- Charles

As of my last post on this (last year) my oil temps and pressures had been overhauled. My IA and I spent quite a bit of time adjusting the oil pressure regulators on both engines in concert with Lycoming's guidance to get the pressures exactly where they should be and I was thrilled so see my oil pressure gauges matching what the calibrated external mechanic's gauge that we'd "T-ed" in was telling us.

I also had purchased Air Parts of Lochaven's complete STC for new Rochester style oil temp probes and Air Part's calibrated "coupler kits" to make them work with the original AC gauges in the aircraft (and Air Parts of Lockahaven also calibrated my gauges and bench tested them with all this new stuff in place. The only outstanding squak after installing all this stuff is (as you can see from earlier posts) my left engine oil temp was running high.

My initial belief was that my left engine oil temp really was high... after all I'd just spent $1K having these old gauges calibrated with new bulbs and calibrated coupler kits so they should be accurate right? As a result of my believe I was often flying with the left engine cowl flap trailing open a bit to keep the oil temp out of the red line. I started suspecting that my left oil cooler may need to be overhauled.

Eventually I became suspicious of my new oil temp gauges because the CHTs were no warmer on the left side so I did some testing. My testing largely consisted of doing a series of test flights, letting the left side get hot (according to my gauge - hotter than the right), landing, shutting down and immediately putting a calibrated digital temp probe down into the oil pan thru the dipstick / filler. My probe is a 3' long K-type temp probe tied to my multimeter and is calibrated to within 1F of dead accurate at freezing and boiling so - good enough. And... I was just using it to compare left to right temps.

Using the same probe I went back and forth between the two engines taking oil pan temp readings right after shut down and guess what... the oil in the two oil pans was always within 1F of each other. Left and Right oil pans were always the same temp! So... if the Left engine oil really was running 40F+ hotter then how could it suddenly cool in the oil pan to the same exact temp as the right engine immediately after shut down??? It couldn't.

So... during my long annual and landing gear overhaul-refurb project at the beginning of this year I pulled all the oil temp probes out, the coupler kits, and the gauges, packed them all up and sent them back to Air Parts of Lockhaven. With these old gauges they have to be sent out as a set because to do an accurate calibration they must all be bench tested in the same configuration as they would be installed. The gauges create some electromagnetic interference and that must be taken into account, hence everything had go go back... Left AND right even tho I though only the left was at issue.

Air Parts confirmed that the left gauge was reading too high (erroneously) in the higher temperature band (if you look at the AC gauges the scale is not linear - it is more fine grained above 200F). Anyway, they corrected this problem, rechecked all the calibration and sent it all back. We reinstalled everything in the aircraft.

Once my gear project was complete and I could fly (around June) I found the gauges were now dead-accurate and I couldn't be happier... except for one small problem.... When I turned power on the right gauge would immediately respond and read ambient temp but the left gauge would do nothing.... for anywhere from 6-14min before it would finally "jump" and start reading the temp. When it did finally read the temp it was dead accurate and both my left and right oil temps were right in the middle of the green! But the start delay was annoying and I several times found myself waiting in the run-up block for the oil temp to start reading before I could go fly.

To make a long story short the problem was that in recalibrating for the second time on that left gauge, Air Parts had "overdone" the silicone in the needle bearing. On these old gauges, a small drop of silicone is put in the bearing / pivot point of the needle of the gauge. This acts as a "damper" so the needle is not vibrating in the plane and gives a steady reading. It's like a shock absorber - same as how a mechanic's gauge is filled with glycerine to dampen the needle movements. Anyway they put too much in so the needle would not move until the coils in the gauge heated up enough to make the silicone more fluid.

So recently my Attitude Indicator needed to be overhauled (subject of another thread) and while that was in progress I pulled both oil temp gauges, the coupler kits and probes all back out AGAIN and sent them all back again... (maybe 3rd time's a charm?) Anyway, I would like to have sent just the left gauge since all that was at issue was the silicone drop in the needle BUT... they insisted that under their 145 cert they have to recalibrate anything that leaves their shop and if they didn't have all my stuff to do the calibration (left AND right - everything) then they would have to use others they had there and then who knows if that would be the same as what's actually in the plane... so...out everything came and went back again.

So now I have everything back and reinstalled. I haven't test flown yet but I did a ground run. The right gauge still responds immediately and the left gauge responds after a few seconds (a few seconds is fine - much better than 14min!). From what I can tell the temps look right but the real test is in the air yet to come. Hopefully 3rd time is a charm.

I like the folks at Air Parts and appreciate what they do with these old gauges. I am however dismayed that it's taken sending my gauges and kits back 3 times to get things right (and hopefully they are right this time - as I said I have yet to test fly for this go around). The MOST frustrating aspect of this is that each time the gauges have come back they have come WITHOUT new copper gaskets for installing the oil bulbs. When I went thru this earlier this year during the annual (on the 2nd attempt) I had to call Air Parts and buy new gaskets from then but they only come as part of a "kit" from Rochester and they were $5.95 per "kit". All this "kit" had was the gasket I needed + 2two tiny nuts and washer for securing the wire to the probe which I already had and didn't need. Remember... these are Rochester oil probes now NOT the original OEM bulbs and these use a solid copper gasket not the normal crush gasket.

Well this go around I forgot what happened last time and sure enough the probes came back without new gaskets. I called and was told I should just reuse the old ones which neither I nor my IA felt we should do. The old ones were dented in and mared from use... yes they are solid but still I'd prefer new ones. Air Parts told me that I would once again have to buy those same kits... that's the only way to get the gaskets. The price...? $40 per kit!!!!! That's $80 plus shipping to get two little copper gaskets (they look exactly like spark plug gaskets only smaller). I refused to pay this and said I thought they ought to just send me gaskets given that I've been thru the R&R labor and shipping expense 3 times now because the gauges they sent were not correct the first 2 times. Their response? A take it or leave it shrug...

I emailed George McKinney at Air Parts and laid it all out.. I asked how gaskets I bought for $6 this past Jan could now cost $40 each. I provided him a copy of his own receipt from Jan showing the price previously paid. His response?... no response, he just blew me off. He's responded to other emails I've sent prior to this so I have no doubt it was received.

Out of sheer principle I refuse to pay $80 for two tiny gaskets which should have just been provided. I took 3 days of searching but I found the source for these gaskets and I want to share this info for anyone else who has Rochester oil probes....

The oil probes I have are Rochester P/N 3080-37. As you can see from the pic below these have different part numbers from Piper, Mooney, and Cessna...

The gasket that goes on the probe is P/N 0015-00724 and the primary source appears to be Cessna! They are somewhat hard to find but are $9.95 each. I bought extra this time just in case. Here's a pic...

While my recent experience with Air Parts was a big frustration I do appreciate what they do to support these old gauges. Hopefully 3rd time's a charm. It does look like the problem of the delayed start to read has been solved and hopefully on my test flight I'll find the gauges nice an accurate as they were before I sent them in. If anyone else needs gaskets for Rochester oil probes (again not the standard crush gasket) see the notes above. I validated this with multiple sources including Rochester and I compared the new gaskets to my old used ones and they are the same part.

- Charles