HIGH,HIGH OIL TEMP!!

How to keep the Cessna 170 flying and airworthy.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

User avatar
dpowell
Posts: 54
Joined: Fri Aug 19, 2011 3:44 am

HIGH,HIGH OIL TEMP!!

Post by dpowell »

'48 170....0-300D F&M Oil filter adapter. Did a top overhaul about 10 hrs ago (Chrome channel)w/steel rings. Oil temp extremely high (almost full right deflection @75-80% power for break-in). Staying at approx. 1000-1500 PA. Cylinder head temps are in the 325 degree range. Prior to the overhaul temp would regularly run on the red line at high power (original gage). Lots of things going on! Just rebuilt my exhaust....no leaks. Baffling appears ok. Temp probe is mounted in the sump Aft side....if think I read it should be on aft side of filter housing. I just did the 'ol heat some oil and check probe trick.....nearly deep fried my arm! Anyway.....connected a ground to the probe housing and the thermometer in the oil read 250 degrees( F) and the gage was reading on the red line (225). Gage was always reading 25 - 30 lower than thermometer! Can this be?? Using Phillips 20W50 mineral oil for break in. Planning to go after a new thermometer and move the probe location. Without the ground attached to the probe housing, the gage read much lower....but I think to check the probe, it does need to be grounded...right??? Ps...during last few flights the OAT has been about 100 degrees! :(
User avatar
n2582d
Posts: 2808
Joined: Mon Apr 29, 2002 4:58 am

Re: HIGH,HIGH OIL TEMP!!

Post by n2582d »

What brand of oil temperature gauge do you have? Originally the 170 was equipped with a Rochester capillary type gauge. Cessna came out with Service Kit SK182-108B and Single Engine Service Bulletin SEB94--12 to replace the capillary type of gauge with a Rochester electrical one.
IMG_0562.JPG
This one uses probe Cessna p/n S2335-1 (which also goes by Rochester p/n 3080-37, Mooney p/n 880009-501, and Piper p/n 553-672). The Aircraft Spruce link above gives the resistance values you should see for the probe. Curiously, it lists thermistor curve "E" while in small print on the Rochester gauge shown above it says "Q curve". Mismatch??? There are other aftermarket temperature gauges like Electronics International which also replace, by STC, the capillary gauge with an electrical one. Whatever the brand I believe you are correct in mounting the probe in the oil filter adapter. Here's what Electronics International says about the probe mounting:
Click to enlarge
Click to enlarge
If you stick with the electric gauge you should insure a good engine ground. Your IPC shows this in fig. 34-14. The TCDS for the C-145/O-300 shows that the oil temperature limit has been increased from 225° to 240° if you use a straight 50 weight oil.
Last edited by n2582d on Tue Jul 25, 2017 2:24 pm, edited 2 times in total.
Gary
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: HIGH,HIGH OIL TEMP!!

Post by Bruce Fenstermacher »

Your temp prob goes in the back of the F&M adapter. Some would suggest the air blast tube be pointed at the area of the F&M where the prob is inserted rather than the accessory case.

Yes it is possible your gauge reads 25° lower than actual. This is why we tell everyone they must calibrate their gauge prior to proclaiming their engine runs to hot or cold.

You should not need to ground anything related to your test thermometer or your gauge bulb in the hot oil test fluid. Neither depends on any grounding to work properly

For break-in I'd only run straight weight mineral unless the cylinder manufacture stated otherwise. The 20w-50 is really only 20w which acts like 50 when all the magic oil additives are working. Straight weight may bring your oil temps down a pinch.

The fact your '48 ran hot prior makes me want to ask, how wide is the lip on your cowl on the bottom rear? It should be close to 3". If it's not, specially if it's only 3/4", you have the wrong lip. More specifically you have a '51 or '52 bottom cowl and lip.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
dpowell
Posts: 54
Joined: Fri Aug 19, 2011 3:44 am

Re: HIGH,HIGH OIL TEMP!!

Post by dpowell »

Well...what we have here is a situation that back in my days of Army Aviation, we used to refer to as fubar. Thanks for the replies! They all seem to be correct. Wrong gage installed (mine is Rochester but No curve....since it is not electric). Probe in wrong location (just moved it). Lip size on bottom of the cowl is 1.5" on the long side, but bottom edge only 1" vertically from the surface of the cowling (so yep, wrong cowl). No, the blast tubes are not shooting onto the correct probe location (will fix that). Thanks for the inputs.....you would think that folks would do proper refits on aircraft......guess that is expecting too much! Will also go to 100 W on the oil. Maybe with all these changes (especially the correct gage) my indicated oil temp will actually be correct! Ps is there a way to use the old blast tubes or is there a tube out there somewhere that points to the back of the filter housing? :roll:
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: HIGH,HIGH OIL TEMP!!

