How does the oil cooler work in the Comanche?

[Zacke]

Hey guys,

I wonder how the Comanche's oil cooler works exactly. Does it have a kind of a thermostat that regulates the volume flow of the oil to keep in the green? Or are there different circuits like in a car's liquid cooling system?

Thanks in advance,
Zacke

[AKar]

Lycomings usually have a thermostat that bypasses the cooler when the oil is cold. The valve closes at about 180° F, or about 80° C, causing the oil to circulate through the cooler. Comanche most certainly has one of these. An alternate design can be found in ancient installations, where the cooler bypass is of "spring and plunger" type and functions only by oil pressure, the flow bypassing the cooler when the oil pressure is high due to cold, relatively thick oil (or for any other reason).

-Esa

[Zacke]

Thanks for your fast reply.

So is the middle white mark in the oil temp gauge the temperature it tries to keep up with?

[AKar]

Well, not really...it is not like it was truly controlled system. The idea of the oil cooler bypass is just to allow for faster oil warmup (actually, the main purpose is just to provide a bypass around the oil cooler should it get clogged for some reason). When the oil is warm/hot in normal operation, it simply stays closed and the oil flows through the oil cooler. Whatever the temperature ends up to be exactly depends on the heat absorbed and actual cooling, in turn depending on the outside air temperature and airspeed, among the other factors.

In practice, in "textbook installation" the oil temperature should stay around 85°...100°C (185°...210° F), never getting below 80° C, due to oil cooler bypass opening, nor ever getting too close to the absolute limit of 120 °C, or 245 °F typically. Some installations are, in cold conditions, 'over-cooled' so that the temperature may actually be controlled by the thermostat opening and closing. The thermostat itself, which looks like this, is not adjustable.

-Esa

[Zacke]

Got it. Thx a lot!

[AKar]

No problem. If interested, this Lycoming's article makes a decent introduction on how the oil travels through these things.

-Esa

[Zacke]

Interesting reading - thx!

[guillaume78150]

Interesting reading. Thanks !

The flow of oil through a Lycoming reciprocating aircraft engine is known to be a necessary function during the operation of the engine.

Indeed !!