Re: OT. Ideling a diesel

Posted by NCWayne on November 15, 2010 at 19:42:26 from (98.21.228.96):

In Reply to: OT. Ideling a diesel posted by JayinNY on November 15, 2010 at 18:28:37:

Just to throw my 2 cents in here on the subject. There are really too many variables to say yes it"s always bad, or no it"s not always bad because every situation is different.
On the bad side any engine with a properly thermostat/temperature control system is going to eventually get to it"s correct operating temperature whether it"s ideling or no. During the summer months when it"s hot that"s not going to be a problem but it could be problematic during the winter when temps get down too low. That"s the reason you see trucks going down the road with covers over the grill to reduce the flow of cold air through the radiator which allows the engine to retain more heat. As for wet stacking it can and does happen but it"s just as much a result of ideling as it is of low exhaust gas temps. Basically there are no piston rings commonly in use, that I know of, that will provide a 100% seal, in other words all engines are going to "use" a little bit of oil wether they idle or not. So, basically ideling an for a few minutes here and there is never going to hurt anything as long as it is run under a load afterwards and exhaust temps are allowed to get to their normal temps and burn off any oil that may have accumulated in the exhaust system. On that note I have seen a crane that was idled day in and day out lifting light loads and it literally wet stacked to the point there was pure liquid oil in the muffler. When they finally wound it up and put it under a load for a few hours the muffler caught fire and burned all of the oil out. It was an old 2 stroke Detroit which are prone to wet stack anyway due to the design of the rings but proof of point is that the high exhaust gas temps got rid of the excess oil.

That said I"m talking about the older engines without all of the new, fancy exhaust systems using EGR, particulate filters, etc, etc. On those I don"t have enough experience with them to say one way or the other.

Now the pluses to ideling a diesel. One is turbo life. Regardless of whether you allow it to slow down, and cool down, or not, when you shut down the engine the oil flow to it stops. I"ve watched the turbo on a customers engine continue to spin for nearly 45 seconds after the engine was shut down. Granted in this application the engine was being shut down from it"s idle position of 1300 RPM but even at a more standard idle speed of say5-700 RPM even 15 seconds o run time without oil pressure wouldn"t be unheard of. The same goes for startup. The turbo is already starting to spool up by the time the oil pressure reaches it so there is going to be a lag time when it has no real oil pressure to speak of. There have been several ways to combat this problem put into production over the years from accumulators to standpipes to hole the oil, etc, but there is no replacement for using a good, quality oil. In my customers case changing to a better brand of oil took his turbo life from around 9 months to nearly 2 years.

To be honest beyond turbo life expectancy the only other plus I can think of is along the same lines. That is diesels typically have compnents weighing alot more than a standard gas engine. As such the crank lying in the bearings is going to tend to displace the oil film if left setting for any length of time. As a result you are going to have metal to metal contact for a split second after startup until the oil can get in place and do it"s job.

It"s a proven fact that the majority of engine wear is put on an engine wear is place on the engine at startup and shutdown for the reasons mentioned. So, if your starting and stopping your vehicle many, many, times a day then you might be better off to let it idle.... but for around town stopping like most people do then letting it idle is doing nothing but wasting fuel.....

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