Hey everyone. A friend of mine noticed while flying with me that my oil temp was around 140-150 degrees in the climb and only 120 degrees in cruise. This seems to be what I'm consistently getting. He found this article from Mike Busch saying that temps below 170 degrees doesn't allow for moisture in the water to be purged. Has anyone had this issue? What did you do? Tape off a part of the oil cooler to try to raise the temperature?

Thanks,
GSP

Here is the article:

Lie #6:
The cooler the engine's oil and cylinder head temperatures, the better.

It turns out that the "cooler is better" notion isn't quite right. While excessively high temperatures are bad for your engine, low temperatures are no great shakes, either.

Take oil temperatures. Most of our airplanes have oil temperature gauges that have a green arc running from 75°F to 240°F, with a red-line at 240°F. Now, 240°F is way hotter than we'd like to see. Keep in mind that the oil temperature probe is usually located at the place in the oil system where the oil is coolest, often near the outlet of the oil cooler. So if the gauge reads 240°F, the oil is probably hitting close to 280°F at the hottest point in its circuit through the engine. That's hot enough to cause petroleum-based oil to oxidize and break down at an accelerated rate. We've either got to bring down the oil temps, or change the oil very frequently.

On the other hand, oil temperatures lower than 170°F or so on the gauge present a different problem...namely, that the oil is probably not reaching the boiling point of water at the hottest point in its travel. Why is this important? Every time we shut down the engine, a slug of water condenses inside the cooling engine and runs down into the oil sump. If we don't get rid of this water the next time we fly, there will be a progressive water build-up inside the engine. That water will mix with the sulfur and nitrogen byproducts of combustion to form sulfuric and nitric acid. And that will start eating away at the innards of our engine. The solution is to make sure the oil gets hot enough to boil off the entrapped water, so that the resulting steam passes harmlessly out the breather.

Oil temperatures of 180°F to 200°F on the gauge are hot enough to get rid of this water, yet cool enough not to accelerate the breakdown of the oil. So that's ideally where we'd like to see our oil temperature gauge in-flight.

What about cylinder head temperatures? The CHT gauge on a TCM engine usually has a green arc from 200°F to 460°F, with a red-line at 460°F. Lycomings generally have a CHT red-line of 500°F. Once again, red-line CHT is way too hot for optimum engine longevity. At those temperatures, the aluminum cylinder heads are vulnerable to cracking, and the exhaust valve guides are vulnerable to accelerated wear.

On the other hand, CHTs below about 300°F create another problem: lead fouling. Our engines operate on avgas that contains large amounts of tetraethyl lead (TEL). Even so-called "100LL" contains enough TEL to keep the EPA awake at night. The purpose of TEL is to enhance the octane (detonation resistance) of the fuel. Unfortunately, it also can cause lead deposits in the engine, particularly on spark plug electrodes and in piston ring grooves.

To prevent such lead fouling, avgas contains a "lead scavenging agent" called ethylene dibromide, whose job it is to dissolve excess lead and let it pass harmlessly out the exhaust pipe. However, ethylene dibromide doesn't do its scavenging job unless combustion temperatures are fairly high. That's why lead fouling problems tend to emerge when CHTs are below about 300°F.

Ideally, we should try to keep CHTs in the 350°F to 400°F range as much as possible. That's cool enough to keep the cylinder heads and valve guides happy, but hot enough for effective lead scavenging.

You can use metal tape on the oil cooler. Start with covering half and see what that does. You can add or take away strips as needed from there. We have to do the same every winter.

CW

Water doesn't have to boil to vaporize, it just does it faster the closer to the boiling point it is. The lower the pressure (higher the altitude) the faster it will vaporize. So if your flights are long enough, I'd guess you're okay, BUT... You should still prob do what you can to get above 170F.

Cowl flaps shut? leaned out. Hows the cabin temp? Do you have a cylindar temp probe too? Just wondering if your oil temp probe is o.k.....just a thought.

Thanks guys.

Bighorn. We put in a new oil temp gauge last spring, so the probe is good. I also have a probe on my engine analyzer (previous owner didn't pay to have it made primary, thus having the other one). Even though they sample at different places, the temps are similar. Cowl flaps closed, running around 65 degrees LOP, cabin nice and cozy (the heater works great in this plane) and CHTs in the mid 300s.

I think I'll experiment with taping it and see what it gives me.

