warm it up first or start out easy ?
 

all;
back before i got started on a 'life of chrime' (read; in my pre-Porsche days) the prevailing wisdom was to warm up air cooled cars first before driving. i probably got this idea from The Complete Idiots Guide in my VW era. sometimes i hear people say they start their car and immediately drive it, easy, until the car warms up. IIRC, the owners manual for my '69 indicates to start the car and let it idle @ 2K RPM for a time. i still need to replace the fast idle lever, but be that as it may. IS there a prevailing wisdom re: warming up the car before driving ?
as always, thanks in advance.
all the best for the new year.
cheers
jerry

Start, let idle for about a minute then take it easy until it warms up then drive the hell out of it.

Only let it idle -- even for a minute -- if it is likely to stall. Drive it easy -- not too high on rpm and not too low -- as soon as you can. On 911's the maximal stress on the cam train is at idle. You can read more about this from Bruce Anderson.

Randy, I don't have my BA book handy...can you quote the reasons why the stress is greatest to the cam train at idle?

Geez...this is the second time I asked for a BA quote..I guess I need to read the book again.

i believe the correct procedure is *not* to let it sit idling, but to drive gently from the turn of the key. don't know why.

What good would a hot engine be with cold brakes, tyres, transmission etc?

no matter what car ( air or water cooled ) , warming up at idle is never good for the engine

one reason is that it will take longer to warm up
and untill it warmed up , the engine is not running in an ideal enviroment

so you want the engine to get up to temp as fast as you can , as smooth as you can, idling is not smooth, engines were not designed with idling in mind, idling is just a necessary evil

fast warmup is also why engines have a thermostat , untill warm , the thermostat limits the flow of cooling fluids ( oil for 911, water for waterpumpers) to the cooler, the thermostat has no other function whatsoever, but yet every engine has it , so it is something engine designers consider to be very important or they wouldn't have bothered with the extra design and cost

for 911, start the car , let it wake up/idle for a minute
then drive it , 3500 - 4000 RPM as max , untill it is properly warmed up , do take your time , a 911 takes a long time to warm up well , can be up to 7-10 miles depending on what kind of traffic your driving in... ( you could slowly raise the RPM as the engine get's closer to warmed up state )

I always tell people to drive a car to warm it up, but to drive it as though there's a raw egg between your foot and the gas pedal. It's cylinder pressure, not rpm, that is bad for an engine when it's cold. Not that you should wind it to 6,000, but driving at 3,000 with a very small throttle opening is far easier on the engine than is 1,500 rpm under half throttle or more.

stephan

No one has stated the reasons why idling is bad..they just keep saying it's bad.

I agree that bringing the engine (esp. our oil cooled engines) to operating temperature by driving it (w/o really loading it) is a good idea...and surely the engine will warm up faster when you are driving it.

BUT! When it's cold, the oil never gets to 210F in a moving 911, and you are still not at 210F after a commute. I really don't see that my engine will live a shorter life than any other if I let my engine idle in the driveway for 10 minutes (not that I do that all the time..but it's happened). I have good oil pressure at idle.

Again, everyone keeps re-stating "drive it right away and don't let it idle"...yet no one has come up with any explanation that I would consider valid. An engine is designed to run from idle-max RPM. That is the operating range. I don't see how spinning at 4000 RPM is better than spinning at 1200 RPM when the engine is COLD or WARM.

driving under load is different than idling without a load
( beep beep once made comment bout it beeing bad for piston rings , so for break in he said accelerate and engine break , that beeing a good thing, can't find the thread)

so your engine will heat up faster, and spend less time in the colder running enviroment

it's quite known how much termal variation there is in all the different components, so to me it makes perfect sense to get warmed up as efficient/smooth as possible, so all the metal parts expand toward their operational temp ( all the clearances measured cold, are calculated so the clearances are perfect when warmed up )

then there is vibration , which on a 911 isn't so much an issue because it's a boxer engine, but on my 924, the effect is quite visible

idle is very shakey , and even worse when the engine is cold
vibrations go away at higher rpm , something to do with the vibrations canceling eachother out at higher rpm

