EGR Valves - Edinburgh andy
HI All,

i am curious about egr valves - doesnt affect me personally i am just quiourious- and have the following queries,

1/ I have heard that egr valves can get gummed up if the car has not had regular oil changes why is this if its is only exhaust gas that goes past the valve?? does oil from the crankcase breather go past the egr valve and back into the air inlet??

2/ At what stage does the egr valve open and close?? is it directly proportianal to engine revs??

3/ What would be the sypmtoms of an egr valve is stuck open or shut when its not meant to be??

4/ I am sure i read somewhere that the exhaust gas is used to cool the bearings in a turbo- im sure its in renaults- is this correct i would have thought that exhaust gassess be rto hot to cool down anything??

5/ Could probs with EGR valves cause black smoke to come out of an exhaust??? and if so why does this happen??

Cheers andy

EGR Valves - sine
1/ I don't see how it would be affected by lack of oil changes either.

2/ No idea but i'd also be interested to know

3/ If its shut then with most cars you won't notice much difference in terms of driveability. Indeed with some engines a cheap fix is just to remove them and put a blanking plate in their place. If open then i'd imagine the car would be a bit slow and have increased fuel consumption.

4/ Kind of true. Recirculating a small proportion of the exhaust gas back into the cylinder has a cooling effect on the combustion thus reducing the temp of the exhaust gas flowing across the turbo, preventing it from cooking. Also reducing combustion temp reduces NOx emissions.

5/ Yes but only on a diesel. Not sure why but i'd guess that if open at low revs the cooling effect of the gas will prevent the fuel from burning properly
EGR Valves - Altea Ego
1/ I have heard that egr valves can get gummed up if the car has not had regular oil changes

Gummed EGR is not caused by lack of oil changes. As you say, no oil should be getting there anyway. My assumption is that lack of engine use that causes gummed EGRs. Ie they need to be worked hard and cleaned out with some sporty driving.

TourVanMan TM < Ex RF >
EGR Valves - Collos25
except that 1000 mile a week Renaults lagunas suffer this .
EGR Valves - jc2
3/5.A stuck open valve will cause poor idling and smoke,not because of temperature but because of the lack of oxygen in the recirculated exhaust gas.A stuck shut valve will usually have a beneficial effect on the engine-a slight increase in part-throttle performance and fuel economy but will cause a significant increase in NOX emissions.
4.If the turbo is that critical to exhaust temperature then the turbo was incorrectly selected in the first place.Also,the turbo will run at it's hottest at wide open throttle when you don't have any EGR anyway.
EGR Valves - jc2
2.Early systems were controlled in a variety of ways-usually dependent on airflow thro' the manifold or on some thro' a venturi seperate from the manifold.Modern systems are ECU controlled using inputs from throttle position,air-flow and engine speed
EGR Valves - Altea Ego
yours did

mine didnt

TourVanMan TM < Ex RF >
EGR Valves - jc2
I should also add that modern systems no longer just open or shut by vacuum but by operating the valve electrically(solenoid or stepper motor) or by having electric feedback from a vacuum operated valve allow the EGR to be calibrated closely to engine requirements by varying the flow.It also is used to signal the engine management system of EGR problems so that the engine management light can be triggered and fault codes stored.

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