Subject: [all-bus-nuts] Idling a DD two cycle: DD's official answer
Recently we had a lot of discussion on one of the bus boards about the advisability of idling a DD two cycle engine. There were varied opinions stated, some "yea", some "nay". And there was some logic on each side of the fence. But when there is something as expensive as one of our DD engines involved I prefer the straight skinny from the manufacturer. Below is their official stand:
Ed,
Your question ranks right up there with the most commonly asked questions we receive. It is also, at least in my opinion, the most commonly misunderstood aspect of the operating parameters of a diesel engine. The short answer is we have always recommended that if the engine is going to be idling, low idle, longer than 5 minutes that it be shut off. The reasoning is a little more complicated but without getting into engineering 101 basically the following is the layman's reasoning.
Diesel engines were designed to operate at peak efficiency running wide open. As there are no spark plugs cylinder temp., obtained by compressing air in the compression cycle, is necessary to ignite the fuel. At low idle the cylinder temp. drops leading to incomplete combustion. This incomplete combustion leads to carbon build up on the valves, in the oil (crankcase), on the fire deck of the head and the dome of the piston along with fire rings on the piston. Engine "slobbering", what appears to be oil, out of the air box drains and the exhaust are other side effects. As worn oil control rings will also give you both of the last two items this is often cited as the cause of an engine "slobbering". The irony is that the carbon build up in the oil will lead to worn oil control rings.
Now the reasons folks give for letting the engine idle. "I need to keep up cab heat / AC in the winter / summer". If you going to be away for less than 10 minutes the engine will keep more heat being shut off than idling for that amount of time. The AC unit will not maintain temp at low idle. "Truckers all leave their rigs running while at a truck stop". They aren't paying for the fuel or the repairs. "When you've been running all day you need to let the engine "cool" down for at least ten minutes before shutting it down". Simply not true!!
I hope this has been of some help to you. If I can be of any further assistance please contact me. Mike Meloche
Senior reliabilt Sales Manager
Cell: 609-932-0253
Fax: 856-667-7024
E-Mail: mike.meloche@detroitdiesel.com