( bit like bridges, at certain low frequency , the bridge can shake it self to pieces )

once read something about oil byproducts :
The longer it takes the car to warm up above the vapor point for the combustion byproducts, the larger the amount of particulate formation and growth. This leads to sludge, varnish and particulates in your oil. In addition to the wear these types of particles cause, you also end up needing to change your engine oil more frequently because these get you to your oil's particulate threshold faster
The same principle leads to the increased acids in the engine
oil, except that when acids are not boiled off promptly
(because you idled your car to warm rather than driving it
moderately to warm it quicker) you get corrosion of the engine
metals.

and another reason , is that it wastes fuel...engines idling run very rich, might as well burn the fuel while driving it

Engine break-in and wearing in the rings are entirely different from what we are talking about here. Idling at start-up is assuming the engine has been broken in. Obviously the engine is not at its most efficient state when it’s idling, but how does efficiency correlate to wear, and to what degree?

Vibration at idle:

How is that worst than the shock and impact to the engine while one is taking it easy? Add to that the loads of the engine pulling the car around for the first 10+ minutes of driving at up to 4000 RPM.

A bridge oscillating at any frequency (most engineers have seen the film of the Tacoma Narrows Bridge tear itself apart) is not the same as a piston traveling up and down the cylinder, nor the rotation of the cams or crank, with adequate oiling.

Stephen is not off base with his egg under the pedal advice. That is good advice. Until I feel my oil and engine is up to some adequate temperature I go light on the throttle too, in my 911 or any other vehicle. But! That still does not answer the question of how idling is worst then starting the car and taking off to let the thing warm up faster.

Cold oil and contaminates:

I too am a believer that unless you can get the oil to temperature, one should limit the running of one’s engine. But think about this. A well cooled 911 with adequate oil cooling may never see oil temps close to 210F degrees when the air temperature is in the 40’s or 50’s during street driving. It is true that some regions of the engine will be at that critical temperature or higher (210F is what I consider operating temperature for a traditional IC engine using oil as a lubricant), but the median temperature is not even close.

On a recent trip in my Carrera (2+ hrs of driving in 45 degree air to and from my distination), my oil temperature never go to 150! And that is with a heavy throttle foot when the road allowed. I know that vaporization of petroleum products can occur at less than 150F, but we are mostly concerned with water and gasoline in the fuel. The other by products of combustion that combine with the water and gas to form corrosive compounds are another matter (and we certainly wouldn’t leave dirty contaminated oil in our engines for months of storage would we? I hope not).

BUT! Ask yourself if you believe oil and water in your oil will be completely vaporized at 150F between your house and the office. Also, ask yourself, if the idling that most folks find so tragic for a 911 (or any engine) before a trip is the same as idling for 10 minutes then shutting the engine off. The point there is that the idling to warm the oil and engine in my driveway is usually before a trip somewhere, involving 10 minutes or 10 hrs of driving!

I agree that the chances of contaminating the oil with water and gas at idle (when cold) is higher, and a quicker warm up is better, but I haven’t found a good argument yet to believe that such habits (before a drive) is so terrible for an engine.

On a 60 degree day, I still let my engine idle a bit before I take off, both to circulate the oil and to allow the CIS to settle while the engine reaches a level of warmth. On a 60 degree day, the above might also be 2-5 minutes…(back the car out of the garage so the garage and house doesn’t stink..and let it idle in the driveway while I go back in the house for my brief case or coffee. We’re not talking about letting the engine warm to 200F! Right?)

So unless the engine has terrible idle oil pressure…someone provide a good argument that idling is such a tragic thing.

There are a lot of myths surrounding ownership of a 911, and I’m not so sure that most of the myths didn’t start with less technically minded individuals who could afford an exotic car, but didn’t have the sense to question what the salesman or there equally technically challenged peers might have said.

I’m not trying to offend anyone, but it seems like folks have been passing certain “advice” around w/o being able to fully explain the “why”. I am a skeptic, and I HAVE to ask for the “why”. This idling busy comes up now and then, yet every time it does no one can provide an adequate argument to satisfy the “why.”

well , i'm not an engineer at a car factory , so can't explain this in detail like they would, but i can say that i've seen this advice in every car manual i've ever seen...

it always mentions not to warm up the car by idling

seen it in a nissan patrol manual , peugeot gti , golf gti , golf tdi and some others as well

couldn't somebody from PCA or any other porsche club get in touch with porsche , and get a proper explanation from them?

