Flew the junker 172 up to Oregon this last weekend and ran pretty hot oil temps up and back. At Reno I leaned for max rpmfor the takeoff, richen slightly for the climb, and by almost TOC I was redlining the oil temp. This was at 7:00am, 8500 msl, 60-70 degrees F.

No cooling in straight and level flight at 2200 rpm, so I got kinda concerned and just went full rich and 2000 rpm for about 30 min and it seemed to drop a little bit. Tough cuz it slows considerably at that power setting and I basically had to just let her descend about 6-700 feet finally to get some cooling effectiveness. After that it seemed to hold at about 85% on the oil temp guage, and I was able to climb back upu to 8500 and keep it at an acceptably warm temp.

Are high air temps just to blame? I leaned for 75 degrees rich of peak EGT, but then just chose full rich over combustion efficiency for fear of smoking something.

Tips?

Zane

Yeah, we run the 100w during the summer. Part of me just wanted to put the tape over the oil temp guage. Not sure what else I could have done, other than stayed on the ground...

Zane, is the 172 powered by Continental or Lycoming? I've always hears that the Lycoming 320's run fairly cool. My experience is that the Cont C-145/O-300 is notorious for running hot in the summer. Also that oil temp gauges --especially the stock gauges with only the redline (225) temp marked on them -- are notoriously inaccurate. Like Jr said, using 50wt (W100) bumps the redline to 240, up from 225 with W80.
I wouldn't worry too much if it bumps up against the redline, just keep an eye on it. But you should take corrective action if it exceeds redline.
This is a rental/club airplane, not your own mount? Maybe squawk the gauge & ask that it be pulled & checked. I check them by dipping the sensor bulb in a pot of boiling water- remember, water boils at sea level at 212 degrees.
Also make sure the baffling & blast tubes are all in good shape.
One of my 170 cohorts has modified his airplane for Arizona op's by opening up the hole in the nosebowl that allows air to blow on the oil sump.

Eric

It's a '74 M model, powered by a RAM 160HP Lyc. The redline on the gauge is 245, and I was bumping right up against that. I've never redlined an engine before, does the needle go beyond the red mark? How can you tell if you're REALLY in trouble?

I was going to squawk it but I was rendered temporarily more stupid by the hot weather on the ramp. If I owned this aircraft I'd be all over it trying to cool it down, like your buddy.

Z

Just got off the phone with the dispatcher at Reno FLying Service, and they have been aware of the problem in that aircraft for while. They are thinking now that it is the sending unit and/or gauge that is the problem.

172M models have the Lycoming O-320.

z

172's came with the Continental 0300D(145 HP) until about 1969. Then converted to the Lycoming 0320(150). Zane, if the sending unit doesn't fix it then I would be looking at the cooler. I've had a few that were partially plugged with junk.

That aside, I generally just adjust my climb airspeed to compensate for hot cylinders or oil. Pretty much any time I fly here in Texas between May and October, I will climb at 110 mph indicated with the cowl flaps open to keep the oil temp below 225.

Bill

Bill,

Good call on the shallow climb. i tried to shallow mine out on the trip back, but only to about 95mph IAS, which is just a little faster than Vy. Didn't help much, I guess I should have shallowed it out more, but there were big mountains staring me down.

Z

Check the oil level.

If it's the 0320 and your running on 4 quarts or so, just bumping the level up to 7 or 8 quarts will cool you down.

Not many people think of this during the summer months. But keeping your oil level up during hot summer days does make a difference.

Zane,

Good idea to enrich the mixture, but your really have to be careful b/c of the altitudes your flying at. 320's have a tradition of fouling plugs unless there leaned correctly (most people don't fly them out west when your at 10,000' @ cruise, so it's not a problem for them). My 172 that I fly in Idaho from a 6000' MSL strip needs a good mixture check when I run it up and at cruise, otherwise I will get a plug that will fowl, and that will usualy get your attention when it starts turning on only three jugs. With that said, a properly maintained 320 should never get anywhere close to the red line. With my experience of 1200 hrs in hawks, I have never seen them get past the mid portion of the oil temp gauge. Your situation would have definitly alarmed me, but if the oil press is staying within limits you probably have a gauge problem. The oil temp gauge on 320's are electrically routed to the gauge, unlike the oil press gauge which is mechanically linked (statistically less faults). For what it's worth, the hawk I fly in the winter in Idaho runs so cool I have to put a cardboard fitting over one of the ram air inlets (like diesel trucks) so I can at least get a little oil temp indication (don't tell the FAA)! The other problem that I've noticed over the years is that rental 172's are usually used for training and who knows what the guy before you was doing with that mixture control to effect the engine down the road.

The 1968 172K was the first 172 with the Lycoming engine, using the O-320E2D. A bulletproof, cool running, non-plug-fowling version of the O-320. This engine was factory until the 1977 172N using the O-320H2AD. This engine is trouble. Note the last two characters "AD". Lotsofem on this engine. It fowls plugs if you don't lean almost to the point of fuel starvation during taxi.

The 172K was also the last model of the 172 utilizing the spring steel landing gear - nice for unimproved runways. It also still has the semetrical leading edge section (used through the "M" model) that still lets you spin the airplane. The "K" model is my favorite 172!

Now that I've spouted all that trivia, like everyone else said, your high oil temp indication is probably a peripheral problem if the pressure is good....

M

Good trivia and suggestions guys...but I haven't flown this aircraft since last july. I guess I should check in on it and see what the deal was. Wellllllll...now that I'm a 170 driver I don't have much use for the rental fleet anymore..yep. [/end faux pompous ass tone]

Zane,

Too late for someone who's fallen into the 170 pit , I reckon, but the FIRST thing to do in a case like this is pull the sender unit out of the motor, put it in boiling water, and see what the gauge says. If it reads 300 degrees, you pretty much have a clue as to the culprit.

O-320's of this vintage are generally pretty cool running motors, so I was them, I'd be trying to track this down before something ugly happens.

I had an O-320 in a Cub that ran hot all the time. Checked the sender, dead on, had the cooler boiled and cleaned, no change. Turned out to be a couple of broken rings, a burned piston, and a LOT of blowby. We found it finally, by following the Lycoming guy's recommendation of using an automotive compression tester. It passed a differential compression test just fine. Failed the automotive compression test on two of four cylinders.

I've also seen at least two of these engines that had been taken off a Twin Comanche. In that application, they use a constant speed prop, and they hadn't taken the rear plug out of the crank when they converted it to fixed pitch. No oil circulation. Both these engines came out of the same aircraft rebuild outfit, by the way, and probably off the same Comanche.

Anyway, none of these are good things, and an O-320 really shouldn't run that hot.

MTV