Checkout_my_Six
Touchdown! Greaser!
I’d prolly run a thermal couple wire to the cooler and get the temp of the cooler. Also verify there are no restrictions in air flow in and out of the cowling.
1975 Cessna 172M - Lycoming O-320-E2D - Calling all A&P Types
- Thread starter Jon Wilder
- Start date
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 11,360
- Display Name
Display name:
Dan Thomas
Check the baffling at the rear of the engine on the right side, the area that has the outlet for the oil cooler SCAT hose. If that baffle isn't up against the cylinder and curling down around it tightly, with a wire between the bottom of it and the bottom of the baffle around the front of the front cylinder to pull them in close, you get extra airflow past that cooler outlet hole that can cost you all the pressure differential in that area and the cooler gets little or no flow. Make sure, too, the the intercylinder baffles are present between the cylinders and heads on that side.
That rear cylinder (#3) tends to run hot due to the airflow to the cooler, as well.
The 182 had its cooler up front because that's how Continental did things. Lycoming had other ideas.
I cannot see that the viscosity valve would cool any better than the Vernatherm, if the Vernatherm is operating properly. And if it's not getting tested, you're not at a loss yet.
How old are those oil cooler hoses? They don't last forever, and the liner can break down and start causing restrictions.
Jon Wilder
Pre-takeoff checklist
Thank you for that. Think the Vernatherm will be the next thing I have checked. Will also have them check the baffles on the right side and the cooler lines while they're in there.
Last edited:
readytocopy995
Pre-takeoff checklist
did you have the HE cooler? or the old one
Jon Wilder
Pre-takeoff checklist
I'm sure the old one. Not the Aero Classics HE replacement.It's the original Stewart Warner 8406E cooler that came with the plane.
Which brings me to the next question. Does anyone know the difference between the Stewart Warner 8406E and 8406R part numbers?
I also noticed that Aero Classics makes two replacements for the SW 8406R cooler. One is 6" long while the other is 8" long. Would either of these be approved on a 172M?
readytocopy995
Pre-takeoff checklist
I'm not sure what is the difference between the E/R. Maybe others would know. What I do know is that there is a significant difference between the old version and the HE. I used to fly the plane a lot with the old cooler and it was a constant worry about monitoring temps, leveling off, speeding up (as much as you can in a 172M). New cooler I can grab the plane on a hot day and it's never even a concern. The old/new are quite different.
https://baspartsales.com/8406e-use-8406r-cessna-172m-lycoming-o-320-e2d-stewart-warner-oil-cooler/
vs
https://www.mcfarlaneaviation.com/products/product/8001733/
I just went through trying to sort out high oil temps in my Titan x-340 (lycoming clone).
After ruling out many possible causes of elevated oil temps:
Faulty gauge/sensor - tested and confirmed accurate
Varnished/clogged oil cooler - replaced with new oil cooler
Excessive blow by - top overhaul
Timing too advanced - checked and confirmed accurate
Too lean - no changes even with full rich climbs
Leaking baffles - baffles checked with light and leaks fixed including wiring under cylinder baffle plates left unsecured by A&P who reinstalled cylinders after OH.
Faulty vernatherm - vernatherm replaced
My high oil temps persisted.
I read about changing to a viscosity valve.
Installed an oil viscosity valve and spring; oil temps dropped 20 degrees or more (both in max and cruise temps).
Lycoming Oil Cooler Bypass Spring, PN 69436
Lycoming oil cooler bypass plunger, PN 62415
New plug gasket PN MS35769-11
With the viscosity valve oil is routed to the cooler at startup as long as the oil isn't too thick from cold ambient temp. With the vernatherm oil bypasses the cooler until the vernatherm temp set point. With the viscosity valve oil stays much cooler through the climb. CHT's stayed 20+ degrees cooler in the climb also.
In the winter, it may result in too cool oil temps which may require taping off some of the cooler or a manual valve to limit oil flow to the cooler.
In my installation, I didn't even need to remove the vernatherm as it didn't interfere with the plunger seat.