Stijn, it is stated in the 911 manual too (I seem to recall reading that in my Carrera manual), but that doesn't answer the "why" that I'm looking for. Is the manual telling one not to idle the car up to 200F or is the manual telling one not to idle the car for the first 2 minutes of operation? Or 10 minutes?

I think the 911 manual actually states to take it easy until all the components have reached operating temperature...well, isn't idling taking it easy?

Someone pull their manual and quote it please? Not that it will explain the "why", but it will be useful to know the exact wording from the factory.

BUT! I also had a discussion with a friend who has a former Porsche engine engineer on his staff who seems rather uptight on what is acceptable....with that in mind, I would bet the Porsche engineers will frond upon a lot of the stuff we've all been doing to our cars! All of which might make idling in one's driveway seem rather trivial.

yeah, i'm with soux on this one. i'd like to hear a reason i could understand without having too much engineering techno-babble...if that's possible. especially when temps are cold in arkansas like they are now, i always take 5 minutes for my starting idle to smooth and then drive...avoids the bucking. and likewise, when it's cold here, my temps may not ever reach operating temp even after an hour or more of driving...more likely in the 150 range.
ryan

sometimes i hear people say they start their car and immediately drive it, easy, until the car warms up.

That's right. If you let it idle, the gearbox and all the other fluid and bearings are still not up to operating temperature. It will take you 20 mintutes or more with idle to warm up a 911. I live in L.A. With average temperature of 70F, my 911 just reached it's operating temperature after a 18 miles freeway drive to my office. Once the car engine and gearbox reached it's operating temperature, you are in heaven.

1988 Carrera Owners Manual, page 23:

WARNING:

"Never leave engine idling. When starting engine, be ready to drive immediately. Maintain moderate speeds until engine is warm."

It adds:

"Do not idle engine to warm it up. After starting, drive vehicle at moderate speeds and avoid engine speeds above 4500 RPM during the first five minutes."


Porsche's advice is good enough for me.

"No one has stated the reasons why idling is bad..."

- I stated the reason above. I do not have time to look up where BA said that and don't remember exact citations (!)

I don't understand the comment re 210 oF. It's clear that the engine will not reach oper. temp. at idle or will do os only after a great deal of time.

Porsche tells you what to do. It's pretty simple.

One addition would be to also not put the engine under load at _low_ rpms - I avoid rpms under 3,000, and try to keep it under 4,000 for a few minutes also.

A cold start is one of the worst things to do to an engine, esp. one w/o electronic fuel injection. Minimize stop & go driving and short trips. Tack a series of short trips together to help the car and the environment (since cold engines pollute a greatdeal more than warm ones).

The reason you're not supposed to let the engine idle before driving it is pretty simple. When you install new camshafts in a 911 you immediately let the car run for 20-30 mintues above 3k RPM because the parts don't wear as wuickly at the higher speed and it allows a chance for everything to get seated and broken in nicely. 911 motors have very loose tolernaces when compared to most other cars, and idling, especially when cold does more wear on the engine than running at higher speeds. Personally I always let it idle for about 1 min just to get the oil circulating, but yes you should start driving them immediately after that, and then there's a balance between not running the engine too fast cold, and not running it to slow either.

I seem to recall that Bruce Anderson wrote that a 911 engine does not warm up under idle conditions. From this I conclude that the Fan takes away more heat than the engine generates at idle. But another issue is Oil Pressure. I am in Socal and I run Mobil 15-50. After start up, I drive off right away and shift at about 2000 rpm for the first mile or two. My oil pressure is often in the 125 psi range. (have after market direct reading guage). This is very high and not good for (engine) Oil Cooler longevity. Yes they do fatigue and bust a "weld". Mostly cannot be repaired.
Only after oil temp comes on to the scale and Oil pressure settles down do I go to progressively higher RPM.
Martin
914-6GTR
Agoura Hills, CA

In my '74 manual, the advice is to keep it below 3K until the car is warm, for another data point.