Oregon Aircraft Design LLC

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How to tell if you are getting correct engine instrument readings

It's always a good idea to check that your probes and instrument are reading properly before installation or when you get an odd reading. Sometimes folks assume they need to start messing with carburation when that's not the problem.

Note that Rotax 2-cycle engines with stock OEM crankshaft seals often leak after 5 to 6 years or around 300 hours run time. This can cause air leakage and increase EGT readings which can lead to a lot of engine damage real fast.

Before attaching the probes to the engine, use a jumper cable to ground it to the engine and connect the other leads to the instrument.

For the EGT probe, use the very tip of a paraffin candle flame (birthday candle) which should read 932 F. If using an analog type gauge, the probe may need to be heated with a propane torch to get it off the 0.

The temps probably won't be exactly 932 F but + or - about 50 F is close enough and it's nice when both probes are pretty even.

For the CHT, water temp and oil temp probes, determine the boiling temp of water at your elevation and use a cut down pop can, vice grips and a propane torch. Take the reading right when it starts to bubble as it will rise 20 F to 30 F if let to hard boil.

If you have 2 of the same probes and find an odd temp reading on one, the leads can be swapped at the instrument to determine if it's the probe or the instrument.

For a static RPM check (tied down, brakes on and throttles rigged correctly) use a hand-held tach that counts the blades. If using a gear reduction, multiply the RPM times the reduction ratio.

Oftentimes I find that especially the analog gauges give faulty readings. I much prefer the digital type and the best value available as of this writing is the MGL E-1 engine monitor. Below is a description and current pricing. Let us know if you need one!


The E1 universal engine monitor combines in one compact 3 1/8" format instrument all that is needed to monitor most smaller aircraft engines, from two-stroke ultralight engines to medium sized four strokes such as from Rotax, Continental and Lycoming. Most automotive engine conversions can benefit from the use of the E3 engine monitor.

The E1 can measure up to 4 total EGT/CHT channels, a universal RPM input, a universal temperature sender input, a universal pressure sender input, and the aircraft's supply voltage.

Oregon Aircraft Design LLC

Email: oad@easystreet.net

Willamina OR 97396

Telephone: 503-876-8980