More info here: https://vansairforce.net/community/showthread.php?t=45548&highlight=Lycoming+viscosity+valve&page=2
Of course this applies to an experimental with Lycoming; not sure if continental has a similar option or how a modification would be done in the certified world.
After ruling out many possible causes of elevated oil temps:
Faulty gauge/sensor - tested and confirmed accurate
Varnished/clogged oil cooler - replaced with new oil cooler
Excessive blow by - top overhaul
Timing too advanced - checked and confirmed accurate
Too lean - no changes even with full rich climbs
Leaking baffles - baffles checked with light and leaks fixed including wiring under cylinder baffle plates left unsecured by A&P who reinstalled cylinders after OH.
Faulty vernatherm - vernatherm replaced
My high oil temps persisted.
I read about changing to a viscosity valve.
Installed an oil viscosity valve and spring; oil temps dropped 20 degrees or more (both in max and cruise temps).
Lycoming Oil Cooler Bypass Spring, PN 69436
Lycoming oil cooler bypass plunger, PN 62415
New plug gasket PN MS35769-11
With the viscosity valve oil is routed to the cooler at startup as long as the oil isn't too thick from cold ambient temp. With the vernatherm oil bypasses the cooler until the vernatherm temp set point. With the viscosity valve oil stays much cooler through the climb. CHT's stayed 20+ degrees cooler in the climb also.
In the winter, it may result in too cool oil temps which may require taping off some of the cooler or a manual valve to limit oil flow to the cooler.
In my installation, I didn't even need to remove the vernatherm as it didn't interfere with the plunger seat.
More info here: https://vansairforce.net/community/showthread.php?t=45548&highlight=Lycoming+viscosity+valve&page=2
Of course this applies to an experimental with Lycoming; not sure if continental has a similar option or how a modification would be done in the certified world.
Last edited:
Jon Wilder
Pre-takeoff checklist
The engine in question is a Lycoming O-320-E2D. According to the service manual for this aircraft, our aircraft serial number AND engine serial number actually had a viscosity valve originally. The text in the 1969-1976 172 And Skyhawk Series Service Manual reads -
Both our aircraft and engine fall within these serial number ranges.
So at some point, they superseded the Vernatherm with a spring and plunger type (viscosity valve) bypass.
This tells me that they went to a smaller cooler (probably to save a few pennies), and the unit and design were small enough to require the oil to flow through the cooler 100% of the time to provide adequate cooling performance, and thus installed the viscosity valve on these aircraft/engines...again saving a few pennies.
Keep in mind these engines were also approved to run 80/87 octane avgas. This may have also had something to do with that change as well.
Which makes me wonder if...with this oil cooler and cooling air arrangement, if the Vernatherm is a bad idea all around, thus making the conversion to a viscosity valve the way we fix this issue.
One can argue that Lycoming issued a service instruction to convert these engines to a Vernatherm. But Lycoming has no way of knowing what oil cooling arrangement the aircraft manufacturer sets them up with. Thus while the Vernatherm has been approved on these engines, Lycoming cannot approve this on these engines on this aircraft. That would require a joint approval from Cessna I would think, of which I've seen no such thing for this variation of 172.
We're also running an Electroair EIS-41000 high energy variable advance electronic ignition system in place of the left magneto. This will raise CHT 20-30°, thus again, I feel, requiring we address this cooling issue ASAP if we're going to keep running this ignition system on this aircraft.
Jon
I'm not familiar with the accessory case mounting in your engine, but if it's like mine with a non-interference fit between vernatherm and viscosity valve it's a super easy install. I took about 15 minutes to install my viscosity valve. It was inexpensive. Result in cooling was immediate and significant.
A larger oil cooler would be preferential if that is a viable alternative, but if not I wouldn't hesitate to install the viscosity valve.
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 11,360
- Display Name
Display name:
Dan Thomas
We had 172s in that serial number range, and all had the Vernatherms. When we ordered engines from Lycoming we had to provide aircraft serial numbers. They sent us Vernatherm engines.
The TCDS lists the O-320-E2D engine for those airplanes. It makes no mention of viscosity valves in any airplanes, and the engine model number hints at no legal difference.
