Why do diesel truck keep their engines running/idling for so long? There is construction going on near us, and sometimes some trucks will come out & 6AM, and sit there & idle for 2 hours until the gates open @ 8am.
Now, I know diesels don’t like to be started & stopped a lot, so if it was for some 10, or even 15 minutes, I could understand it. But TWO hours?!? And truck drivers are always complaining about the high cost of fuel, and this can’t be cheap.
Are these cement trucks, by any chance? Those may need to idle because of the cement mechanism.
This may not apply, but large diesel trucks are often left running during cold weather. They can’t reasonably be expected to start in -20°C weather, so they are left idle if the driver leaves them unattended for relatively long periods of time. It may not save fuel, but it does save money (by not being late for deliveries).
Refrigerated trucks abound. They have to be left running.
I’ve been wondering this too. I work for a trucking company and there seems to be a popular misconception among the drivers that leaving the truck idling actually saves diesel since it apparently takes a lot of fuel to start the engine.
The company has tried to shoot this thing down with numerous posters plastered all over the place stating the company’s overall fuel costs ($12 million a month!), and the need to turn off engines when not in use. Like everything you tell truck drivers, these words fall on deaf ears, however.
(My favorite poster : “Business is hot … and safety is COOL!” Yeah, well I was going to drive that forklift straight into a tank of methyl ethyl ketone at 15 mph just to see what happens, but that poster sure set me straight. Thanks boss!)
Other than cement trucks and reefers as already mentioned there is no good reason today to leave most diesel trucks running.
I base this statement on the informed opinions of fleet maintenance managers and automotive engineers that I have worked with in the past. Many years ago diesels were hard to start when cold but that doesn’t seem to be true nowadays.
It’s part of the truck drivers lore though and “They are not going to let something like facts get in the way of their belief” - statement made at a TRMC (Maintenance Council) conference 15 years ago by a disgruntled fleet manager.
The previous posters are correct that it would save fuel to shut down the diesel engines rather than to let them idle for a long time, but it is also true that diesel engines idle much more efficiently than gasoline engines, so it’s not quite as big a deal as it would be with a car.
Gasoline engines have a separate “idle” setting on the carburetor (or fuel injection system, whatever) to keep them running while idling. This setting has an extremely high fuel/air ratio in order to keep enough fuel in the cylinder for it to fire under the low-speed, low-air flow (nearly closed throttle) conditions at idle.
Diesel engines, OTOH, don’t have a throttle, per se. Their speed is governed by the amount of fuel available, so at idle they are using an absolute minimum of fuel, just enough to overcome the engine’s internal friction.
In extremely cold weather (i.e., arctic conditions) it is necessary to leave the engine running, not because it is hard to start but because the fuel will gel if its temperature gets too low. The fuel tanks are close enough to the engine so that the engine heat keeps the fuel above its wax point.
But, as noted, they usually leave them running just because they’ve always done it that way.
Finally, most refrigerated trailers have a separate “reefer” unit that keeps the trailer cold. It may use the same fuel as the tractor engine, but it has a separate engine of its own. So you may hear an engine running but it’s not necessarily the truck’s engine.
Another reason is the air brake system. Older trucks sometimes take a while to build up pressure. There must be at least 60 pounds of air pressure or the spring brake system will not let the truck move.A safety feature.
It’s funny that this question came up this week. We were told monday to shut off our trucks if we were not expecting to drive soon. If we had a dirty drum even wash out. I drive one of those cement trucks.
Wondering why we were told to shut them off?
Fuel costs $1.00 more a gallon than it did last year.
IIRC, and from what I’ve seen- Refrigerated trucks have a seperate engine to run the compressor for cooling the cargo. There’s no need to leave the truck engine itself on to power it.
I also remember hearing that they run the engines in cold weather to avoid vapor lock.
Then there are the Norwegians who, I am told, turn off their car engines at traffic lights to save fuel.
Yeah:
A lot of people in Europe turn off their engines in, e.g., a traffic jam. Saving money and less air polution are the reasons. Plus, less cars have aircon in Europe as opposed to the US, so the engine doesn’t NEED to run in order to keep cool.
I wouldn’t turn it off for a single traffic light though. But serious gridlock? Sure.
Sometimes those trucks can be tempermental. If you are first in line and you can’t get your truck started guess who is going to be yelled at. Actually idleing doesn’t use much fuel. Maybe two or three gallons an hour.When you have a load maybe worth a half million dollars,or maybe only sixty dollars, three or four bucks is not very significant.
Just a side note here. Vapor lock is a term that typically refers to a condition where the fuel in the fuel lines gets too hot, and thus vaporizes. Fuel pumps typically cannot pump the fuel if there is vapor at the suction side, so the engine stalls until the lines and pump cool down.
This can happen more often in mid or rear-engined cars, especially if the fuel pump is mounted in a position that sees poor cooling air flow. One of my FIAT X1/9’s would vapor lock terribly until I bought and installed an electric fuel pump that was mounted away from the engine heat.
We are in San Jose, so no very cold weather, and they are not reefers or cement trucks. I like neutron star’s answer the best.
Dan,you wern’t clear as to what kind of trucks they were.
Sometimes construction material is delivered on the day it is used. If the load has been on the road all night and arrived early you can see the drivers reluctance to shut it off because it may not start.
The dump truck drivers are sometimes independents and are hoping for the first and last load. More money in their pockets.Hurry hurry hurry
Many drivers are paid milage and aren’t paid for waiting time. You can see that if the load is ready and they have to wait for their trucks air pressure to come up they are losing money.There again same problem if it won’t start.
Also if you can get unloaded early you can get home early.
Some trucking company policies are not printed. I’ve been called on the carpet several times for not doing something "the right way " and called in again for doing it the way I was told and it still wasn’t "the right way."So what the hell I usually do it my way because it makes sense to me.
For that matter, a lot of truck drivers will leave their engines running to power the radio, microwave, TV or whatever else it is they have inside their truck. If you’re going to wait for two hours outside a gate, you might as well listen to some tunes. Likewise with those trucks at the rest stops, purring away into the night.
I remember reading that a lot of such trucks have batteries for most of that stuff now, but old habits die hard.