Oil Cooler for O-300's

[170C]

I seem to remember in the Continental engine overhaul or parts manual that there was a reference to a factory oil cooler, but I have never seen one or talked to anyone who said they had done so. I visited with a friend yesterday who took me to his hangar and showed me an after market oil cooler on his '56 172 w/ a O-300 engine. There is apparently an stc on the unit, but the "kit" includes the oil cooler, which looks like those on other Continental engines. It mounts on the firewall (and I think you have to fabricate the mount), if you already have andFM oil filter adapter, you only have to get a new piece that goes between the adapter and the filter. For those without the FM filter, one can also get the full adapter itself. This "extra" item has two female threaded openings where hose adapter's are screwed in. Hoses go from the adapter to the cooler and back to the adapter. You also have to put a opening in the rear baffel & put a scat hose adapter into it. The scat hose goes to the cooler and again you have to fabricate an adapter to fit the scat hose & to fit on top of the oil cooler. That is a long description, but for those with true high oil temperature problems not the result of poor engine cooling or ring problems there is a means of adding an oil cooler to our engines. I don't have the info to get the stc, but if anyone is interested I can get it. Fortunately, operating here in TX, I have managed not to have a serious oil temp problem. It can get pretty high sometimes, but not over the limit.

[GAHorn]

The TCM oil cooler is only for the C-125 engine, although it has been adapted to C145/O300 engines, and is also optional for the 172 seaplane.

TCM oil cooler.JPG

A "sandwich" adaptor is sold on the open market which fits between a spin-on filter and the engine adaptor. This would allow a person to hook up hoses to/from a remote oil cooler. I once thought about experimenting with such a setup and changed my mind. I have the new, unused sandwich-adaptor, still in it's box and would love to get my money back on it. $35.

[Robert Eilers]

170C's post got me thinking - what would cause high oil temp problems other than poor engine cooling or ring problems? I bought my 170B from a gentleman in Phoenix who owned the airplane for 30 years. To deal with the high OAT in Arizona he enlarged the opening in the cowl in front of the oil pan - nice job, professionally done, you wouldn't notice it unless very familiar with 170s. Here in Northern Calif. summer days can get into the 100s F and I have not had any high oil temps problems. On the other hand, in the Winter when temps get into the 30s and 40s I have trouble keeping to oil temp warm enough and resort to taping off a portion of the cowling intakes.

[GAHorn]

Robert, look at the 1st Qtr "The 170 News" for the article I wrote on high oil temps.

Inspect your exhaust riser flanges for leaks which allow hot exhaust onto the pushrod tubes, which serve as a return pathway for oil from the rocker boxes to the sump.

[clanier]

I would like to buy that adapter
Carlton

[N2625U]

I think I found this on the Swift site. It might explain a little about oil cooling on the Conny.

Continental was opposed to external oil lines on their engines, and the "C"-series of engines was designed without them. Although an oil cooler design was produced by TCM (Continental Motors Corporation), Cessna was opposed to using it, probably for price considerations. So the C145/O300 installed in a Cessna runs hotter than the same engine in a Fairchild/Stinson/etc.. It also runs cooler in a Swift due to the updraft cooling.
Why would updraft cooling help? For one reason, the oil sump gets a nice first-chance at the cool air. But another major reason is because the pushrod tubes, being sheet-metal, and because the Cont. engines pump relatively high quantities of oil to the rocker boxes (much more than the Lycomings because of the better hydraulic lifters that Cont. uses) that subsequently runs back down those tubes to the sump, ...those pushrod tubes act as oil coolers and on the updraft cooling systems they also get a first-shot at the cooling air.
On a downdraft cooling system such as on our airplanes, the pushrods aren't in such a good position, as they sit downstream of those nice warm cylinders. Nonetheless, they still perform a function of cooling. And that's the problem.

If your exhaust flange gaskets leak, or if your exhaust riser clamps leak and spray hot exhaust onto your pushrods, a surprisingly large increase in oil temperature will result. So look for signs of exhaust blowing on your pushrod tubes.

There is not too many reasons for a 170 engine (C145/O300) to suddenly start running much hotter than 210-220 F. The most common reason for a sudden change is a faulty gauge. The next most common reason is a leaking exhaust flange. The third reason is faulty cooling baffles. The fourth reason is a broken or stuck piston ring, which can be detected with a compression test and subsequent blow-by into the crankcase.

Even a C145/O300 engine that has run all it's life with oil temps at or near redline will make TBO as often as other engines that run much cooler. The high oil temp does not seem to hurt the C145/O300 as much as it does some other engines. One reason for that is due to the location of the oil temp probe. Our oil temp probes are located at the oil inlet to the engine (at the oil screen.) Most other engines measure their oil temps at the outlet of the oil cooler. That's why they commonly indicate oil temps in the 180 degree range. Therefore it's not appropriate to compare the C145/O300 engine oil temp indications to other engines. If you'd measure the oil temps of most other engines at the inlet of their oil coolers their temp readings would be frightening.
So,...run SAE 50 wt oil in warm weather (above 40 degrees F) and SAE 30 in cooler weather (below 40 degrees F) order to take advantage of the higher 240 degree oil temp redline. (I've never seen SAE 30 aircraft oil, personally. Interestingly, SAE 40 oil is never approved for 240 degrees in our engines, apparently because it's not approved for use below 40 degrees F.)

