Andy-P

Probably best to sit and idle, depends how slow your off boost drive is.

[Edited by Andy-P - 11/2/2002 6:12:16 PM]

MGJohn

X-posted from the Quote of the day thread ...

Turbo cool down ... recommended if you've recently been on boost within say past couple of miles of your trip, particularly on a hot summers day ... yes, I know BUT we DO get them sometimes ... hot days that is ...

I believe the continued throughput of the cooler lubricant for the turbo at engine idle speeds is just as important for the well being of the turbo as the actual cooling process after switch off. I believe these things rotate at up to 130,000 rpm on full boost and sustained or repeated boosts generate huge temperatures. Failure to allow time for lubricant and turbo to cool sufficiently after such treatment will sooner or later result in a cracked turbo main body housing assembly. Cracks sometimes across one of the bearings... OUCH ... and yes, EXPENSIVE ...... so double


You've been warned ...

mkyboy

Sound advice!!!

I always give it at least 1min even though i look a prat sat in my car.

snowcrash

uhm, yes - doesnt it say this in the manual and on a sticker in the car ???

LB4

Try ... not always easy i know.....driving off boost a couple of miles before you are going to stop and switch off..... got to be better than sitting there with your engine running, your engine/ turbo must be cooler after you stop this way with air flowing through radiator whilst on the move than sitting there ticking over.???

S55 HOT

Most common oversight is motorway service stations - remember that when you pull in for fule you've been running on boost and leave the engine running for a few mins

scooby-k

I thought the reason why you don't switch off straight away is that the turbo would still run but with the engine off it wouldn't get any lubrication. hence the bearings would not last.regards ken

andrew420

If that was the reason turbo would still run regardless of when you switched the engine off

RichardPON

The best bit is when you're in another car (wifes/run around etc), and you sit there letting it cool, forgetting it's actually a n/a Renault 21 Savannah Estate

S55 HOT

Scooby K

I think both reasons are true.

swan

Hence the market for turbo timers. That way you can leave your car and people just think you forgot to switch it off.

Jay m A

iTrader: (2)

Just to clear it up, if you turn off the engine when the turbo is too hot the oil is now not recirculating, hence the oil heated up around the turbo bearings is not being replaced by cooler flowing oil. The turbo can get so hot so as to burn the stationary oil, leaving deposits in the bearings, which in turn leads to bearing failure. Also, the heat not dissipated by the non-flowing oil has to go somewhere - stressing the turbo itself and the casing.

Justin

Barnaby

Out of interest, has anyone ever heard of turbo bearing failure on a Scooby?

I don't remember it ever being mentioned.

lucky_strike

I'd also add that it is better generally for the engine to run at tick over for a while when you return, not just for the turbo (although the reasons for that are sound).

When you stop if the engine is very hot (but within tolerances) i.e. just been working it hard then the tmperature of the water in the radiator is higher than normal, stop the engine and this then gets warmer in certain places of the engine before it eventually starts to cool down, leading to hot spots in the engine and additional stresses on the metal components around - remember when the car is stopped there isn't the airflow going through the radiator to cool not only the radiator but the whole engine bay.

Definately worth letting the motor tick over a bit - or driving slowly prior to stopping.

stevenuk300

I tend to sit in the car for a minute if I've been driving normally, but if I've driven it hard, I normally wait 5 mins. I spend the time either changing CD's or playing games from my mobile.

MGJohn

Lucky_strike makes a very valid point about ALL car engines. Heat build up following hot run switch off is considerable. To illustrate this, next time you know your non-turbo car is hot switch off and five minutes later, switch on the IGNITION ONLY (dont start it!) so that the instruments become activated. Allow the temperature gauge to reach and settle at its reading. It should read considerably higher than normal. Then, start the engine and observe the gauge. If all's well with your thermostst etc, you should soon observe a fairly rapid reading drop as cooler coolant is drawn into the engine. Apart from possible serious engine damage (cracks etc), heat transfer to the fuel lines can cause start or running problems until cooler fuel is drawn from the tank. Even comprehensive heat shields designed to reduce this sometimes will not cope on really hot running days.

So yes, allowing a little run on time aftera hot run is beneficial. Repeated hot engine switch offs can eventually cause fatigue cracks in alloy, iron and steel castings etc.

MGJohn

Stevenuk300

Think you're over-doing things a bit there but ... better safe than sorry ...

lokokkee

In the older Audi n/a models (100CD,90), the electric fan will continue to operate for a while even after switching off until the engine temperature (as measured by the thermostat) is down to the cut-off point. This shows the importance of proper cooling for the engine and I was told that this is a carry over from the turbo models. Maybe the older generations of turbos were not oil/water cooled but air cooled. Just my 2 p. worth.

stevenuk300

At the end of the day it's the turbo that makes the car, so look after it, and like mentioned before, it's better to be safe than sorry. My new Blitz Turbo Timer will sort out the sitting in the car problem for me

jonny gav

iTrader: (1)

steven- make sure your alarm can cope with a turbo timer first or you will be waisting your money!

MGJohn

What EXACTLY does a turbo timer do? If engine's not running, where is the all important cooler oil supply to the turbo bearings coming from after switch off ... ? The old Montego turbos and Maestros have a standard fit timing device which allows an electric fan to run on for up to 15mins after switch off but this is to supply cooler air to the fuel lines etc ....

So how does the turbo timer work ?

Andy-P

Turbo timers run the engine for a period of time after you have theoretically removed the key from the ignition and locked the car up, therefore running the engine and allowing the engine and turbo to cool and avoiding heat soak into the engine and turbo.

It also cools the turbo and prevents oil burning up and evaporating inside the turbo, which would result in galleries and oil pipes in the turbo becoming blocked, and then oil starvation to the turbo; which = bad.

As already mentioned, its also recommended to let the engine idle to allow the turbo to stop spinning (or slow down to it's slowest speed), so that it is not spinning excessively with no oil feed when the engine is switched off.

Some cars have electrical coolant pumps for the engine which run on after the engine has been turned off to prevent heat soak around the engine and turbo's, Audi V6 biturbo's for example. They only pump coolant, not oil though.

grabber

so what's the best action to take ,a slow drive off boost or a 1 min wait at idle?

stevenuk300

Johnny,
How can I find out if the alarm can cope with the turbo timer? The alarm is the standard Subaru one.

Cheers
Steven