PA38 - High Oil Temp/Pressure

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talkingbob

Pre-takeoff checklist
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Would LOVE some PA38 owners to chime in on this!

I was flying on a cross-country (1 hour 20 minute flight) recently and noticed the following indications on my engine-related gauges. The light blue lines in the attached photos indicate the position that the needle was in during cruise.

I was cruising at 4500 feet and leaning for "max power", which seemed to be where the top of the mixture lever was near the bottom of the "M" in the word MIXTURE to the left of the mixture lever. OAT was around 60F.

I was watching the gauges the whole flight and they never seemed to move really. Enriching slightly MAY have caused the Oil Temp to go down a TINY bit, but it was hard to tell.

Soo... Should I be concerned?
 

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Your oil pressure was at the top of the green, right? So you're good there.

The oil temperature was in the green, but near the top, right? On a 60F day, that's a bit higher than you'd like. One thing to check is if the SCAT hoses going back to the heat exchanger on the oil filter are attached and in good shape. Also, make sure the heat exchanger isn't clogged with bugs or bird nest material. (Yes, the Tomahawk has a silly little oil filter heat exchanger that pulls air from the baffles via SCAT tubing. I'm sure it helps a little.) Beyond that, I don't have any suggestions. My Tomahawk always had higher oil temperatures than I liked, but short of installing a real oil cooler, it may just be symptomatic of the breed.

Did reducing power help any? Might try that next time.
 
check the voltage...
 
kyleb said:
Your oil pressure was at the top of the green, right? So you're good there.

The oil temperature was in the green, but near the top, right? On a 60F day, that's a bit higher than you'd like. One thing to check is if the SCAT hoses going back to the heat exchanger on the oil filter are attached and in good shape. Also, make sure the heat exchanger isn't clogged with bugs or bird nest material. (Yes, the Tomahawk has a silly little oil filter heat exchanger that pulls air from the baffles via SCAT tubing. I'm sure it helps a little.) Beyond that, I don't have any suggestions. My Tomahawk always had higher oil temperatures than I liked, but short of installing a real oil cooler, it may just be symptomatic of the breed.

Did reducing power help any? Might try that next time.
Click to expand...

Thank you for the insights. I will take a look more closely at what you talked about. I have always been proud of my preflight thoroughness, so I really hope that I didn't miss any sort of nest, etc!

Yes, I continued the flight since the needles were in the green still, but it was very odd to see them so close to the edge.
I had oil temps get near the edge once in a Cessna 172N, but that was during a climb to 12,000 feet - never during cruise flight at 100 Knots IAS.

Trust me, I would rather have higher oil pressure than lower, but I had never flown something with THAT high of an oil pressure reading...

I did not attempt to reduce power.
 
tyndall said:
Too high or too low voltage can cause an electric gauge to read high or low.
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Yup. High oil pressure and high oil temperature don't jibe. System voltage is the first thing I would check. YMWV
 
Clark1961 said:
Yup. High oil pressure and high oil temperature don't jibe. System voltage is the first thing I would check. YMWV
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Interesting...
The ammeter reading (see attached image) during cruise was at the blue line and the red line was during decent/landing.
During cruise the only power draw would have been from the radio and the beacon (strobe) lights. During decent/landing, I had the landing light, position lights, radio, electric fuel pump, beacon and the instrument panel lights all on full, so it makes sense that the ammeter reflected the change in load.
 

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talkingbob said:
Interesting...
The ammeter reading (see attached image) during cruise was at the blue line and the red line was during decent/landing.
During cruise the only power draw would have been from the radio and the beacon (strobe) lights. During decent/landing, I had the landing light, position lights, radio, electric fuel pump, beacon and the instrument panel lights all on full, so it makes sense that the ammeter reflected the change in load.
Click to expand...

Got a voltmeter in there? If not, and if you have an accessory outlet (i.e. cigarette lighter), you can buy a digital voltmeter that'll plug right in. About $5 on Amazon or Ebay.

http://www.amazon.com/Cigarette-Lig...144426&sr=8-12&keywords=12+v+outlet+voltmeter
 
talkingbob said:
Interesting...
The ammeter reading (see attached image) during cruise was at the blue line and the red line was during decent/landing.
During cruise the only power draw would have been from the radio and the beacon (strobe) lights. During decent/landing, I had the landing light, position lights, radio, electric fuel pump, beacon and the instrument panel lights all on full, so it makes sense that the ammeter reflected the change in load.
Click to expand...

Sounds like the charging system is okay. The minor concern is that the ammeter is looking at a shunt load and is calibrated for the system. It is a minor concern.

That said, if you are monitoring system voltage you know for certain what the instruments are using and can make a judgement based on that. I have a digital voltmeter plugged into the cigar lighter port to monitor actual voltage.

The powerplant guys on this board can give you the low-down on high oil pressure and high temperature. Maybe it's a failed pressure regulator or a failed vernatherm. I don't know. It is an unusual condition.
 
Clark1961 said:
Sounds like the charging system is okay. The minor concern is that the ammeter is looking at a shunt load and is calibrated for the system. It is a minor concern.

That said, if you are monitoring system voltage you know for certain what the instruments are using and can make a judgement based on that. I have a digital voltmeter plugged into the cigar lighter port to monitor actual voltage.

The powerplant guys on this board can give you the low-down on high oil pressure and high temperature. Maybe it's a failed pressure regulator or a failed vernatherm. I don't know. It is an unusual condition.
Click to expand...

What's a "shunt load"?

I read in the POH about how under full load it should read "30", but it never got that high. The VOR is INOP, so if that's not pulling any power, maybe that's enough to not reach 30 Amps with everything else turned on?

I own a multi-meter, but I don't think the PA38 that I fly has a cigar lighter port... :(
 
talkingbob said:
What's a "shunt load"?

I read in the POH about how under full load it should read "30", but it never got that high. The VOR is INOP, so if that's not pulling any power, maybe that's enough to not reach 30 Amps with everything else turned on?

I own a multi-meter, but I don't think the PA38 that I fly has a cigar lighter port... :(
Click to expand...

The shunt is just measuring the voltage drop across a resistor that is parallel to the main current output from the alternator. It has to be calibrated to the actual output from the alternator. Calibration shouldn't be a problem unless the avionics have been significantly altered.

No cigar lighter? Pretty much standard along with the ashtrays on older Pipers.
 
I've been know to remove the dome light and check voltage across the terminals.
 
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