Thread: A myth busted! For me anyway

ohh crap, here I am idling the engine away for 5minutes (yes, the wife takes a long time to come out to the car) thinking its all good Hmm, so looks like ill have to cut that habit.

Most of my machines on the golf course are Diesel, some NA and 3 are Turbo'd and as a rule of thumb, I tell the guys to let it fast idle for about 20 to 30 seconds until it is running nice and then full throttle (most other than 1 tractor are Hydraustaic) and drive out.

I have heard this before but I have also heard arguments for Idling but knowing how a Diesel works and the fact that the amount of air that goes into a NA diesel doesnt change per stroke a significant amount it wouldnt surprise me if it were true but may not be a detrimental as they make out.

Turbo engines are a little different as at idle the turbo is doing nothing but when engine revs increase, so does intake presure so the amount of air in increased alowing more fuel to be pumped in to produce more power so I would believe that Idleing a Turbo motor for more than 5 mins would be quite detrimental as the bigger the bang at optimum revs the more heat that is produced and the morethe engine would cool down in the process.

My machines when they return at smoko have the revs dropped as they come past the back of the shed and then the lower them more to enter the shed, then idle them for 10 to 30 seconds depending on if it is turbo and how hot it is and then shut it down.

After 30mins smoko, all the machines are still pretty much at operating temp when restarted so I dont see the problem with that.

I have seen some very glazed Ford and perkins diesels over the years from excessive idleing in tractors as they would have a flat battery so they would roll start it in the morning and not turn it off until they left.

All you see is pure white smoke pooring out of the exaust of cold unburned fuel and it doesnt clear for ages in which time they normally think they should be more gentle and not rev the engine which makes it worse.

I used to just put them on full throttle for a luch break or 2 and it would clear, then fix the starting problem but some of them needed a decoke and hone to bring them back to life.

Well I'm be. I have tended not to switch off when out bush in convoy. If we all stop at an obstacle I let it run with all fans on full to suck as much heat out as I can. Thought this would be good for the gearbox and engine during summer. Guess I will start to turn it off quicker.

It's a shame you always get told the opposite.

I think the key term to understand here is "low idle" which is different to the engine speed when warming up (usually a high-idle). I usually warm my engine up at about 2000 - 2500 RPM. That way the oil is circulated and things heat up relatively quickly but with no stress to the engine. I then pull out and maintain about 2500 RPM down the hill (I live on top of one) in a slightly lower gear (3rd usually) to get the oil moving around in the gearbox.

Essentially what I read was that letting the engine idle on tick-over is bad, but idling at higher revs (for warming up or keeping air etc. running) is not such a problem - just maybe a waste of fuel.

G'day Folks

That is interesting, but aren't Detroit Diesels 2 stroke?? the same as Cummins? if so they are a whole different kettle of fish to a 4 stroke diesel and particularly an older British /European Type that is why they fit Radiator Blinds, as the principal of a diesel is Compression Ignition, so the hotter the Block is, the better the ignition, or that was what I was taught, that was before the high speed 2 stroke diesels appeared on the market, the reason a diesel is left running during short stops, is that it is often more damaging to restart (oil drained back to sump) and more expensive, use of starter than to leave it running as diesel use is minimal.

cheers

Originally Posted by UncleHo

G'day Folks

That is interesting, but aren't Detroit Diesels 2 stroke?? the same as Cummins? if so they are a whole different kettle of fish to a 4 stroke diesel and particularly an older British /European Type that is why they fit Radiator Blinds, as the principal of a diesel is Compression Ignition, so the hotter the Block is, the better the ignition, or that was what I was taught, that was before the high speed 2 stroke diesels appeared on the market, the reason a diesel is left running during short stops, is that it is often more damaging to restart (oil drained back to sump) and more expensive, use of starter than to leave it running as diesel use is minimal.

cheers

Detroit and cummins dont only make 2 stroke Diesels but that is what they are famous for.

At idle, my understanding of that artical is that the cold air inducted into the engine being the same amount as at higher revs, cools the engine from the inside out as a diesel engines speed and torque is determined by the amount of fuel that is injected into the cylinder or combustion chamber.

Originally Posted by solmanic

I think the key term to understand here is "low idle" which is different to the engine speed when warming up (usually a high-idle). I usually warm my engine up at about 2000 - 2500 RPM. That way the oil is circulated and things heat up relatively quickly but with no stress to the engine. I then pull out and maintain about 2500 RPM down the hill (I live on top of one) in a slightly lower gear (3rd usually) to get the oil moving around in the gearbox.

Essentially what I read was that letting the engine idle on tick-over is bad, but idling at higher revs (for warming up or keeping air etc. running) is not such a problem - just maybe a waste of fuel.

I think your about right with the high idle thing and some auto trans cars wont go into top gear or lock up until the engine and/or trans are at a cirtain temperature so why not do that, it couldnt hurt.

Beware of shutting turbocharged engines off immediately after high revs. Remember the turbo is spinning very fast and is lubricated by oil pressure. Shutting engine down equals nil oil pressure to turbo bearings.