Ineffective Oil Cooler on O-200

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proppastie

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Higher hp allows higher angle climb at redline rpm.... usually fixed pitch prop can't get redline in the climb.....
Reference power flow exhaust or 150 to 160 hp Cherokee conversion...C150-150
 

Pops

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C-85's in Ercoupes have a hole in the nose bowl below the spinner and a baffle under the engine and close to the front of the oil tank for extra cooling over the bottom of the engine and oil tank. Could do the same for the 0-200.
 

rv7charlie

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A corollary to my previous post is that if he's flying the same speed at the same altitude and the same OAT, the engine is making the same HP as before, and the heat (cooling) load didn't change, even though the engine got 'pumped up' in capability. Something changed other than the heat load.

One of my neighbors built an RV7 and as soon as he started flying it, he fought oil cooling issues for months. Changed all sorts of stuff, all the way up to replacing the oil cooler with a significantly larger cooler, and nothing helped. In frustration, he finally grabbed his laser thermometer and pointed it down the oil fill tube after a flight. wups...oil in the sump was cooler than his gauge said it was coming out of the cooler. This cannot be, if the oil temp sensor is plumbed according to standard practice for aircraft....
 

Marc Bourget

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In addition to oil heat-in vs. heat-out, since a box is installed on the air supply side, consider installing a water manometer fore and aft of the cooler to check the Delta P across the cooler. You can do this with a single plastic tube and piccolo tubes at the end and loop it in the cockpit. Use colored water backed by a white card.
 

Bob H

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I don't have answers for the O-200 situation but do have a surprise heat exchanger improvement story.
The Rotax 912 engine on a Pulsar had an oil cooler of ~48 sq in. shingle-mounted in front of the radiator with about 1.5" spacing.
Both coolers are located behind/below the rear of engine. Incoming cowl air passes thru the oil cooler and then passes thru the radiator and out of plane. On long 6000' continuous climbs from desert airport to Big Bear airport at 7000', oil would get hot to 240+F and CHT to 245+F.
Ambient temps around 100F at start of flights. I changed to an 84 sq in oil cooler but it blocked off more radiator area and I thought the oil temp would decrease but the coolant temps would increase. Turned out just the opposite in that both oil and coolant dropped by 25F.
The air temp thru the oil cooler must have dropped as expected and that cooler air entered the radiator to reduce the coolant temp.
Bottom line was a benefit in temps for both the oil and coolant.
 

wsimpso1

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Can you please elaborate on this statement? There are many things to do to an engine to increase efficiency/torque output at the same RPM. Throw a big turbo on an O-200 and it will make several hundred percent more power at the previous data plate redline RPM - for a minute or two.

Porting, induction, exhaust, big compression, EI, camshaft profile - all contribute to the BMEP of any Otto cycle engine.
My premise, and you quoted it, is using the same prop before and after. Zenith 601's use fixed pitch props. Now maybe this one is unusual and has an electric controllable prop, but I seriously doubt it. In level flight and at any air density and prop pitch, there is a single curve of prop torque consumed vs rpm, and thus a single curve of hp expressed vs rpm. So, if the owner is turning the same fixed pitch prop at the same rpm and altitudes before and after the engine mods, it is making the same power over the duty cycle as it did before, and will have the same heat rejection.

Sure, there are many ways we can modify any engine to make more torque and thus power available at useable rpm, but we have to be able to react that torque or you will not make the power. If we add some pitch or diameter or blade width to the prop, we will then move the whole torque vs rpm curve for that prop, and maybe the engine can make all of its power. That is the beauty of the constant speed prop. An adequately selected set of blades in a constant speed prop and with stops set appropriately will allow us to extract as much power as the engine can make. But using the same fixed pitch prop at the same rpm and airspeed IS the same power...

Billski
 

Marc W

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Temp sensor was replaced-no change.

He isn't making more power than he made in Alabama. DA starts out around 7500' on the field lately and increases rapidly as you climb. We are in a valley surrounded by 10,000' to 12,000' mountains so we have an inversion layer. Another pilot, with a DA readout on his efis said it was indicating 10,000' DA just above pattern altitude of 6,200' a few days ago.

Anyway, lots of good info in this thread that I will relay. His plan is to lock the bypass valve closed to see if that helps.
 
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A number of us old timers did do our fair share of building hot car engines and I would say ALL of us had to deal with higher engine temperatures. Raising compression by installing higher compression pistons 8.5 low side to 10.5 on high side by LightSpeed, Lycon boys and others as well as re-working C85 pistons create issues that must be dealt with. Fuel, ignition and timing, engine cooling, breathing and many other issues. 0-200 operating at 2700 prior to surgery and after surgery operating at 2700 will generate more heat. I am not a engineer but no from practical experience years ago.
 

Victor Bravo

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A friend has a bit of a puzzler. He has a Zenith 601 with a Continental O-200. He bought the airplane in coastal Alabama. He winters there. He few it there and oil temperatures were good. He left Alabama in the spring to fly the airplane to western Colorado. He didn't make it far. One of the rocker pins came adrift and wore itself through the valve cover. Engine didn't like that and he made a forced landing.

He had the engine rebuilt and repaired the airframe damage. The engine rebuilder installed different pistons to make a claimed 118 HP. My friend flew it in the southeast for a while and said oil temps were normal. He started west and started having high oil temperature problems over New Mexico which have continued.

