Revving an engine before shutdown?

[Sapporo Guy]

A lot of cars with turbos here in sonyland (aka Japan) have "turbo timers" (after market accesory) that let the car idle for a good 5 minutes or so before they shut down on their own. Of course, by then the owner is either in their house or some resturant.

We also do the idle before drive routine over here too.

Now ... I tend to think that warming the car properly before driving is a probably a good idea but ... I don't seem to see too many folks gunning their cars and killing it too. Come to think of it, I don't see the kids on the mountain passes nor the Skyline GTR folks doing it either. Rather they let the car cool down before the kill the ignition.

hmmmmmmm

[CT944]

I bought a Callaway VW Rabbit years ago, and the owner (who worked at Callaway as well) told me never to rev a freshly started turbo motor...ever...until it was at operating temp. That was about the only thing he told me not to do with that car. Remembering now, that was very fast.

Should never have sold that car

[spuggy]

I've come to believe that idling the motor when cold is the worst thing you can do - oil is thick and sluggish, and the flow is the worst it'll ever be. I always run @ 2,000 RPM until the internal engine thermostat bounces open a few times in quick sucession (90 seconds, 2 minutes - you can't see it do this with a 5 bar oil pressure gauge), and then drive it, keeping revs down and load light until the oil is up to temp. The owner's manual says to not idle the motor to warm it up, too.

I was always told the theory behind the "blip and shut down" was to get a spurt of oil flow to the top end, but I was also told the contra-theory about washing the oil off the bores.

Turbo cool-down procedures are a different beast again, especially when you don't have to drive through your neighborhood off-boost for 3-4 miles before shutdown.

The factory put a 10-30 second "turbo-timer" that cuts fuel but keeps the ignition running on the 930's, apparently to burn off as much fuel as possible and keep pumping oil through the turbo bearings even if you switch the key off whilst it's red-hot...

Some folks do the fast-idle thing on shutdown on 930's to ensure that the turbo scavenge pump gets its act together, and swear by it. I find that mine will puff oil on startup when it feels like it, regardless of what you do.

[70SWT]

I'd bet if you took 2 identical cars, did the quick blip-and-cut-off thing with one and not the other, you'd see little or no difference between the two that you wouldn't see otherwise.

[911mot]

With a CIS fuel injected engine the fuel would be switched off as soon as you kill the ignition. Therefore I would expext LESS fuel to be present in the system as the engine would have tried to suck it out of the lines.
With Motronic I would have thought the injectors would have stopped pulsing when you switch off and again I cant see a bore wash issue here.
Carbs a different story entirely

[Dantilla]

I've always heard the reason for the blip was to build oil pressure to insure everything is well-coated with oil while the engine is off.

[ljowdy]

Personally, all of this is bunk. Rates right up there with Harley owners that think it's necessary to rev their engines at every stop light.

Just turn off your engine. If it was important to rev your engine, it would be in the owners manual.

[DARISC]

Originally Posted by ljowdy

Just turn off your engine. If it was important to rev your engine, it would be in the owners manual.

Real simple, isn't it?

And, re start and go, the owner's manual does say "start and go" (garage warmups are bad).

[Zeke]

Some strong opinions here.

As I have been told over the 40 or so years I have been around cars, trucks and farm machinery, the process of shutting down might be of some benefit to the engine, depending on the type of engine. The process never involved "blipping" the throttle, rather gently raising the RPM a little and then cutting the ign/fuel while there was still some oil pressure. If the engine uses a carb and the butterfly is nice and tight, some oil will be sucked onto the valve stems and piston rings. Diesels will do it too since the fuel cutoff IS the switch. The key is there must be a good vacuum or nothing happens.

Some of the statements here are as ignorant as the myth itself.

[DARISC]

Originally Posted by milt

Some of the statements here are as ignorant as the myth itself.

Always enjoy your posts, Milt (even though you haven't posted very often here) - would be fun to read your comments on, or at least a list, of the ignorant statements.

[aigel]

Originally Posted by ljowdy

Personally, all of this is bunk. Rates right up there with Harley owners that think it's necessary to rev their engines at every stop light.

Just turn off your engine. If it was important to rev your engine, it would be in the owners manual.

