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TOPIC: High Oil Temp

High Oil Temp 2 months 2 weeks ago #607

Got this some years ago and it may explain the Connie O300 engine oil system.

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.)
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High Oil Temp 2 years 11 months ago #139

  • Jen D
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I put this question to our technical expert, Steve Ells and this is what he had to say. Please let us know how it goes if you end up using one of the vendors:

High oil temperature indications are not uncommon on Continental power Cessna 172s such as yours. Still, your troubleshooting proves that the oil temperature indication system is non-linear to say the least. The oil temperature system in your 172 is a Bourdon tube type gauge. This type of gauge consists of a closed fluid system with the temperature bulb at one end, and a Bourdon tube at the other. A capillary tube connects the two. The fluid expands when heated; this causes the bourdon tube to change shape which changes the position of the needle on the temperature gauge. These systems are removed intact--don't cut anything just pull the capillary tube and temperature bulb back into the cabin to remove it. Be careful not to bend or kink the tube during re-installation.
The part number of the oil temperature gauge assembly for a 1963 Cessna 182 is 0513144-2. I don't have a 1961 Cessna 172 book but I expect the part number is the same. One well known company that repairs and recalibrates these bourdon tube type systems is Air Parts of Lock Haven (www.airpartsoflockhaven.com).
On a whim I typed the part number in to my favorite search engine and found this company in Oklahoma. In addition to the new surplus gauge assembly listed here it also advertised an overhauled gauge assembly. I don't know anything about the company. I ask about a return policy when buying from a company I don't know.
Happy Flying

Condition:New Surplus

Phone: (800)542-8565
or (580)661-3591
Fax: (580)661-3783
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High Oil Temp 2 years 11 months ago #130

I have a 1961 172B and during climb out the oil temp pegs the gage. I see no difference in oil pressure and oil on dip stick is 7 qts. Service manual states 7 is ok although it holds 8. I heated oil in a deep fryer to 180 degrees, put the probe in the oil and the gage went to middle. As I increase to over 190+ I pegged all the way to the end. Same as when I was flying. I have not put on an oil cooler or an extended oil filter. I have however plugged most open areas with high temp caulk and baffling is all new in 2013. Just bought it two years ago and learning to fly it.
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