Idle before shutting down?
 

I've noticed that rotary drivers usually leave their cars at idle for a few minutes or so before turning the engine off, what is the purpose of this? I'm someone who has no experience with cars in any way, what would happen if I just shut it off?

It shouldn’t be just rotary drivers. ANY turbo vehicle that has had some spirited driving should be allowed to idle to let the oil and turbo cool off

Same could be said on a n/a rotary being as rotary’s oil temps are higher then piston engines

Is it better to let it idle at a standstill or to just take it easy for a while driving after the "spirited" portion?

Does this apply to oil AND water cooled turbos? Doesnt the water keep the oil from coking?

Yes, but remember when you turn off the car the coolant is no longer flowing through the turbo and cooling like its suppose to. Therefore you would have super hot oil just sitting in the CHRA which leads to premature turbo failure.

Actually, Coolant does continue flowing after you turn the car off, if you have the turbo clocked correctly. The higher temp water creates a thermal siphon that keeps the water flowing.

https://cimg2.ibsrv.net/gimg/www.rx7...b32a1a6200.png

I usually let mine idle for a minute or two if I was just driving it semi hard but if I'm on my way home I try take it easy for 5 or so blocks before I pull if into the garage. Not sure if it's the right or wrong way but it feels right :dunno:

Very interesting, I did not know about the thermal siphon. Now it has peaked my curiosity on how much coolant will flow thru the turbo as a result of thermal siphon on a properly clocked turbo.

From Garrett's website. "Full benefi t of the thermal siphoning effect will be realized and internal turbo temperatures will be minimized. Garrett® laboratory testing has shown that peak temperatures in the center housing can be reduced by as much as 90°F (50°C) when the center housing is rotated to allow the hotter outlet water to escape from the higher port. Rotating the housing more than 20° from horizontal may further reduce temperatures slightly but may also impede oil drainage, so stick with 20° as a maximum."

You learn something new everyday. Now i have to clock my turbo 20°.

Haha right? I think they say dont clock past 20* because your not supposed to have the oil lines clocked past 15*. FYI I had my GT35 clocked at ~25*ish and I never had any problems. I always felt comfortable after shut down when i could hear the water bubbling through the turbo lines.

By the time i drive from the highway to my house, open the garage, and park the car inside my levels have cooled significantly, but additional cooling never hurts.

It's hot as hot gets in Mississippi and I've never felt like I needed to keep a car running in the garage to cool it down. I've always taken it easy for a while before pulling in to let things cool off while there's fresh air to run through the rad/ic - doing the cool down in the garage just seems like putting strain on the cooling systems.

^Good call. That’s exactly what you should do. Sitting and idling for any length of time causes both oil and coolant temps to rise on any car, turbocharged or not. On the FD twins the turbos are water-cooled. So unless you just finished rowing thru gears under hard boost, the minute or two it takes to drive a block before shut-down and park in your garage is sufficient. Anything more is counter-productive. Also why turbo-timers are kind of waist of money on these cars. My car had one installed by the previous owner YEARS ago. The ONLY time it was of any use was at a few autocross events where the course was long but the paddock was just off he finish line. I’d use it then but set it for no more than a minute while I opened the hood, lit a cigar and winced as they announced my slow time.

I heard that you should rev the car to 3000 and then shut it off to burn more excess carbon/prevent flooding.
Is this normal/ safe for the car? It sounds a little strange to me.

I thought the advice of drive it gingerly the last few miles of your trip and don't idle it for several extra minutes sounded like what I will do.

I have not heard of reving the engine to 3000 rpm before shutting it off. I let the turbos cool down prior to turning the car off like others have stated either by regular driving for a few minutes or just letting the car idle for a few minutes after heavy driving. The carbon will burn off from doing hard driving under load, its the high heat that causes it to burn off. I dont think reving the engine while not under load will produce enough heat to burn off the carbon as well as actually going out and driving the car hard.

Ari from Rotary Performance explained it to me like this...once you're parked, slowly rev it up to about 2,000 - 2,500 and hold it for a sec or two. Turn the key to shut down the motor and as you do that, push the accelerator to the floor. You'll hear the motor take an extra sec to finally stop. This has cured all hot start issues I've had since then due to flooding.

A lot of people eliminate the system of water that goes thru the turbo thinking its unnecessary. Big Mistake!. All cooling possible is needed for the turbo to last. That's why it was there in the first place. A lot of research is done before anything is done on engines and if its there, its for a purpose.

I believe i read in the owners manual that there is an automatic fuel cutoff if the engine is off and the gas pedal is fully pressed, for FC

Only on S5's, not S4s.

so really no one really mentioned turbo timers to solve the issue, but there are cons and pros to them.

Yes they were. See post #13. WHAT "issue" do you think they would solve?

This is an interesting topic and reminds me of owning another early 90s turbo car with a turbo timer. I thought it was kinda cool, but probably mostly pointless. I never let my car idle before turning it off and have 140k on the original turbo. I think the best solution on most vehicles is to just let it cool off by driving around the block or taking a cool down "lap". This was, all of the heat exchangers have an opportunity to receive a constant flow of air while cooling down. I discovered this was the better option when datalogging and looking at my coolant temps pegged at 217 with the car "cooling down". Now I just drive around slowly for a few minutes to allow the radiator and oil cooler to do their job.