Death Rattle?

[haydn callow]

BDC...I dunno'...I thought because they have a much higher compression ratio they were hotter..
I could well be wrong...often am I am told.
I'm sure someone will be along with the correct answer.

[scanner]

Both my diesels rattle like that until they warm up - in fact I think all the ones I've had did so.

I think it's just the extra knock caused by the alteration in injector timing that the cold start thingy does - I think it retards timing a bit.

But I'm no expert either.

[francophile1947]

I've never seen a thread with so many people who know so little Everybody knows that petrol engines are hotter, because of the huge amounts of heat generated by the spark from the plugs , maybe

[haydn callow]

Diesel engines have a higher compression rate, because the higher it is, the greater the thermodynamical efficiency (gasoline cannot be compressed so much together with air, but Diesel engines compress air without fuel!).
So, Diesel engines run, intrinsically, hotter than gas engines; but they usually run at lower rpm, with a bit more fuel than what is required and have heavier pistons; these 3 things prevent them to get too hot.

Just googled this

[Grahame at work]

Hi - I don't know much either

However, I do have what sounds like the same thing -
Only happens in the winter (just started a few times last week)
It is not really related to the engine revs and comes and goes untill it disappears completely but not at a regularly rate.
My impression is (and this is somewhat vague) that it is related to cold and damp.
Not just damp and not just cold - when it's really cold it is hardly evident at all and not at all when it's raining. Just when its been cold AND damp over night / early morning.

I tend to think it is auxillary system related and Dandy's suggestion sounds good to me.
I'll try it next time.

Regards to all
Grahame

[haydn callow]

And this

Both petrol and diesel are hydrocarbons, they are made up of hydrogen and carbon. Hydrogen and carbon make up chains eg:

CH3-CH2 - CH2 ...
Although the chains are not allways straight, they can have branches and rings etc.

the big difference between the two is that petrol has 5-10 carbon atoms in it where as diesel has 17-20. this has various effects the first being that because diesel has longer chains they tangle and stick together better so it has a higher boiling point - it doesn't evaporate so quickly. This also means it is not nearly as flamable, because you have to evaporate the fuel to get it well mixed with air in order to burn.

This difference in property makes how you ignite the two fuels in an engine different.
In a petrol engine you compress the air an fuel a bit, in order to get more of it in the cylinder then use the spark plug to cause ignition firing the piston down the cylinder.

With diesel a spark is not nearly enough to ignite it, what you do instead is compress the fuel and air very violently causing it to heat enormously and ignite.

There are two reasons diesels get a better mpg than petrol.
1. the fuel is denser so you get more of it in a litre.
2. The high compression cycle is in fact intrinsically more efficient.

A diesel engine may be simpler than a petrol and requires less ancillary components due to the simplicity of its design however the diesel engine runs at a much higher temperature and compression ratio than the petrol variant and therefore requires a much heavier and stronger block which adds greatly to the overall weight of the vehicle.

[scanner]

but they usually run at lower rpm, with a bit more fuel than what is required and have heavier pistons; these 3 things prevent them to get too hot.

I don't know who wrote this that you found, but it is absolute ********.

Diesel do not run with "a bit more fuel that what is required" they always run with a surplus of air (unless the injectors are *******) and the running cool is nothing to do with the weight of the pistons or speed of rotation, just the greater thermodynamic efficiency mentioned earlier.
Diesel cylinder temps may be initially higher, but they convert more of that heat into useful work and dump less of it as waste heat, either by way of the exhaust or the water jacket.

http://en.wikipedia.org/wiki/Diesel_cycle

[Harry]

Well guys thanks for all the replies.

If I understood half of what you are rattling on about I probably wouldn't have needed to ask for help in the first place.

I know nowt about engines...so I employ a motor mechanic to look after mine.

I just wondered if anyone had had a similar experience so if I need to I can point my mechanic in the right direction..

I quite like the idea of the timing being slightly out deliberately when it is very cold to help it start....thats a maybe.

I've not idea what 'piston slap' is.

The ancilliary eqipment sounds plausible as I get the feeling from the racket that the noise isn't coming from within the engine itself.

Sounds more like some kid is in there holding a steel ruler against a fan.

H

[dandywarhol]

but they usually run at lower rpm, with a bit more fuel than what is required and have heavier pistons; these 3 things prevent them to get too hot.

I don't know who wrote this that you found, but it is absolute ********.

Diesel do not run with "a bit more fuel that what is required" they always run with a surplus of air (unless the injectors are *******) and the running cool is nothing to do with the weight of the pistons or speed of rotation, just the greater thermodynamic efficiency mentioned earlier.
Diesel cylinder temps may be initially higher, but they convert more of that heat into useful work and dump less of it as waste heat, either by way of the exhaust or the water jacket.

http://en.wikipedia.org/wiki/Diesel_cycle

[dandywarhol]

Well guys thanks for all the replies.

If I understood half of what you are rattling on about I probably wouldn't have needed to ask for help in the first place.

I know nowt about engines...so I employ a motor mechanic to look after mine.

I just wondered if anyone had had a similar experience so if I need to I can point my mechanic in the right direction..

I quite like the idea of the timing being slightly out deliberately when it is very cold to help it start....thats a maybe.

I've not idea what 'piston slap' is.

The ancilliary eqipment sounds plausible as I get the feeling from the racket that the noise isn't coming from within the engine itself.

Sounds more like some kid is in there holding a steel ruler against a fan.

H

Like I said Harry - just turn the steering a quarter turn when the clatter is there - if it disappears it's the power steering pump. I chased my tail for months with that one convinced my engine had an oil pressure problem making it clatter for 5 seconds on startup - it was the PS pump

[The Great Pretender]

Pinking is another word for Pre ignition regarding a petrol engine. Deisels run hotter so they are looser and as they expand heating up, go a bit tighter.
I THINK...I am not a expert at anything

I'm no expert at anything either, but i thought diesels ran colder because of their slower revving nature? Like i said, i'm no expert....

Haven't 'experts' prooved that a bee can't fly?
Pinking is caused when there is a problem with localised overheat in the combustion chamber igniting the fuel before ignition point trying to reverse rotation in a petrol engine.
Similar happens in a diesel when the IP is advanced I believe.

The temp in the combustion chamber dosn't matter BDC as petrol and diesel/veg both are water cooled. It is the power they produce that needs cooling.
If you have a car that has 300BHP and you only drive it around town at 30/40 MPH you can cool it with a radiator from a 1lt car

[haydn callow]

My power steering rattles when idling, goes away as soon as I move the steering wheel...it has always done this...so did a Ford Mustang I had years ago.

[Mr Halibut]

Diesels do take longer to get to a working temperature though especially on a chilli morning due to their efficiency over petrols

[scanner]

Diesels do take longer to get to a working temperature though especially on a chilli morning due to their efficiency over petrols

I believe some modern diesels even have an auxiliary diesel burning heater to warm the car up because of that.

[teenmal]

Hi Harry,just read the post,I recon Dandy is on the right track,the other thing I was thinking about was the injector pump.
The advance and retard piston chattering,only a thought.

Mal..