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Thread: High Oil Temp readings that aren't accurate.

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  1. #1

    High Oil Temp readings that aren't accurate.

    (Moved from another thread.)

    Summary:
    On many flights, my Oil Temp readings are rock solid in the 187F range, pretty much unwavering. But sometimes oil temp readings will rapidly climb up into the 230-240 or higher ranges. I might cruise along for 2 hours with oil temp at 187, and then the temps climb up with no apparent trigger. When this happens, CHT and EGT readings are still very good. CHT's are typically 330-350 in cruise even when this happens. I've never seen Oil Temp come back down in flight once this happens, but I can stop the airplane and immediately restart and the readings are OK again. I've already replaced my vernatherm and oil temp probe, and this problem persists.

    Notes:
    - When this happens, there is no effect on Oil Temp with changes in power or mixture settings.
    - Disabling ALT, in flight, causes oil temp to immediately drop back to normal temp.
    - After shutdown, the temp reading also drops immediately into the normal range.

    Last advice from AFS:
    - check engine ground.
    My engine ground looks good. It's a heavy gauge wire (4AWG), and solidly connected to both engine and primary ground point on firewall. I did notice, however, that the wire grounding my panel was loose. The nut holding the panel ground terminal to the primary ground post had backed off, and although the ground wire terminal was still on the post, it would definitely have been a weak ground for the panel. Before next flight, the nut will be tightened back down with locktight (or with a nylock nut). I'll update the forum if the problem doesn't recur in the next several flights.

    - I also noticed there is mention of going with a 2-wire oil temp probe in some older posts. I am considering this. If I install one of these 2-wire sensors, do I run one of the two leads to the oil temp input and the other to case ground?
    Last edited by dhall_polo; 11-29-2010 at 10:39 AM.

  2. #2
    I had this exact problem.

    I'm using a 3400EE in an RV10 with a stock engine. I have the single wire sensor mounted in the oil filter housing per the AFS instructions.

    I ended up putting a #8 or #10 ground wire from the oil filter adapter to the firewall. That fixed the problem for over a year.

    It started again earlier this year. I ended up just remaking the connection on the sensor stud and that's been working for about 100 hours now.

    It seems like the connection/ground is very sensitive and has to be perfect to work correctly.

    Dave

  3. #3

    thanks

    Quote Originally Posted by Dave Saylor View Post
    I had this exact problem...
    ...I ended up just remaking the connection on the sensor stud...
    Glad to know I'm not the only one with this wacky problem. Worth a shot, especially since it is so easy to do. Finally a use for one of those gazillion unused ground tabs I have on the firewall side.

    Thanks.
    Last edited by dhall_polo; 11-30-2010 at 11:48 AM.

  4. #4

    problem solved

    I had high reading oil temp when the boost pump was turned on for landing. I found that cutting the loop for the over voltage warning light on the alternator solved the problem, stopped the ground loop. I know it sounds funny, but it works!

    Gary

  5. #5
    I'm having the same problem. It happens when I cycle my gearpump.
    Checked all my grounds. Did use a groundwire for the oiltemp probe. (single wire)
    Last chance is my alternator. It's a kelly ALX-8521LS on a IO-390x

    Christian

  6. #6

    Thumbs down No dice

    Nothing has fixed my problem. Everything is properly grounded at this point - double and triple checked. I guess I need to try a two-wire probe. Starting to suspect a flawed design of the AF3500 and probe combo.
    Last edited by dhall_polo; 01-06-2011 at 08:41 PM.

  7. #7

    Update:success!

    I ordered a 2-wire UMA 1B3 sensor from Aircraft Spruce. I connected one wire to the original probe wire and the other to firewall ground. I ran through the documented calibrations steps. Install done, working. But what about in flight?

    YES! I finally have an oil temp reading that shows NO sensitivity to voltage or current levels.

    squawk_count--;

  8. #8
    Glad to hear that solved your problem Don.
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

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