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Vernatherm required or not?

DavePlaneGrips

Well Known Member
I'm trying to figure out exactly what I need to swap my oil screen for a oil filter. So far I have a 204418-155 filter adapter. But the lycoming oil filter kit pdf talks about installations where there is no "thermostatic bypass valve" which I take is the vernatherm.

Is a vernatherm required?

What else do I need other than the filter adapter, gasket, and vernatherm (if required)? I'm not sure I know what plugs into this other port on the adapter.
 
I'm trying to figure out exactly what I need to swap my oil screen for a oil filter. So far I have a 204418-155 filter adapter. But the lycoming oil filter kit pdf talks about installations where there is no "thermostatic bypass valve" which I take is the vernatherm.

Is a vernatherm required?

What else do I need other than the filter adapter, gasket, and vernatherm (if required)? I'm not sure I know what plugs into this other port on the adapter.

Vernatherm is not strictly required with that filter adapter. The alternate plan is to install a remotely operated ball valve in one of the oil cooler lines, and keep your "viscosity valve", the spring and piston typically installed as a companion to the screen adapter.

In this scheme, cold oil (high viscosity) will force the piston, compressing the spring, and allowing most oil to bypass the cooler path. Same thing happens when you close the ball valve. So, it's manual control of oil temperature. Take off with the ball valve open, and close it down later to hold temps up if needed.

The other threaded hole is for an oil temperature sender.
 
This is what I found:

Lycoming Engines were originally equipped with a bypass valve which was controlled by a spring. Referred to as a spring and plunger type, it functioned as a result of the amount of pressure in the oil system. The spring-controlled bypass system was superseded by a system controlled by a Thermostatic Oil Cooler Bypass which reacts to oil temperature changes.

Lycoming referred to this as a viscosity valve. It basically bypassed cold, thick oil back to the engine before going through the oil cooler. When the oil warmed up, and was therefore less viscous, the valve closed due to lower pressure, and allowed the oil to circulate through the oil cooler. The Vernatherm replaced the viscosity valve and did the same basic thing, except the bypass was based on temperature, rather than viscosity, which was the real reason you want to bypass the cooler anyway. However, on my ECI O-360 engine on my first RV8, I had a 90* oil filter adapter, with a vernatherm opening machined in to it. The four attach bolt holes for the adapter were noticeably larger than required for the longer than normal 1/4” bolts. This made alignment of the adapter slightly variable. This variation made the exact alignment of the vernatherm very imprecise. My vernatherm was only contacting it’s seat in the adapter on about 66% of it’s circumference, which allowed some of the oil to continue to bypass the cooler, even when warmed up. I removed the vernatherm, and installed the ‘viscosity valve’ that I purchased from Lycoming (~$30.00). This one thing lowered my cruise oil temperature about 12*.

The viscosity valve assembly mounts in a machined opening in the accessory case near the oil cooler. It has a hex plug in it typically, and is mounted vertically. Very simple, poppet type plunger and spring. Remove the hex plug, insert the valve/spring assembly, re-install the hex plug.

Worked for me. I think I still have that vernatherm somewhere if you need one. Nothing wrong with it probably. Just a misaligned oil filter adapter. I’m no expert, so you should research this if you decide to do something similar.

After doing is little more research, it looks like the ‘viscosity valve’ bypasses the oil cooler, but also bypassed the oil filter. The vernatherm allows oil cooler bypassed oil to continue to flow through the oil filter. My 90* adapter issue bypassed the oil cooler, but still allowed the oil to be filtered all the time. My problem was higher than desired oil temperature because of incomplete vernatherm bypass valve seating.
 
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Vernatherm is not strictly required with that filter adapter. The alternate plan is to install a remotely operated ball valve in one of the oil cooler lines, and keep your "viscosity valve", the spring and piston typically installed as a companion to the screen adapter.

In this scheme, cold oil (high viscosity) will force the piston, compressing the spring, and allowing most oil to bypass the cooler path. Same thing happens when you close the ball valve. So, it's manual control of oil temperature. Take off with the ball valve open, and close it down later to hold temps up if needed.

The other threaded hole is for an oil temperature sender.

Thanks for the explanation, I think I see where the viscosity valve is (circled in the pic).

2RzYAAc.png


I'd like to avoid managing another control if I don't have to though.

I just found your annotated photos of the oil system, quite a help thanks.

This is what I found:

Lycoming Engines were originally equipped with a bypass valve which was controlled by a spring. Referred to as a spring and plunger type, it functioned as a result of the amount of pressure in the oil system. The spring-controlled bypass system was superseded by a system controlled by a Thermostatic Oil Cooler Bypass which reacts to oil temperature changes.

