TDi Cooldown - ?

HungryJoey

Hello,

I was just wondering... Just came accross this thought. About a year and a half ago, My fathers Car was in for some work doing to it, He was given a Toldeo 1.9 Tdi 110 BHP If I recall correctly. Yet it was a very basic car, It was very good to drive So he was saying.

Anyway, What I am asking is, At the garage they told him.. Everytime before you switch of the engine... Leave it for about 10 seconds + for the Turbo To cool down ? Now I have not heard of anybody mention this elsewhere.. Thought I would ask you's why he was told to leave it cooldown before it was switched off. The Car was in perfect working order nothing wrong with it.. He was just told its better for the turbo ?

Why was this ?

Hj

Stephen

Haven't heard of this for bog standard turbodiesels, but i've heard of performance petrol turbos needing to be cooled down to maximise their life, which is why people with flash cars get turbo timers installed, which will idle the engine for a couple of minutes after they get out of the car, before switching it off altogether.
The turbo is cooled by circulating coolant. When you just switch it off after running at high rpms for a while, the flow stops, but the blades will continue turning for a while. Leaving it to idle, the coolant will get around the system fully etc.

edit: see here: http://en.wikipedia.org/wiki/Turbo_timer

HungryJoey

Oh yea, That sounds about right. I remember the Evo 7 I was in ( which I will never forget ) Beautiful it was... When we got out, You could control the start/stop from the Key.. He left it run as we got out. I presume for this reason..

But as far as Tdi, How does it affect anything ?

Hj

maidhc

You should NEVER switch off any Turbocharged car at revs. It isnt related to coolant, but the circulation of oil in the fluid bearings. If you switch off an engine while the turbo is spinning it will continue to spin even after the engine (and oil pump) have stopped. Result is a turbo dead before its time. Guaranteed.

In fact with older turbo engines (and hydraulic systems in machinery) the advice was to idle them for at east one minute before using the machine and at least one minute after full load, and not to exceed half load for the first 10 minutes of operation.

Toyota still recommend you idle the D4D for about a minute before shutdown.

Cerberus

In a TDI there is no need do this unless you ragged the car all the way up to the point where you stop and get out. If you're after cruising on the motorway for a couple of mile at high speeds then you should allow it some cool down time before turning it off. But a half mile (say for instance the spin down your estate to your house) at low enough revs is plenty of time for this cooling down period. More important to the TDIs is the heating up period. Don't rag it straight from cold.

HungryJoey

Cool, Thanks alot guys.

Makes sense.

Hj

stratos

just to add to this in reality no engine should be switched off after being driven.
It should be allowed idle time before being switched off.
The engine block is a large mass and will continue to heat after the engine has been switched off, however with the engine off and the vehicle stationary no cooling is afforded, this can damage the engine.
A lot of modern cars run the fans for a while after shut down to help alleviate this problem. For hi spec turbo's it's essential.
God be with the days when we had time to warm our cars up before going to work oh well ..

Aidan1

isnt related to coolant, but the circulation of oil in the fluid bearings.

For a turbo, the oil in the fluid bearings is the coolant for the bearings. Turning the engine off after running at high rpm, even if it has been idling for a short while, will stop the flow of oil through the bearings, resulting in a termination of the cooling effect and the formation of 'hot spots' in the bearing. If you leave it idle for a minute or two, the oil will run through the bearings, carrying the heat away into the sump (and oil cooler). If you don't, well, when a turbo lets got at 15,000 rpm, it makes quite a mess.

maidhc

Aidan1 wrote:

For a turbo, the oil in the fluid bearings is the coolant for the bearings. Turning the engine off after running at high rpm, even if it has been idling for a short while, will stop the flow of oil through the bearings, resulting in a termination of the cooling effect and the formation of 'hot spots' in the bearing. If you leave it idle for a minute or two, the oil will run through the bearings, carrying the heat away into the sump (and oil cooler). If you don't, well, when a turbo lets got at 15,000 rpm, it makes quite a mess.

Makes a lot of sense, I was never entirely sure why a minute or more was always suggested.

The issue of the turbo being cared for is one thing that always bothered me about buying a diesel s/h.

css

maidhc wrote:

Toyota still recommend you idle the D4D for about a minute before shutdown.

Only if the car has been driven hard, or been used to pull a big load..

In normal driving conditions you should be absolutely fine. But if you've had a patch of hard revving just before you come to a stop, i'd idle it a minute or so.

maidhc

css wrote:

Only if the car has been driven hard, or been used to pull a big load..

In normal driving conditions you should be absolutely fine. But if you've had a patch of hard revving just before you come to a stop, i'd idle it a minute or so.

Pg 210 Avensis Owners Manual

Time for idling engine after driving:
City Driving: Not necessary
50mph: 20sec
60mph: 1min
Driving above 60mph/steep slopes: 2mins

Maybe the easiest thing is to idle for at least a minute all the time. If you own a Diesel it is likely you do more than pottering around.

IDMUD

It should also be noted that this isn't so much of a problem now that turbos have water cooling aswell.