Starting and Switching off a car

[kramerman]

Hi,

I know this isn't a problem in the word itself, but I think most of the knowledgable people about cars are in this area so might be able to offer more help.

What I'm asking is regarding the starting of cars, and the switching off of cars. I have heard many stories/myths/reports etc about how one should start and switchoff a car.

Some say that you should start a car, and drive off immedietaly because that is the fastest way to warm up the engine. Of course stick to low revs, but this is also fuel efficient because you can start moving already.

The other group would say that you have to start a car, and let the engine warm up for a while before moving off. This ensures the engine is well-lubricated before moving. However, still at low revs till engine reaches normal operating temperature.

On switching off, some say you should just park and turn off the engine straight away. This reduces unnecessary wear and tear, and keeps the engine oil on the moving parts, and also reduces fuel consumption. This group also says that if you leave the engine running, it lets the oil drain to the bottom of the engine rather than staying on the vital components.

The other group has the stand that you should let the engine cool down a little bit, rather than an immediete cool-off which might cause heat shrinkage problems. (Note: I understand that turbos have to be cooled, but this is in respect to a non-turbo car. Also, I stay in a climate where the temps are usually above 20 degrees C, so no harm of extreme temp change in winter conditions etc.)

Thanks in advance!

[Onix]

if you have a reasonably modern car, then just going a bit easy on the revs until it warms up and then turning it off when you get to your destination should be fine

even at idle speeds an engine is pumping a lot of oil around the engine, so those saying you need to turn it off or leave it running for reasons of where the oil goes are talking crap, modern ohc engines generally have the cams themselves sitting in a bath of oil which never totally drains (this is partly why straight after you do an oil change the oil is dirty again, unless you removed the cam cover/s and syphoned that oil out)

maybe if you just thrashed the hell out of your car and its seriuosly hot(radiator fan on) when you stop it could be a good idea to let it idle until the fan cuts out, but otherwise leaving it running at idle will probably increase the temperatue rather than cool it

the only cars you need to leave running to cool are turbo'd ones, where switching off the engine as soon as you stop will cause the oil in the turbo bearings to carbonise and that will clog the oilways in the turbo and eventually kill it, as they have a supply of oil fed from the engine oil pump, stopping this oil circulation when the turbo is very hot is BAD.

[kramerman]

Thanks Dan, I think that was a pretty good explanation. I forgot the part about letting the radiator fan cut out, but that was another tip given to me too. Now at least i'll feel more at ease doing what i'm doing! :D

[asthenia]

I start driving as soon as there's oil pressure (which is as soon as the engine fires up), and I kill the ignition before the car's even come to a complete stop. Never had a problem, and the 31-year old engine cranks up right away, every time.

I think the important thing is not to hammer it until your oil temperature goes up.

[TT]

Hehe reading asthenia's post I realised that sometimes, ppl not giving a fuck about their cars, can do 300'000 km w/o even servicing them, while sometimes ppl caring about it like if it was a child, they have lot of problems (it was my case with my previous car just to let you know LOL)...

[kramerman]

Heh, when you say that it sorta reminds me of people who smoke their whole life and don't have problems, and then some dude who smokes for a short while, stops, and then gets some problems...

The irony of life I would say....

[mhn3773]

the only time i ever think about turning the car off or on is when i drive my dads car...i usually just wait till the temp guage is in the middle b4 i do anything stupid lol

but when i goto stop it runs itself for about another 1-2mins so id say if u were driving the car really REALLY hard then let it idle b4 u turn it off shouldnt be to much to worry about

ah by runs itself i mean after i pull the key out and lock teh doors the engine will continue to idle untill its satisfied then itl shut off

[kramerman]

That probably means that your dads car has a turbo timer (or something similar) that is linked to the temperature of somewhere (?) so it runs till it's satisfied like you said...

Does your dad drive a turbo car?

