Ineffective Oil Cooler on O-200

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Skippydiesel

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Its main purpose is to close the bypass, not open it.
Ha ha! - chicken or egg statement.
The bypass closes off the oil flow to the cooler, when the engine/oil goes below a pre set temperature.
In the real world this will usually mean its closed on the first start of the day or after any period of sufficient shut/cool down, only opening when the oil temp gets up to the preset level.
There may also be a partial or total shut down during a prolonged low/nil power decent.
 

Dan Thomas

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Ha ha! - chicken or egg statement.
The bypass closes off the oil flow to the cooler, when the engine/oil goes below a pre set temperature.
In the real world this will usually mean its closed on the first start of the day or after any period of sufficient shut/cool down, only opening when the oil temp gets up to the preset level.
There may also be a partial or total shut down during a prolonged low/nil power decent.
The bypass does not shut off the flow to the cooler. There is no shutoff. The oil is free to go through both the cooler and the bypass if it wants. The vernatherm is ONLY CLOSING THE BYPASS HOLE. It has no effect on either the oil to the cooler or from the cooler. Only the increased viscosity of the oil when cold discourages flow through the cooler, and that's it.

I don't know what's so hard to understand about this. I get a bit annoyed when PPLs try to educate experienced aircraft mechanics.

Furthermore, this thread is about an O-200, which uses only a relief valve that opens under increased pressure to bypass the oil cooler. It is not temperature-sensitive like the Lycoming's vernatherm. From the O-200 overhaul manual:

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TiPi

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in simple terms, the oil cooler bypass valve acts as a relief valve to limit the pressure drop across the oil cooler. When the pressure difference from oil cooler inlet to outlet exceeds the set pressure of the valve, it starts to open and allows oil to bypass the oil cooler by releasing it directly from the oil cooler inlet to the outlet side. As soon as the pressure difference is below the set pressure (low rpm, increased temperature), the oil is forced through the cooler. The viscosity (temp dependent) and volume (rpm dependent) create the pressure drop across the oil cooler.
 

Skippydiesel

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My apologies Dan it would seem that this particular engine uses pressure, which is of course related to viscosity AND temperature, to activate the by-pass.
You are correct - I had no idea.
I do wonder though, if this difference actually translates into a real world operation difference ie One opens/closes on temperature, which is related to pressure & viscosity. The other opens/closes under pressure which is related to temperature & viscosity.
 

Dana

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The simple bypass valve lets oil bypass the cooler when oil in the cooler (for the most part) is too cold, mostly at startup. The Vernatherm, OTOH, operates based on the temperature of the oil in the engine.

How accurately does the vernatherm control the temperature? I gather it's nowhere near as tightly controlled as an automotive thermostat. I ask because I don't have one on my Lycoming; supposedly it can't be used with the retrofit oil cooler adapter which sandwiches between the accessory case and the pressure screen housing. Instead I play the game with strips of tape as the weather changes, though I'm thinking about a cockpit controllable shutter.
 

Skippydiesel

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The simple bypass valve lets oil bypass the cooler when oil in the cooler (for the most part) is too cold, mostly at startup.
So, going by what you say, if the oil cooler oil stays cold, when & how does the system (oil cooler) start to let oil enter it ?

How accurately does the vernatherm control the temperature? I gather it's nowhere near as tightly controlled as an automotive thermostat. I ask because I don't have one on my Lycoming; supposedly it can't be used with the retrofit oil cooler adapter which sandwiches between the accessory case and the pressure screen housing. Instead I play the game with strips of tape as the weather changes, though I'm thinking about a cockpit controllable shutter.
Many an Australian Rotax uses the very same, highly sophisticated/costly method, for seasonal "tuning" of the oil cooler (& sometimes the liquid cooling as well) system. Its cheap, relatively easy, almost full proof, as long as you remember to remove all or part, as the weather warm up.
 

