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TSIO-520-B High Oil Temperature on Approach

I have been noticing that my engine oil temperature will slowly rise to red line on approach and stay high through landing and taxi. During cruise it stays stable around 210. I have flown it on trips up to 2 hours and the temperature is always stable until I start to descend for my approach. Cowl flaps are closed on descent and final and open after landing. I am always in the green for manifold pressure until I pull throttle to idle above the runway.

At first I suspected the temperature probe, but I do notice ambient temperature around my feet increase as the temperature increases on the dial, so I do think it is getting hot. I have the stock gauges; no aftermarket EIS. CHTs always show normal and do not rise with oil temp. Do I have an oil cooler issue? What should I have my mechanic look at?

Thank you in advance!

Model: Bonanza V35A-TC
Aircraft Serial Number: D-8705
Posted 6/2/2023 - 8 months ago

Replies Sort

On the TSIO-520-D (or DB) in your in your V35A-TC, oil temperature is your friend, but can be an enemy.

Oil temperature and MAP are inter-related, so as a cross check without any other available instruments, when the oil T is at 210 after landing, do a static run-up, if you get the same MAP as on a normal TO, then you may have an indication issue on the OT indicator, and is worth investigating. If your MAP is low, then the OT indication is probably not far off. These engines should be set up for 32.5" MAP at 170 - 180* OT; less OT means more MAP, more OT means less MAP.

Next thing I would look at is the seal around the oil cooler. On the bottom, there is a baffle plate that goes from the oil cooler to the bottom of cylinder #2; with a seal on the aft end at the oil cooler. If that seal is bent down, air will bypass the cooler. There is also a seal on the inboard side of the oil cooler to the crankcase, that can deform and blow back, either of those seals not being properly positioned will rob air from the cooler; they can be repositioned and 'glued' into place with RTV; let it cure overnight before flight.

The lower airspeed on approach giving a higher OT; one or both of those seals are the likely culprit.

ABS Tech Advisor

Posted 6/2/2023 - 8 months ago

I was finally able to take it up last weekend and perform a static run up after it got up to temp. MAP indicated same as TO.

The baffles around the oil cooler are already RTV’d in place and look as you described.

Posted 8/7/2023 - 6 months ago

I have been working on Mr. Novac's Bonanza in reference to the high oil temperature and this is what I have accomplished:
1. Replaced baffle material above oil cooler as it was dry rotted and ineffective (see pictures attached).
2. Conducted MX flight and temperature gauge reads 240 degrees immediately at takeoff and stays between there and just shy of the red arc at 260 degrees the entire flight, regardless of manifold pressure setting (see pictures)
3. Found the firewall shutoff in the "open" position, thus the hot air coming into the cabin at his feet. Pulled the cable to close the vent. Did not see any noticeable change in temperature - however, the outside air temp was close to 100 degrees.
4. During the test flight, I found that all three (3) engine controls became extremally hot to the touch. Any thoughts here?
5. The vacuum intake filter is located directly above the oil cooler. Could this interfere with air flow over the #2 cylinder and eventually through the oil cooler itself?

The only items that have not been removed from the system and looked at are the temperature probe from the oil cooler and the temperature gauge itself.

I have uploaded pictures and would appreciate any further troubleshooting help at this time.

Robert Benda
ABS BPPP Instructor and A&P

Remove the temp probe and hook up the wire to the cockpit. Put probe in a container of water and heat water to boiling 212F and see if probe reads the same. Probes are known to get way out of tolerance at times.

Bob Ripley
ABS Technical Advisor

Posted 8/16/2023 - 6 months ago

TSIO-520-B High Oil Temperature on Approach