Use of plug gasket CHT probes?

Folks:
I was considering installing gasket-type CHT probes and am wondering about their use and life. I have been in the habit of installing new plug gaskets when, for whatever reason, I remove a plug with >25 hours in it. With gasket-type CHT probes, I'd be reusing the same gasket over and over, up to the point of replacing the probe.
So the questions are:

1. What, if any, are the issues with reusing the probe gasket?
2. I noted that MGL's probes have a connector between the gasket and the lead. Does that mean you can replace just the gasket part? (They don't list that part separately on their website.)
3. What is the typical "working" lifetime of a gasket-type probe? How many times can you remove/replace a plug before the gasket won't seal properly?
4. What is the delta in temperature reading compared to a bayonet probe?
5. Is that delta different if you install with the top plug vs. bottom plug? Is one location preferred?

Thanks,
Andy

I'll answer a couple of your questions. Typically, we find that a gasket CHT probe installed on the upper spark plug will read 25-50 degrees cooler than a probe installed in the cylinder well due to the engine baffling. Conversely, we find that gasket CHT probes installed under the lower spark plug will read 25-50 degrees hotter than a cylinder well probe due to the proximity to the exhaust.

a caution about plug gasket CHT sensor

Not on an RV. I had a Moni with the KFM engine, used a plug gasket for the CHT sensor. Even with soldering, the vibrations were hard on the wires and breakage was common.

I don't know if this is a comparable situation but just in case..

hevansrv7a said:

Not on an RV. I had a Moni with the KFM engine, used a plug gasket for the CHT sensor. Even with soldering, the vibrations were hard on the wires and breakage was common.

I don't know if this is a comparable situation but just in case..

Click to expand...

Soldering was probably causing the breaking. It holds the wires too rigidly and quickly fatigues the joint. I use gasket senders on my radial with no issues

I have a Jabiru engine and it had under plug CHT sensors. Nothing but a pain in the you know where. I replaced them with sensors screwed to the cooling fins. Better but not as good as those fitted to my Lycoming o-320.

I use the MGL plug gasket CHT sensors on an O-200. Just over 100 hours with maybe half a dozen plug on/ off events. I've found them to be fairly robust so far. It is important to anneal them every time you remove and reinstall them, but this is simple and takes 5 minutes. Also be sure to have good strain relief on the wires- I zip tie mine right to the plug barrel which seems to work well. MGL uses as fast-on connector to attach to the plug which does seem more robust than soldering. It also allows you to remove the wires before removing the plug which prevents getting them twisted up.

It's not my ideal set up but so far it has been workable.

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Charlie

I used spark-plug CHT sensors for the first three years I had probes on all cylinders. I had to re-attach the sensors to the rings multiple times as they would vibrate or melt free. They all read hotter because they were on the lower plugs. I never liked re-using the rings every time I checked the plugs... They looked pretty beat up by the time I stopped using them.

Eventually I replaced them all with the proper bayonet in-cylinder probes. 5 years later and no issues with any of them.