Helmetfire
Registered User
Caldwell, Texas
I have an O-320 cub that I've been fighting a high oil temp problem for a while. At first I thought is was the cylinders were running a little too warm and the baffling wasn't the greatest...didn't have a CHT gauge. After a top overhaul with new cylinders (massaged by LyCon) and the installation of a 4 cylinder CHT gauge and some baffle work the oil temps were still too high. 75 degree OAT will yield oil temps 230-245 depending on rpm...basically unacceptable.
CHT's run between 310-350...pretty darn cool given the high oil temps.
Recently installed a new cub cooler in the nose with new -8 Aeroquip lines fabricated with no change in temps. Tried blocking off all openings around the cooler, starter hole, and even the air intake ('58 cub with square intake brackett filter)...no change.
Was taking things apart today and took the right side (delivery) line off the cooler and oil came out of the line and cooler as expected. Next i removed the left side (return) oil line at the cooler and didn't get ANY oil dripping out of the line when removed. I thought that was pretty weird so I looked a little closer at the hose and found it was completely dry inside. Removed the line at the back of the engine and found the same thing.
To verify the flow through the lines and cooler, I re-attached both lines at the cooler and left the rear (return) line open into a catch jar. Turned the engine over with the starter for a few seconds and found the oil to be flowing at what seemed to be a healthy rate into the jar...this verifies I have pressure and flow through the oil cooler and lines.
Still somehow in the last few hours of flight time with the new oil cooler and lines, the oil never even made it past the cooler into the return line and back into the engine. During the few hours I would check the temp on the oil cooler and found it to be warm...not as warm as the oil sump, but still warm (180-190) so I figured I had flow through the cooler, but something was heating the oil too fast for the oil cooler to keep up. Thought maybe a spun bearing or something else???
Tomorrow morning I'll remove the AN elbow at the return into the sump and see if anything obvious is blocking the way, but I'm at a loss here and wanted to get some input from the great minds here! What, if anything, could be blocking oil flow back into the accessory case??
A few other things that might help:
Replaced oil screen and housing with new (overhauled), no vernatherm.
Replaced Oil pressure relief plunger and spring with new
Oil pressure runs 80+ on takeoff, after oil warms between 65-75, after landing idle with HOT oil 20-30 psi.
Tried straight weight and multi weight oil with basically no changes
Oil usage normal with seemingly no blow-by (oil not turning black right away)
CHT's run between 310-350...pretty darn cool given the high oil temps.
Recently installed a new cub cooler in the nose with new -8 Aeroquip lines fabricated with no change in temps. Tried blocking off all openings around the cooler, starter hole, and even the air intake ('58 cub with square intake brackett filter)...no change.
Was taking things apart today and took the right side (delivery) line off the cooler and oil came out of the line and cooler as expected. Next i removed the left side (return) oil line at the cooler and didn't get ANY oil dripping out of the line when removed. I thought that was pretty weird so I looked a little closer at the hose and found it was completely dry inside. Removed the line at the back of the engine and found the same thing.
To verify the flow through the lines and cooler, I re-attached both lines at the cooler and left the rear (return) line open into a catch jar. Turned the engine over with the starter for a few seconds and found the oil to be flowing at what seemed to be a healthy rate into the jar...this verifies I have pressure and flow through the oil cooler and lines.
Still somehow in the last few hours of flight time with the new oil cooler and lines, the oil never even made it past the cooler into the return line and back into the engine. During the few hours I would check the temp on the oil cooler and found it to be warm...not as warm as the oil sump, but still warm (180-190) so I figured I had flow through the cooler, but something was heating the oil too fast for the oil cooler to keep up. Thought maybe a spun bearing or something else???
Tomorrow morning I'll remove the AN elbow at the return into the sump and see if anything obvious is blocking the way, but I'm at a loss here and wanted to get some input from the great minds here! What, if anything, could be blocking oil flow back into the accessory case??
A few other things that might help:
Replaced oil screen and housing with new (overhauled), no vernatherm.
Replaced Oil pressure relief plunger and spring with new
Oil pressure runs 80+ on takeoff, after oil warms between 65-75, after landing idle with HOT oil 20-30 psi.
Tried straight weight and multi weight oil with basically no changes
Oil usage normal with seemingly no blow-by (oil not turning black right away)
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