Hi Guys,
I know we are supposed to wait about 10 seconds before we shut down the engine after a drive.
I just would like to know the mechanical reason why do we have to do it? What are the consequences if I immediately shut it down.
If I had a long drive say, 2 - 3 hours, should I wait for more than 10 seconds before turning it off?
Thanks.

 

Old wives tale.
If you have a car with a turbo then yes, you MUST wait 10-15 seconds for the turbo to cool down or else you will "bake" the bearings.
No real good reason to wait with the Rover, you wont hurt anything either way.
Now if you were towing a heavy trailer then yes, I would wait for a minute, just to pull the heat away from the cylinder heads.

 

Hi Spike
So 10 - 15 seconds is enough to cool the bearings? Gotcha.
I have a 300 Tdi, so it applies to me.
Thanks.

 

You didnt say in your first post that you had a turbo diesel...so yes, you must let it idle for 10-15 seconds before you shut it down, the harder you drove it the longer you must let it cool.
You must also wait that long after you start the engine for oil to start lubricating the turbo bearings.
Longer if it has been sitting over night.

I used to drive truck, we had a guy fry lots of turbos, he would pull into rest area to use the bathroom and just shut the truck off, it doesnt happen overnight, but he fried the bearings inside the turbo.

 

OK Thanks Spike,
Whew, Its a good thing I shut down the engine after more than 10 secs of idling, sometimes up to a minute after a long trip.
But I didn't know you have to wait at least 10 secs after starting too.
I don't idle my engine at least 10 secs after starting the engine! I usually drive off slowly.
Is the consequence worse than shutting it down immediately?
Thanks.

 

Not necessary for a gas engine, and as Spike mentioned, it is a good idea with diesels, more so for the tubro to prevent "COKING" the tubro burning to much oil and carboning it up.
So people actually install timers so the engine will continue to run after the key is turned off, allowing the additional oil flow thru the tubro to drop the temp first.

 

The main reason is to allow the turbo to spin down from the very high RPM (100k rpm isn't unusual) that it spins at while it's still being fed oil by the mechanical oil pump in the engine. Shut the engine off before it's had a chance to spin down and you cut the oil feed - that's what ruins the bearings.

It's the same for petrol turbo cars, although they typically have the turbo begin working at higher RPM than a diesel (my Tdi hit's peak boost at around 1,800 RPM whereas my old MR2 turbo it was closer to 4,000 RPM) you can avoid prolonged idling (also bad for the engine btw) by simply driving it nicely for the last few miles of your journey and avoid heavy turbo usage.

Some turbos (no LR ones to my knowledge) are liquid cooled by the engine coolant although the second generation MR2 turbo certainly was and heat soak from the turbo could, potentially, boil the coolant in the turbo if the engine was shut down without allowing the engine to idle and cool the turbo off first. This coupled with the oil stavation could ruin the turbo, or in extreme cases blow the turbo coolant piping which leads to a total coolant loss - if you don't notice before driving it again (I know... but you'd be amazed at what some people don't notice) you could kiss goodbye to the head gasket, the head or even the whole engine.

TD, Tdi and TD5 (sorry, don't know about the TDV6 and 8's) Land Rover engines do not feed coolant to the turbo and spin down will take less than 30 seconds. If you've been using the engine and turbo very hard (long uphill for example) immediately before shutting off, give it the full 30 seconds before you shut it down

Cheers,

 

How quickly you can drive after start up depends on many factors, has it sat overnight? How cold is it out side?
If you have been driving it, shut it off to go inside the store and then come back out a few hours later, start it, put on your seat belt and drive away.
If it is 0 degrees out side and it has sat all night...give it 10 minutes to warm up.
But you need to allow the oil to pump through the whole engine before you drive away.
Typically the oil goes directly from the oil filter to the turbo bearings and then returned to the sump.(there is a seperate tube to do this)
That way fresh filtered oil is the only oil that goes to the turbo bearings.
Quality of oil has as much a factor on turbo life as the way you drive.

 

When I had my Dodge diesel I always waited to shut it off until the turbo had time to cool. If I was towing, I would even let it run while refueling to prevent coking the bearings in the turbo. I finally added a chip to my Dodge with a turbo timer that would keep the truck running until the turbo reached a certain temperature.

With your TDI, give the turbo a few seconds to spool down and cool before shutting down. Gas engine, no need.

 

Thanks for info guys -very informative indeed.
I live in a tropical country, the coldest we get is around 20C or so.
To make it simple for me, can I safely shut down the engine after 10 to 20 secs for short trips (less than an hour)
and at least 30 seconds for long drives (more than an hour)?
And idle for at least 10 secs before I drive off?
Man, another thing to worry about turbo diesels. As if periodic maintenance isn't enough.
The good thing about diesels is that they are cheaper and burns longer, right? More bang for the buck.
Cheers.