I understand the theory behind letting the car heat up prior to pushing it...but... can someone explain the cooling down theory :confused: comments on what you guys do would be appreciated as i do not have a turbo timer. Is that something that i should get?
Ok, the idea of letting a turbo\'d car cool down is to let cooler oil (+water) circulate around the turbo pack.
If you dont do this, over time there will be a build up of burnt oil around/in the turbo\'s.
This is not good.
You should try driving off boost for the last 5 minutes of your journey, this is also another good way of cooling down.
Fish
Basically turbos run very hot and so when the engine is turned off any oil sitting in the turbos will cook and turn to nasty sticky mess, reducing turbo life. Letting it sit for a couple of minutes after ragging it around lets the oil feed to the turbos flow oil round while they cool a bit. Turbo timer is not a neccessity. Just remember to take it easy for the last 5 mins of your journey or let it sit for a couple of mins before turning off.
Thanks guys appreciate that. Feel better knowing that i aint damaging the car
aah, nice clear explanantion of turbo cooling, cheers!
i usually take it easy at the end of my journey, but after turning off the engine the engine fan starts up.
i let it run till it turns off automatically (sometimes 5-10 min!), is this basically what a turbo timer does? is it necessary for me to wait for the fan to finish?
But with the engine switched off the cooling system is not working, only the fans cooling the water in the radiator and not the engine!
Fish
You\'ve got your answer in two parts above, but...
Basically, you need to avoid uneven cooling of bits of the engine to prevent warping, thermal stresses, etc.
The problem is most of the vital parts - especially the internals of the turbos and rotaries - are well shielded from the ambient air. The ONLY thing carrying the heat away are the coolant and oil going past.
If the engine is switched off then the water is just sitting in the channels and the oil has mostly drained back into the sump - hence nowhere for the heat to go. Furthermore, if the car is not moving there\'s no air passing any of the coolers so they don\'t actually do much cooling.
I\'m not a great believer in turbo timers - gentle driving for the last few mins allows the radiators to do their job efficiently and keeps oil and water pressure up which is good. Sitting idling on your drive isn\'t half as good (and idling cars is badness in general.)
Oh yeah, and brakes, bearings, and your slippy diff are all cooled by air movement only - so the above applies double for them!