Low oil temps

[LBPilot82]

Do you have a dedicated ground from your new instrument panel to airframe?

Yes, I have ALL instrument panel grounds going to a common buss.

The test you did with your airplane probe and the Fluke probe seems to validate that the airplane probe is working correctly, but if in fact the airplane probe is a resistance device, then a poor connection anywhere in the circuit will affect the reading. You might try repeating the oil submersion test with the probe using the aircraft wiring exactly as normally installed, if possible.

When I did the submersion test, I was thinking the same thing. I wanted to ensure no outside factors would influence the reading. I tested the probe using permanent installation wiring only. Would you guess a poor connection would affect other instruments? The same guage uses a transducer for oil pressure. I would think this would also show incorrect readings???? I also have the EI volt/amp guage which seems to show normal readings (normal cruise 13.9-14.1V and somewhere around 1-2amps).


I just got back from a trip to SoCal. Each leg was about 2hrs. OAT to SoCal: 40F, oil temp: 134/135, RPM 2450, EGT #2: 1280. OAT to Vegas: 44, oil temp: 135/136, RPM 2450, EGT #2: 1280-1290. Each leg had quite a long climb out, especially leaving Vegas. Highest oil temp I saw was almost 150 after about 25 min.

I appreciate everyone's input.

[LBPilot82]

Well, I made an attempt to be a little more scientific and fool proof today. I removed the oil temp probe and submerged it in water this time. Once the water was boiling, my Fluke meter was reading 208.9, while my oil temp gauge was reading 203. It seems that although I may be off by a few degrees, it isn't anything significant. I also recently played around with reading #2 CHT in flight using a temporary installed gauge. CHT also seemed normal (375-400 cruise) indicating airflow through the cowling is normal. I just got out of annual and closely checked the baffling against the IPC. Everything checks out, even the inner-cylinder baffles. While flying in the pattern today for about an hour, oil temps were between 140-150 with OAT of 90. The highest I saw was after a long taxi to the hangar at 164. Bruce, I think I may try your suggestion about blocking 1 of the blast tubes to oil filter neck and see what happens.

[GAHorn]

I would SO much rather see low temps than high temps. (I would not block any blast-tube air...not to mention there's no basis of approval for that action.)

I still can't help but feel there's a stray electron somewhere causing this abnormally low reading. I"d first suggest you go back to a new capillary system to confirm what the electronic system is indicating. If then it agrees... it supports the theory of actual, lwo temps...even tho' that is counter to all experience with this engine.

[Bruce Fenstermacher]

...even tho' that is counter to all experience with this engine.

I don't recall if I mentioned this but my current A model also runs about the same low temps. (Ok, yes I did) Besides replacing the temp gauge with a new one that read the same as the old. Yes I am still taking some heat from my partner Leroy for that blunder but he is keeping the old gauge for future use on some tractor so it's not the end of the world. I've not done and don't plan to do anymore testing to figure out why our temps are low. I'm just chalking it up to more air through the cowl as fast as my green plane flies. There is no explanation why Richards red airplane would be running cool.

[GAHorn]

I take it, Bruce, you have a "capillary" type?

[Bruce Fenstermacher]

I take it, Bruce, you have a "capillary" type?

Not following you George.

[GAHorn]

I take it, Bruce, you have a "capillary" type?

Not following you George.

Capillary type:

Non-capillary (electric/electronic/thermocouple) types: which use sending units like these:

[Bruce Fenstermacher]

Ahh capillary verses electric. I couldn't think what other kind I could have other than a capillary type (in my very stock airplane ). Yes I have a stock capillary type, both old and new, very much like the one you pictured. Except of course it has correct range markings (unlike some planes )

[LBPilot82]

I have a friend who is willing to loan me a capillary style gauge. I'll get that hooked up and let you know what happens.

[LBPilot82]

I received my friend's Mitchell oil temp gauge and sending unit (not capillary). I first tested it in boiling water which revealed about 200 degrees. After installing the gauge, sending unit, and new wire, I took her up for a spin. After an hour in the air, I had somewhere around 125-130 indicated. This was with OAT at 19C, oil sump inlet blocked on the cowling, and 1 of the 2 blast tube holes (down to the oil filter neck) covered up. I think I have proven with little doubt that my EI gauge is reading accurately. The EI gauge is a 2 wire setup which doesn't require grounding at the probe. The Mitchell is a single wire and must be grounded. I verified engine grounding to the airframe and found no problems. Really scratching my head now (no wonder I have no hair!!!). I may not be hurting the engine with temperatures this low (if they actually are), but it sure isn't making any sense.

[GAHorn]

I notice you're in Nevada. What elevation? The gauge should show 212 degrees F in boiling water at Sea Level....and somewhat lower temp at higher elevations.....(208 degrees at 2,000 MSL). Your friend's gauge might be off about ten at the 200-range. It may be further off at lower temps. But I agree.... your oil temps sure seem cool. Makes little sense to me.

[Bruce Fenstermacher]

Richard if you reread my first post (second on this thread) you will see you have just confirmed what I've learned in the last two years. '48 and early 170As had a big lip under the cowl from stock which is somewhere in the 2-2 1/2" range in width. There must have been a reason Cessna went to a smaller lip and this one became the seaplane lip.

Most likely all the hot temperatures we've heard about are on B models with the smaller (3/4") lip but no one correlated that fact. Makes sense to as most 170s are B models.

My own 170A serial 18837 has temperatures in the 140 to 160 range but I'll bet our baffles aren't in as good a shape as yours. Something to be said I guess for old worn stuff.

Conclusion, if it really bothers you figure a way to block of some of the exit under the cowl until the temperature rises or leave it as it is.

[LBPilot82]

I notice you're in Nevada. What elevation? The gauge should show 212 degrees F in boiling water at Sea Level....and somewhat lower temp at higher elevations.....(208 degrees at 2,000 MSL). Your friend's gauge might be off about ten at the 200-range. It may be further off at lower temps. But I agree.... your oil temps sure seem cool. Makes little sense to me.

Boulder City is just above 2000ft MSL. My flight the other day was at 5000ft. You are certainly correct about the gauge being off a bit, but then again, the way the Mitchell is laid out with its markings, it makes it difficult to read it accurately.

Richard if you reread my first post (second on this thread) you will see you have just confirmed what I've learned in the last two years. '48 and early 170As had a big lip under the cowl from stock which is somewhere in the 2-2 1/2" range in width. There must have been a reason Cessna went to a smaller lip and this one became the seaplane lip.

I thought about this before and did re-read your posts. I don't have the larger "seaplane" lip. Mine is the smaller 3/4in lip which further adds to my head scratching.

This whole problem has been digging at me for a while. I now have 100 hours on the new engine because I don't see this as a huge problem. However, it is definitely something that doesn't follow the "norm" from what I gather from other 170 drivers. If I were 10, 20 or even 30 degrees cooler than what other 170's are seeing, I wouldn't think twice about it. But a 50 degree difference sure seems to be excessive. Like I said before, my biggest concern is not consistently running warm enough to evaporate water in the oil and reduce the life of the engine.

[hilltop170]

Hey Richard, how much water condensation could you possibly get into the engine? That could be a problem along the coast somewhere but at Boulder City? My skin starts cracking the moment I go outside when I'm in that part of the country.

[FredMa]

Richard, have you considered that your gauge may be reading accurately but is being affected by RF interference while in normal operation. It would check perfectly fine with engine shut down but could read low while in operation. This Is very possible with thermalcoulple or transducer type instruments. Does it have a shielded harness?What have you done to inspect and ensure proper shielding?