Technical Starting up idling/warming query

[devakanth]

Hi All,

I have a UNO Diesel and somebody was telling me that in the morning when I start the car, I should let the engine idle for some time (1-2 minutes) and then move the car.

But on the other hand I've read that one should start moving the car immediately after starting as the engine warms up quicker when it moves, which can be good for the engine as the lubricants perform better when they are warm.

Any ideas who is right in this case?

Devakanth

 

[custard]

i was always told its better to drive of as soon as possible but to keep the revs low till the engine is warmed up.

 

[alexGS]

I agree with custard boy, and this is the general opinion these days. Also, the oil circulation is potentially reduced with the engine idling - at a time when it needs to be at its maximum.

It is true that engines consume more fuel while cold and under load, so there was the theory of warming up the engine first to reduce fuel consumption. It would probably take nearer 5 minutes idling to warm the engine in any worthwhile fashion, during which time fuel consumption will be 0mpg. So it's best to drive off instead (but keep the speed and loading down, to reduce fuel use).

I think there is an exception. If the car is in a really cold environment (say, near freezing) and the cooling system thermostat is possibly faulty, it might never actually warm up while driving but will warm slightly while stationary. So it may be beneficial to run for a few minutes to ensure the engine doesn't stall in traffic etc. (and to demist the windows!) But this is a special case.

What you should do, though - having a diesel - is let the pre-heater plugs do their job by waiting until the pre-heat light goes out before cranking the engine. This gives less stress to the starter motor & battery, and reduces exhaust emissions.

Cheers,
-Alex

 

[SteveNZ]

Drive off straight away if the engine is runing well. If it is really cold, my Tipo (carb) needs to fast idle for about 10 seconds before it will idle by itself. I drive off straight afer that.

 

[devakanth]

Thanks a lot Custard Boy, Alex and Steve.

I will start implementing your suggestion of starting to move immediately as I start the engine.

Actually the temperature here is almost more than 35 degree celcius so the question of near freezing temp is never there. The minimum goes to around 10 degree celsius.

Thanks again. I am sending a copy of this thread to my brother also who owns a Fiat Petra. He would be most interested in knowing this.

Devakanth

 

[Louie Bee]

To add to the oil viscosity issue, the pistons and rings will more than likely be the wrong shape and size when cold.

If I recall , the theory here is that cold pistons aren’t exactly cylindrical. At the bottom where piston joins to conrod, the metal expands by different amounts due to thickness variance. They are engineered to be correct at operating temperature.

Also, cold piston rings won’t seal correctly, resulting in more blowby gas (cylinder leakage).

Always good to take it easy till the engine has warmed up fully .

Regards All,
Louie Bee.

 

[devakanth]

I've read that one should not accelerate too much when the engine is cold and I do follow that. I gradually increase speed and try not to push the engine too much. I keep an eye on the temperature indicator and when it rises slightly then I work with the engine more freely. Though I have made a habit of not accelerating too much so that I can save fuel. The Uno Diesel that I drive gives 15 kmpl. My brother who used to drive it earlier never got this much. Don't get me wrong... he is a great driver.

What exactly is the optimum temperature you would say looking at the temperature gauge that I can say the engine has warmed up substantially?

Devakanth

 

[sumplug]

never drive off imedaitely when started from cold. let the engine run for 10-30 secs to allow the oil to circulate. piston rings do not generally expand much and seal even cold, if not, you would have an oil vapour coming from your exhaust.
optimum temp should be around 88-90 degrees with temp needle about half way. in very hot countries like india, sometimes cars have a lower opening thermostat to help then cope with the high outside and internal heat. and they use a more efficient radiator too. basically the cooling side is beefed up to cope.

 

[devakanth]

Ok. Now I am a little confused. But I guess the final conclusion is coming down that I should warm the engine a little (10-20 secs) but there is no need to let it idle for 2 mins or so. I've actually formed a habit of waiting for around 30 secs, since I've been doing that since last 10 months. I'll have to break that habit and reduce the time.

Devakanth

 

[premrajeev]

I dont think reducing your idling of 30 sec to 20 or 10 sec is going to do any difference.Considering u have a diesel car, and diesel warms up slowly compared to petrol (not in all cases,though) your practice is good.That all depends on how good is your engine is..If it's really in good shape, you can probably get to a start in less than 30 secs !..

Yes here in india (not considered as a very hot country - The normal temp is in the range of 25 to 33 degrees..)one should not be keeping put hs feet on the accelerator for long, to warm the engine..

Rajeev