Why do the EGT's rise on a mag check

[woxof]

Apparently, this is something to look for on your engine analyzer if you have one. One mag is selected off and the EGT's should rise. But the question is....why?

 

[pburger]

That's easy. In layman's terms (because I'm a layman) -- When only one plug is firing in a cylinder, the mixture is only ignited in one spot which doesn't give as good a burn, so when the exhaust valve opens, the burn isn't complete yet (there's still some fire going on). So, as the still burning mixture exits out the exhaust valve a hotter temperature is seen in the exhaust.

 

[Tom-D]

That's easy. In layman's terms (because I'm a layman) -- When only one plug is firing in a cylinder, the mixture is only ignited in one spot which doesn't give as good a burn, so when the exhaust valve opens, the burn isn't complete yet (there's still some fire going on). So, as the still burning mixture exits out the exhaust valve a hotter temperature is seen in the exhaust.

Exactly,, goodonya

 

[BigBadLou]

^^^ What he said.

Now ... please hold for 15 pages of wrong answers, namecalling and personal attacks ....

 

[nrpetersen]

An alternate explanation is that running w one mag still gives complete combustion, but since the combustion isn't done til later in the cycle, there is less mechanical energy extracted from the combustion gas expansion. Hence it leaves hotter.

There are several causes of higher EGT's which reflect a loss of efficiency of the engine removing energy from combustion.