Mailing List flyrotary@lancaironline.net Message #66736
From: Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net>
Subject: Temperature probe placement
Date: Sun, 25 Apr 2021 02:26:38 -0400
To: <flyrotary@lancaironline.net>
I'm stumped.

With my new coolant return plumbing (got rid of sharp 90 deg fitting) I relocated my temp sensors.

Return from left rad used to sit on (black) 45 deg fitting and return from right rad on a 90 deg brass fitting.

Now I have the right sensor under a silicone hose contacting the 3/4" alum tubing out of the radiator.

The left sensor contacting the 3/4" tubing going into the return (was planning on moving it to left rad output tubing).

The right probe now reads significantly lower (60F) than a non-contact thermometer pointed at rad and also when pointed at silicone hose.

All sensors read the same when cooled down overnight.

I realize I could clamp the right probe to the silicone hose, but felt that the hose would act as an insulator.

Probes are LM35 or equivalent ICs. I had tested them in boiling water and ice baths and they were accurate within 1 to 2 deg F.

I feel I'm missing something. An alum tube is a good heat conductor, right?  Does its color matter when sensor is directly touching it (with heat sink compound to ensure better contact)?

I'd rather not go the route of inserting 3/4" copper tuning (with well for sensor) into the return hoses, but perhaps the only way to get accurate measurements?

Finn





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