Wayne DelRossi on engine instruments
I have four-position EGT and CHT gauges in my Alon Aircoupe. They are the Westberg K28PCX and K29PCX TSO's kits. These kits are relatively inexpensive, and work well.
A few observations:
1. The EGT gauge has graduations that are so close together, I don't use mine for leaning purposes. 50 degrees is a very small span of the scale on this gauge, and that makes it difficult to see movement of the needle when making small mixture adjustments. I lean by slowly backing out the mixture control until I can just feel the engine start to run rough, and then enrich the mixture by about four turns on my vernier mixture control. I mostly use the EGT just to switch through the cylinders and see that they all look "normal".
2. The CHT gauge is quite useful, and I normally leave the switch set to the hottest cylinder (No. 1), and again, once in a while, I'll switch through the cylinders and see that all of the CHT's look "normal". My engine is very well baffled, and my CHT never gets anywhere near the redline, so if I see a cylinder getting really hot, that means something bad is happening. (I also have a problem with my oil never getting hot enough. On the hottest summer day, it never reaches 180 DEGF.)
3. I consider these gauges a "nice to have" item, but they really are not needed on the small Continentals. The time that they are really nice to have is when you get a fouled plug on run-up. By knowing which mag fires the top plugs, and which mag fires the bottom plugs, you can quickly tell exactly which plug is fouled by switching through the EGT positions with the right mag selected and then the left mag selected. The mag switch position tells you if it's the top or bottom plug, and the EGT switch position tells you which cylinder the fouled plug is in. (The EGT on the cylinder with the fouled plug will be much lower than the EGT on the other 3 cylinders.)
4. The selector switches on these units are not sealed, and they do tend to get dirty after a while, causing the meter indication to be erratic once in a while, especially just after switching from one position to another. Usually, just wiggling the knob on the selector switch will cure the problem. A better fix is to spray the switch with electrical contact cleaner at every annual inspection.
5. The internal lighting on these gauges works very well.
6. All in all, if you want better general info on how your engine is running, and a good tool for troubleshooting engine problems, these gauges are a good option. If you want a precision way of leaning your engine, then you'd be better off with a more sophisticated EGT gauge or engine analyzer.
Best Regards, '' Wayne DelRossi''
One observation about TSO'd instruments in our Ercoupes
The consensus of AOPA legal department, EAA, and my mechanic (and my common sense?) was that since none of the
original instruments/equipment were TSO'd and the plane was certified that way, then you don't have to replace them with TSO'd
equipment. The exceptions are new technology (transponders, ELT's, radar, etc.) that were not a part of the plane at time of
certification and now a part of the system. (They don't want to rely on non-tso'd transponders in the system....if they existed.).
I did not ask the FAA for a ruling because I didn't want to give them a chance to give a no answer (which might be given with
no thought involved and CYA.)
Dan C
Here a letter from the EEA:
