View Full Version : What if I don't WAIT TO START diesel

Jul. 16, 2009, 12:40 PM
Half the time I am sitting in my gas engine vehicle waiting for the WAIT TO START light to go out when there isn't one and occasionally I climb in the diesel (Ford 7.3) and forget to wait to start.

What harm am I doing (not for the gas engine) and how can I remediate it? shut it off right away and wait to start or hit myself on the side of the head and say DOH and drive on?

I live in SF where the temperature is almost always moderate. never freezing and rarely 80.

Jul. 16, 2009, 12:48 PM
The "wait to start" light stay on to allow the glow plugs in the diesel engine to warm up.

I found this: "Diesel engines, unlike petrol engines, do not use spark plugs to induce combustion. Instead, they rely solely on compression. The piston rises, compressing the air in the cylinder; this, by natural effect, causes the air's temperature to rise. By the time the piston reaches the top of its travel path, the temperature in the cylinder is very high. The fuel mist is then sprayed into the cylinder; it instantly combusts, forcing the piston downwards, thus generating power. The pressure required to heat the air to that temperature, however, necessitates the use of a large and very strong engine block. The problem posed is that in cold weather, if the engine has not been running (as is the case when the car is left to sit overnight), that large engine block becomes very cold; when one then attempts to start the engine, the cold engine block acts as a heat sink, quickly dissipating the heat generated by the pistons compressing air. The engine is then unable to start, because it can not generate and maintain enough heat for the fuel to ignite. For that reason indirect injected diesel engines are manufactured with glow-plugs in each prechamber.

A glowplug is a pencil-shaped piece of metal with a heating element at the tip; that heating element, when electrified, heats due to electrical resistance and begins to emit light in the visible spectrum, hence the term "glow" plug; the effect is very similar to that of a toaster. The heat generated by the glowplugs is directed into the cylinders, and serves to warm the engine block immediately surrounding the cylinders. This aids in reducing the amount of thermal diffusion which will occur when the engine attempts to start."

I am sure someone can explain it better :) I am in Texas (hardly any cold weather) and I still wait to start both my diesel truck and my Tahoe :rolleyes:. Habit I guess.

Jul. 16, 2009, 12:53 PM
Thank you. I was a fair gas engine mechanic before I got too old to get the grease out from under my fingernails. I need to spend some time reading Diesel for Dummies. That paragraph explained a lot.

this is my first (and last because I am keeping it forever) diesel. I love driving it.

Jul. 16, 2009, 01:37 PM
Oooh, I bet a diesel is fun on those hills!

Jul. 16, 2009, 01:54 PM
Per my diesel guy at Ford when I had my '99 diesel, not waiting to start in our climate (I am just over the bridge from you in the East Bay) will not do much to the engine. Like other have said its for the glow plugs to warm so the ignition happens. It really doesn't get that cold here, so its not like there is much to warm (ever notice the light turns off faster when its hot to when its cold, its the toaster effect). Should you wait, yeah probably, if it happens every once in a while are you going to kill your truck....no. Just don't turn the truck back off if you start it to soon, it already ignited, so no need to turn the truck off just to restart it, just extra wear and tear. Now I have a 2003 diesel and no more glow plugs! Just get in and turn on, no waiting required.

Jul. 16, 2009, 02:10 PM
I had a friend that had a 1997 F250 Diesal that she kept having to have the glow plugs replaced on (we are talking about 5-6 times a year). The last time she took it in to have them replaced the mechanic questioned her to try and find out why she was having to replace so many times. She did a lot of short trips and errands (this was her daily driving vehicle as well) where she would drive to town, stop at one store, go in for 5 mins., go to next store, in for 5 mins, etc. and she would wait to start at each stop until the light went out. The mechanic told her that was her problem and she did not have to wait if the engine was already warmed up. She stopped doing this and would only wait when she first started up or the engine had a chance to fully cool and never had to replace another glow plug that I am aware of.

Jul. 16, 2009, 06:49 PM
Agree with pupakin, if you ignore the light you stand to damage the glow plugs.

Jul. 16, 2009, 10:28 PM
thats not what pupakin said....I also to do not "wait to start" if engine is warm.

Jul. 17, 2009, 01:10 AM
I have a 1993 model diesel tractor. There is no "wait to start" warning. There is no mention of "wait to start" in any of the literature or instructions. It does have a pre-heat function for use if needed in cold weather, and that's about it.

I don't see damaging your engine by not "waiting to start".

Frank B
Jul. 17, 2009, 10:34 AM
We use the preheat on the barn's diesel tractor in cold weather.

During warm weather, it'll start right up with no preheating, even after sitting overnight.