GP

My 206 is only 1 year older and I think the oil cooler is in the same spot. 520 Cont. but here in Minnesota I have not had and issue getting the oil temp where it should be......wish I could help more.
when we had the 172 we taped off part of the cowl (no oil cooler) and that helped. The Champ needs to be taped as well. Just get it warm before you want to remove some tape and it comes off fine.
It did get up to 18 yesterday so I had to take some off the Champ.

Let us know on yours.

Cory I just made a round to SLC Wednesday and back yesterday saw oil temps at 145-155 temperature inversion most the way using 9500 msl going north and 10500 coming back OAT was 35-40 ground temps 20-25. You might check your vernatherm it's hard to get to with the prop on but I made a tool to get it out with prop on, take a sacrificial socket (I'm thinking it was about 1 1/2" or so) cut about 3/8" off of the end off then weld a 8-10" piece of flat like 1/2 x 3/16" across the short socket piece that you cut off.

If you can get it out inspect it real close and see if it's got a full circle around the end that shows it's seating tight, put into one of Dee's nice clean stainless steel pots when she's not around with a pulp thermometer bring the temp up and watch it to see if it functions like a thermostat of a car. You probably just need to cover part of your oil cooler but 120 is way to cold. Might check your gauge and sending unit too.

BTW I flew into U42 South Valley they tucked 64Z into their hanger overnight oil temp was 50 in the morning. OAT on T/O was 15 climbed out south bound temps came up real nice. Fueled at CDC and came home, turning downwind to base I heard a click noise in my headset a couple times looked over at the amp meter saw a full -50 amp discharge 2x and then smoke out the right panel , shut the master on final before the fire started and the smoke stopped.

Got to the hangar pulled the right seat and part of the panel out found the stall warning horn hot wire had been rubbing on the heater vent cable and shorted out. Don't know why the circuit breaker didn't take care of that but I will resolve that.

There is this gizmo called vernitherm in your oil cooler. It is essentially a thermostat for your oil system. It stays closed when your oil is cold and opens up when it is warm and allows the oil to circulate, as pointed out like your radiator in your car. Sometimes they break, work poorly, or some shade tree mech changes it out with one to open at a much lower temp to combat high oil temp. You may want to have this unit checked, or you can use tape. Kind of the redneck way to do it, but it will work. Most oil cooler shops can check it out for you. You can do the hot water technique, but it is best to have a shop test it, as they have a test rig and it checks sealing and spring tension.

Cessnas that operate in cold weather up here usually have installed covers over the oil cooler and that partially cover the cowl inlets. Piper high wings usually just have the oil cooler cover. The vernatherm is an important unit, but it does not make the oil cooler completely close off, and the temperature difference in my PA-22 from putting on the oil cooler cover is almost 30 degrees oil temp.

First, YES you do want to get the oil temp up to at least 170-180 deg F, on every flight if at all possible.

Depending on your ambient temps, you may have to cover the entire cooler or just part. Start out covering half the cooler (duct tape works fine, and is cheap) and increase coverage or decrease as appropriate.

Bear in mind, this implies you will need to pay close attention to temps on every flight...don't get complacent.

For years, I put duct tape on the whole oil cooler in a Husky and a 206 in Fairbanks about Oct 15, and it came off as temps raised in April. But, the temps there generally STAY cold all winter.

I ran the "official" Cessna winter covers my first winter in FAI, but took them off soon, because of inversions. I never did like blocking off the front of the cowl on any airplane.

MTV

mtv wrote:First, YES you do want to get the oil temp up to at least 170-180 deg F, on every flight if at all possible.

Depending on your ambient temps, you may have to cover the entire cooler or just part. Start out covering half the cooler (duct tape works fine, and is cheap) and increase coverage or decrease as appropriate.

Bear in mind, this implies you will need to pay close attention to temps on every flight...don't get complacent.

For years, I put duct tape on the whole oil cooler in a Husky and a 206 in Fairbanks about Oct 15, and it came off as temps raised in April. But, the temps there generally STAY cold all winter.

I ran the "official" Cessna winter covers my first winter in FAI, but took them off soon, because of inversions. I never did like blocking off the front of the cowl on any airplane.

MTV

I don't like blocking off the cowl either but I have viewed it as the lesser of 2 evils..............do you have an alternative
to get the temp up?