Post by Bruce Fenstermacher »

It may not be as fubar as you think. A Rochester is not necessarily the wrong guage. The originals where Rochester with a arc mark. The same gauge is sold with no markings. Many many Rochesters with no marks are installed.

Once you are satisfied that your gauge reads consistently the same at a given temp which for our purpose really is red line. And by red line I mean 225° which is the original red line. Yes I know under some circumstance we can go to 240°. So once you know where 225° in on the gauge it is usable. You would only need to change it out if you want one more accurate to the face indication.

Sounds like you have the wrong cowl by your lip description. Post a picture taken 45° to the front of the lip so I can see the front and one side of the lip and I'll tell you if you actually have the wrong cowl of if someone modified your '48. In any case the answer is to add an extension back on to the lip. Mine was modified from the original 3" down to 2.5 and my '49 runs a bit on the cold side. I'd add about an inch to yours and see what temps you end up with. My anecdotal evidence is the 3" made the engine run to cold and the 3/4" generally has the engine at red line on 90+ days.

The blast tube are positioned by a tab off the tube to the accessory case. You need to tweak the tube so it aims at the new location and then design a method to attach the tab securely at the bottom.

I'd swap to 100w because 20w is to thin in my opinion. You might see slightly cooler temps just from this change but you may not either.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
n2582d
Posts: 2808
Joined: Mon Apr 29, 2002 4:58 am

Re: HIGH,HIGH OIL TEMP!!

Post by n2582d »

Well, sorry about my rabbit trail. I assumed when you said that you "connected a ground to the probe housing" you had an electric probe.
Gary
User avatar
dpowell
Posts: 54
Joined: Fri Aug 19, 2011 3:44 am

Re: HIGH,HIGH OIL TEMP!!

Post by dpowell »

Thanks guys.....no rabbit trails...no worries. I attached a ground in a vain attempt to see if it made a difference (didn't think it would on a mechanical system). I read one reply about a service bulletin that required going to a different gage and sender on the 0300d. I suppose that I reasoned that if my old original gage was requiring replacement by SB....that something must be wrong with the original gage and sender.....like maybe there could be some sort of defect that resulted in high readings???? Wishful thinking??? :roll: Thought about trying to modify the blast tube with some scat tubing??
User avatar
dpowell
Posts: 54
Joined: Fri Aug 19, 2011 3:44 am

Re: HIGH,HIGH OIL TEMP!!

Post by dpowell »

Went back to hangar....gage is the old style with a green arc and a red line at 225. This is definitely a small lip on the lower cowl, I don't know if it is original?
Attachments
Pic may be hard to see....cowling is black.
Pic may be hard to see....cowling is black.
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: HIGH,HIGH OIL TEMP!!

Post by GAHorn »

I'll add a couple comments....
Firstly, there's no need to heat OIL to check your gauge... in fact, that can be dangerous. Oil can fume and suddenly a flash-fire! (Also the boiling point of oil is different than water.) Use ordinary water to boil, which occurs at 210F (sea level) and then dip your gauge probe into the boiling water to see if the gauge also reads 210. Be sure the probe does NOT touch the bottom or sides of the pan.

Next... in order to utilize the increased allowable oil temp of 240... it's not an option....you MUST use a straight weight SAE 50 oil. AeroShell 100W is such an oil.

Anecdotally, I've heard the size of the lip is not of much import except on seaplanes (for which the increased lip size is often called a "seaplane" lip.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: HIGH,HIGH OIL TEMP!!

Post by Bruce Fenstermacher »

Looking at your cowl, you have a cowl bottom appropriate for a '48 through '49. The lip you have left the factory at 3". When I say 3" I mean as measured along the flap skin from the bottom of the main cowl body ti the edge of the lip. You called this the long side and measured it at 1.5". This is half what it should be.
Gahorn wrote:Anecdotally, I've heard the size of the lip is not of much import except on seaplanes (for which the increased lip size is often called a "seaplane" lip.)
And why do you think a seaplane might require a larger lip? Could it be because it is swinging a larger prop, running at higher power settings and traveling slower through the air thus less cooling air through the engine? Maybe Cessna found out their new 3/4" lip after '51 was a problem causing oil temps to high n seaplanes. Did you know there is no seaplane lip for the '48 to '49. do you know there is no seaplane lip for a '48 and '49 or cowls prior to 19200?

