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Posted

Hello, I have a 64 M20E with the IO360.  It has 400hrs SMOH and 18hrs since IRAN (New cam, lifters, bearings, cylinders were reconditioned with new rings). I have been running Aeroshell 80 SAE 40 mineral oil for break in. I have original instrument cluster and a JPI 700 engine monitor with oil temp. When I start the engine I get 75ish psi at 1000rpm on the oil pressure gauge.  When I push it up to 1500rpm the oil goes pressure goes up to mid 80s. At 2300rpm on the ground it goes to mid 90s.  I have confirmed the pressure with a calibrated shop gauge.  The pressure is in the green while I taxi and at takeoff power.  once I level off I notice that the pressure starts to come down.  In cruise I see roughly 55psi indicated at 24 squared.  My oil temp is in the 180s per analog and JPI 700 gauges.  I know that the vernatherm should be operating around roughly 180 to allow oil to flow to the cooler. The cooler was overhauled in 2011 before I owned it.  The pressure relief valve has 6 washers (9 max per IPC) under it.  I added a 7th washer but was seeing 115psi cold at 1500rpm. I did not want to go any hiring with the rpm. I opted to take out the 7th washer.  I am going to remove oil cooler and flush out and see if that helps.  Does anyone have any ideas on why the pressure drops like that? 

 

 

Posted

That is normal - Oil pressure drops with temperature. With multi weight it doesn’t drop as much because it’s not as high starting out when it’s cold. High oil pressure can be bad for the engine. My turbo specifically states oil not up to at least 100 degrees can have oil starvation at T/O power settings. When oil is very hot like summertime operations it can be a struggle to keep the pressure above the minimum if the oil gets too hot.

Posted

He’s also running 40 wt oil. But I concur it’s too low a pressure.

If the oil temp is 180ish, there is nothing wrong with the cooler.

‘It’s possible your pressure relief valve seat needs staking, I’d check that first, simple and easy.

This comes from a Lycoming publication that explains how to stake the valve seat, a valve ball is welded to a rod and used as the stake. I’d find the Lycoming pub but I have to go get my teeth cleaned

https://www.cessnaflyer.org/maintenance-tech/item/1149-hone-in-the-range-lycoming-oil-pressure.html

Posted
12 hours ago, gtsio520 said:

Hello, I have a 64 M20E with the IO360.  It has 400hrs SMOH and 18hrs since IRAN (New cam, lifters, bearings, cylinders were reconditioned with new rings). I have been running Aeroshell 80 SAE 40 mineral oil for break in. I have original instrument cluster and a JPI 700 engine monitor with oil temp. When I start the engine I get 75ish psi at 1000rpm on the oil pressure gauge.  When I push it up to 1500rpm the oil goes pressure goes up to mid 80s. At 2300rpm on the ground it goes to mid 90s.  I have confirmed the pressure with a calibrated shop gauge.  The pressure is in the green while I taxi and at takeoff power.  once I level off I notice that the pressure starts to come down.  In cruise I see roughly 55psi indicated at 24 squared.  My oil temp is in the 180s per analog and JPI 700 gauges.  I know that the vernatherm should be operating around roughly 180 to allow oil to flow to the cooler. The cooler was overhauled in 2011 before I owned it.  The pressure relief valve has 6 washers (9 max per IPC) under it.  I added a 7th washer but was seeing 115psi cold at 1500rpm. I did not want to go any hiring with the rpm. I opted to take out the 7th washer.  I am going to remove oil cooler and flush out and see if that helps.  Does anyone have any ideas on why the pressure drops like that? 

 

 

I don’t have any help solving, but I’d say most of us with an io-360 see ~75psi in cruise.  The higher pressures with cold oil are normal, but not your cruise pressure.  The only time I see that low (55psi) is after landing - hot oil and 1000rpm.  This sounds like more than just what type oil you’re using…

  • Like 1
Posted

Back when I was chasing OP issues in climb / cruise before my engine overhaul, seems like I remember a higher OP with single weight oil than multi weight oil particularly when the OAT was hot in the summer.  But I live in SOCAL.  DIdn't have to deal with winter.  Would be interesting to see the result with multi-weight in this airplane in the winter.  I'm no expert though.  Just curious how this will be resolved.  I chased it for years with a very experienced mechanic.  

Posted

Preheat oil to at least 60 degrees or so before cold starting.   You’re in NJ in winter.  That’s a must for straight weight oil.  You need to do that and also take washers out until 75-80psi in cruise at operating temp.  You may need to let oil warm to 150 or 160 before take off.  Straight weight is not as versatile as multi grade.  

Posted
19 minutes ago, Pinecone said:

A 20W-50 multi weight oil is the same viscosity when hot as a straight 50 weight.

Cold, it is the same a cold straight 20 weight.

 

Theoretically.   I think I'd like to see a comparison plot.  Viscosity vs. temp over the range of operation and over the life of the oil.  I'll bet there's something out there somewhere like that.  I'm sure I've consistently gotten higher OPs when hot with single weight over the last 20 years and on two different engines (but that's operating in SOCAL mostly).  

Posted

That is the definition.  Yes, it is when the oil is new.

Synthetic oils are naturally multi viscosity, as the viscosity by weight is based on regular oils.

Non-synthetic multi viscosity oil use viscosity improvers.  They are molecules that change from small to larger with temperature.  So as they get warm, the viscosity increases.

These do get sheared and stop working over time.  But in aircraft, we tend to change the oil much more frequently that cars, so not a huge problem.

Posted
21 minutes ago, Pinecone said:

That is the definition.  Yes, it is when the oil is new.

Synthetic oils are naturally multi viscosity, as the viscosity by weight is based on regular oils.

Non-synthetic multi viscosity oil use viscosity improvers.  They are molecules that change from small to larger with temperature.  So as they get warm, the viscosity increases.

These do get sheared and stop working over time.  But in aircraft, we tend to change the oil much more frequently that cars, so not a huge problem.

It's always seemed to be a bit too miraculous for me.  The miracle of chemistry.  That's why I'd like to see a plot with tons of data; wonder if there are operating ranges where the two diverge some.  I'm sure it's been done but then there's marketing too.  

Posted

The rating is for two temperatures.  All oils get thicker when colder and thinner with hotter.  The question is how much.  Full synthetics don't get really thick until stupid low temps.

So yes, the curves will diverge.  But LOTS of data out there on multi viscosity oils.

If you do oil analysis, you can get data on the actual viscosity at the two temps for your used oil.

  • Like 1

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