MGL CHT issues

[cduster]

I'm sorting out a recently purchased HR2 with the MGL G3 iEFIS. The CHT readings are out of sight, but luckily, I don't think the indication represents reality. The probes are, as much as I can tell, type "J" with the black sheath, white + and red -. I've set that up in the display. Durning flight, the CHTs indicate very high. If I land and immediately use an IR temperature gun to check the CHTs, they will read from 60-100 degrees less than what the display indicates. Even when waiting for the jugs to even out a bit, assuming that the bottom of the cylinder might be hotter than the top, it still indicates about 60 degrees hotter than the IR gun shows. I checked the IR gun against some boiling water and it was within 5 degrees of the expected value.

I also double checked that the RDAC XF was properly grounded to the engine itself. The Fluke measured the same ohms along the ground wire from the engine to the D9 pin as it did when the leads were touched together.

Has anyone experienced this issue, and more importantly, has anyone solved it?

[mtnclimber]

I fly with the MGL Odyssey and believe that the Type K (chromel?alumel) is typically used for both CHT and EGT on the iEFIS also.

Might check with Matt at MGL , best customer support I've ever experienced.

Roger

[F1R]

When my Rocket was new to me , it had a large 10" All in one BMA EFIS. Both the CHT and EGT probes were GRT. All temps were good before the 10" EFIS died.

I purchased an MGL efis. Supposedly, they are configureable to accept all known probes. The GRT EGT probes did work fine with the MGL RDAC and Mini Extreme. However, the MGL in all possible set up probe type configurations never did accept the GRT CHT probes. I finally gave up and bought MGL CHT probes and new inconel probe wire compatible to the MGL CHT probes.

All is back to normal and very low CHT's as was the indication when the GRT probes were in service with the BMA. The plenum works very well in flight and CHT's rarely exceed 330F on the warmest pair( the front 2) 10:1 CR
In spite of the concerns raised on this forum, the coin slot cowl intakes can cool very well and I have no plans to re work to large round intakes.

Once landed, as soon as the tail drops, if OAT is over 85F I try to avoid long taxi sessions as this is when the coin slot intakes are not at their finest. That is the only time CHT's get my attention. You won't see me at Kosh.

[Rainier Lamers]

A quick way to to a ballpark test on the iEFIS G3 - under your RDAC setup menu -> go to the TC channel setup.
With your engine still fairly warm flip the CHT channel type between K and J.

With K type selected the reading should be somewhere around 30% or so higher than J type.

J types provide more voltage for a given temperature compared to K types.

Be careful with wire colors - this can be country dependent. I have seen K-yype probes with white and black wires so that is no guarantee that this is a J-type.

Grounds normally have little influence on the CHT readings unless for some reason the ground potential on the block is very different to that of the RDAC - It measures deferentially but the voltage range is restricted to not more than about -2V relative to its own ground.

Be careful using an infrared thermometer to measure "Under the plug" type CHT probes. It is all but impossible to get a good enough focal point with these things so what you are really seeing is more or less an average over a larger area that includes the fins on your cylinder heads - and those are much cooler. One tends to think that these infrared meters look at the very spot the little red laser dot is visible but that is not the case.

The best way to use infrared is to use one of the little FLIR thermal imagers (the little inexpensive mobile phone plug ins work quite well and have a nice spot temperature readout). You will be surprised what kind of temperature differences you will see between the spark plug seat and the rest of the head just a few inches away.
In fact - these things are really great to get an overall view of what it going on around your engine from a temperature point of view.

Rainier
CEO MGL Avionics