TiPi

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There is always some oil going through the cooler, whatever the pressure difference can push through at that viscosity.
I removed the thermostat on my Rotax as it made no difference to the warm-up time and control the temp with partially blocking the oil cooler.
 

Dan Thomas

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So, going by what you say, if the oil cooler oil stays cold, when & how does the system (oil cooler) start to let oil enter it ?
Thick oill still moves. It's not concrete. The cooler is gradually flushed of the cold stuff.

Viscosity and temperature are linked, but a thermostat doesn't know the difference between Aviation 100 and Aviation 60 oils, or between multigrades or single-weights. Like Dana says, it gets the oil temp up sooner by letting the oil bypass the cooler.
 

Skippydiesel

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Thick oill still moves. It's not concrete. The cooler is gradually flushed of the cold stuff.

Viscosity and temperature are linked, but a thermostat doesn't know the difference between Aviation 100 and Aviation 60 oils, or between multigrades or single-weights. Like Dana says, it gets the oil temp up sooner by letting the oil bypass the cooler.
So you agree with my origional premise - the oil/cooler bypass, is primarily to speed engine warm up. If the bypass "thermostat doesn't know the difference between Aviation 100 and Aviation 60 oils" its primary function can not be to avoid over pressurising the oil cooler.
 

Dana

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The simple bypass valve does two things: it speeds warm-up by bypassing the cooler, and it protects the cooler by bypassing it if it's clogged.

The vernatherm takes it one step further by providing some temperature based control.
 

Dan Thomas

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So you agree with my origional premise - the oil/cooler bypass, is primarily to speed engine warm up. If the bypass "thermostat doesn't know the difference between Aviation 100 and Aviation 60 oils" its primary function can not be to avoid over pressurising the oil cooler.
If you go back you will see that I said that it does not protect the cooler from overpressure. The cooler is plumbed into the system no matter what, and if the oil in the engine galleries is stiff, there will be a pressure spike. It DOES prevent cooler overpressure by allowing the oil to bypass the stiff oil in the cooler. If there was no bypass, the cooler could suffer.
 

Skippydiesel

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Full disclosure; I have not had experience with crankcase oils that do what you suggest "if the oil in the engine galleries is stiff, there will be a pressure spike" Due to winter operating strategies, my two winters, working on a farm in S Alberta, did not have this problem.
Dan - In the Engine Oil Design conversation, you show crankcase oil recommendation charts, from Lycoming & Continental - they both have 20-50 oils & Continental also recommend's 15-50 oils. Are you telling me that a 15-50 will be so "stiff" on start up, it could do damage within the oil reticulation system or somehow block the oil cooler with , with similar results?
Is it not usual, that for extremely cold weather operations, aircraft engines (just like car/truck/tractor) would be prewarmed by some external method?
 

TFF

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Skippy, when you talk about Continentals, you must take the whole history not just a 550 in a SR-22. 15-50 only counts for certain applications and time frame. Fly in Alaska, North Dakota, and Canada and 15-50 can be rock hard.

Traditional airplane engines, the oil cooler sees the same oil pressure as the bypass. The bypass is path of least resistance so warmer and warmer oil will circulate. The cooler sees warm oil bleed into it slowly until the Vernitherm senses it’s warm enough and shuts the bypass. All the oil going through the cooler then.

I know someone who had an engine OH done. Continental sent a different dash number. Correct but not the same. It ended up with two Vernitherms. When warmed up the second one when it closed, shut all the oil pressure off as the second bypass would have been the cooler path.
 

