The International Cessna^® 170 Association

I’m fighting a problem with high oil temperatures. I’ve read and done searches on the subject here but have come up short after trying all solutions using the stock setup.

Plane: 1951 170A with O-300A (TSMOH 670 hours) and Sensenich 74DR with 58 pitch (cruise).

Area: NW Colorado with a field elevation of 5240’ and much higher terrain if you want to get out of the basin.

Symptoms: Following repairs to a leaky exhaust system the engine oil continues to heat up to 225 in a very short time. One evening at about 78 degrees I shot one quick T&G then on the second round climbed to about 1400’ AGL at full throttle before she hit red line (1 person, 1/3 tanks). She stayed at 225 as I made a full power (about 2600 rpm) decent at about 120 mph indicated to about 200’ AGL on final.

After making additions to the baffling to hopefully force more air past the oil sump and other improvements I took her up when the temperature was about 70 degrees. I climbed at 85 to 90 mph to about 2250’ AGL before she hit 225 degrees. Oil temp didn't start backing down until I completely pulled power on short final. 1600 RPM decent held the oil temp steady.

Work so far: Replaced all exhaust flange gaskets and left side exhaust risers (major exhaust leak found on #2 and minor leak on #6). Removed and had the exhaust port faced on the #2 cylinder. Replaced intake gaskets, hoses, etc. on left side while I was at it. Muffler tape used on all exhaust clamps per George. Exhaust system pressure tested and passed the soap test.

Oil temp gauge checked before and after with the fryer thermometer in the dipstick hole method. Everything on the money.

Cylinders compression checked…all between 73.5 and 75. All cylinder temperatures and exhaust gas temperatures are in the normal range. Oil pressure maintains strong at about 50-55.

Baffling was in reasonably good condition. Improvements in baffling showed no apparent effect.

One blast tube to the oil filter adapter...the other to the generator via scat tube.

Engine runs smooth without any unusual noises. Filter was clean for metal particles 10 hours ago.

Timing is only slightly off by about 2 degrees…not enough to cause my problems.

Pulled the rockers on #2 and the pushrod tubes look clear without any sludge buildup.

Being at a lose…I.A. suggested putting in 2 quarts MMO in crank case and running it for 10 hours. I’m at about 3 hours with no notable improvement. I’m running 50 wt and know I can take it up to 240 degrees but am using a limit of 225 with the MMO addition. Before I put in the MMO the temps would still climb without signs of leveling off at 235 unless I backed her down to 2100 rpm or less in level or descending flight.

This is the first summer we’ve had this plane so there is no other points of reference on this machine.

I realize there are several modifications that can be done (legally of not) to treat the symptoms but I understand that shouldn’t be necessary if the engine is functioning properly. I would rather find and treat the problem instead of the symptoms.

Any suggestions??? I’m at a lose for where to go with it next.

Thanks in advance for any words of wisdom.

(Yes George…I’m in the process of becoming a full card carrying member of TIC170A.)

I wonder if you have the small lip on the bottom of the cowling where the air exits the cowling. I have the larger one and a climb prop 7651 and I never see oil temps above 200 degrees. In fact I have trouble keeping the temps up in the winter. Bill K

Make sure that all of the inter cylnder baffles are installed and properly so.
I've seen them installed improerly.

3958v wrote:I wonder if you have the small lip on the bottom of the cowling where the air exits the cowling. I have the larger one and a climb prop 7651 and I never see oil temps above 200 degrees. In fact I have trouble keeping the temps up in the winter. Bill K

I have also heard of owners putting the Seaplane lip on the bottom cowl for better cooling.

I checked the inter cylinder baffling and everything checks out against the parts manual.

Same goes for the cowl lip...all standard. While a larger lip may help cooling we have bigger problems here.

Partner ended up pulling the oil filter yesterday. All gunked up with sludge, carbon, etc....no metal. Put the oil screen back on (no filter available locally for replacement). I haven't been able to take her up yet to confirm if this was the problem...hopefully this afternoon or Wedn morning. I was under the impression that there was a bypass valve built into the filter that should have kept oil circulating even if the filter media was plugged off. We have our fingers crossed that this may be the final cure to our problems.

To add to the story...a cowl plug (bird problem) was left in the oil sump opening before the last oil change. Engine temps got hot. I don't know exactly how hot it actually got but no abnormalities were reported on the oil change and filter inspection immediately following the incident.

Oil temps were running a bit high a couple hours after the incident but not redlining. By hour 2.5 I did have to back down from a climb to keep temperatures in check. On the return trip from a cross-country I was fighting high oil temperatures and babying the throttle, playing updrafts, etc. to clear terrain without going over redline. Redline is at 225 and with 50 weight she should be good to 240 so I kept it well under maximum.

