[madone]

Originally Posted by ColinW

I have never heard so much garbage talked on this forum about the EGR valve. I am so suprised that droves of R75 lemings are heading for the cliffs, based on half truths and miss-information, to the extent that they are removing a crucial bit of automotive design, in the mistaken belief it is costing them a few HP.

There seems to be this idea that the introduction of a small percentaqe of exhaust gases into the inducted air is going to increase the air temperature and not cool it, as Honest John & others have suggested.

IT HAS NOTHING TO DO WITH AIR INTAKE TEMEPERATURE!

IT HAS ALL TO DO WITH COMBUSTION TEMPERATURES - IN THE CYLINDER!

It is a great pity the majority of forumites do not understand the chemistry of combustion in a diesel engine.

The fuel takes as much oxygen as it needs. At low revs there is a surplus of oxygen, such that the flame temperature starts increasing as the fuel/air mix gets more diluted. Ultimately, this produces Nitrogen Oxides (NOX), which are not only toxic , but are bad for the environment.

The introduction of exhaust gases, which are low in oxgen, dilute the oxygen in the cylinder, thus reducing the combustion temperatures.

The suggestion that turbo bearings etc can be affected by these increased temperatures is perfectly valid. Even exhaust valves could be at risk.

People have suggested that disabling the EGR doesn't affect the MOT emmisions. This is only because they are done at max revs, where most of the oxygen gets used up correctly, so it is low in NOX's

The other misconception is when the EGR valve actually operates. It is supposed to be closed at idle, otherwise there can be erratic idling, which I'm sure a few suffer from.
However under full acceleration (wide open throttle), it should NOT be open also. At cruising where the engine is operating more effeciently then the valve should open, as controlled by the ECU.

So it is quite possible that by removing the EGR, cruising fuel consumption could be compromised.

So why many people are prepared to pay good money for EGR by-pass tubes , for the sake of an indeterminate increaser in power is beyond me. Although I will accept that at wide open throttle, then the marginal restriction could lose a few HP- big deal.

Leave well alone, but clean reguarly.

Colin

Cheers Colin for such an in depth knowledgable reply. Thank god I have not done this mod. No doubt someone will have a different opinion whos knowledge is greater than B**'s and Rovers technical gurus. BTW I will change my opinion if someone convinces me otherwise.