Thread: a Td5 question for the gurus......

Originally Posted by Redback

Hmmm a diesel with carbies, never seen one, but then you reckon Melbourne is downhill

have you seen a map of australia.......?

you go up to get to brisbane........and down to get to melbourne.....

Its a good point mate. My 02 runs petrol and LPG and even the LPG shuts off the solenoid for the LPG after 3 seconds or so or no throttle being applied (only above 2000 rpm or so) because it takes its cue from the petrol fuel injector pulse, and the fuel injector pulse cuts off completely as a fuel saving strategy under such conditions - the petrol cut off is covered well on the RAVE cd...I know that on LPG if you on a long downhill run you squeeze the throttle and you hear the solenoids opening (I have the rear tank solenoid inthe load area with the tanks) and off she goes with no hesitation, however if you tromp the throttle in such situations there is a slight hesitation because the vapour hose is empty or almost empty of LPG and it has to pick up from the convertor - on petrol of course the fuel is in the rails and ready to be injected in a split second so its not noticeable at all on petrol.

Cheers

Originally Posted by Tank

The Combustion Chamber in most diesels is in the top of the piston and requires no "oil Lubrication" the cylinder walls and the underneath of the pistons are lubed through oil squirters either from a hole in the con rod or oil nozzles in the crankcase aimed up at the pistons, no damage through "lack of oil lubrication" will occur because of deceleration. Many diesel engines suffer from fine cracks in the heads usually running from the injector nozzle to the valve seats. A lot of this damage is caused by working the engine hard, say up a long hill, with a load and then coasting down the other side, which cools the combustion area very quickly. It is good practise after a long hard (hot) haul up a hill to actually drive down the hill instead of coasting with no throttle, it stops the head from cooling rapidly, Regards Frank.

The engine gets the same cold air charge in every stroke whether it's working hard uphill or idling. The only difference is any heating due to the turbo and cooling from the intercooler.
From there the thermal mass in the engine keeps it from cooling anywhere near fast enough to crack.

Accelerating a truck downhill is suicide (murder-suicide if anyone else is on the road). I know one truckie who tried it, hit 160km/h then asked for a speed limiter to be put in the truck to save him from himself.

If it was necessary to keep heat in the engine, an exhaust brake does just that.

Go West Instead You cannot go wrong

BradM

Originally Posted by DEFENDERZOOK

actually i was curious to find out if we are actually wearing out our engines faster than we should be......


in the days of carbies......fuel was entering the engine even in overrun conditions.......
so the fuel was actually lubricating the upper cylinder....thats all the bits above the piston rings......up to the valves.....


but with todays technology......the fuel can be shut off completely in overrun situations......


its more of a general for all injected engines.......petrol and diesel......


its just curiosity more than anything else.......i was just curious if anyone had actually read or heard any facts regarding this........


its nothing to stress over......the engines are just doing what they are designed to do........

In a petrol engine unburnt fuel actually "delubricates" the combustion area and the bore, not good.
Zute has the right idea, do what he said.
Regards Frank.

quote=Dougal;636960]The engine gets the same cold air charge in every stroke whether it's working hard uphill or idling. The only difference is any heating due to the turbo and cooling from the intercooler.
From there the thermal mass in the engine keeps it from cooling anywhere near fast enough to crack.

Accelerating a truck downhill is suicide (murder-suicide if anyone else is on the road). I know one truckie who tried it, hit 160km/h then asked for a speed limiter to be put in the truck to save him from himself.

If it was necessary to keep heat in the engine, an exhaust brake does just that.[/quote]


The engine produces more heat under load up a hill because 1. it is not moving as fast, so less cooling air at, say 15klm/h than at 100 klm/h and 2. the engine is working harder at and at or near max. revs. I didn't suggest that you drive downhill with pedal to the metal, only an idiot would do that, occasional use of the throttle where appropriate.
Maybe you have an alternative theory as to why diesel heads tend to get hairline cracks in the combustion area and valve seats, I guess Mercedes-Benz and Cummins tech bulletins are wrong, Regards Frank.

Originally Posted by Captain_Rightfoot

Do we know if this specifically happens in td5's?

If I can I try and do this to save fuel

Usually not, but it is common in full size trucks, if your TD5 gets hotter , pulling a load up a long hill, then that's normal, use a bit of throttle downhill, where appropriate, the engine will cool less quickly, Regards Frank.

I've read similar discussion on other cars forum, and they came to conclusion that using engine breaking technique on long distance wearing an engine faster.

Personally, I prefer combination of neutral+wheel breaks and engine breaking.