Revving engine to remove carbon deposits

[jenevers]

just read this in an article about bore glazing

 

"Yanmar's workshop manual suggests that after two hours of low-speed operation their engines should be revved in neutral to maximum speed in about five bursts, to clear out carbon deposits. They also suggest that periodical operation under full power, while underway will benefit the engine, for similar reasons."

 

You don't hear car drivers revving up their modern engines before switching off so much these days. Is that why it used to be done?

[Guest]

just read this in an article about bore glazing

 

"Yanmar's workshop manual suggests that after two hours of low-speed operation their engines should be revved in neutral to maximum speed in about five bursts, to clear out carbon deposits. They also suggest that periodical operation under full power, while underway will benefit the engine, for similar reasons."

 

You don't hear car drivers revving up their modern engines before switching off so much these days. Is that why it used to be done?

 

I guess the reason you don't hear car drivers doing it is because in lots of cases it is harmful to an engine which is turbocharged which lots of diesel cars these days are. A car with a turbo charger should often be allowed to idle for a minute or so before switching off if its just been ran at high speed. This is in order to avoid damage to the turbo charger bearings.

 

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Edited April 6, 2015 by MJG

[dave moore]

My understanding is that Diesel engines are happiest when working hard, running them lightly loaded or slowly seems to encourage sooting up, at least judging by the amount of the stuff thrown out of our exhaust when we are able to run hard. ( Kelvin J3 diesel ).

Years ago a sea going friend told me that ship engines are given a 20 min blast at full power for similar reasons. I think the offered advice to be sound.

 

Cheers

 

Dave

[Phil Ambrose]

Never had a turbo charged diesel car but have always been of the opinion that a car needs a good "blast" from time to time,they seem to appreciate it.

Phil

[Ray T]

Never had a turbo charged diesel car but have always been of the opinion that a car needs a good "blast" from time to time,they seem to appreciate it.

Phil

 

My car gets a good "blast" from time to time.............................

 

_JEN2100

 

Also, it is interesting that perceived wisdom that with an engine it should be started and driven straight away, not left to warm up on idle. Yet, if you go to any race meeting it is a regular occurrence to see cars being warmed up in the paddock so the engine is nice and hot with the oil up to temperature before a car goes out onto the race circuit.

[Stilllearning]

IMO it is good practice to start an engine and let it tick over to warm up, before thrashing the nuts off it.

[LEO]

Hi,

 

I run a diesel powered car, the Turbo 'idling' advice before switching off the engine is correct and I like to 'idle' the engine for a while before setting off, although the handbook indicates that long term idling for the engine used in the car is to be avoided.

 

L

[koukouvagia]

 

I run a diesel powered car, the Turbo 'idling' advice before switching off the engine is correct and I like to 'idle' the engine for a while before setting off,

 

Better not bring your car to London then link .

[Southern Star]

Known as an "Italian tuneup". http://en.wikipedia.org/wiki/Italian_tuneup

[Arthur Brown]

It's a matter of degree. Idle warm up uses more fuel that driving away soon and gently, but if you want to go straight to race performance then warm the engine and circulate the oil first.

 

For economy, start driving in the direction you want to go, by parking that way first! It uses much more fuel to do a three point turn with a cold engine.

[Paul C]

The reason for idling before shutoff in a road car is different to the bore glazing issue mentioned in the OP though. Its to do with spooling down the turbo, because once shut off, there will be no oil circulation to cool it and localised areas of the turbo could overheat.

 

Bore glazing is a different issue - to do with the build up of contaminants within the cylinder - most of which come from the additives of engine oil. AIUI modern engines, including those of canal boats pretty much from the 80s onwards, are designed to not suffer from bore glazing (so much) so its a bit of a myth. I suspect the reason Yanmar warn against it is 1) to over their arse and 2) because the engine its advised for is very basic. There does seem to be a school of thought that canal boat engines in particular, are prone to suffer from it because whilst they might produce 40hp, they'll often be left idling for long periods eg charging batteries at a small fraction of their available power. Also engine size is often overspecified in canal boats, although if same boat is planned to be used on a river, then this would explain why a larger-than-suitable-for-canals-only engine is specified.

 

Personally I'd not worry too much about it.

[LEO]

 

Better not bring your car to London then link .

 

There be wolves in London...............I shan't be agoin there.............good job they don't have the same rules in the sticks with them auld vintage injins - like Kelvins, Listers, Nationals, Rustons and Dormans - Gardners excluded 'cos they don't smoke....

 

L.

[Cloudinspector]

I recall having a conversation with our fitter at work, heavy haulage & plant hire, about bore glazing. He told me about an earth moving plant hire company where he once worked and they would regularly start up loading shovels, excavators, dozers etc and after a very short period at fast idle they'd run them at full throttle for a while to give them a good de-coke.

[mark99]

I'm never sure when gunning it whether the soot is from the engine proper or the exhaust stack which is lined with soot.

[MtB]

The latter.

[jenevers]

I also read somewhere that the ideal colour on the inside of the end of an exhaust should be a mid-brown (not black), which indicates correct fuel/ air mixture.

[jenevers]

 

 

What colour is yours??????

Edited April 7, 2015 by jenevers