+1

And warm up procedures are in there with that too. Here in CA, the engine is pretty warm to start with. If you stay away from WOT redlines for the first 10 minutes after cold start, that's about all that matters.

I had neighbors once who would sit in their running truck and SUV for at least 3 minutes before starting to drive. It was nuts, especially because they would always get a new model within 2 years.

George

[Gunter]

Revving an engine before shutdown is one of those myths like:

"You have to come to a full stop before re-setting the Odometer"

Or: "KN filters increase HP"

Any others?

We should have a "Myth-list" on PP.

[porsche930dude]

I would think on turbo cars its very bad because you dont want the turbo spinning at 30,000 rpm when you cut the oil to it. As for starting and imediatly driving off i find the car warms up much quicker when its sitting still and fresh air isnt being blown over it. But i dont follow any sort of regiment as far as thats concerned because there doesnt appear to be a definitive way to do it

[Trotskyite]

Originally Posted by ljowdy

Personally, all of this is bunk. Rates right up there with Harley owners that think it's necessary to rev their engines at every stop light.

Just turn off your engine. If it was important to rev your engine, it would be in the owners manual.

As a long time Triumph man, I can tell you Harley owners do that to keep the engine from quitting. They may never get it started again.

[Goth]

I was hoping someone else would answer this, so I wouldn't have to give away my age.

Some of the muscle cars we had in the late 60's and early 70's had run on problems. Probably due to some combination of high compression, advanced timing, lean idle (for smog in 70's), cheap gas, and a hot motor (as we always ran em hard all the way to wherever we where going).

So when we pulled up at our destination; we just blipped the throttle & cut the ignition. This sent a rich gas mixture into the engine, which prevented the run on (i.e. dieseling). If you didn't do this, some of these cars would sit there and diesel for about 20 seconds (pretty embarrassing).

Some cars got around this by putting a solenoid on the throttle stop. When you cut the ignition, the solenoid would deactivate, allowing the throttle to close down all the way.

Hope this helps as I'm feeling old now...

[911pcars]

Engine rev with the vehicle at rest can only occur with the ignition ON. Whatever happens before ign. ON is different from what happens after ign. OFF (engine can't rev with the ign. OFF).

Opening the throttle introduces more fuel into the intake. Ignition OFF immediately after this event will leave excess hydrocarbons (unburnt fuel) in the chambers. Not good for long term cyl. wall lubrication.

The racey rev from Cadenet's on-camera shutoff procedure is of no consequence to most of us - it's not his car anyways, but repeated practice is bound to have a cumulative effect.

YMMV .... with throttle blips.

"So when we pulled up at our destination; we just blipped the throttle & cut the ignition. This sent a rich gas mixture into the engine, which prevented the run on (i.e. dieseling)."

I remember the symptom well. It happened on most early emission-equipped vehicles. The richer mixture probably cooled the chamber parts just enough to raise the preignition threshold.

Sherwood

[dshepp806]

Those who warm up by idling are heading down the wrong path. It's well known that you should never do this, cold....even noted in the manual. I never touch the gas pedal at startup, either. It's about 30-60 secs of idle (get to hear my sold throwout bearing rattle)then she's on the road.....never lugging her in any way and keeping the RPMs around 3K,..(usually 3rd gear for a while, once on the backroads....). Once I see around 150 degrees F, then we invite 4Ks (but no higher). THEN, when operating temp is hit, we dance well upward on the RPMs! Usually at 10-15 minutes on the backroads, I'll see around 150 degrees (during this southern winter) then at the interstate entrance ramp ramp, we start generating some real heat!

Just standard operating procedure for me (and her).

Blip? Nadda...........

Best,



Blipping the throttle just before shutdown (on a 911) is not something I would do, at all. (WTF?) I let her settle for about 30 secs and turn her off.

[911pcars]

Forgot to add an opinion about cold starts. If one is from the, "let the car sit until the engine is at operating temperature" camp, then what about the other lubricants in the vehicle? Don't they get an equal chance to warm up too? That includes gearbox, wheel bearing, steering box, etc.

If the engine has modern emissions equipment (i.e. catalytic converter), in order to reduce emissions (greatest at startup), starting and driving is quickest way to bring the cat up to temperature.

Sherwood

[RWebb]

Gunter - DONE!

[PSportoVeloce]

i always thought it was a racer's practice to combat fouled plugs...