As we know and I'm sure George will agree, in 95° temps, oil temps in 170s tend to run above 200, many close if not at 225°. What I have paid close attention to over the last 15 years is that none of them are '48 to '49 airframes with the correct 3" cowl. I've NEVER run across a single one. What is typical the temps I see in my '49. I have a 2.5" lip. Most months of the year my oil temps barely make it higher that 170°. Even in the winter, even with winter baffles. On the hottest days here in PA we may see 190°. My first 170 had a '52 cowl with the 3/4" lip. Guess what? Oil temps near 225° in the summer. Same operator flying in the same temperatures, using the same flying techniques, same prop, same RPMs, maintaining the same engine and baffling to the same standard. One difference. The lip.

When I call my evidence anecdotal, I'm leaving just a bit of room. Fact is I've studied it, I've taken note of who has hot running engines and their cowling, I've owned and operated both cowl lip sizes. But what I haven't done is cut my large lip down to see if the oil temps increase and when I was chasing high oil temps with the 3/4" lip, I didn't realize the effect the lip has.

I also notice your lip seems to have holes across the bottom. They would make excellent holes for screws to hold an extension which could be installed or removed as necessary and see what effect it has. Just maybe we will get George to listen to my anecdotal evidence or maybe you will shoot a hole in mine.

And last, a little contest to see how close attention to detail others pay to 170s. How do I know looking at the picture of the dpowells cowl, that it is a '48 or '49 cowl?
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: HIGH,HIGH OIL TEMP!!

Post by GAHorn »

Bruce Fenstermacher wrote:Looking at your cowl, you have a cowl bottom appropriate for a '48 through '49. The lip you have left the factory at 3". When I say 3" I mean as measured along the flap skin from the bottom of the main cowl body ti the edge of the lip. You called this the long side and measured it at 1.5". This is half what it should be.
Gahorn wrote:Anecdotally, I've heard the size of the lip is not of much import except on seaplanes (for which the increased lip size is often called a "seaplane" lip.)
And why do you think a seaplane might require a larger lip? Could it be because it is swinging a larger prop, running at higher power settings and traveling slower through the air thus less cooling air through the engine? Maybe Cessna found out their new 3/4" lip after '51 was a problem causing oil temps to high n seaplanes. Did you know there is no seaplane lip for the '48 to '49. do you know there is no seaplane lip for a '48 and '49 or cowls prior to 19200?

As we know and I'm sure George will agree, in 95° temps, oil temps in 170s tend to run above 200, many close if not at 225°. What I have paid close attention to over the last 15 years is that none of them are '48 to '49 airframes with the correct 3" cowl. I've NEVER run across a single one. What is typical the temps I see in my '49. I have a 2.5" lip. Most months of the year my oil temps barely make it higher that 170°. Even in the winter, even with winter baffles. On the hottest days here in PA we may see 190°. My first 170 had a '52 cowl with the 3/4" lip. Guess what? Oil temps near 225° in the summer. Same operator flying in the same temperatures, using the same flying techniques, same prop, same RPMs, maintaining the same engine and baffling to the same standard. One difference. The lip.

When I call my evidence anecdotal, I'm leaving just a bit of room. Fact is I've studied it, I've taken note of who has hot running engines and their cowling, I've owned and operated both cowl lip sizes. But what I haven't done is cut my large lip down to see if the oil temps increase and when I was chasing high oil temps with the 3/4" lip, I didn't realize the effect the lip has.

I also notice your lip seems to have holes across the bottom. They would make excellent holes for screws to hold an extension which could be installed or removed as necessary and see what effect it has. Just maybe we will get George to listen to my anecdotal evidence or maybe you will shoot a hole in mine.

And last, a little contest to see how close attention to detail others pay to 170s. How do I know looking at the picture of the dpowells cowl, that it is a '48 or '49 cowl?

I'm not interested in entering into a contest, and I was not referring to your comments Bruce, when I made the post about "anecdotally". I was referring to reading various materials over many years of studying the high oil temp issues of 170's.
I'm sure your question was rhetorical when you asked "And why do you think a seaplane might require a larger lip?..." ...as I'm sure you know that I know.