Dan Thomas

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Full disclosure; I have not had experience with crankcase oils that do what you suggest "if the oil in the engine galleries is stiff, there will be a pressure spike" Due to winter operating strategies, my two winters, working on a farm in S Alberta, did not have this problem.
Dan - In the Engine Oil Design conversation, you show crankcase oil recommendation charts, from Lycoming & Continental - they both have 20-50 oils & Continental also recommend's 15-50 oils. Are you telling me that a 15-50 will be so "stiff" on start up, it could do damage within the oil reticulation system or somehow block the oil cooler with , with similar results?
Is it not usual, that for extremely cold weather operations, aircraft engines (just like car/truck/tractor) would be prewarmed by some external method?
Some operators will use a straight-weight like 80 and don't preheat on a cold morning. Now that oil is stuff. In some engines the oil system's pressure-regulating relief valve is at the end of all the galleries, and if those galleries are full of stiff oil you can get a pressure spike on startup as that stiff oil doesn't get moving inatantly. Your car's pressure relief is at the pump. Comparing airplane engines to car engines is always a big mistake, since the aircraft engine's design and operating environment are vastly different.

You have much to learn, but if you think you already have it all figured out, you will not learn it.
 

Toobuilder

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The simple bypass valve does two things: it speeds warm-up by bypassing the cooler, and it protects the cooler by bypassing it if it's clogged.

The vernatherm takes it one step further by providing some temperature based control.

I've lost the bubble on whether we are talking about Lycomings or Continentals, but in a Lycoming equipped with a cooler the two schemes are a "viscosity valve" and the Vernatherm. The viscosity valve is a spring loaded piston that closes the oil cooler bypass port and "always"directs all oil through the cooler "unless" the oil is so congealed that the delta p lifts the piston, uncovers the bypass and allows oil to go right back to the engine. This can set up a situation where the engine oil continues to heat up (high power take off) and the oil cooler turns into an ice cube because of freezing airflow and no oil flow, and results in an oil temp runaway. The Vernatherm, OTOH, lives in a flow of engine heated oil and at a certain tempreature, a wax pellet actuator extends and pushes a piston against a seat to seal off the easy return path to the engine and force the hot oil through the cooler. In addition, the piston is acting with a spring so in case of oil cooler blockage the piston will lift and bypass the cooler (despite the wax pellet commanding otherwise).

The quality of the piston/seat seal in the Vernatherm determines how effective a Lycoming cools. Some are great, some are garbage. OTOH, the older, "obsolete" viscosity valve almost always provides a very tight seal and will instantly "fix" many Lycoming high oil temp issues. This is why I install a viscosity valve for Summer ops in the Rocket. It is extremely effective in maximizing oil cooler effectiveness.
 
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Dan Thomas

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The Vernatherm has a steel cone that just seats in a hole in the aluminum casting. Nothing fancy at all.
 

Skippydiesel

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Some operators will use a straight-weight like 80 and don't preheat on a cold morning. Now that oil is stuff. In some engines the oil system's pressure-regulating relief valve is at the end of all the galleries, and if those galleries are full of stiff oil you can get a pressure spike on startup as that stiff oil doesn't get moving inatantly. Your car's pressure relief is at the pump. Comparing airplane engines to car engines is always a big mistake, since the aircraft engine's design and operating environment are vastly different.

You have much to learn, but if you think you already have it all figured out, you will not learn it.
You seem to have a "wriggle" statement for all occasions -
"Some operators will use a straight-weight like 80 and don't preheat on a cold morning."
First what constitutes a "cold morning"?
"don't preheat on a cold morning" - -45C why would you not preheat?
Then "some operators" - some operators probably don't get their engines serviced, does this mean that LyCon design an engine & its operating liquids to accommodate aberrant behaviour? - I would suggest not.
So why use an oil that has characteristics that may, under "some" management conditions cause a problem, when perfectly good alternative oils (multi viscosities) are available.
Given the range & peculiarities, of human behaviour, I am sure your argument is valid "some" of the time.
"Comparing aeroplane engines to car engines is always a big mistake" - I would suggest, only to those who insist on retaining obsolete concepts/technologies. In saying this I am not trying to overlook/minimise the difference in operating environment & expectations, what I am alluding to is the potential for shared technology & design (You referred to aircraft hydraulic tappets being adopted by automotive engineers, Liquid cooling has been around pretty much for ever. Did not the Germans have diesel aircraft engines in WW2., Overhead cams, May be oil technology? Rotax 9'setc etc)
 
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