Lycoming referred to this as a viscosity valve. It basically bypassed cold, thick oil back to the engine before going through the oil cooler. When the oil warmed up, and was therefore less viscous, the valve closed due to lower pressure, and allowed the oil to circulate through the oil cooler. The Vernatherm replaced the viscosity valve and did the same basic thing, except the bypass was based on temperature, rather than viscosity, which was the real reason you want to bypass the cooler anyway. However, on my ECI O-360 engine on my first RV8, I had a 90* oil filter adapter, with a vernatherm opening machined in to it. The four attach bolt holes for the adapter were noticeably larger than required for the longer than normal 1/4” bolts. This made alignment of the adapter slightly variable. This variation made the exact alignment of the vernatherm very imprecise. My vernatherm was only contacting it’s seat in the adapter on about 66% of it’s circumference, which allowed some of the oil to continue to bypass the cooler, even when warmed up. I removed the vernatherm, and installed the ‘viscosity valve’ that I purchased from Lycoming (~$30.00). This one thing lowered my cruise oil temperature about 12*.

The viscosity valve assembly mounts in a machined opening in the accessory case near the oil cooler. It has a hex plug in it typically, and is mounted vertically. Very simple, poppet type plunger and spring. Remove the hex plug, insert the valve/spring assembly, re-install the hex plug.

Worked for me. I think I still have that vernatherm somewhere if you need one. Nothing wrong with it probably. Just a misaligned oil filter adapter. I’m no expert, so you should research this if you decide to do something similar.

After doing is little more research, it looks like the ‘viscosity valve’ bypasses the oil cooler, but also bypassed the oil filter. The vernatherm allows oil cooler bypassed oil to continue to flow through the oil filter. My 90* adapter issue bypassed the oil cooler, but still allowed the oil to be filtered all the time. My problem was higher than desired oil temperature because of incomplete vernatherm bypass valve seating.

Interesting thanks for info. I don't know exactly how these work but looking at the adapter can the Vernatherm hole just be capped? Is there a way I can use the adapter and stick with viscosity valve?

I'd be interested in a vernatherm too since that seems to be the standard installation, I'm ready to move on from figuring out my oil filter situation. Sent a PM with my info.
 
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After doing is little more research, it looks like the ‘viscosity valve’ bypasses the oil cooler, but also bypassed the oil filter.

No. All flows pass through the filter, unless the filter restriction becomes high enough to force open the filter bypass, a different component separate from the vernatherm or viscosity valve.

Thanks for the explanation, I think I see where the viscosity valve is (circled in the pic).

Correct. Should be a spring and piston under that cap. Remove them if you install a vernatherm.

Interesting thanks for info. I don't know exactly how these work but looking at the adapter can the Vernatherm hole just be capped? Is there a way I can use the adapter and stick with viscosity valve?

Yes. The best way to cap the hole is to remove the guts from an old dead vernatherm and install just the machined aluminum tube portion.

Using the viscosity valve without a ball valve to throttle oil cooler flow may result in oil temperature too low, given low OAT.
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Dave,
I answered your PM. Basically, if I still have the vernatherm, it’s yours - just pay shipping. In looking at your picture above, I think the hex plug you have circled is where the oil temp probe goes, but not sure. Your accessory case looks different than mine. I don’t see where the viscosity valve would go. I have an overhaul manual and parts manual for an O-360 at the airport, and will try to figure it out when I get back to my hangar. Your oil filter adapter should have an opening for a vernatherm. It might even have an oil temp probe opening. I’ll send you an email later and let you know what I find out. Below is pic of the viscosity valve like I bought. Mine came with a spring. It looks like ACS sells it separately now.

https://www.aircraftspruce.com/cata...qb8NTrcMiXkB_JkO-I6fDO_TUrn5GPxQaArQiEALw_wcB

A few years ago I called Larry Vetterman to talk about oil temperature control. Larry had a cockpit controlled ball valve, just like DanH mentioned above, on his RV4. He said he could control his oil temperature to within one degree, and he knew his oil temperature sweet spot for smoothest engine operation. I’m considering doing something like that on my RV4, because it’s difficult to get my oil warm enough during cooler/cold seasons.
 
I’m pretty slow on the draw here. That circled nut in your pic is about where my viscosity valve was, so I clearly don’t know what I’m talking about. But, I think I do have a vernatherm, and if I can find it, it’s yours.
 
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