But to address the issue of the "lip" one has only to look at the 170 IPC to understand there was only ONE "lip" for the 170/ragwing, PN 0552000-41 and it was the so-called 3" lip.
ALL SUBSEQUENT models of 170s used the same lip, PN 0552001-41. However, floatplanes used a BOLT-ON extension of that lip, PN 0552001-60, which was the so-called "seaplane" lip.

The holes in dpowells lip may be intended for the bolt-on extension (despite the fact that his airplane is not a seaplane, although he needs a few more of them.... it calls for 14 screws/nuts. And his tailpipes are reversed.)

The anecdotes to which I've referred have boiled down to:
1. The seaplane lip was developed because of the long taxi periods many seaplanes experience that may result in high engine CYLINDER temps. Oil temp control was not the purpose of the lip.
2. The seaplane lip had little additional effect during flight. It was only at water-taxi speeds that it was particularly useful.
3. The various lips found in the fleet which differ from the IPC's are likely experiments conducted by owners seeking to affect engine/oil temps, and are in most cases not consistent with approved installations, and rarely help high oil temperature issues.

Bruce, despite your personal experience, in my opinion the comparison you make with the two different lips versus oil temps are actually not a valid comparison if you consider the fact that it was actually TWO DIFFERENT airplanes you have compared... Am I correct in that assumption?
Also, it would be expected by most operators that the cool winter months experienced in PA would also provide cooler, 190-degree-range oil temps. Again, it's not a valid comparison to the rest of the fleet or even to a different airplane in the same locale.

Most high oil temp issues are caused by:
1. Poor condition/incorrect PN's/missing engine baffling.
2. Leaking exhaust riser clamps (blowing hot exhaust onto pushrod-tubes which are the oil-return path to sump from the rocker box.)
3. Inaccurate or improperly-ranged gauges.
4. Operator abuse (high AOA, slow IAS, long climbs, abusive training techniques.)

It is my experience that most 170B models in good condition, using 100W oil, 100-degree Texas wx, oil temps indicate 210 regularly in cruise and slightly higher in long climbs at 80 mph IAS. Continental was particularly loathe to use external oil coolers or lines because of other engine mfr's issues with those items. These C145/O300 engines are not harmed by running at oil temps in the lower 200s range, and with SAE 50 wt oil are fine to 240-F.
Do not use comparisons to other models and engine installations. Swift owners (updraft cooling...which is especially effective at cooling pushrod tubes) are particularly bothered by LOW oil temps and water-condensate in their sumps. We don't have that problem.

(Intake air scoop) 8)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
dpowell
Posts: 54
Joined: Fri Aug 19, 2011 3:44 am

Re: HIGH,HIGH OIL TEMP!!

Post by dpowell »

gahorn......when you commented that my tail pipes are reversed are you referring to left vs. right OR facing forward vs. backward?? Just curious, It came this way to me. Also I have a pancake muffler on the co-pilot side and a round Hanlon on the pilot side. Don't know if that affects tailpipe orientation. :?: Thanks!
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: HIGH,HIGH OIL TEMP!!

Post by GAHorn »

I was referring to their orientation front/aft. It's not a serious matter, tho'.

Many people worry (needlessly) if the exhaust-cut faces forward that relative wind might restrict engine performance by resisting exhaust-exit. It's a silly idea, but persistent. (If one considers the force which a pumping piston expels the exhaust versus ambient atmosphere.... which at sea level is 14.7 psi... etc, :P

Anyway.... the cut facing forward was Cessna's design to reduce soot impinging onto the lower cowl. :wink:

The conversion of exhaust from so-called "pancakes" (officially called "Cessna stacks") to Hanlon Wilsons are covered by SK70A51-1 which prohibits the mixing of the two types of systems. See the MX Library
http://cessna170.org/forums/viewtopic.php?f=36&t=6919
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
dpowell
Posts: 54
Joined: Fri Aug 19, 2011 3:44 am

Re: HIGH,HIGH OIL TEMP!!

Post by dpowell »

Thanks again to all. I will let you know how things go after I change and add a few items. :roll:
User avatar
n2582d
Posts: 2808
Joined: Mon Apr 29, 2002 4:58 am

Re: HIGH,HIGH OIL TEMP!!

Post by n2582d »

And last, a little contest to see how close attention to detail others pay to 170s. How do I know looking at the picture of the dpowells cowl, that it is a '48 or '49 cowl?
I'll bite. The air scoop assembly is shorter on the early model cowl?
Gary
Post Reply