the hot glow plug protruding into the cylinder, ignites, and hopefully starts the engine running. Since the engine is now running, with the increased RPM over what the electric starter can provide, the intake air charge should be heated enough by compression so that the engine should be able to stay running on it's own without assistance from the glow plugs.
- Another way glow plugs are used, is to pre-heat the air in the intake manifold before the engine is cranked to start. Yanmar uses this method on several of their engines... other mfgr's likely do as well. My Mahindra 3525 uses a variation of this technique. The glow plug is energized, and then either by itself warms the air inside the intake manifold, or it ignites a very small quantity of fuel inside the intake manifold. Once this fuel is ignited it warms the air in the manifold, and then the engine is cranked and the warm air inside the intake manifold is drawn into the cylinders. Since the air is already pre-warmed, compression raises the temperature of the air in the cylinder to above the ignition point of the fuel, the fuel is injected into the cylinder, ignites, and sets the engine running.
A modern, high compression diesel engine in good condition, should not
require glow plugs to start unless the temperature is very cold, and especially should not require them in summertime temperatures. For example, my VW TDI diesel engine does not energize the glow plugs at all unless the ambient air temperature is 34*F or below... I started my Mahindra 3525 several times at temperatures below 20*F this past winter, and did not allow the "cold weather starting aid" (intake manifold glow plug) time to heat up at all (went from OFF directly to START) and the engine fired and was running within 3 seconds of cranking. On my Mahindra, the glow plug comes on for 41 seconds when the key is turned from OFF to either the ON or START position... automatically, whether you want it to or not. I'd prefer to have it on a switch so that I can control when it operates.
Now as the engine wears, and compression drops, it may become more dependent on the glow plugs to get it running at warmer temperatures... but that's hopefully a long way and lots of hours down the road.
I think the mfgr's put the "auto glow plugs" on these machines in an attempt to make them as (... how do I say this without offending anybody...?) idiot-proof to start in any weather condition as possible.
If your tractor won't start cold in the summer without the aid of the glow plugs, there's probably something wrong with it, or else it's just getting old and low on compression. And using the GP's when they're not needed only shortens their life... you gain no benefit from them if they're not needed. And I can't see what harm you could possibly do to the engine by
not using them.
But, if using them gives you a warm fuzzy feeling when you turn the key, you're certainly free to continue doing so... it's not harming anything either, other than using up cycles on the plugs (they'll only heat up so many times before they fail.) Which may leave you unable to get your tractor started when you truly DO need them.