[mhn3773]

not a turbo but it is a timer and it is prety nifty

b4 i had to sit inside the car and wait for 2 mins b4 i could get out lol

my dad also said that starting ur car and just driving away can be different to the engine depending on the oil u use..like some has to heat up more to become thiner so that could hurt then engine if u take off down the street and the oil is still to think to pump properly..this is a drastick thing..like 1 out of every 1000 cars will have problems beucase of not being warmed up b4 u drive off..now every car will break if u dont warm it up and procede to drive on the redline..it will die

[kramerman]

Interesting comment about how you have to wait for the oil to warm up before moving off. I think that could occur in cold countries where the oil is less viscous (sp?) because of the cold, but where I am, it's kinda same all year round, and the oil we use is rated normally from like 5-40 degrees celsius, so this probably isn't too much of a problem.

[mhn3773]

yah in cali i dont think it hardly gets to the point where ud need to worry about that kind of stuff

[Epic2112]

If you're really trying to take good care of the car, what you need to consider when warming it up is not only the temp of the engine, but also the temp of the drivetrain. The transmission, differential, etc. also need to be warm to lubricate properly. I really baby my M3, and what I usually do with it is let it run idling for 10 minutes or so, then I know that the engine is reasonably warm and then I start driving. With just the engine idleing the drivtrain doesn't get warm at all, so for the next ten minutes I don't exceed about 35 M.P.H. (2nd or 3rd gear only), and also SHIFT SLOWLY! You'll be able to feel it become easier to shift as teh transmission warms up.

Of course, I'm absuredly anal retentive about that car. You don't need to do things like that, but it can't hurt. Just keep the drivetrain in mind and don't go speeding off after letting the car idle for twety minutes. ;)

[kramerman]

Ummmm.. M3 sounds nice.. :) I definately don't trash my car once I start it, just wondering if there's a real benefit in letting the engine warm up :) Thanks for your input!

[blah]

thi is why the M5 lets you know when its ok to go all out.

[Epic2112]

Yep, the new M3 does that too I think. Still I'd rather have the info directly and decide when it's ok to go all out. My M3 has a temp gauge for water temp and one for oil temp, and my Porsche has one for water temp and oil pressure. using the input from the combined gauges lets you get a much better idea of what's going on in there than just the one water temp gauge that most cars have.

[mhn3773]

i think he means in the m5 the rev counter instead of turning red at say 6k will turn orenge from 6k to 4k saying do not rev past this line untill warm as the car warms up the orenge will fade away saying its ok to push a little higher..itl continue to do this untill just the redline remains u can then whomp the S**T! out of it and have a nice day =) hehe

[Epic2112]

Right, the new M3 does the same thing.

[sickx]

Take it from a guy who has seen thousands of hours of engine testing--No need to wait on shutdown unless you have a turbo engine and have been boosting it within the past minute. Then it's wise to let it sit a minute to let the oil cool down the turbo to prevent the oil from coking due to the immense heat the turbo generates.

[kramerman]

Thanks for the sickx, it's always good to get a viewpoint from someone who works closely with the engines and knows exactly what can and can't be done to them.. :) Any other tips on startup and shutdown you have.. please share!

[sickx]

Actually, the previous posts have been quite on regarding startup--if you really want to baby the engine, then no high revs until oil is up to operating temperature. Odds are you don't have an oil temp gauage, so use the coolant temp as a proxy.

[sickx]

One more thing--gasoline engines are not meant to idle for prolonged perioed of time. Diesels can idle all day long, but gasoline engines tend to run a bit rich when idling, which accelerated carbon buildup in the combustion chamber.
FWIW, YMMV, etc...

[Epic2112]

Just be weary that the coolant temp sender is usually at the top of the engine near where combustion occurs so it will get hot much faster than the oil actually does, because the oil sits in the bottom of the engine. When you have an oil temp gauge the sender is down in the oil pan underneath and gives a much more accurate idea of what's happening down there. Certainly watch the coolant temp too, but don't go nuts as soon as it's up, wait a few minutes for the rest of the engine to warm up too.

[sickx]

Yup, Epic's right on...
Of course, it totally depends on how long you're keeping this engine--most modern engines are designed to be fired right up and drive away--even in cold temps...but if you REALLY want to get a lot of miles out of it, baby it when it's cold.

