idling too long

[obkev]

Hello,
anyone ever have trouble letting their 911sc idle too long and then the car dies when trying to take off. It was raining so maybe someting got wet, but when I let it idle for too long it will not run, I stalled on the interstate. The owners manual states not to let the car warm up idling, anyone know the reason.

Thanks, Kevin

[livi]

Welcome (from Sweden)!

Canīt say whats going on with your car but any engine suffers more from running cold and idling till warm takes longer than driving gently.

Or so I understand it at least..

[mschuep]

Reasoning for not idling to warm up is a dry sump issue, idling no good for dry sump.

[svandamme]

Originally posted by mschuep
Reasoning for not idling to warm up is a dry sump issue, idling no good for dry sump.

idling to warm up is not a dry sump issue, it's in every car manual i've seen so far, be that water pumpers, air cooled engines or even diesels...


reason for not idling to warm up is that it justs doesn't warm up fast enough...and you do want to get to operating temperature as fast as possible (withing reason and without abusing the cold engine that is )

that also why there is a thermostat on the cooling plumbing (oil for air cooled, or water for watercooled)... because untill it's warm enough , the coolant should not be cooled, because engine manufacturers want to reach operating temp asap.

idling does not put a load on the engine, without a load, the temp doesn't go up quick enough

and engine will heat up faster in 5 minutes driving , than in 10 minutes of idling


http://www.tocmp.com/manuals/Buick/1963/BreakIn/pages/union76-7_jpg.htm

that's a 63 Buick, and i'm sure it doesn't have a dry sump, and i'm sure it's a water pumper

968 manual

http://www.cannell.co.uk/Boxster_Manuals/986%20owners%20manual.pdf

page 62 ... "Do not let the engine idle to warm up "

[livi]

So, I guess we are in full agreement there, Stijn.

[svandamme]

i'm sure there will be another thread in a month or 2 where this point will come up ...


going back to the initial problem ... probably some thing with CIS , mixture bit off, vacuum leak , or something else, the CIS guru's can comment on that

running some Techron on a CIS system also has very good results... cleans things out ....

[mschuep]

Well, after some more looking around, I think I was mistaken. I would swear I had read that dry sump was main reason not to do this (obviously there are other reasons like Stijn mentioned). My apologies, I am the jackass today.

[svandamme]

not a jackass, besides i think i'm a bit on edge here, bit to harsh, spent to much time on OT...

my apologies

[Nine9six]

Originally posted by livi
Welcome (from Sweden)!

Canīt say whats going on with your car but any engine suffers more from running cold and idling till warm takes longer than driving gently.

Or so I understand it at least..

After three reads, only one word comes to mind...
"punctuation!"

[svandamme]

996? how do you say punctuation in swedish?

[livi]

Alright then. I had to read it three times myself. No luck.

I meant what Stijn explained in more words, anyway.

Give me a brake. Its past midnight here in Viking country. I am a durn for'ner and I donīt know the first thing about Porscheīs.

[Paulporsche]

I heard a long time ago that prolonged idling puts undo stress on engine bearings since the idle speed is constant. I'm not sure if that is true, though.

One thing that is true, it wastes fuel and increases pollution unnecessarily.

[mkimber]

Let me add to the confusion. Here's the thread when I posed a similar question back in October.

Long idle time...Poor performance

[svandamme]

untill somebody can tell me some real technical information as to WHY idling would be bad for a dry sump, i'll keep calling it BS.

the point about warming up the engine while driving , and not idling is all about getting to operating temp as quickly as possible (withing reason , no redline with a cold engine).. and this is not a dry sump or aircooled thing, this is a general thing for all combustion engines...



i can't imagine that Porsche would produce cars, that can't take 10 minutes of idling , i'm sure there were traffic jams and other situations why engines would be left to idle back in the sixties and seventies

i cannot imagine, how a dry sump would run into trouble because of idling , the oil pump scavenges the sump, chucks the oil in the tank
and at the same time , build oil pressure to lubricate the whole engine
at idle , the engine is designed to provide enough of both, scavenging & lubricating. so other than oil circulation , what would be special about a dry sump ????

[Joe Bob]

Originally posted by svandamme
996? how do you say punctuation in swedish?

Dunno...but in California, it's "Bite me".....

[Oh Haha]

So do you guys that drive 911's year round just freeze your a$$ off until the car heats up in winter conditions? I don't, but my Vibe sits out and I start it when the temp is below 20 in the morning. I let it run while getting my road coffee and taking care of the doggie.
In regards to 911 engines, does the no idling deal only apply for a cold engine?

[livi]

OK, so lets say we agree that running a cold engine is more harmful than running a hot engine. Generally speaking. Right ?

Hence, on upstart from cold, the engine will reach healthier temps faster. Thereby shorten the harmful running period. OK, but..

.. disregarding the time frame - will not idling per se put less stress on the engine than higher driving RPMīs. Even at 2k the friction energy should be much worse than at say 800 idling.

No ?

[svandamme]

it's not about the RPM , it's about having a load on the engine

just revving the engine higher on a cold start will not make that much difference from just idling, it's the driving off , and loading the engine

same reason why folks need to drive the engine and brake on the engine during engine break in time...

the problem with a cold engine is not friction wear , the problem is that everything is designed with tolerances, the engine components all have tolerances with heat expansion in mind.... so untill the engine is warmed up , everything is out of spec, hence the requirement to get to operating temp asap.

now if you leave an engine to idle and warm up , it will take 10 minutes if at all it reaches optimal temp

if you drive, the thing slowly , don't rev to much , but do drive
it will be warmer after 5 minutes, then 10 minutes of idling.

try it , i have , it's no joke , that is the way it behaves
for testing purposes , try it on a winter day , that's when the differences is the most noticable, no point comparing it on a scorching hot day , that's an outside variable heating up the car...

look , if you don't believe my explanation , fine , i don't work for Porsche or any other car company , but the old Buick Manual says don't do it , the modern Boxster manual says don't do it... i remember a thread about the same thing where some one posted a link to a 3.2 carrera manual , and that one said , don't idle to warm up

it's no coincidence if you ask me , and if you want a fully technical explanation as to why , guess you'll have to call the manufacturers

but it's not a dry sump issue , the Buick doesn't have one , neither does a Boxster. or a Diesel engine for that matter ( and my old Tdi did have the same comment in the manual )

[livi]

I am with you, Stijn, as far as the shorter cold period the better. But time aside, will not putting load (driving) on the cold engine be more detrimental than not (idling)?

I believe you are right and the cold-period shortening by driving it hot is logical.

But all things equal, I still donīt grasp how it would be less harmful putting more load on a cold engine.

Then again, I am certainly no engineer. Just curious.

[svandamme]

my guess is , that , with things cold, and out of spec
there is more vibration , more things moving in ways they shouldn't be moving.... and that's the thing that causes exessive wear

as it warms up, things expand, tighten up and eventually settle down in a normal running condition...

it's very noticable , a cold engine shudders , shakes , smokes, rattles
a warm engine doesn't