Hi all
Can someone please explain and also give examples of laboring your car's engine.
I am driving my car in a certain manner and I am wondering if I am not causing damage to it.
The Nissan Almera has a 1.6 engine in it. Now in the mornings when I drive to work the car is very cold and I don't want to use high revs.
What I do is I change gear at 2000rpm using a very light throttle up to 3rd gear and then in 3rd gear hold revs at 1500 to 1600rpm for about 2km. This is not in traffic but in a very quiet back street where I live, so it is possible without disrupting traffic and also because I drive to work very early in the morning. Now, when the temp is between normal and cold on the gauge, I then go to 2500rpm and mostly change gears at 2500rpm to get good fuel economy. When in busy traffic where everyone is in a hurry I use 3000rpm to keep up. Please keep in mind I don't use anything more than 30 to 50% throttle in these cases.

The following is the worrying part for me:
When we went to the coast April, I used 50% throttle in 5th gear up against 2 or 3 mountain passes (don't know if it is the right word. You guys know these mountains roads that you need to drive that are very steep). Well, the revs would drop to 2500rpm in 5th gear and with 50% throttle it would remain at 2500rpm not dropping further. Am I laboring the engine or is it acceptable just as long as I don't use full throttle to keep it constant at those revs.

imo

going up a hill in 5 gear

or changing gears too early and the motor is having a hard time pulling you along .

they normaly shake / rattle

If you are able to hold 5th @ 2500RPM at 50% throttle, then the roads cant be all that steep.
When the engine is usually labouring the revs tend to drop, not hold [typically towards WOT]. IMO There is nothing wrong with pulling conserative high revs on a factory std engine. Your 1.6lt Almera would be happy to see the ocassional rev to the 4.5 - 6 K range. Smaller 4 cylinder petrol engines usually make their power in the higher rev range, when compared to larger capacity engines which have better torque characteristics.

Well, I can definitely say it never shaked, rattled or made a sound like it is pinging. This I heard on some cars going around a corner when walking in the streets in town and then I know that guy is trying to go around a slow corner in 4th gear with a heavy right foot.

Thanks Benny
Yea, my one friend said he read somewhere that you must not drops lots of revs with full throttle as the car is then starting to struggle and you must shift down a gear.
He also read that a car must not hold low revs at full throttle. Just wanted to get other people's opinions as I don't want to damage my family car.

very very generally it's about going full throttle (or near enough) under high loads, when the motor is below the start of its powerband. On a modified car, this might be 2500rpm or higher, on a stocker it might be 1500 or so. Generally if it gets 'the shakes' it is too low for the given load/consditions.

You've got a few competing issues, but the main one (apart from damage from too high a bearing speed before oil is at operating temps/thickness, which is a possibility) is wear/loss of compression from ring flutter. Basically rings are held out against the bore, and located at a certain point in relation to the piston ring groove by combustion pressures, not their spring tension or whatever you want to call it. If the combustion pressure is too low - basically in this case because the rpm is so low that the volumetric efficiency sucks (and it's actually at it's very worst at idle) the rings will flop about (for want of a better term) inside the ring groove, and that changes the angle/face the ring presents to the bore, and knocks it about.

Put it this way - if you were to keep an engine idling for 10 minutes each morning before you took off, you'd likely cut a year or more off the engine life (and that is engine life based on ring seal, which is one of the big ones, and once that goes, it contaminates the oil quicker and stuffs the rest up quicker) potentially. That is to say nothing of the cam on a pushrod engine - which gets its lubrication primarily from that thrown off the rods during use. Now we all know that running a cam in requires us to keep the revs above about 2500rpm. This is because during the cam run in (which is a type of work hardening) the oil is both lubricant and coolant. After teh cam is bedded in, it can tolerate lower oiling situations to _some_ extent but not indefinitely.

Then you've got the next issue - a cold engine will see petrol condense on port walls and cylinder walls (which is why richer mixtures for starting 'work' the way they do, the put that extra fuel 'back' as available for combustion). So the longer the engine is cold, even without using the choke (but worse still with it) the more it condenses and gets on cylinder walls, compromising ring lubrication (microscopic as it is from tiny oil retention on the bore walls) the quicker it wears out.

So they all tend to contribute to the issue, and all have some interaction with one another. Obviously the quicker (without doing harm by the process itself) you can get the oil up to temp, and the motor itself, the less harm/oil degradation etc will take place. So even if idling didn't produce ring flutter, it'd also have the motor running cooler for longer, and affect things still.

So what is the answer? For something like an a12, which has a modest stroke, and a decent oiling system, you won't be doing harm by starting it, and as soon as you get oil pressure, lifting the rpms to about 2000rpm. RAther than sitting there, start driving, keep the engine 'busy' in a reasonable rpm range - up to around 2500-3000rpm and moderate (say no more than 50%) throttle. If it won't maintain 2000+rpm in a gear, gear down , stick with part throtttle and keep it up between 2500-3000 (typically the lower end thereof) until it reaches an ok operating temp. Oil temp and water temp aren't directly linear either, so you have to make an educated guess. You also have to consider that most temp guages on these motors are C----H not listing specific temps. In general, once the motor is up to about 160F, you can start driving normally. Which, from what I read, is basically what you are doing with just a few minor tweaks.

Another thing that might also be apparent - there's stuff all wear once the engine is up to temp and at more moderate rpms and throttle loads (compared to stop start traffic and idling for extended periods) which basically shows some of the engine oil adverts where they take car X and drive it around a test track for a simulated few hundred thousand km's with scheduled oil changes, and detect no wear when the motor is stripped down. Under those sort of test conditions, you could take the cheapest discount oil, do the same oil change frequencies, and get the same results.

Last little tid-bit - since getting to operating temp is so important, one of the other things you can do to help this is to replace the thermostat every 12 months or so. Keeping it, and the coolant in ship shape means it will stay closed till up to the prescribed opening temperature (whereas older ones can sometimes get a little sticky and not close fully, which means it takes far longer for the coolant in teh block itself and the block itself to get up to temp

jmac, you're the man.

WOW VERY WELL EXPLAINED jMAC

sticky :)))