1975 Cessna 172M - High Oil Temp

[Jon Wilder]

Hi all.

We have a 1975 Cessna 172M with Lycoming O-320-E2D engine. In this engine we have AeroShell W100 Plus oil filled to the 6 QT mark.

The other day while flying straight and level at 3,000' MSL, 69*F OAT, full rich mixture, CHTs were in the 350-375 range, and 2500 RPM, the oil temps rose to about 242*, just 8* below red line. I reduced the power to 2350, then two minutes later, we started the descent to land (we were getting set up to fly an RNAV approach). During the descent, the temps came down.

We shot two more approaches in the standard traffic pattern, and the temps never got that hot again.

I spoke with the owner about it, and he informed me that this particular model/variant always ran hot. It never went over the limit but it's always gotten pretty close. Talk of possibly installing a larger oil cooler was also mentioned.

Were these engines in this airframe known to run hot? Or is there something else in play here?

 

[Domenick]

I'm a Piper Cherokee guy, so only have a general comment.
Check the baffling, metal and soft stuff. If the soft baffling is OEM or has gone stiff, replace it with silicone.

Any holes/cracks/gaps in the upper airbox will reduce airflow through the cylinder fins.

There are specific Piper P-28 tricks to bring down oil temp, and I suspect there are specific C172 tricks too.

 

[bnt83]

Hi all.

We have a 1975 Cessna 172M with Lycoming O-320-E2D engine. In this engine we have AeroShell W100 Plus oil filled to the 6 QT mark.

The other day while flying straight and level at 3,000' MSL, 69*F OAT, full rich mixture, and 2500 RPM, the oil temps rose to about 242*, just 8* below red line. I reduced the power to 2350, then two minutes later, we started the descent to land (we were getting set up to fly an RNAV approach). During the descent, the temps came down.

We shot two more approaches in the standard traffic pattern, and the temps never got that hot again.

I spoke with the owner about it, and he informed me that this particular model/variant always ran hot. It never went over the limit but it's always gotten pretty close. Talk of possibly installing a larger oil cooler was also mentioned.

Were these engines in this airframe known to run hot? Or is there something else in play here?

It shouldn't run that hot with an OAT that low. Temp gauge accurate? Baffles good? Oil cooler duct clean?

 

[Dan Thomas]

First, as others mentioned, baffling.

Then the oil cooler, which is supposed to be flushed every 1000 hours and at engine overhaul according to more recent SM revisions. Even at that, those coolers get internally coated with varnish, insulating the oil from the airflow. I fixed once 172 with high oil temps by replacing the cooler.

The vernatherm, which closes the oil cooler bypass as the oil warms up, might be shot.

An oil cooler inlet cover plate might be installed on the aft baffle above the #3 cylinder. That's for very cold weather. Remove it.

If this airplane has been upgraded to an electric oil temp gauge, poor engine and alternator grounding will cause intermittent high oil temp readings. And that, I think, is most likely, along with whatever else is found. I seldom saw really clean, tight, decent grounding on old airplanes. It just isn't in the minds of the mechanics doing the inspections. Paint, oil, dirt, corrosion, looseness of ground clamps and bolts and terminals all contribute to it.

 

[Larry Korona]

I have the same make and model with the same engine. I also had high oil temperatures and CHTs especially in the summertime during initial climb out. I also have a PowerFlow exhaust system installed, which was part of my problem, after several calls with PowerFlow I corrected my high oil and CHTs after increasing my fuel flow rates.

 

[Magman]

It’s not the MODEL.

It’s the MAINTENANCE.

 

[Gary Ward]

Kentucky Captain had the same problem with his M model with high cly head temperatures.

I believe he solved his problem when the carburetor was overhauled. He reported that he got a different size main jet in his carburetor and fixed his problem? I think?

 

[Jdm]

I’ve got the same exact make and model. Never once had an issue, or known of such a trend as described by this owner. I’m gonna say the owner is incorrect! Probably a baffling situation as others have suggested.

I did have an interesting engine problem to sort out recently on the 172M that resulted in improved performance. Carburetor situation but unrelated to a temp condition such as you’re describing.

 

[RussellJ]

I owned a '75 M for several years. It would run hot when cruising at 2500 and do okay at 2400. Found some info about an update to the atomizer or metering jet, I don't remember exactly, something inside the carburetor. I swapped out the carb for the latest revision and the temperature issue went away.

 

[Jeff767]

In addition to the above thoughts check the magneto timing. A Mag with even a few degrees advance beyond the normal advance will increase temps. 242 is way to hot for the oil. The entire cooling system needs to be inspected.

 

[Jdm]

Found some info about an update to the atomizer or metering jet, I don't remember exactly, something inside the carburetor. I swapped out the carb for the latest revision and the temperature issue went away.