[mhn3773]

the new m3 does the same thing as the m5? sweet..i remember the m5 i drove was different then the same years m3 and that was one of things the m3 was missing aside from power =) lol

[Epic2112]

Right sickx, I'm super anal retentive about my cars. There is certainly no need to treat every car like that. If you get in a car and start driving right away many people will even say it's better because everything warms up together, just make sure you shift early (but not too early!). As for me, I'm content being anal retentive ;).

[Wutputt]

Maybe I'm going to repeat some things said before, but this is my opinion regarding treating your car.

When you start your engine it's best to let the engine run idle a few seconds until every component gets sufficient oil pressure, etc.

Then you drive off, so the engine warms up on a natural (loaded) way. But you don't want hit high revs and high loads before the oil temperature rises to its normal level. (Like Epic said, in fact you also have to warm up your other drivetrain parts, like transmission and differential(s)).

When switching off your car you have to wait till the engine runs idle (with atmospherical engines). If you switch off the engine when still running higher revs, the oil pressure will drop and the lubrication of cylinder wall - piston won't be optimal anymore, resulting in excessive wear.

Like already said, with turbocharged engines you have to let the turbo spin out and cool down. This is very important, certainly for petrol driven engines since turbo temperatures are higher for petrol engines then they are for diesel engines.
If you immediately switch off a turbocharged engine, the turbo won't be fed with fresh oil. The oil temperature will rise excessively and lubrication won't be proper anymore. The shaft connecting turbine and compressor will wear or if temperatures will be even higher the shaft could even bend a little bit.
The higher you used the potential of your engine, the higher the turbo temperature will be, and the longer you will have to let it spin out and cool down.


Like Epic said, it's not really necessary to take all these points into account. But I recommend warming up your engine properly and if you have a car equipped with a turbocharger to let it spin out for a while.

[kramerman]

Thanks Wutputt for a pretty good summary of all the above points put together! :) Looks like this has been a good exercise for those involved to find out more about their cars.. i certainly did.. heh.

Thanks to all as well.

[Epic2112]

I'm happy to be able to offer advice :D

[sickx]

Most importantly-- enjoy the ride!

[cikay1]

That leads to another question? What if you drive your car somewhere, everything warmed up, then you leave it for an hour or so and come back to drive it. Is it still necessary to leave the engine idling a couple of minutes like you do during the morning when everything is still cold. Or is the engine already semi-warmed up and ready to get some trashing?

[cikay1]

That leads to another question? What if you drive your car somewhere, everything warmed up, then you leave it for an hour or so and come back to drive it. Is it still necessary to leave the engine idling a couple of minutes like you do during the morning when everything is still cold. Or is the engine already semi-warmed up and ready to get some trashing?

[graywolf624]

Wut putt is dead on.

"couple of minutes like you do during the morning "

Not a couple of minutes. A few seconds. Mazda for instance suggests 60-100 secs for the 6. It isn't for warmth as wut putt said. It is to get oil circulation. Then you drive it like a granny for a little bit then its fine. How long the granny would depend on the restart.
You do not want to sit there and idle for 5 minutes. Not only is it poor for the engine but it is horrible for gas mileage. A gas engine is most inefficient when it is idleing.

[sickx]

Yup... enough idling, and the carbon deposits build up within the combustion chamber, which leads to (eventual) pinging.
If the car was driven in the past hour (and it's not freezing cold outside), simply start it up, give it just a couple of seconds to get some oil pressure, drive it gently for a couple of minutes, and you're good to rip.

[dm_aus]

That leads to another question? What if you drive your car somewhere, everything warmed up, then you leave it for an hour or so and come back to drive it. Is it still necessary to leave the engine idling a couple of minutes like you do during the morning when everything is still cold. Or is the engine already semi-warmed up and ready to get some trashing?

The engine might be warm, but depending on the oil, engine design etc, I would suspect 95+ % of the oil has drained out, so the same rules apply.

The crucial thing is always the oil flow.

My thoughts - as others have said, when starting a car from the cold, drive it gently until oil has had time to circulate. Then feel free to let that baby howl :D