Oil pressure and temp

Please may I give you our symptoms and ask for thoughts?

AFS 3400 indicates an oil pressure and temp in the cruise of 90 psi and 150F in outside temps of 40-70F.

During first take off of the day at 2650 rpm then the pressure always reaches the 115psi limit at oil temps of 90F+.

Should we adjust the oil pressure relief valve or replace the vernatherm or both?

Thanks as always

Sandy

Unless you have a high quality Kavliko sender, and especially if you have a VDO sender, they tend to fail, and fail to the high side. The wiper on the variable resistor just has too small a wear capacity.

If a VDO, usual suggestion is plumb in a direct reading gauge on a tubing long enough to reach the cockpit and do a ground run.

This verifies the motor is normal.

Then, replace the sender or upgrade it.

You may also want to add a direct read gauge to the panel whether or not you upgrade the sender. I don't know if there is a Kavliko for the AFS.

I have 3 Kavlico senders with my AFS 5600. They came with the FWF kit.

Good morning and thanks for your responses

I am interpreting the responses that you think the sender on the AFS 3400 is the issue? I am not sure if you mean the pressure sender or the temp sender or both?

Is it possible that the vernatherm is the problem? It is an IO540 on an RV10. I wonder whether a higher oil temp would lead to a lower pressure.

Would blocking off part of the airflow to the oil cooler be an alternative? Is my understanding correct that if the vernatherm is working correctly then no oil should go through the cooler until a min of 180F? If that is the case then would you expect the oil temp to gradually reduce from 170F at top of climb to 150F in the cruise as currently happens?

Machsandy said:

I am interpreting the responses that you think the sender on the AFS 3400 is the issue?

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Diagnosis 101: Always useful to compare sender-generated values with a known standard.

Is it possible that the vernatherm is the problem?

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A vernatherm extends when warmed to block a cooler bypass opening. The extension is based on thermal expansion of wax capsule, a fundamental physical principle. A vernatherm can fail to extend because the wax escaped the capsule, but failing to retract is very unlikely.

I wonder whether a higher oil temp would lead to a lower pressure.

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Yes, it would.

Would blocking off part of the airflow to the oil cooler be an alternative?

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Some operators do that in cold weather, but 40~70F OAT isn't cold.

Is my understanding correct that if the vernatherm is working correctly then no oil should go through the cooler until a min of 180F?

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No. Some oil always flows through the cooler, although a high percentage of total pump output does short-circuit through the bypass opening when the vernatherm is cold and short. Without some flow, oil could/would congeal in the cooler passages at low OAT, blocking cooler flow, and making it unavailable if subsequently required.

By specification, a Rosta vernatherm extends 0.160" between 150F and 185F. It is expected to be fully seated in the bypass hole between 183F and 187F.

Machsandy said:

oil pressure and temp in the cruise of 90 psi and 150F in outside temps of 40-70F.

During first take off of the day at 2650 rpm then the pressure always reaches the 115psi limit at oil temps of 90F+.

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Lycoming? Sounds pretty normal except 180F is recommended after warmup to burn off moisture. Some sort of block-off or door is usually needed to keep it there. 115 psi is the max recommended for taxi, takeoff. This from the engine handbook.

Thanks Dan and Kent

This is very helpful info.

Kent you think our temps are normal for a Lycoming IO540. I raised the query as the IO540 manual suggests that:
For maximum engine life, desired oil temperature should be maintained between 165?F (73.8?C) and 200?F (93.3?C) in level flight
cruise conditions.

So I was trying to discover if we needed to do anything or whether our experience was normal?

Dan as we never get anywhere near 200F would it be worth trying the partial blocking of airflow through the cooler matrix?

Is there any further oil pressure regulation than the adjustable relief behind the number 5 cylinder? The reason I ask is that on first take off with cool oil the pressure always indicates 115psi, not 114 or 116 but exactly 115. So although other temp and pressures vary this is a constant with cold below 120F. Almost as if there was an ultimate pressure relief as well as the adjustable spring?