The latest recommended Marvel-Schebler carburetor for my 0320-E2D is p/n (setting #) 10-5217 as Verified through Lycoming and M.S. I switched to this carb a few weeks ago. Excellent results! Best this engine has ever run. Be sure to tune it to book specs.
If you end up going with another carb, I recommend an in house overall from Marvel. Not a rebuild, just an OH. They can be purchased through McFarland, Spruce and a few others. Much better overhaul and flow checking equipment from the factory than some of the independents. Priced the same if not better. Also easy to talk with a shop tech at Marvel if there are ever any issues, warranty, etc. They do a very nice job. Located on the field at KBTV

 

[c310flyr]

The latest recommended Marvel-Schebler carburetor for my 0320-E2D is p/n (setting #) 10-5217 as Verified through Lycoming and M.S. I switched to this carb a few weeks ago. Excellent results! Best this engine has ever run. Be sure to tune it to book specs.
If you end up going with another carb, I recommend an in house overall from Marvel. Not a rebuild, just an OH. They can be purchased through McFarland, Spruce and a few others. Much better overhaul and flow checking equipment from the factory than some of the independents. Priced the same if not better. Also easy to talk with a shop tech at Marvel if there are ever any issues, warranty, etc. They do a very nice job. Located on the field at KBTV

That would be at KBUY, not KBTV

They are in Burlington, NC, not Vermont

 

[Jdm]

That would be at KBUY, not KBTV

They are in Burlington, NC, not Vermont

Yep, typo. You’re absolutely right. The guys next door at Triad are the ones who told me about the services at Marvel.

 

[Dan Thomas]

242 is way to hot for the oil. The entire cooling system needs to be inspected.

From the TCDS for the O-320-E2D:



242 is under the redline and acceptable. I wouldn't want it there either, but the manufacturer is the one that designs and certifies and accepts the liability for that engine.

The fact that the OP said that the temp spike was a temporary thing and didn't rise again tells me that he has an temperature indication problem as I pointed out in post #4. If that is so, then none of the indications are reliable, and the first thing, after making sure there is nothing obviously wrong with baffling or oil cooler ducting, should be to check that indication system, including engine grounding. Cessna put out a service bulletin years ago addressing this, and called for a wire from the engine case next to the temp probe to the oil temperature gauge's metal case in the panel. This removes any voltage potential between the two parts of the system.

 

[Domenick]

A lot has been learned about metallurgy in the 55 years since 1967. That TCDS is for the entire O-320 line, and I would NEVER let my O-320-D3G hit 500F. I start lowering the nose on climb when max cylinder CHT passes 380F.

 

[Dan Thomas]

A lot has been learned about metallurgy in the 55 years since 1967. That TCDS is for the entire O-320 line, and I would NEVER let my O-320-D3G hit 500F. I start lowering the nose on climb when max cylinder CHT passes 380F.

The TCDS are regularly revised to reflect updated knowledge and metallurgy. The TCDS for the O-320 series was last revised in April 2013.

If the revisions affect a POH or AFM or Engine Operator's Manual, they get revised as well.

No, I wouldn't like 500 degrees either, but that limit is based on cylinder pressures and the aluminum casting alloy's physical properties at those temps. There are a lot if older airplanes without any CHT indicators, but everything is just fine until the owner installs a system and starts to panic over what he sees.

 

[Magman]

As others have said; take a good look at the baffle system.

Look inside the top cowl with a flashlight. There should be no gaps and seals should be folded forward and side seals up so ram air will help tp seal.

The filter inlet seal in the lower cowl that should be intact to prevent air entering the lower cowl and disrupting the pressure differential.

Assure the metal baffles on the cylinders are a tight fit so that air is forced between the cooling fins. If the spring/wire retainer is loose air may bypass the fins completely. Safety wire is commonly used to sub for the spring/wire system but is not always effective.

 

[Dan Thomas]

The filter inlet seal in the lower cowl that should be intact to prevent air entering the lower cowl and disrupting the pressure differential.

That seal assembly is just plastic, with a bit of rubber strip around it, and it gets brittle with age and heat and UV and gets busted, so mechanics often remove it. And then you could have overheating problems, as you say. And a new one, last I checked, was obscenely expensive. Ridiculous. Dynamic Propeller makes a fiberglass version, PMA'd for far less and it's much stronger. Much more cost effective. Still not cheap.

http://www.dynamicpropeller.com/cessna-172--182-airbox-products.html

Note that earlier 172s didn't use them. They showed up in maybe 1970. Parts manuals have the details.

 

[Magman]

I know someone with an “M” also. He says a new one is over $1000.
Currently one is being mad-‘ er, repaired.

My recall is earlier aircraft used a type of welting that was stapled to the lower cowl opening.

 

[Jdm]

I just installed a 172M dynamic propeller induction seal a couple weeks ago. Yes apparently it’s PMA’d but STC’d also. I didn’t think it was going to seal that well, but it actually turned out very nice once fitted.

 

[I threw it on the ground]

We’ve done a few STC remote oil filter housings recently and if you run air to them properly you can get 20-30 degrees cooler temps. We in Alabama so they always hot