Outer Limits 4x4 Board

So can ANYONE explain to me why DIESELS have a PREFILTER ????

Seems odd in that they max out at around half the revs of a petrol engine even tho they may be of the same engine capacity....

for a weird example....
My SD33's filter ( the one on the actual throttle body ) is nearly 3 times the size of the one on the statesman and easilly double that of the one on the 350chev in the Patrol...., yet the SD33 has a prefilter aswell as the aircleaner ...

The IVECO truck I drive only has a prefilter yet its almost the exact same size as the prefilter in the MQ SD33 Patrol, which again has an aricleaner aswell....


signed

confused

p/s
the thread that asked the silly question in the first place....
http://www.outerlimits4x4.com/PHP_Modul ... p?p=447049

Shoot me down...

Because they are extremely sensitive to moisure due to the much higher compression. So need to make sure air and fuel is real clean.

Petrol engins actually run better in some circumstances with a small amout of water in the fule as it helps to atomise the petrol better. Not the case with diesel.

Dirt inflicts more damage on diesel engines, probably because of the higher working pressures with the higher compressions.
Same with the fuel system, high pressures and fine tolerances require better filtration.
Plus a prefilter saves on filter changes.
J Top

Yeah it's all about the compression ratio of diesels. As you know a diesel uses compression to ignite the fuel unlike petrol engines that use spark plugs. To do this you need to run much higher compression so the fuel/air mixture is compressed to get hot enough to self ignite. Also the diesel fuel we have in OZ is crap compared to Europe.

cant say ive ever heard that petrol works better with water in it??
As has been said, precleaners just save on filter changes, as most diesels will be operating in dusty conditions at some stage and a prefilter (labrinth style) catches alot of dust etc before your expensive filter. But if you only drive in the city dropping the kids at school you dont need it!!
(just kiddin!!)

fisho64 wrote:cant say ive ever heard that petrol works better with water in it??
As has been said, precleaners just save on filter changes, as most diesels will be operating in dusty conditions at some stage and a prefilter (labrinth style) catches alot of dust etc before your expensive filter. But if you only drive in the city dropping the kids at school you dont need it!!
(just kiddin!!)

It's called water injection - tiny bit of water mist in the cylinder cools the flame front, and you get a smoother revving engine, and can actually run higher advanced ignition timing / leaner mixtures as it's less susceptable to detonation.

It's an old art, and often only useful on older engine, or probably not even useful at all. My dad has mucked around with it in the past and reckons the engine does run smoother. It makes sense to a certain degree.

As a side topic, you can actually decoke/decarbonise your engine by having the engine at wide open throttle, and poor water down the carby - it will choke the revs a bit, but the hydrolic compression (ie, water won't compress) knocks the carbon loose and it comes out the exhaust. Sorta like steam cleaning your internals.

I've heard of people using brake fluid to do this as well, but honestly there is nothing wrong with water. The only downside to this is if your engine is so old/worn, that the only reason it still has compression is the coked/carbonised cylinder walls, in which case you'll need to rebuild your bottom end

Actually on another side note, I've heard of people using diesel oils in a petrol engine for a short period of time (500km or something), just enough for it to wash out in the insides - diesel oils contain much higher levels of detergents, and it apparantly gives the internals a good clean out.

If it aint broken, don't fix it

water injection is nothing to do with water in the fuel!!
Water injection is used to prevent detonation, but it is NOT in the fuel!!
Water going thru your injection system is BAD, whether petrol or diesel as it causes small amounts of rust on very finely machined(read expensive) parts. Just in case someone trys it!!
It is often used in dragsters etc and is sprayed in a fine mist into the air intake and merely slows down the burning process
The high compression can cause the fuel to explode due to the diesel effect before the spark, or at a speed much faster than it should and this is detonation
It'd be a brave person whoed tip water in the intake of a revving engine, and coke/carbon doesnt form on cylinder walls, it does clog up rings though. Glazing (or varnish) does though and generally can be safely removed by a good thrashing UNDER LOAD. But I have heard of it being done.(water in the intake)
The only reason coking/carbon would directly affect the bottom end is when the conrods come out the side of the block from from a hydraulic lock at high speed!!
Having said that, on ships, turbos etc are regularly cleaned by spraying water or a special cleaner into the turbine at close to maximum power output (at a measured rate) as they coke up quickly using bunker oil, which is a bit like mud when not heated

Think about where these vehicle are designed to be operated as well, your Statesman isn't designed to be driven for thousands of kilometres through bulldust, although most 4WD don't see these conditions some do, a far higher percentage then Statesmans anyway

It comes down to the fact that diesels love and need clean dust free air......dust and diesels equal wear at a big rate........I know this issue was raised in the Patrol forum a while ago with someone experiencing failure of 4.2TD cause dust got into the motor at very low kays....

I had a mate who owned a cordia turbo. He used a water\methanol injection system into his air to increase performance.

Seemed to do the trick - but I never knew the reason for the water part until now.