The International Cessna 170 Association

Hi gang i got a question aboout oil temp's in the cold winter cond. I have been flying around home lately with temp's in the 20's and my oil temp. will not go above 100 deg. I have my oil pan hole blocked and just wanted to know if this is normal. this is my second winter in it and last year my oil temp gage took a dump so i don't know what it was reading last winter so any info would be great.

We'll assume your oil gage is working correctly now.

100 degrees seems a little cool but I'm not surprised. You need to block of probably as much as half of the from cool air intakes.

Here is one of many threads about this very thng.
http://www.cessna170.org/phpBB2/viewtopic.php?t=3029

I've also been flying recently in temps lower than 30F, the oil-pan air opening blocked with duct tape. My gauge is showing temps of about 150F. I'm going to try taping 1/4 of my cowling inlet closed next time I go up.

100 degrees F sounds kind of cold for oil temp with the vent closed off.

You should try to get about 180 so as to rid the engine of any condensate.
with the sump and inlets plated I would red line the oil temps in high cruise, I removed the sump plate and I cruise in the range of 190. But then again my temps were always a little high.

My '53 has the blast tubes that route cold air on the oil screen / oil filter adapter. I blocked the inlet of those blast tubes with 3/4 x 1" rubber plugs. Now when it's 25 F outside my oil temp has gone from 120/130 to 150/160 range.

Thanks for the info. now i have a good reason to go back out to fly in the cold. think iam going to try the blast tubes and cyl. inlet's should do the trick. Bruce did i meet you at sentimentle this past summer? my 52 is polished with blue trim...........

Covering up the blast tubes that duct air to the oil screen does not really raise your oil temp. It only increases the indicated temp by raising the temp at the sensor in the screen. If you want to really scare yourself, leave the cover over over the blast tube and see what happens to your indicated oil temp on a 90 degree August day. If it makes you feel better, go ahead, but your oil temp really does not change as much as the guage indicates. Like many of us, my oil temp barely comes off the peg on cold days. I have a cover over my oil cooler inlet the winter months. Fortunately, in Tennessee we rarely get temps lower than the high 20's. I do condone using multi weight oil in the winter months. Seing the oil pressue guage come to life instantly on a 30 degree day is comforting. With 100W, it seems like you could die of old age waiting for the needle to move. ONLY FIVE MONTHS TO THE PETIT JEAN 170 FLY IN. For any of you who are within weekend flying distance of Arkansas, do not miss it. If you are curious, check the postings in the Fly In's forum.

Bodine it was me at Sentimental Journey. Will be there next year as well. Perhaps we should have a 170 gathering there.

I agree with t7275tr. Blocking the blast tubes only raises the indicated oil temperature and won't raise the overall oil temperature significantly.

I have the older non-pressurized cowl. I block 2 out of the 4 openings horizontally and block the oil sump cooling hole as well. My temps will make it over 180 in 20 degree weather. BTW I use a plane old round inspection cover for a rag wing to cover the oil sump cooling hole.

The oil temperature sending bulb is located in the center of the output oil screen and is surrounded by oil. Oil is the medium that transfers its temperature to the sensing bulb. That's the oil temperature as the oil starts its journey through the oil galleys of the engine. That starting point is the standard location for oil temperature sensing on all engines with pressure lubrication.

N9149A wrote:I agree with t7275tr. Blocking the blast tubes only raises the indicated oil temperature and won't raise the overall oil temperature significantly.

You're correct that I do not know how much (if any) cooling those blast tubes are doing, but now with that cold air blocked off I do feel my gage more accurately reflects the true temperature of the oil. And it does make me feel better to see my needle in the middle of the range now instead of way at the bottom.

An AP friend says you want to get the oil temp above 160 once and a while to boil off the acids in the oil??
Duct tape, duct tape, and more duct tape.
Oil 15w-50 year round.
As temps drop in the fall
1st. Blast tubes on rear baffle taped up.
2nd. Oil cooler hole on from nose bowl (this is progressive)
3rd. Front cowl openings this also progressive starting on the inside and moving out. Not much past the cylinder barrels about half way is as far as I go.

Flying back the other day my temp were as follows:
OAT Oil Temp
10F 185
0F 165
-10to-20F 140 to 145 this was while desending and doing low level scouting.

N9149A wrote:I agree with t7275tr. Blocking the blast tubes only raises the indicated oil temperature and won't raise the overall oil temperature significantly.

There is an opinion that is commonly held, that the blast tubes' purpose is to blow air onto the probe to "trick" the oil temp readouts. I feel that is an incorrect interpretation.
The oil suction screen, where the blast tube directs it's air, is the pickup point for the oil pump. The design criteria for the engine calls for oil temp readings to be taken at the oil "inlet"....and the screen is indeed the inlet point of the system (since it happens to be where the pump picks up the oil for distribution.)
The blast tubes help assure that the oil temps in the screen are kept at the specified "inlet" temp.
If, the oil in the inlet (screen) is denied cooling air in the winter.... does that mean the oil temp we see indicated in the cockpit is no longer valid? Does it only raise the "indicated oil temperature and won't raise the overall oil temperature significantly"? I don't think so.
I think that if the oil in the sump is running 180 degrees, and the blast tubes lower it at the screen where it enters the pump, down to 120... then blocking that blast tube so that the indications come back up to 180.... is a valid indication of the oil in the sump AND the screen. This is because the screen is no longer contributing to the cool-down of the oil on it's way to the pump inlet. In other words... if the blast tubes are blocked off...then the blast tubes will no longer COOL the oil down as they did before. The oil reaching the inlet will be more like that in the sump. (But truly,....it will not actually "raise" temps above that already in the sump.)

gahorn wrote:

N9149A wrote:I agree with t7275tr. Blocking the blast tubes only raises the indicated oil temperature and won't raise the overall oil temperature significantly.

....... In other words... if the blast tubes are blocked off...then the blast tubes will no longer COOL the oil down as they did before. The oil reaching the inlet will be more like that in the sump. (But truly,....it will not actually "raise" temps above that already in the sump.)

George I think we said the same thing differently.

t7275tr wrote:Covering up the blast tubes that duct air to the oil screen does not really raise your oil temp. It only increases the indicated temp by raising the temp at the sensor in the screen. If you want to really scare yourself, leave the cover over over the blast tube and see what happens to your indicated oil temp on a 90 degree August day.

I've heard this one ever since I bought my airplane. The story goes that Cessna cured an oil temp problem by just cooling the sensor. Well, it's just my humble opinion, but I believe this an old wives tale. I don't see how you can change the temperature of the sensor without changing the temperature of the moving oil it's immersed in.

Miles

Miles I think the oil at the sensor is cooler but it doesn't accurately reflect the temperature of ALL the oil. An yes by it's nature the blast tube would cool the oil but not significantly.

Since the temperature readings we use in other seasons has the blast tube cooling that spot how would you compare a reading of 180 degrees i the summer with the blast tube against 180 degrees in the winter without the blast tube. In other words your changing the calibration of the measuring system. IMHO

My point all along is that I have not found it necessary to block the blast tubes to raise my oil temperature to 180 degrees at an OAT of 20F.