[GAHorn]

I think I found this on the Swift site. ...
... Although an oil cooler design was produced by TCM (Continental Motors Corporation), Cessna was opposed to using it, ...On a downdraft cooling system such as on our airplanes, the pushrods aren't in such a good position, as they sit downstream of those nice warm cylinders. Nonetheless, they still perform a function of cooling. ... There is not too many reasons for a 170 engine (C145/O300) to suddenly start running much hotter than 210-220 F.....)

The bold-highlighted areas in the quote indicate that this was not from a Swift site. (Why would they quote Cessna, discuss "170 engines" and concern themselves with downdraft cooling?) It seems remarkably verbatim to an article I wrote several years ago which was published at GlobalAir. I recently (1st QTR 2008) wrote a parallel article for The 170 News, which addressed similar issues.

The Swift Association does have an excellent technical-support guy, Jim "Monty" Montague, who is very knowlegeable about this engine as it pertains to Swift installations, but this engine was never a factory installation in that airplane. It was only installed in the Swift as an aftermarket STC. Also, the Swift has provisions for an oil cooler as the result of it's factory-installed C-125 engine...a sister to the C-145/O-300. A bypass restrictor must be installed in the forward oil gallery to accomodate an external cooler, and many installations failed to do that with problems as the result.

[c170b53]

Get used to it George good writing always finds another home.

[PilotMikeTX]

I briefly considered adding an oil cooler after I had a "Oh S*&%!" moment last year. I took off in 90+ degree weather and climbed directly to 8500'. Around 6500' I noticed the oil pressure was considerably lower than it was a couple of minutes before. And the temperature was near the redline. I had just changed the oil and leak checked the engine, but my feeble brain interpreted that information to mean that I was losing oil, and thus causing the reduced pressure and corresponding increase in temperature. Of course, a prolonged climb at a high power setting with relatively low airspeed would produce the same symptoms. But I still turned around and leveled off so as to improve my options for the impending catastrophic failure. After a few minutes in cruise, the temperature and pressure stabilized, and then I began a long descent and by the time I arrived in the pattern, the temp was actually a little on the cool side and the pressure was up at the top of the green. I landed and confirmed there was no leak.

I determined through some testing that week that if I hold 95-100mph in the climb I can keep the oil temperature under control. I only need to operate like that on the hottest days. So, just like a few lessons with a pro will help your golf game more than a new set of clubs, you can probably modify your flying technique a little and save a couple thousand bucks for fuel. Also be sure you're departing with a full 8qts of oil if you usually like to run around with 7 or 7.5.

I don't know if there are any hot climate seaplane 170 drivers out there, so I can't speak for them, but unless I decide to start towing gliders or banners, I'm going to pass on the oil cooler for now.

[GAHorn]

I would like to buy that adapter
Carlton

Carlton , send me an email so we can get it in your hands.
gahorn146ys (at) hotmail

[blueldr]

If the designed cooling system on the C-170 is scrupulously maintained as designed, there is really no need for an oil cooler.

[DMACJR]

170C's post got me thinking - what would cause high oil temp problems other than poor engine cooling or ring problems? I bought my 170B from a gentleman in Phoenix who owned the airplane for 30 years. To deal with the high OAT in Arizona he enlarged the opening in the cowl in front of the oil pan - nice job, professionally done, you wouldn't notice it unless very familiar with 170s. Here in Northern Calif. summer days can get into the 100s F and I have not had any high oil temps problems. On the other hand, in the Winter when temps get into the 30s and 40s I have trouble keeping to oil temp warm enough and resort to taping off a portion of the cowling intakes.

Can you please send me a pix of the "enlarged opening" and what the dimensions are. thanks fighting similar issues in the summer wx of SWFL....

[ghostflyer]

I would take a deep breath on the matter on enlarging the hole in the cowling for cooling the sump . Enlarging that hole will change the pressure differential between the top plenum chamber and the bottom plenum chamber area. This pressure differential and velocity is very important for cooling the barrels and cylinder heads . Not only in level flight but in the climb mode also . That's why it's important to have all baffle seals in good condition and sealing correctly . The cooling air velocity in the lower chamber will be affected also . Many people will say that there is a winter kit that closes that cooling hole off , yes but the pressure differential between the top plenum and bottom plenum doesn't change that much to change the cooling efficiencies of that design . It's now been recognised that the air flow ( pressure and velocity) in the bottom plenum chamber is far more important than the air flow moving in the upper chamber. To clarify that statement is look at some of the newer aircraft with the small openings for cooling air ( Cirrus aircraft ) . It's how the air exits is very important . Take a look at the exit opening at the bottom of the cowl on later model cessnas and see they have rounded piece of aluminium on the edge of the fuselage where the hot air exits . Plus this could be viewed as a illegal mod.

[blueldr]

If the cylinder and inter cylinder baffling in in good condition and properly installed, a stock engined C-170 should be able to run under almost all conditions without overheating.