She has been essentially grounded with only short local flights to help ID the problem since.

Scott

Scott

It would seem you've followed all correct steps. Are you sure the oil temperature would exceed 240? If not you may be chasing a problem that does not exist.

One thought and this is a stretch. The prop your using is an option but not the normal prop found which is the McCauley. Accourding to the owners manual your prop is not as efficient. It is very close but just doesn't have the same performance numbers.

Perhaps your engine is just working harder to achive the same effect as other 170s but pushing the engine parameters closer to the limits. Non the less it was certified and all perameters should remain in the operational limits.

The Sensenich cruise prop is a concern. I hope to get her repitched when we can make it out of the basin. It probably contributes to higher oil temperatures but I doubt it is stressing the engine enough to elevate the oil temp from 100 degrees to 225 in about 5 minutes in cruise climb...it wouldn't have a snowball chance in hell of getting approved.

It would be nice to think that the oil temperatures would stabilize below 240. However, from my many runs up to 235 there was no indication of it stabilizing unless drastic measures taken...such as greatly reduced power settings. Any attempt to climb even another 300 feet and the needle just kept climbing. These tests were all conducted with a ground temperature of less than 80 degrees...once when it was in the low 50's.

My test flight after fixing the exhaust leak problem showed similar results. After the initial flight I parked it to let it cool down to about 170 and tried her again. On takeoff I could see the needle climbing before I left ground effects. Had to do a climbing 180 to return to the runway in the opposite direction. By the time I had the runway in sight again the oil temp was up to 225 and climbing...at about 400 feet AGL.

This engine stays cool, but in flight performance tends to suffer!!



Keep cool everyone

Swung by the airport and looked at the old filter. It wasn't caked with coked oil like I had invisioned. I'm not as optimistic now that the problem was found.

I'll fly her in the morning to see how she goes. I need to get her to another airport Thursday morning before my home base runway is being repaved. Nearest airport is 40+ miles so it could be a challange. I might have to throw the engine oil in the freezer overnight for added heat sink and elevation gain for the trip.

Scott

Does the oil turn black?
If so how long does to take to turn black?
Dave

The oil turns black faster than normal. When it was changed Monday it only had 10 hours on it but wasn't what I would call 'black' yet. However, it was darker than I would normally expect.

If the oil turns black in a short period of time you may have combustion gas getting passed the rings. If gas gets passed the rings the oil temp will be elevated.
A leak down test will not be a good indicator of this. I have seen a cylinder with 80/80 and pulled the cylinder to find a top stuck or broken ring. Check for blow by and oil out the breather. If the rings are stuck from the oil turning to some thing like burnt sugar, the fix may be to just replace the top ring on the few cylinders that were hot.
Please let us know what you find. Good lock with the hunt.
Dave

mrpibb wrote:This engine stays cool, but in flight performance tends to suffer!!



Keep cool everyone

Hey Vic,

Is there an STC for that exhaust?

Dave,
Thanks for the tip. The one cylinder/piston I pulled looked good in that respect...but that doesn't mean the others are also good. We get oil out the breather to a limited extent when below 7 quarts and it pretty much blows out the 8th quart.

I took her up this morning to evaluate operations to get her to another airport. Very little sign of oil out the breather...however, almost all my flight was under reduced power...even on climb out.

This morning I made a quick ground check, applied full power on takeoff, and backed power off to about 2100 rpm, 85 mph indicated, and 250-300 fps on climb out. The oil temperature needle slowly raised but continued climbing to where I backed off power to about 2000 rpm when it reached approximately 210 degrees at 1800 feet AGL. Oil temperature seemed to stabilize at bout 220 degrees with a very slow upwards creep. After maintaining flight and oil temperatures for about 1/2 hour I applied full power and the oil temperature made a rapid climb. I backed off power when the temperature hit about 235 after only gaining about 600 feet. Oil pressures stayed at 50 psi.

Looks like my partner can put his A&P to use and start pulling cylinders once I get the plane back to him tomorrow.

Scott

if you're looking into blowby, then do a normal compression test and listen at the oil fill cap for blowby into the case. But that will only tell you if there is a problem at the top of the cylinder.

if the cylinder walls are washboarded (ripples), then the best way to isolate your problem cylinders is to move the piston (prop) up and down the cylinder while someone listens to the oil cap. I've even hooked an old airspeed indicator to an oil filler cap and used that to quantify my leakage as the rings skip across the ripples.

that test will tell you which of your cylinders are contributing to the problem if that is it, although genrally you'd have higher oil usage too with this. But you aren't flying long enough to use much oil, I think.