to the stop linght instead of downshifting? I was told it's not good to leave the car on idle . If i should downshift, should i down shift one at a time or wait until i get close to a stop and shift to the proper gear? I had driven many cars with stick before but i don't think i did it right.
thx.

 

All I can say is that brake pads are cheaper than clutches.

Put the car in neutral and let it roll to a stop light is economical and a smart thing to do. There is nothing wrong with that.

Letting the engine idle for a long time is bad for the engine, but not at that short of interval.

 

Hmm...

I always downshift through all the gears when I come to a stop, but it's certainly not necessary. I think I mostly do it for fun and practice. Instead of putting the car into neutral and coasting to a stop, why not leave it in gear, and wait to depress the clutch until the revs drop way down (say, around 1000 rpms)? I don't like the idea of coasting in neutral because should the light change from red to green before you come to a stop, what are you going to do? What if something unforeseen happens, and you need to accelerate to avoid a potentially dangerous situation? I don't know that it's bad for the car, it just doesn't seem like good practice.

 

Those were concerns of a boy racer.....does not apply to lay abidding citizens driving their p-cars.

 

If the light changes from red to green before coming to a stop, what's wrong with shifing to a gear, 2nd ,3rd or whatever; it only takes less than a second to shift.

Also, pulling off from the current gear (3rd or 4th)to neutral at a low rpm like DJ mentioned is a not very smooth and takes a little effort. Is it just my car?

 

Try to step on the clutch quickly, you should avoid that rough feeling.

 

Robin,

How bad is it to the engine to let it idle for a long time? What damage could I have done? Pls advise. Many thanks!

 

Jimmy,

I think that is a question for Steve Weiner. I was taught about the adverse effect of long term idle on a passenger vechicle engine long ago, but I can't seem to remember the exact negative effects on it.

 

Jimmy,

Your question has me wondering as well. I've always thought that it was a bad idea to turn on the car for only a few moments (e.g. to move it out of the garage for a wash), because you don't get the engine warmed up.

In the old days (356 era), you could foul the plugs. Nowadays, I thought it was a problem from the standpoint of not burning off water, and not reaching proper operating temps.
Therefore, I usually let the car idle for 5-15 minutes before shutting it off. Is this a misguided attempt which actually does more harm than good? (Steve?)

 

Only problem I see with coasting up to a light in neutral is forgetting to hit the brakes before you clobber the car in front of you or roll thru the light. As far as wear & tear, far less injurious than dowshifting in each gear all the way to 1st.

This is based on driving manual tranny cars since Woodstock (the FIRST one). Have never owned a wimp stick. Downshifting to 1st as approach a light puts big strain on 1st gear synchros, clutch plate, and throwout bearing. Much better to coast in neutral.

Idling in neutral problems are caused by numnuts who occasionally start cars in winter, then let them just idle in garage without driving them. This never heats the engine evenly, and causes more wear than not starting it at all. No problems far as I know with nomrally heated engine - and I got over 120K on '84 Carrera (engine wouldn't have to come apart exc. for a snapped spark plug) and about 160K on a '90 Audi Coupe Quattro 20V engine(sold car then and got my A4).

 

Anir,

15 minutes sounds a bit high to me but I'll let someone else with more knowledge take that on. As for my practice, I let it idle for two minutes at the end of a drive as per the manual. Previous owner did that too.

As for idling prior to the start of drive, I only let it idle until all the warning lights are off (i.e. about a few seconds - maybe its 10 or 20 secs I guess).

Cheers

(Modification of post - I forgot to mention that reference to idling for 2 minutes before switching off applies only to turbo cars at the end of a drive).

[ 07-06-2001: Message edited by: Ran ]

 

Anir,

Starting a cold engine for a short interval and shutting it off is certainly bad for the engine and the environment. The very rich fuel mixture during cold start up also breaks down the proper oil lubrication needed for the piston rings, and that's where most of the wear and tear can occur. Also on several occasions with all three different brands German cars (MB, BMW and P-cars) shutting the engine off right after a cold start causes the hydraulic lifters to not function correctly (loud tapping noise) during the next start up. This occurred to me on several occasions when I just back the car out of the garage to wash it and drove it right back in.

The guideline I use for the amount of time to warm up my 993 before shutting it off is based on the vacuum sound interval. During cold start you can hear a high pitch electric motor sound from the engine bay area, almost sounds like a vacuum cleaner runner in your engine. (That's the SMOG pump/air pump, it pumps fresh air into the exhaust manifold to mix with rich unburned fuel mixture during cold starts before it enters the atmosphere) it generally runs for several minutes, depending on the air temperature and how fast the CAT. Heat up. I shut the car off after the electric motor stops.

 

Robin,

I know you are referring to tapping sounds just after starting it up after prior cold starts but what about clicking sounds AFTER shutting down engine - this does NOT happen on my Porsche (too new to experience) but since you brought up BMW cars, I have to say that all my BMWs as well as other BMW cars that I have driven make that clicking sound after I switch them off. Maybe my Porsche does it too but I have not had the chance to examine it as yet. My guess is you are talking about some other kind of tapping sound because this click or tap that I hear is normal to the best of my knowledge and of course what I am talking about occurs only AFTER switching OFF the car, NEVER after starting the car. Just thought I'd try to figure the reason while this discussion was going on. I was once told what it was but forgot. Its noticeable in the quiet of the garage but not elsewhere.

 

Ran,

You are talking about a different clicking noise. The loud tapping and clicking noise I was referring to only happens on few occasions after cold start up, you can certainly tell something is wrong with the engine because it will not idle correctly. And it comes from the top of the valve train, and sounds very much like the hydraulic lifters that is not receiving oil. Very similar to the sound the lifters makes right after an oil change on the first start up. I have two theories as to what is happening there.

(1). That during the rapid shut down of a cold running engine there are very rich fuel mixture that gets into the oil galley to the hydraulic lifter and washes away the oil needed to operate the hydraulic lifters. That's which explains the loud tapping noise goes away after few minute as newer thicker oil is re-circulated back into the lifters.

(2). My 2nd theory is that during the cold start up and immediate shut off the fuel rich mixture gets into the valve/intake runner area and breaks loose some carbon and the carbon gets stuck in the oil galley of the valve lifters area and prevents the valves from working correctly.

Anyway, like I said these are just my theories of what happened. But one thing for certain is that you have not experienced this symptom in your BMW. Because you will know for sure when this is happening.

BTW, the factory technicians had no idea what was happening either when I asked them about this. I had the same thing happen on my MB E320 and I called roadside assistance to have them come out to take a look, and magically after few minutes the noise went away and the car ran fine again. And during all these occurrences one common factor was that the previous day I had pulled the car out of the garage to wash it and pulled it back in and shut the engine of right away.

 

Hey Ray,

I should have been more clear about 'shifting down through all the gears'... I rarely downshift into 1st. First gear is just too low, and it's not worth the trouble to match the revs to get into first gear only to come to a stop a 1/2 second later. I shift down to second before a stop. Also, I agree that it's more wear and tear than not downshifting, but I think you'll agree that doesn't cause much wear if it's done correctly. I've never had to replace a clutch...