High Oil Temperature

[2718]

'47 C-120: C-85-12F non-electric, 6qt. oil tank, oil filter
2700TT; 800 SMOH (1991)
O.H. #3 50hrs. ago, Installed new baffling
Annual 5 hrs.ago: 76/78/78/78 comps.
Switched from Type 'M' Phillips to 20W50 X-Ctry.
Installed remanufactured left and right mags

OAT 70-80F. Oil Temp. climbs to "red-line" (225F) after 25mintes.
Gauge checks okay.

Thanks in advance for all help, input and advice.

[2718]

Forgot to mention Oi Pressure holds 34-36psi

[6643]

Check your baffles.

Do you have the blast tube that blows on the oil screen housing?

[tonycondon]

what was the method you used to check the gauge?

[2718]

Early 120s did not have blast tube for screen. It did have 0450166 oil sump baffle
which I believe does not fit and/or do any good for six quart sump. Not installed.
I will recheck to make sure the inter cylinder baffles are present and correctly in place.
Immersed temp. probe into sauce pan of water and heated with Coleman stove. with food therometer(2).
Gauge is remarkably accurate.
p.s. Engine used less than 1 quart of oil in 5 hrs. since annual.

[6597]

My parts manual sez the '46 birds had a blast tube, here's a screen shot of the page, see 37-26. There's a Neal Wright article on how to make a simple alternative, and I recall an article somewhere that someone used lawn chair tubing to make one.

https://www.cessna120140.com/Forum2018/ ... ?f=10&t=99

I don't recall the dynamics for needing a blast tube on the oil temp sensor housing.

Untitled.jpeg (93.77 KiB) Viewed 119 times

[6643]

I don't recall the dynamics for needing a blast tube on the oil temp sensor housing.

It cools the oil!

All the oil passes through the oil screen housing. Buried in the center of that oil is the temp sensor. If the gauge reads lower it's because the oil is cooler.

The C90 is supposed to have the 5 quart tank and baffle, and the blast tube. It's also supposed the have a lip on the bottom of the lower cowl to decrease the pressure in the lower cowl, and increase the airflow through the cowl.

From the Aircraft Specification:
When the Continental C-90-12F engine is installed, it is necessary for Cessna 0450240 blast tube assembly and Cessna
0452183 lower cowl assembly with Cessna 0452208 lower cowl bottom doubler or the equivalent to be installed.

Mine has all that stuff. The "equivalency" of my doubler is questionable. When it's not hot out (say, less than 80 degrees) I have trouble getting the oil temp up to 180. I attribute it to tight baffling. The seals between the outer edges of the baffles and the cowl are critical.

[edit] I don't know why I thought we were talking about a C90... Old timer's disease, I guess. Anyhow, if I can keep my C90 cool, it should be a cakewalk for a C85.

[2718]

Gentlemen, I appreciate the dialog. My C-120 was built in February 1947. Have owned it for 40 years.
Half of the total time I put on it. It has never had the "blast tube" from the factory, nor added.
She always ran relatively hot on 90 degree plus days. 205-210 degrees.
The baffling and cylinders are in as good a condition as they have been in years.
Maybe just a coincidence, but with the new mags, all of the sudden 225 degree(red-line) oil temps.
I trust my I/A as he used to have a C-140A. I am confident the timing is exact.
But is there something going on inside/internal timing. He will be mad when he reads this, but we're still
friends, I hope.

[tonycondon]

if changing the magnetos effected the oil temperature, then the new timing is definitely suspicious. I know timing being off just a little can have a major effect on CHT!

[8281]

If You know how to read a Spark Plug, that's where I would start! This will tell a Knowledgeable person
what is going on in the combustion chamber.
Since the mags were changed out and the trimming is correct(assuming),
where was the trimming set with the old mags? (Probably low)!
Hince, if the trimming is correct, then the air/fuel ratio is not correct!
My Opinion!