A myth busted! For me anyway

your cooling the turbo not the diesel engine thats why they have a cool down before you switch off advice after sustained highway driving

A quick question on all this,
If you drive up a hill in traffic at night and sit on about 3000rpm, mines a auto by the way if you look in your rear view mirror can you see smoke in the lights of the trailing car?? I do. That being said if i do the same hill in the day time i cant see any smoke so could it be just particles showing up in the lights??

Aaron

Yeah Aron, I get the same thing. Only real way to tell is to follow in another car.
Back to topic. Ive often fitted mechanical oil gauges to some of my cars and they give you a better idea, of how long it can take for oil to get to every part of the engine. The needle will flick slightly as oil moves into oil galleries and as air is displaced. Some times this can be up to 2minutes.
I think 2minutes idle when cold is still best practise.
We've got a turbo timer, which is set for 1 minute. Some times it feels way longer. If it hasn't turned off and I need to drive off again, you can just turn the key to on and keep going.
But you need to turn off the timer when re priming the fuel system.:angel:learnt that the hard way.

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Originally Posted by UncleHo

G'day Folks :)

That is interesting, but aren't Detroit Diesels 2 stroke?? the same as Cummins? <snip>

cheers

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geez, not for over twenty years !

The DD60 series engine was the first electronically controlled, unit injector modern 4 stroke diesel nearly twenty years ago. Way before the Euro engine builders. I think these blokes might know what they are talking about ;)




Idling is bad for diesels, contrary to all the old school advice. It primarily leads to bore glazing and cylinder wear.

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Originally Posted by rick130

Idling is bad for diesels, contrary to all the old school advice. It primarily leads to bore glazing and cylinder wear.

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Don't know about old school!

"The injectors of any diesel engine will quickly become fouled if the engine is allowed to idle at low speed. If the tractor is not working shut it off...." - Operator's Handbook, Chamberlain Champion 306, 1968.

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Originally Posted by mcrover

At idle, my understanding of that artical is that the cold air inducted into the engine being the same amount as at higher revs, cools the engine from the inside out as a diesel engines speed and torque is determined by the amount of fuel that is injected into the cylinder or combustion chamber.

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turbo boost would change the amount of air being drawn/forced in to the engine...

That is what I have always done with the Disco since I got it. The manual is very clear about not running the engine to warm it up, but to wait until the oil lights are off before moving off. And on stopping, to let the engine run for a few minutes before shutting off if it has been pulling a load or running on the highway.

When I did a course with a LR trained 4WD instructor that is also what he said and every time we stopped to open a gate or do something outside the vehicle he repeated his mantra "Secure the vehicle and shut it off, get out then shut all the doors".

Were crossing over two very different engines here too with these generalisations.

Big commercial diesels such as Detroit and Cummins have much lower operating ranges than what our "high performance" (These things are relative!) 4/5 cyl turbo intercooled diesels. They don't work at anywhere near the rev range we subject ours too.

The more modern the turbo design the more likely you are to get away with a quicker shutdown. A lot of the bearing failures attributed to the earlier turbo's was because they relied on oil cooling. If you shut your engine down while the turbo was still red hot the oil boiled off and at startup there was very little lubrication, over time this took it's toll on bearings.

To overcome this water cooling was added. The main advantage of water cooling is that even after you shut off the engine the water still circulates through natural convection so continues to pull the heat away (although obvioulsy not as effectively as if you had allowed the engine to idle for a couple of minutes)

I was also told that problems arose with mineral oil which would carbonise on hot turbo bearings when the motor was shut off too quickly, but with synthetic oil it doesn't do that.

I still idle for 20-30 sec normally and a couple of minutes after a highway run though, can't hurt.

Idle down time for turbos has much to do with their operating speed.

As you know, a turbos oil supply comes from the engine. Now if the engine has copped a flogging, the turbo will be hot and the compressor wheel will be rotating at high speed.

If they're still spinning at full tilt when the engine is shut off you will have a hot turbo with no oil supply.