Cooling down period?

[ambroseg1]

I have wondered about this issue especially with this new stupid Stop/Start technology and keeping in mind that almost all of the new BMWs are turbocharged petrol or diesel.

The other day i was driving a new 120d flatout. braked really hard and the car shut down because of the stop/start efficient dynamics crap. I really dont think it is good for the turbo to be shut down when it is still glowing from the heat.

Interesting, but I am sure the people who developed this start stop technology must have factored in some safety protocol in these cars?? :fencelook:

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Cant take you nowhere.

Hello Amby my brother from another mother.....

:biglol:

LOL..... sorry for sounding like a prick....but who are you? Know lots of shauns.

 

[Philip Foglar]

Good thread with loads of info, but has been discussed a number of times, and with lots of varying points of view.

Now I just scanned through all that has already been said, so not sure if this has already been mentioned, but one other thing to consider when comparing the cooling down period for say a turbo diesel bakkie and a turbo diesel car is if there is a viscous fan running most of the time or just an electric fan. So let's say you are nailing the engine and stop, you do risk the chance of heat-soak, especially if the electric fan isn't running at that moment - so while the engine is idling and there is no airflow through the engine bay the heat is actually building up.

But, and this is where the general consensus seems to stand, if you do your cool off period as you are nearing your destination, as in drive gently and try and use off throttle conditions as much as possible, by the time that you do stop the engine and turbo temperatures have already stabilised to a more sensible temperature range to prevent damage, but idling should still take place even if only for a few seconds to a minute.

Another thing to consider is that diesel engines run at lower overall temperatures compared to petrol engines, but this is also when under normal loads etc...

 

[Steven Peplar]

Just like to add something. Don't know if anybody has seen it before but with Subaru you get the functionality that you can use when you drove hard or whatever then when you stop you can switch of the car take the key out and lock while the car still idles for 30sec to a minute.

I have seen this a few times too.

So logically I would say the car company says let the turbo breath a bit first.

 

[Philip Foglar]

Yep, that and some vehicles like my Isuzu has an oil pump that pumps oil through the turbo for a few minutes after the engine has been shut down...

 

[netercol]

your turbo is still spinning away happily but with minimal lubrication

this is plain and simple not true.. a sleeve bearing turbo rotating at idle comes to a virtually instant stop when the driving force (exhaust gasses) is removed.

Not wanting to argue with you. But have you ever driven in a VW Polo 1.9TDi or a Ford Focus TDCi? I have noticed in both these cars if you switch the ignition off you can still hear the turbo whistling for a good 5-10 seconds. My college had a 320D with a decat, so the turbo was very clear if you're standing outside the car.

So might be that my theory is irrelevant to most BMW's? I'm just saying out of personal experience...

possibly with BALL BEARING turbo's this can happen (have no idea if the cars you mentioned is fitted with ball bearing turbo's or not), but with sleeve bearing turbo's this just does not happen.. perhaps you hear something else spinning down...

i have not on one of my personal turbo diesels, or any of my petrol turbo's ever heard a sleeve bearing turbo spinning after the car was switched off.

the issue is purely heat remaining in the turbo after switch off.. oil through the bearing cools it too..

 

[mikecw]

Yup, I'm starting to notice in the car basement at work, that a lot more chaps in their diesel cars sitting and letting their engines idle.
During those 2mins of cooling down period, they often get too carried away thumping away on their phones, and start smoking out the basement with diesel fumes

 

[Clownshoe]

i think the main reasons for warm up is:
--oil pressure
my jeep has a oil pressure guage and oil pressure can take up to a minute to come up. until that happens the turbo is not getting fresh oil
i think the main reason for cool down is:
--oil left in turbo can cook and become a gooy mess that jams up the bearings and prevents good oil getting there.

occasionally not following a cool down warm up routine is not an issue. but making it a habit will help. be careful on holiday runs. imagine you have a turbo diesel you are towing a double axle caravan and a 20ft steamboat behind that. you have just got to the top of the groot ballas pass and you pull straight into a 1stop. then you are looking for kak.

 

[Philip Foglar]

i think the main reasons for warm up is:
--oil pressure
my jeep has a oil pressure guage and oil pressure can take up to a minute to come up. until that happens the turbo is not getting fresh oil
i think the main reason for cool down is:
--oil left in turbo can cook and become a gooy mess that jams up the bearings and prevents good oil getting there.

occasionally not following a cool down warm up routine is not an issue. but making it a habit will help. be careful on holiday runs. imagine you have a turbo diesel you are towing a double axle caravan and a 20ft steamboat behind that. you have just got to the top of the groot ballas pass and you pull straight into a 1stop. then you are looking for kak.

Yep, with a cold diesel always best to start with small throttle inputs and keep the revs low, so short-shift to prevent the turbo from spooling up too much, depends on the engine and if you can normally hear the turbo, this helps find the ideal throttle position/revs to use...