Removing vernatherm M20J

[redbaron1982]

Hey guys,

I have a low oil temp issue (engine is not running cold, like 380F) and OAT is 26C (hot Houston summer). Oil temp at cruise is 140F (at 25in/2500RPM).

I want to take out the vernatherm to see if it is stuck open. I've read the maintenance manual for Lycoming IO 360, and I think everything is pretty straightforward.

My only doubt is, do I need to drain the oil? When I removed the pressure relief valve, I did not and everything was fine. But the Vernatherm is closer to the oil filter and I'm not sure if I'm going to get a bunch of oil when I remove it.

[Fritz1]

Are you sure it is not the oil temp gauge? 

[redbaron1982]

10 minutes ago, Fritz1 said:

Are you sure it is not the oil temp gauge? 

I'm quite sure. Before starting it reads same value as OAT. During climb it gets to 180F or 190F. I mean, values look reasonable. 

[N201MKTurbo]

The vernatherm is well above the oil level, you can just remove it at any time. Just cut the lock wire and unscrew it. 
 

I’ve never heard of this problem. It is always the other way around. High oil temp. I can’t think of a failure mechanism that would leave the vernatherm fully extended all the time. 
 

I have the old one from my engine rebuild, I could send it to you. It was working fine. You could install it and go fly and see if it changed anything.
 

I’m curious to hear the outcome. 

[RoundTwo]

Following as I too have “lowish” oil temps but agree that a failed vernatherm normally equates to an hot engine, not cold. 

[A64Pilot]

I think all J’s run low oil temp, mine does.

However a vernatherm works just opposite of what we are used to with car thermostats, when cold the vernatherm is “open” as in retracted that allows oil to flow through the cooler and bypass it both, when oil gets above set point the vernatherm “closes” that is it gets longer and blocks the oil passage that oil bypasses the cooler and all, flow is therefore through the cooler. It’s for this reason in real cold Wx that you have to block airflow through the cooler, because no matter how cold it gets there is some flow through the cooler.

If you do oil analysis it should tell you moisture content, if your content is normal I don’t think you have any problem.

 

[redbaron1982]

Is not possible for the vernatherm to be locked in the "closed" position? That is my thought.

I know it works opposite to car thermostats.

[N201MKTurbo]

1 hour ago, redbaron1982 said:

Is not possible for the vernatherm to be locked in the "closed" position? That is my thought.

I know it works opposite to car thermostats.

Never say never, I just can’t think of how it could happen. 
 

http://acversailles.free.fr/documentation/08~Documentation_Generale_M_Suire/Moteur/Circuit_d'huile/Valve_thermostatique/Anatomy_of_a_Vernatherm.pdf

https://www.vernet-group.com/wp-content/uploads/2019/12/vernatherm_catalog.pdf
 

[redbaron1982]

10 hours ago, N201MKTurbo said:

The vernatherm is well above the oil level, you can just remove it at any time. Just cut the lock wire and unscrew it. 
 

I’ve never heard of this problem. It is always the other way around. High oil temp. I can’t think of a failure mechanism that would leave the vernatherm fully extended all the time. 
 

I have the old one from my engine rebuild, I could send it to you. It was working fine. You could install it and go fly and see if it changed anything.
 

I’m curious to hear the outcome. 

Hey, thanks for the offer! I will start by taking mine out, inspecting it, testing it in hot water to make sure it opens and close fine. If everything seems ok, I will reinstall it and try to find anything else.

FWIW my last, first, and only oil analysis since I owned the airplane has detected 0 water.

[Utah20Gflyer]

Make sure to verify the right part # is installed.   I don’t have any real reason to suggest this other than sometimes the wrong part won’t produce the right result.  

[0TreeLemur]

26 minutes ago, redbaron1982 said:

testing it in hot water

Manufacturer's instructions are to test using a hot oil bath.

[A64Pilot]

On 9/22/2023 at 12:49 PM, 0TreeLemur said:

Manufacturer's instructions are to test using a hot oil bath.

I’ve seen them tested in an oven too. I don’t think water will harm one but who knows?

 

 

[RoundTwo]

On 9/22/2023 at 12:22 PM, redbaron1982 said:

Hey, thanks for the offer! I will start by taking mine out, inspecting it, testing it in hot water to make sure it opens and close fine. If everything seems ok, I will reinstall it and try to find anything else.

FWIW my last, first, and only oil analysis since I owned the airplane has detected 0 water.

I’m assuming by now you’ve worked through your cool oil temps. Have you come to any conclusions?