Starting and stopping diesel engines. - Fuel Economy, Hypermiling, EcoModding News and Forum

Spencer Fitch · 03-28-2012, 12:31 PM

I refuse to do the pulse and glide so I'm not talking about that but say in stopped traffic or every morning when I get to work I gotta stop get out walk over to a button hit it and wait for it to open. Is it worth it to kill the engine for a minute? I have always heard not to start and stop diesel engines and to leave them running instead of turning off for 1-8mins. Truth behind it?

redpoint5 · 03-28-2012, 01:14 PM

What do you drive? I've read that it's good to let the engine run while the turbo cools before shutting down, so I would leave it running. I would imagine it's harder on turbos, fuel pumps, and starter motors to have excessive starting and stopping, so I would avoid it. Maybe I would consider killing the motor if I knew there would be more than 3min of idling.

gone-ot · 03-28-2012, 01:21 PM

..."tradition" has it that turbocharged diesels are better left ON rather than continuously being stopped & started.

Spencer Fitch · 03-28-2012, 01:28 PM

It's a 2012 jetta tdi. Yea I'm just gonna leave it running from now on not to mention I hear diesel starters are EXPENSIVE.

mechman600 · 03-28-2012, 04:42 PM

Yes, traditionally diesels are supposed to be left idling.
Not anymore. Treat your diesel like a gas engine. The starter won't care. The turbo won't care. Excessive idling isn't good for modern aftertreatment systems anyway.

slowmover · 03-28-2012, 06:02 PM

I don't do "engine off", ever.

niky · 03-28-2012, 08:02 PM

Depends on your turbo lubrication. The diesel engine part won't mind. The finicky turbo (especially if it's a variable geometry one) will mind if it's oil-fed... and variable geometry turbos almost always use oil as part of the system that works the vanes (can't recall one that doesn't).

Probably not a big deal if you don't run hard enough to get it hot... but I've seen turbo failures on these "modern" diesels from owners who don't understand the peculiarities of the system.

mechman600 · 03-28-2012, 09:12 PM

Most VGTs (if not all) have engine coolant keeping them cool, so idling to "cool them" off really does nothing but waste fuel.

Frank Lee · 03-28-2012, 09:23 PM

Yet another prime example of an old time habit that won't die.

Sure, if you have just parked your semi hauling 50,000 lbs across the mountains, that engine has been working very hard and a cool down period is advisable. Likewise if you have just plowed 50 acres with your Steiger. Likewise if you have just pitted from going 180mph in a Le Mans race. But just in from puttering around on the street? I don't think so.

Piwoslaw · 03-29-2012, 04:29 AM

Quote:

Originally Posted by niky

Depends on your turbo lubrication. The diesel engine part won't mind. The finicky turbo (especially if it's a variable geometry one) will mind if it's oil-fed... and variable geometry turbos almost always use oil as part of the system that works the vanes (can't recall one that doesn't).

Probably not a big deal if you don't run hard enough to get it hot... but I've seen turbo failures on these "modern" diesels from owners who don't understand the peculiarities of the system.

You can kill the engine at a red light because the turbo already cooled down (if it was hot in the first place) while you were slowing to the light.

If you are hypermiling, then your turbo probably didn't get too hot to begin with.

If you're constantly flooring it trying to gut the engine, then your turbo will be glowing red, but then you probably don't care about saving fuel anyhow.