Thanks guys. I'll start working on checking that out. I should have mentioned, I've seen these same temps all year long. I also just put on the winter kit since it has gotten cold here (below 20 degrees). Out of the inversion it was about 38 and was where we saw the temps I referenced.

Russ, glad you got home ok. Man, that had to get your attention!

Bighorn, not sure where it is on the 520. On the 470 the probe is below the oil cooler on the sump. The probe for the EDM 700 is just after the cooler.

What are you describing as the "Winter kit"? The Cessna winter kit for these airplanes includes a block off plate for the induction with a circular hole in the center, about three to four inches in diameter, and block off plates that cover both upper cowl air inlets, each of which has a rectangular hole in it. The one on the right (oil cooler) side has a sort of ramp to direct some air to the oil cooler from that rectangular hole.

I found that with those front covers in place, anything above about +10 or so the engine CHTs ran waaaay too high, and as a result I had to stay low in the inversion.....duh. And, once airborne with those on, you had to watch CHT very carefully at all times, even in cold temps. Finally, these block off plates effectively reduce cabin heated air flow to near nothing. I never ran those upper block off plates again, and I would NEVER run those unless I had a reliable six probe CHT gauge. If you go to northern Alaska, you will almost never see Cessnas with the winter fronts installed. The induction block off plates, yes, the upper block off plates no. And, most operators just cover half or all the oil cooler with duct tape. Common practice.

On the other hand, any time temps get below about freezing temps, I WOULD install the induction block off plate. This plate is designed to prevent "overboosting" the engine at max power, since the engine is capable of more than rated power at very low density altitudes (dense air). That plate restricts the flow of air through the air filter, and at max power, the engine is demanding more air than can be pulled through that small circular opening. This draws a vacuum in the induction, which opens the alternate air door, which is spring loaded. That door then permits warmer air from within the lower cowling to feed into the engine, effectively warming the induction air. Since in winter there's LESS chance of particulate in the air, the risk of unfiltered induction air is minimal.

MTV

If you are seeing those temps with any of the winter cover options installed, then something is very out of whack.

Troy Hamon wrote:If you are seeing those temps with any of the winter cover options installed, then something is very out of whack.

Agreed.

MTV

I'm doing some digging on this. I came across a thread off of some site that suggests that it might have to do with LOP ops.

http://aviating.com/pipermail/beech-owners/2012-October/218258.html

Thoughts?

As for the winter kit...or as the illustrated parts manual calls it, the Winterization Equipment, are just two plates that screw onto the intake to reduce flow.

Okay, remind me what model airplane are you talking about?

That illustration is precisely the kit I was talking about, minus the induction block off plate to prevent over boost.

My experience with those front covers has been that if OAT is over about 20 degrees F, you'll see some pretty high CHTs....as in near or over recommended limits.

LOP ops will SLIGHTLY lower CHTs, but these block off plates SERIOUSLY reduce air flow through the engines cooling system.

Again, go to northern Alaska and look at the cowling of all the working Cessnas up there, and you will rarely see one of these kits installed, simply because you'll often have warmer temps aloft. And nobody wants to have to drive around down low in the inversion. These are airplanes being run routinely in temps well below zero.

Unless your ambient temps are consistently and constantly below zero F, I'd never run those things.

Again, I agree with Troy....if you're running those things in temps above zero, and CHTs are staying low, I'd check your CHT system....something is wrong.

Cover half the oil cooler with duct tape and see what that does for your temps. Adjust coverage as necessary. On IO 520 and 550 engines, running in very cold temps out of Fairbanks, I generally kept half the cooler covered, ran in cruise with cowl flaps shut and oil temps always ran at or above 180 once warmed up. With those engines, I like to see CHTs just above 300 F. Any CHT s close to 400 are too high in my experience.

MTV

You indicated above that you were confident in your gauge, but I think I would get the measurement end of that oil temp unit in a vat of boiling water and look for 212F. The temps you cite are so far off that I wouldn't do too much before verifying the accuracy.

And if accurate, then definitely the oil cooler needs blocked off at least partially.

And, before you run those winter fronts, verify the accuracy of your CHT probes.

Also, I assume you are using the cowl flaps AND that they are rigged to actually close fully?

MTV

MTV, question for you. In my citabria, how does one get the oil temps higher without blocking off the cowl inlets? No oil cooler to tape off, so does one just tape off as much if the cowling inlets as is needed to insure temps over 170? Its a tough one for me as I dont currently have a CHT, but that is on my short list of things to install...