O-235-C1 Oil Temperature

Sector95,

At this point to help you several points need to be clarified. First as mentioned the magnetos mis-timed could be causing the problem but we did not hear if those were re-checked and verified as timed correctly. Second it was mentioned by Desert7GCBC that a laser temp prob could be used to measure engine temps at various locations. Can you or have you done this? Many A&Ps already have this tool in their tool box. Might serve you well to confirm with this tool.

Based on the fact that your CHT's are coming up as normal I still suspect that somewhere here something is obviously being missed.

Also a question here, you stated earlier that your cylinder head temps as in plural are normal, however with the style gauge you have that CHT is reading only one CHT on one cylinder and not all 4 cylinders. So what are the other 3 reading? and which cylinder is that CHT probe on?

I guess you could follow Bartmans lead here and just plunk down more $$ for the B&C oil filter but that does not get to what is really happening here.

Also Bartman shows a pic of the B&C oil adaptor from the engine facing side of the adaptor. That large cavity and threaded hole is where the vernatherm goes in this oil filter adaptor and the smaller hole is where the oil temp probe goes. As to whether there is a oil passage to that temp probe area that is a pass through allowing oil circulation, I can not say with out grabbing one from a supplier and looking at it with a good flashlight or calling B&C and finding out if there is one. If no answer is forth coming here I can assure you I will make a call to B&C and see what they have to say. There is the possibility of a design issue and it would serve us all well to get to the bottom of it if that were the case.

I will be humbled by anyone coming up with the obvious issue here if that is the case but I don't see this as a simple issue based on what has been said.

Cheers, Brian
 
Thanks Brian, trying to collect as much data as possible ahead of time that might be useful for when I meet with my mechanic.

Mag timing hasn't been re-checked yet, but it is on my list of things to re-check this week if I can get on my mechanics schedule. From what I've read though, I would expect to see lower EGT and higher CHT with a mag timing out of spec, and I don't think I'm currently seeing that.

I haven't used an infrared temp gun, mostly because by the time I'm through the pattern and back on the ground and stopped, temperatures have cooled significantly. Maybe I'm missing the intention here, am I looking for something in particular with the temp gun that's still detectible once on the ground? Would a temperature differential between cylinders still be detectible, for example? I'll drag a temp gun out there with me this week.

You are correct, I have a single CHT probe. Believe it's on number 3 right now, I think we can probably move that probe around pretty easily to see what the other cylinders are reading in-flight. It's an interesting thought, I suppose it's entirely possible a single cylinder is generating a bunch of heat and I just can't tell from where my probe is at.
 
Sector95,

The timing on both of your Mags has to be checked before you continue chasing your tail here. If they are confirmed good then you can start down this path again.

The Laser temp gun is a no brainer. Land, taxi to a clear position out of any wind if possible. Get under the cowl opening and point it at all 4 cylinders at their base closest to the engine case. Then the oil sump drain plug or the oil sump it self. Compare temps.

Do the above with the Laser temp gun, AFTER YOUR MAGNETO TIMING HAS BEEN CHECKED!!
 
Appreciate it Brian. Just want to be clear, I have already scheduled time with my mechanic this week, I just want to do as much homework as I can prior to meeting with him. His time is much less available than mine, so I'm looking for pre-work. I'll be checking mag timing with him this week.

So far on my list of things to check:
- Mag timing
- Laser temp the cylinder bases and sump temperature
- Move CHT probe to other cylinders, see if #3 is actually the hottest
- Still have oil screen installed, will be flying in one of the upcoming hot days to see if temps are the same/different as with the filter adapter

Anything else I should check prior to meeting/while with him?

I'll be sure to report back my findings, thanks again everyone, appreciate the guidance
 
Sector95,

You will not need to move the CHT probe to check other cylinder temps if the issue is found by Checking the Magneto timing or seeing it with the laser temp sensor.

Depending on the engine these single point CHT probes are put on the #3 OR #4 cylinder as they are normally the warmest.

I can not think of anything else to put on the list to check before your mechanic looks at it.

At this point I should probably reference you back to the last paragraph of my April 30 reply.

Also on a separate note, I would like to thank Bartman for being the administrator on this forum. At this point I've come to believe that he may be under appreciated.

Good Luck!

Cheers, Brian
 
While checking your mag timing is a good idea I believe you'd be seeing higher CHT (which WILL raise the temp of the oil) readings if that is the problem. How are your compressions? Any exhaust blowby getting to the crankcase? Any possible restrictions in your oiling system? If you have a vernatherm is it opening and closing all the way?
Just other things to check.

Chris
 
Met with my mechanic today, he had an appointment fall through, so he gave me a ring and I ran out to my hangar to meet him. Asked him about the mag timing, he said he didn't think that is the issue, but had no problem re-checking it for me. He even used a "flower pot" thing on the nose cone in case the markings on the ring gear were off (turns out they were not). Ultimately the mags were properly timed anyway, so check that off the list.

We started discussing everything we had already checked and things I had read and talked with you fine folks about. There's no real indication that the cylinders themselves are the issue. Compressions aren't stellar but aren't bad either, no indications of excessive blow-by, no excessive oil consumption, no indicators of any cylinders getting too hot, power is good, and other than the oil temperature, seems to be a happy engine.

