Quote:
Originally Posted by 123mike
i have noticed that big trucks often leave diesels running and don't turn them off. I have been leaving mine running a lot when I go shopping or stop at the bank. Since I have to turn off key, reach under dash, find brown vac lines pull chopstick out of one, then connect it to line that shuts off fuel. Then unconnect brown line and reinstall chopstick plug. It's even more fun in the dark! Anyone else do this? Am I harming my beloved 83 300d turbo? I'd feel better if it removed the key, but then wouldn't the glow plugs turn on again when I reinserted the key? Is that a bad thing? Mike
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This is what I was told in Diesel Mechanics Tradeschool. When Big Rig Trucks move they are generally loaded. When the pull off of the Freeway and stop at lets say a Truck Stop to eat if they shutoff the Engine (remember the Engine was pulling at a considerable load) the heat spikes and the Oil runs off of the Parts leaving the engine dry for the next start.
So lubrication is one of the reasons they leave it running.
The other reason is that if they Engine was shut off when they came backe from eating they would have to warm up again because it is a bad idea to jump in and drive off and go to full load with a cold Engine.
Winter Weather makes that worse.
The last part is less obvious. As it has to do with Heat transfer to other parts. The Engine and Transmission and so on get hot at different rates. So if the Engine is hotter than the trans so for a while there is heat coming off of the Engine and transfering to the trans or which ever is cooler. Eventually that stabalizes.
Leaving the Engne running helps to keep everything stabalized heat wise.
In the Case of a Car you seldom operate at full load especially if you were going shopping to several places and in stop and go traffice everthing that could absorb heat has a lot of time to dump off the heat so that if you park in a parking lot to shop while the Oil does drain off the parts the heat spike is not any where near what is on a big Rig pulling off of the Freeway and stopping.
If if you did get into the Car with the Engine Cold and take off right away you are no likely to be fully loaded.
I know people will not agree with this but that is what I was told.
I was also told that it was Detroit Diesels that in Winter Weather can get too cold while idling because when the Exhaust Valves (the only valves it has) are open the Blower is blowing a large volume of Air through the Cylinder Ports and out of the Valves. That volume of Air is a larger volume than a Cylinder full of Cold Air that a 4 Cycle engine would. Any way the effect is that at idle the cold Air during Winter cold can sometimes over cool the Cylinders.
Delivery Trucks often leave the Engine running to keep from wearing out the Starter. Picture how many times a UPS of FedEx Driver would start an Engine if they did that at every stop they made.
And, they also have that hot Oil draining off of the Parts issue to add to that.