The Lycoming parts manual for these engines, direct from Lycoming, shows the viscosity valve, but not for the -E2D engine. Parts 23-24-25-26:
Parts #8 is the Vernatherm.
It appears that the Vernatherm is installed in all engines, and the viscosity valve is in addition to it in some engines, not a replacement for it.
Last edited:
Jon Wilder
Pre-takeoff checklist
We were looking at that first sheet as well, and did realize that Lycoming did not spec parts for the viscosity bypass on the E2D. Yet this seems to be in conflict with the Cessna 1969-1976 172 and Skyhawk Series Service Manual.
This is the exact oil filter setup on our E2D. This page was found directly under the Engine section for the Lycoming "Blue Streak" engine, which is the E2D variant of the O-320.
While Lycoming may very well supply these engines with a Vernatherm, this appears to have been a Cessna change. This is what I'm trying to get behind. Why did Cessna do this, and was this something they did in order to make the remote mount 8406 oil coolers work on this engine?
This is the exact oil filter setup on our E2D. This page was found directly under the Engine section for the Lycoming "Blue Streak" engine, which is the E2D variant of the O-320.
While Lycoming may very well supply these engines with a Vernatherm, this appears to have been a Cessna change. This is what I'm trying to get behind. Why did Cessna do this, and was this something they did in order to make the remote mount 8406 oil coolers work on this engine?
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 11,360
- Display Name
Display name:
Dan Thomas
This implies that a spring and plunger are installed in the Vernatherm cavity instead of the Vernatherm, and the L-30414 engines and on have the spring and plunger in the accessory case, not in the filter adapter or screen housing. In that case, the Vernatherm's bypass port would need blanking off or the bypass would still be wide open.
Note again the position of the spring and plunger in the upper left of the accessory case in that catalog picture I posted.
Jon Wilder
Pre-takeoff checklist
Yes the viscosity bypass would install in the accessory case on ours as our engine serial number is after the published start serial number.
Interestingly, there's just a threaded plug in the accessory case where the viscosity bypass would go, and the Vernatherm is installed in the oil filter housing.
Would that mean the upper bypass is supposed to be blocked off if a Vernatherm is installed? Because there is currently nothing installed underneath the plug.
Interestingly, there's just a threaded plug in the accessory case where the viscosity bypass would go, and the Vernatherm is installed in the oil filter housing.
Would that mean the upper bypass is supposed to be blocked off if a Vernatherm is installed? Because there is currently nothing installed underneath the plug.
It might be worth reading Lycoming SI 1008C. The way I've always interpreted it is that you install the vernatherm or the viscosity valve, not both. Every engine I've worked on has been that way as well.
Jon Wilder
Pre-takeoff checklist
So I have looked at that service instruction. That one shows engines that use the pressure screen in place of the full flow oil filter. It does not show Lycomings with the full flow oil filter. And again...while the Vernatherm is "approved for use" on this particular engine, Lycoming has no way to know what sort of cooling system the aircraft manufacturer is adapting to it, thus have no way of knowing if installing a component that allows for preheating the oil is going to be safe given the particular oil cooler that the aircraft manufacturer has adapted to the engine. Thus I would think the aircraft manufacturer's service literature would supersede any sort of "optional" service instruction that Lycoming approves for their engines that would in any way be affected by someting within the scope of control of the aircraft manufacturer (i.e. oil cooling system performance for instance, which Lycoming has no control over).
But I do interpret it the same...install one or the other.
Here is the same oil filter housing shown in the 1975 parts catalog. Our aircraft falls right within the published serial number range. Where the Vernatherm would go, it's calling out a plug, part number S2259-1 (part number 11 in the diagram). I'm not sure if this is just a hex bolt plug or maybe a plug shaped just like a Vernatherm, but with no moving parts and meant to plug off that whole entire part of the housing. I'm not sure as I cannot seem to find a photo of this part anywhere. If someone happens to have a plug p/n S2259-1 and can take a picture of it and post it, it would be greatly appreciated.
Last edited: