Turbo Charger Question

[Need4Speed]

Hi guys i had a question.

Why is it advised for cars with turbo chargers to let the engine idle for a couple of minutes before switching it off.

[Egg Nog]

Originally Posted by Need4Speed

Hi guys i had a question.

Why is it advised for cars with turbo chargers to let the engine idle for a couple of minutes before switching it off.

It's not?

[Matra et Alpine]

Originally Posted by Need4Speed

Hi guys i had a question.

Why is it advised for cars with turbo chargers to let the engine idle for a couple of minutes before switching it off.

The heat in turbo is immens.

Most decent installations have oil feeds to the bearings and some have cooling too.

So by letting the engine idle for a few mins after some hard use it gives the turbo a chance to cool down and for the oil to build up in the bearings.

The A610 has both, the cooling fan is a real pain coz every time I park near anyone as I walk away I'm always called on to say somethigns still runnin. I keep thinking I'll get a sign made up .....

"Tuned sports car, drives like a cheetah and likes to gently purr after"

[SilverArrowZ]

Is that the reason i use to see some turbo diesel car owner just lock up everything after he park and then just walk away but the car is visibly still having its engine running? Where everybody thought the owner forget to cut the engine, it runs by itself for a few minutes and then shut off...

[Matra et Alpine]

Originally Posted by SilverArrowZ

Is that the reason i use to see some turbo diesel car owner just lock up everything after he park and then just walk away but the car is visibly still having its engine running? Where everybody thought the owner forget to cut the engine, it runs by itself for a few minutes and then shut off...

Don't know any car that leaves the engine running, but for sure a pump.

[pmurf125]

Some turbos have white metal bearings and if you turned the engine off after a hard run they simply melted and the turbo was scrap. I dont know if any newer turbos still have these bearings but whatever, it is a good idea to let a turbo car idle for a few moments after a hard run. Under normal every day driving conditions in modern turbo cars this is not necessary.
You can buy a device called a "Turbo Timer " (just do a search on google)that lets you walk away from your car and leave it running for a pre set time.

[Egg Nog]

Originally Posted by SilverArrowZ

Is that the reason i use to see some turbo diesel car owner just lock up everything after he park and then just walk away but the car is visibly still having its engine running? Where everybody thought the owner forget to cut the engine, it runs by itself for a few minutes and then shut off...

You must be mistaking the engine runing with the radiator fans. Many cars run the fans for a few minutes after engine shutoff.

[KnifeEdge_2K1]

i dont know much about this subject but it makes sense

turbo charger turbines get up to 150,000 rpm. turning off an engine right away after driving hard would result in a really hot turbo turbine that isnt moving, on a turbo with fluid bearing/s (is it plural?) which must be constantly pumped around the shaft this could result in overheating, same thing goes for ball bearing turbo's but to a lesser extent.

[Need4Speed]

Originally Posted by Egg Nog

You must be mistaking the engine runing with the radiator fans. Many cars run the fans for a few minutes after engine shutoff.

No he is right i have seen some turbo cars which have had the engine on for a while after you take the switch out, some electrical system (Turbo Timer as pmurf125 mentioned) which keeps the engine running for a while and turns it off itself, (the actual engine, not a fan).

[megotmea7]

jason to the rescue yet again...

you leave your turbo charged car running after hard/extended driving because as its been said turbo's get very hot and by shutting down the engine you cut the fresh supply of oil to the turbo which carries away the heat. letting it run will safely cool down your turbo butmelting bearings is hardly a problem... the true problem is the lstagnent oil in the hot turbo "cooking" and becoming a coked up mess impeading shaft rotation which can lead to turbo failure also blocking oil passages which can prevent proper cooling while the engine is in operation and increasing turbo temps which could lead to warped housings, broken shafts, or any number of problem. turbos need a constant supply of oil for cooling and lubrication purpouses. block the supply or have cooked gummy oil in and you have a funny looking hunk of metal thet is either scrap or in despeate need of a teardown

[Matra et Alpine]

Originally Posted by MetA

So by letting the engine idle for a few mins after some hard use it gives the turbo a chance to cool down and for the oil to build up in the bearings.

Originally Posted by megotmea7

jason to the rescue yet again...

you leave your turbo charged car running after hard/extended driving because as its been said turbo's get very hot and by shutting down the engine you cut the fresh supply of oil to the turbo which carries away the heat. letting it run will safely cool down your turbo butmelting bearings is hardly a problem... the true problem is the lstagnent oil in the hot turbo "cooking" and becoming a coked up mess impeading shaft rotation which can lead to turbo failure also blocking oil passages which can prevent proper cooling while the engine is in operation and increasing turbo temps which could lead to warped housings, broken shafts, or any number of problem. turbos need a constant supply of oil for cooling and lubrication purpouses. block the supply or have cooked gummy oil in and you have a funny looking hunk of metal thet is either scrap or in despeate need of a teardown

Do I get a prize for saying it in less words ??

[megotmea7]

but the oil doesnt "build up in the bearings" it flows around lubricating and carrying away heat. you want to prevent it from buildding up in the bearings or it will cook

[Matra et Alpine]

Originally Posted by megotmea7

but the oil doesnt "build up in the bearings" it flows around lubricating and carrying away heat. you want to prevent it from buildding up in the bearings or it will cook

hmmm, well didnt' want to get too technical.

but spinning at 150,000 rpm the turbo bearing oil seperates into 2 surfaces of heavier oil and a turbulent section in the middle which becomes 'refined' by shear and centrifugal force. So the oil becomes a LOT thinner due to fluid dynamics.

If it's then stopped the oil IN the bearing at the time is not "good" oil for the bearing coming to rest. The laminar oil film on each surface is only a few molecules thick. By 'idling' and letting more oil flow then the 'traditional' look of an oil bearing with a thin area at the bottom and thicker area at top and a subsequent break in laminar flow gets more thicker oil ( longer chain molecules ) into the surfaces so that when they slow to come to rest their is a 'good' oil cushion. If you take a hig spinning bearing, and quickly stop it without pumping oil in you dont' get the cusion and the subsequent settling on the bottom edge of the bearing causes damage to the white metal.

So there IS more oil needed in the bearing at these times. I didn't mean it to sound as if you pumped oil into the bearing. As the turbo slows down and cools you are pupming oil through the bearing as normal, but now the oil gets a chance to build the necessary 'cushioin' for the bearing to come to rest.

Still think it was best with the shorter description. This is now just showing how nerdy I am about cars and engineering

[megotmea7]

just showing how nerdy I am about cars and engineering

arent we all