We poked through the log books some more for more hints, the cylinders on this engine are no more than 500 hours old, and #1 was about half that (replaced a second time). The new baffles, the fins on the oil filter, and the blast tube to the oil filter adapter all indicate that the previous owner(s) were likely chasing this same problem. Unfortunately for me, it seems like the problem is now bad enough that I get to be the one to conclusively solve it.

The downside is, unless I there's some lingering option that we haven't covered yet, this basically leaves us with a list of problems that can only exist within the crankcase, and would ultimately require a tear-down or engine replacement. His best guess right now is something like a spun crank bearing partially blocking the oil feed, which can evidently happen when cylinders are changed. He said he was going to think on it overnight and get back to me in the AM, but I'm not getting my hopes up-- I think the engine is either going to need to be replaced or rebuilt to actually solve this issue.

Didn't get the opportunity to fly today (thunderstorms this afternoon), so no laser temperatures for you guys, but getting the sense that it might be a moot point. Started researching engine options. 😞
 
Well thanks for sharing that info and a valuable lesson for me here.

If it is in fact a spun main bearing because of a cylinder change that especially stinks because there is a remedy for preventing that from happening to begin with and involves keeping tension on the case halfs during any cylinder change.

Mike Bush from Savvy aviation has covered this topic extensively through more than one article and has made multiple comments over the years about excessive cylinder changes and or multiple cylinder changes on one engine when they in reality probably should not have been changed. It is a very extensive subject matter and there is a lot of data out there on this subject.

Although this is pretty tough info to digest, you did catch it prior to a engine failure in flight.

Sorry that happened to you. Please keep us updated on this situation.

Brian.
 
The 0-235 normal maximum temp (top of the green) is 245°F per the factory.
I realize most lycoming engines call for lower limits (210°) but according to Lycomings publications 245° is fine for normal ops and is covered with the 2400 hour TBO.
Also, if you had a spun bearing you would see glitter in the oil and you would have oil pressure problems.
When you pulled the 90° adapter was the orfice plate in place between the accessory case and the adapter? Without it the oil flows thru the accessory case too fast (which is really part of the oil cooling system) and can cause hot oil and low oil pressure!. I did this to my first AA1B and it took a while to figure out what I'd done.
The O-235 is an odd duck in several ways maintenance wise but is a great little motor. It's just a little bit different.
Chris
 
I would think a spun bearing would result in rapid failure, especially if oil was blocked from one or more connecting rod bearings (no other way for pressure oil to get there).

I too think Chris may be on the right track. My Decathlon always runs 210 or hotter, and it has for the two decades I have owned it.
 
Yeah, if the temperature was just hanging out just south of the redline I wouldn't be concerned. The issue I'm running into is I can't do any extended climb if it's warmer than 80 degrees out without hitting (and eventually exceeding) the 245 degree redline. On a 95 degree day I didn't even make it to 2k feet before redline on climbout after a full-stop taxi-back... That's borderline not flyable, particularly if I'm around any terrain :(

Orifice plate was in place, yeah. Pressures have always been solidly in the green arc, about 75 PSI.
 
How about the air movement out of the cowling? Does the cowling opening allow cooling air to get both in and out of the cowling? Remember; without an external cooler the only cooling taking place on the 235 is thru the oil moving thru the accessory case and the oil sump...if hot air if piling up at the bottom of the cowling you might need to re-work the exit with louvers or an extended lip to create a good low pressure area at the exit.
Just another something to consider.

Chris
 
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Would that manifest with higher CHT's? The lower cowling looks to me like it's totally unrestricted to me, but how would I know if it were an issue?

The only think I can think of heat wise in the lower half of the engine there is the exhaust radiating to the sump, but I figure with all the air flowing through the muffler shroud for carb and cabin heat that shouldn't really be an issue.
 
While CHT's might be affected, the cylinders have the advantage of being force-fed cooling air from the top...the sump is just sitting there dependent on the air below the baffles absorbing the heat and being sucked out of the space. The 7AC was required by SL13 to enlarge the ramp at the bottom of the cowling and in some cases enlarge the cowl flap to increase the low pressure area exiting the cowl when changing from the A65 to the C85/C90. It wasn't due only to high CHT'S it was for better oil cooling too.
I also remember ACA putting gills and messing with the cowling exits around the 1980's due to cooling issues.
You could always put a temporary larger cowl flap on for a few flights to verify this isn't your issue.
Just something else that would be cheap to try...

Chris
 
I've even heard of people using an old altimeter to measure the pressure between the baffles and the firewall. This pressue shouldn't be beyond a certain value. There should be a certain ratio between the air comming in and leaving the engine compartment. Also if the exhaust does not extend enough out of the cowling it could cause a pressure build up preventing the air from leaving the engine compartment. If you measure a too high pressure , you should change something like Chris already metioned. Not sure about the values anymore , but Google is your friend. If you like I can look it up for you tomorrow.

Simon
 
Okay, so I had read something a while back about oil turning dark quickly being an indicator of blow-by... I pulled the oil after 3 hours to check the pick-up strainer for any evidence of foreign material, and was shocked at how dark the oil was already:

PXL_20230513_195435454.webpPXL_20230513_195845100.webp

I drained oil out of the club 172 that was lighter than this after 40 hours... Is it possible to have excessive blow-by without anything coming out the crankcase breather?
 
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