[Swapnil4585]

For comparison, my Altis fires up at 1700-1800 RPM on cool mornings. Then settles down to its 800 mark. Toyota does not find any issues in that.

[landcruiser123]

Nothing strange, you don't need to worry at all. Revving between 1000-1500 RPM for a new seconds is normal to warn up the engine quickly.

Originally Posted by GTO

Diesels....Their cold-start & warmed-up RPM remains more or less the same. Why is that?

Petrol engines need to warm up quickly to reduce emissions. The only way to heat the engine is by operating at a high RPM while reducing the dependence on the rich mixture.

OTOH, Diesel engines have glow plugs to heat the combustion chamber & aid the compression ignition process; High RPM on a cool engine will unnecessarily pollute the environment.

[Prowler]

Originally Posted by GTO

I have always noticed this with NA petrol engines, but weirdly, never with diesels. Their cold-start & warmed-up RPM remains more or less the same.

Diesel engines have higher compression ratio 22:1 as against the petrol engine's 8:1 (typical). This high compression raises the temperature to 850 degree C which is the minimum temperature required to 'fire'. All this means that by the very nature of diesel engine compression, the engine reaches the operating temperature fast enough when compared with petrol engines. The difference rpm between the initial phase as against the warmed up phase is minimal in the diesel engines.

The Indirect Injection diesel engines have timed glow plugs to heat the combustion chamber in the initial stages. But the Direct Injection (Direct Injection Common Rail DICOR) engines are bigger and hence raise the combustion chamber temperature to the required limit faster thus obviating the need for a glow plug.

[SnS_12]

High engine idling is normally to warm up the engine and oil to operating temperature and to get the oil circulation quickly throughout the internals of an engine.

What one needs to check is if the idle RPM is not below the factory recommended limit which can lead to oil starvation.

On a different note our petrol Tata Indica had two different engine operating temperature or at least the temperature needle displayed it that way. When the car run without the air-conditioning on the the temp needle would reach the half way mark and with the air con on it would be at the quarter mark

[AntPaul]

Originally Posted by gopaneel

it's only recently that I noticed that there seems to be 2 levels of cold start rpm, sometimes it's 1100 and sometimes close to 1500. The usual idle is around 650. I've only noticed a single high rpm in cars I've used earlier and also in the Glanza until now.

The question OP is raising is not about higher idle in cold start, but not so high idle during cold start some times, not always.

Is your Glanza a micro hybrid? Does that car idle rough, or have less torque when cold idling at 1100 rpm?

My G13B idles around 1500 rpm when cold(morning), then slowly settles down to 800-1000 rpm. With AC on, same cold start idle hovers around 1300 rpm. The idle rpd does stay around 1000 rpm higher for around 5 seconds and settle back if i blip the throttle.

I used to have very high cold idle (2K-2.5K rpm) with really rich mixture and took longer time to warm engine a few years back. That was traced to a bad water temperature sensor.

[gollabhat]

Originally Posted by GTO

I have always noticed this with NA petrol engines, but weirdly, never with diesels. Their cold-start & warmed-up RPM remains more or less the same. Why is that? Or is it a turbo thing?

I have observed this difference b/w my humble Punto Diesel & Verna N/A Petrol as well. Even i was wondering why. Any thoughts / inputs anyone?

[gopaneel]

Originally Posted by AntPaul

The question OP is raising is not about higher idle in cold start, but not so high idle during cold start some times, not always.

Is your Glanza a micro hybrid? Does that car idle rough, or have less torque when cold idling at 1100 rpm?

My G13B idles around 1500 rpm when cold(morning), then slowly settles down to 800-1000 rpm. With AC on, same cold start idle hovers around 1300 rpm. The idle rpd does stay around 1000 rpm higher for around 5 seconds and settle back if i blip the throttle.

I used to have very high cold idle (2K-2.5K rpm) with really rich mixture and took longer time to warm engine a few years back. That was traced to a bad water temperature sensor.

Yes, you've understood the issue correctly.

My Glanza is not a micro hybrid, it's the K12M engine. It's very smooth when idling and even while moving, there's absolutely no issue felt.

[ssjr0498]

At a very high level, the reason why the rpm's raise up on a Fuel injected engine is to raise the "Coolant temperature" (which is done for a lot of reasons which I'm not stating here as it can have a separate thread of its own!). This is true for petrol, diesels, IC & Rotary engines.

This "high" idle phenomenon, will happen, irrespective of which part of the day and how many times you have driven the car on that day, as long as the coolant temperature drops below the minimum required value by the ecu!

This phenomenon is more pronounced on cars that have had their thermostats removed!

[Gamerk]

I'm surprised no one else has mentioned this already, but the catalytic converter needs to be at around 450°C to operate effectively. Which is why engines run at higher RPMs during cold starts. Raising the RPMs during cold starts will bring the Catalytic converter upto operating temperature faster, and it will also warm up the engine faster, thus providing cabin heat faster.

OP doesn't have anything to worry about, as this is normal behaviour and your Glanza just taking care of you and the environment

[mikem]

I've noticed a similar quirk with my E-Class E350 (W212).
If I switch on the Aircon before the engine is warmed up, the gear upshifts at higher RPM's of 2200 odd. Whereas If I drive off without the aircon switched on, the gears upshift at around 1500-1600 rpm. After 5 minutes of driving the gear shifts move back to the lower RPM.

[AntPaul]

Originally Posted by Gamerk

OP doesn't have anything to worry about, as this is normal behaviour and your Glanza just taking care of you and the environment

If there is a change in behavior from normal, its good to keep an eye on it. It could be the correct behavior by ECU for current weather/ambient temperature/pressure. It could also be a dirty sensor giving incorrect value or dirty Idle Air Controller valve, or higher/lower load on the engine due to any one of the components engine is driving (Alternator, water pump, ac compressor, oil pump, pully or bearing).

Waiting for Leoshashi to get piqued by this thread

[IP_Man]

This is absolutely normal for petrol vehicles. They need richer air to fuel mixture at cold start. This is done by choking air in carbureted engines. But the problem with richer mixture is engine tends to stall. To prevent this, engine RPM is increased slightly. This is done manually by pulling choke lever in old cars and automatically in newer ECU based cars.

As stated by GTO, Diesel engine idle RPM is rock steady at cold start and warm up. Because diesel engine works on quantity governing, air is not choked at cold start.

[ashwinprakas]

It's a Maruti thing I used to believe, idle so pathetically low in order to return FE.

[AutoNoob]

Originally Posted by GTO

I have always noticed this with NA petrol engines, but weirdly, never with diesels. Their cold-start & warmed-up RPM remains more or less the same. Why is that? Or is it a turbo thing?

Originally Posted by Kosfactor

Diesel , on a cool morning you would notice a CRDI engine runs a bit faster at cold start, this is done to warm up (ever so slightly) soon as well as to keep the vibrations down, when it gets really cold there is very little even the ECU can do on that department though, it will run like an old tractor for a minute.

Originally Posted by DevilzzzzOwn

Actually, in my first hand experience, my XUV 3OO Diesel revs at close to 1K rpm for around 30 seconds. While it is doing that, I use the time to buckle up, connect the Android Auto (wired), check my mirrors. After 30 seconds or so, the engine settles down at around 800 rpm and I move away.

Originally Posted by landcruiser123

OTOH, Diesel engines have glow plugs to heat the combustion chamber & aid the compression ignition process; High RPM on a cool engine will unnecessarily pollute the environment.

In NCR, temperatures fall to single digits in Dec~Jan. I have a push start diesel vehicle. Almost every morning, once I push the start, it doesn't crank immediately. A glowplug MIL lits up on the speedo and only after 4~5 seconds actual cranking happens. Further, engine idles at around 1200rpm for about a minute before settling at around 800rpm.

From March to November, engine starts without glowplug delay, though it sometimes idles at higher rpm for few seconds.

Originally Posted by DevilzzzzOwn

I am so paranoid about cold starts and turbo that for the first 2 kms or so, until I hit the main highway...
But once I get 2 bars on the temp gauge, everything smoothes out, I am settled, engine is settled,

I too follow similar rule. I don't know how much it helps the engine, but it does help my mind.

Definitely OT, but since we are talking about temps, did we reach a conclusion on how long to idle a turbo diesel AFTER stopping? I know there are multiple threads with the discussions but they don't seem to reach a conclusion ever. Of course, it's natural that everyone is different. But I follow the 10 second rule. Park the car with no throttle inputs, stop the music, unbuckle and then shut off the engine. Thoughts?

I change my driving pattern before coming to halt; driving below turbo range atleast 15~20 seconds before and then idling for another 15~20 seconds before turning off.

[IP_Man]

Originally Posted by AutoNoob

In NCR, temperatures fall to single digits in Dec~Jan. I have a push start diesel vehicle. Almost every morning, once I push the start, it doesn't crank immediately. A glowplug MIL lits up on the speedo and only after 4~5 seconds actual cranking happens. Further, engine idles at around 1200rpm for about a minute before settling at around 800rpm.

Which diesel car you have?

I remember at Kodaikanal highest peak and Lamayuru, in the morning Storme was covered with thin ice but started at half crank and idle RPM was steady 900.