Myth? Plugged EGR burns geo metro exhaust valves?

[GasSavers_Erik]

I saw this on the Geo Metro section of Wikipedia.

"A flaw exists in (1.0 l) Metro 3-cylinder engines equipped with an EGR valve - if the valve fails or the EGR passages become blocked, the center combustion chamber can get too hot, and over time, lose compression due to exhaust valve failure."



I know 3 things:

1. Wikipedia is written by people who consider themselves experts so its not always reliable

2. The fastest way to burn a valve is to not give it enough clearance (lash) so that it can't seat tightly into the head (this is also supposed to be the way that exhaust valves get rid of their heat).

3. EGR actually reduces the formation of nitrogen oxides by lowering combustion temperatures. So, there seems to be a little logic behind the valve burning statement

Has anyone here ever heard of exhaust valves on any vehicle being damaged by a plugged up EGR valve?

[GasSavers_maxc]

I detonated an engine and put fine cracks in the exhaust seats. It did it quick too. Iron heads and harden seats.

[kamesama980]

I think the theory is sound but actual testing is impractical due to all examples of said engines being many years old and driven under different conditions. things down to even how the engine was broken in will alter the results. if, however, there are a dozen examples of metro engines torn down that have burned exhaust valves and clogged EGR then It'd lend some credit to it.

[bzipitidoo]

Saw this assertion that ODB-II hurt FE on Wikipedia's Geo Metro page. Doesn't sound right to me.

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

1996 - OBD-II (On-Board Diagnostics, Second generation) is added to Metro models, at a cost of some fuel efficiency.

[QDM]

A plugged EGR system may have something to do with it, maybe coupled with the hydraulic lifters. My 1.3 (Swift) pings like crazy when the EGR system is plugged. If I were driving a 1.0 I'd test the EGR system at every oil change and clean as necessary.

Q

[kamesama980]

^sounds like you need ot clean out the combustion chambers. I know some of the engines in the metros were highly prone to oil leakage. carbon buildup from oil leakage in the combustion chamber can often lead to pinging for multiple reasons.


OBDII means more computerization, more sensors, and more emissions components. that means more restrictions on free gas flow through the engine (especially the exhaust. some cars went from one cat converter to multiple or more restrictive and complete ones)

[frank b]

The EGR reduces the CC temps, so if the valve is faulty or the passages are clogged, the CC temps will rise. This will not only increase emissions, but will increase detonation(ping) by providing a false ignition source, hot parts. If the head gets too hot, and the valves get too hot, they will distort or crack.

[QDM]

Carbon isn't the problem on my engine. I removed all carbon when I had the head off just a few thousand miles ago while doing a ring and valve job. The car only uses 1/2 qt of oil in 3000 miles.

My theory is that the computer is running this engine as lean as it can get away with to achieve maximum fuel mileage. The little 1.3L 4 cyl does slightly over 50 mpg on the highway cruising at 60 to 65 mph. When the EGR system has a problem, it pushes the combustion temp over the edge and causes pinging.

Originally Posted by kamesama980

^sounds like you need ot clean out the combustion chambers. I know some of the engines in the metros were highly prone to oil leakage. carbon buildup from oil leakage in the combustion chamber can often lead to pinging for multiple reasons.

[8307c4]

I don't know what exact damage it could cause but I do know EGR stands for exhaust gas recirculation... It is intended for cold engines to be able to warm up quicker for one, and if it is plugged and it stays in a closed loop then the exhaust will build up higher than normal temperatures during normal driving.

The increase in temperature is minor during normal driving but can be substantial during heavy or sustained acceleration, so I do suppose high manifold temperatures could reach back towards the valves and affect them, but I don't know for sure.

[GasSavers_JoeBob]

huh?

Originally Posted by 8307c4

I don't know what exact damage it could cause but I do know EGR stands for exhaust gas recirculation... It is intended for cold engines to be able to warm up quicker for one, and if it is plugged and it stays in a closed loop then the exhaust will build up higher than normal temperatures during normal driving.

The increase in temperature is minor during normal driving but can be substantial during heavy or sustained acceleration, so I do suppose high manifold temperatures could reach back towards the valves and affect them, but I don't know for sure.