He installed an oil cooler adapter under the oil filter and installed a nine row oil cooler. The oil cooler adapter is on the left side of the engine and he hung the oil cooler on the right side of the engine so there is a good three feet of AN6 hose coming and going. He originally had a 2" scat hose feeding air to the cooler off the baffles on the right side. The oil cooler didn't help at all. He then replaced the oil temp sender. I suggested he run a 3" scat hose instead and he did that. He tested it today and it didn't make any significant difference. Hard to say if it helped because conditions were not the same.

He doesn't have an ideal setup. The scat hose first makes a 30 degree bend downward from the plenum and then makes a 90 degree bend to enter the cooler. He has at least 6' of AN6 hose connecting the cooler to the adapter. Also elbows on the adapter and the cooler. Not an optimum setup. Even so, it seems like the oil cooler should help some.

The oil cooler adapter has a pressure relief spring that bypasses the cooler when oil is cold and oil pressure is high. It sends oil to the cooler when the oil warms and the oil pressure drops. I am suspicious of that unit also but he claims they checked it.

It may be a perfect storm of poor airflow to the cooler because of the bends in the scat hose and to much AN6 oil hose with to many 90 degree elbows. Also the higher density altitudes here. However, I am wondering if there something that could have happened inside the engine to dump more heat into the oil? Incidentally CHT's are fine, somewhere around 300 degrees.

Sucking the airflow out of the cooler is as much or more important than blowing air "at" the cooler.

SCAT tube and "quick and dirty" ducting ain't gonna cut it when you have hot-rodded the engine AND you don't have high airspeeds and pressure differentials.

High deck angles when climbing can turn a (poorly designed) cooling air "exit" into a horrible scoop trying to reverse the flow thru the cooling system, because the air "inlets" at the front of the cowl are in a lower pressure area with the nose high.

IMHO if you have a 2 or 2.5 inch SCAT tube supplying air to a crude diffuser... that might work OK on a 120 climb/200 cruise airplane... which the Zenairs aint. And the SCAT tube has ducting losses as mentioned by someone else.

If you are interested, take some pictures of the bottom "air exit" under the back of the cowl, and some pictures of the front air "inlets", and post them here. Myself and several others might have some useful insights, suggestions, etc. based on the photos.
 
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Paul Saccani

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Try deleting the by-pass valve - its sole function is to speed engine/oil warm up in cold climates. Its an unnecessary complicating, that may also be defective. I have always found oil coolers to be effective, even with minimal air flow they will do something to cool the oil.
That is not correct. The by-pass valve prevents oil starvation when cold, thick oil is clogging the cooler. It also prevents oil starvation if the cooler becomes clogged with debris/sludge. Dependant on the susceptibility of the cooler to these issues, the latter functions can be vastly more important than a fast warm-up. The by-pass does need to be checked, including for correct orientation. Removal for test purposes is reasonable. However, the first priority in this instance is check and calibration of the instrumentation - replacing the instrument does not in itself assure that the temperature data is correct.
 

D Hillberg

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After 'overhaul' was the engine properly broken in, in accordance with the engine manufactures procedure?
Had a few Aircoups that worked for a few hours then petered out after overhauls because the owners just didn't know...
Ran good in Alabama then Hot running lack of power in New Mexico???. A few hours??? Top End?
Snort Bon ami scouring powder ? [cuts the glaze]
 

Victor Bravo

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Snort Bon ami scouring powder ? [cuts the glaze]
There was a break-in abrasive compound for small 2 stroke model airplane engines many many decades ago called Fox Lustrox. You were supposed to put a tiny coke spoon's worth of this stuff on the edge of the carburetor venturi, and it would slowly siphon off a tiny little bit at a time over a mnute or two, and then "break in" (or hone or polish, whatever) the engine internals.

But using abrasive like Bon Ami in a full size 4 stroke aircraft engine... that sounds like a recipe for getting abrasive into all sorts of parts that you don't want abraded. Bearings, bushings, cam lobe faces, hydrauic lifters, gears... OMFG... Don what'cha been snorting up there in the desert?
 

Marc W

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The owner of the airplane and oil cooler made a test of the installation this morning. He had made one change since he flew it last. He shifted the cooler over a bit to give the 3" scat hose feeding the cooler a little straighter path to the cooler. The move also gave the exit air more room to exit.

This morning he blocked off the air to the cooler and flew the plane. OAT was 67F. Density altitude would have been in the 6000' range. The oil temp quickly climbed to 220 degrees so he landed. He then restored the air flow to the cooler, invited me along and we took off again. The oil temp was 185 on takeoff. It went to 207 in the climb and stabilized there. It dropped back to 202 in cruise. So he is satisfied for the time being since the airplane is now useable in cooler temps.

The engine has 65 hours on it since OH. I don't know how long it takes an O-200 to break in?
 

D Hillberg

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The owner of the airplane and oil cooler made a test of the installation this morning. He had made one change since he flew it last. He shifted the cooler over a bit to give the 3" scat hose feeding the cooler a little straighter path to the cooler. The move also gave the exit air more room to exit.

This morning he blocked off the air to the cooler and flew the plane. OAT was 67F. Density altitude would have been in the 6000' range. The oil temp quickly climbed to 220 degrees so he landed. He then restored the air flow to the cooler, invited me along and we took off again. The oil temp was 185 on takeoff. It went to 207 in the climb and stabilized there. It dropped back to 202 in cruise. So he is satisfied for the time being since the airplane is now useable in cooler temps.

The engine has 65 hours on it since OH. I don't know how long it takes an O-200 to break in?
It takes an hour and 15 minutes to brake in on the schedule - power and rest power and rest monitor oil and CHT it's in the manual

Usually over haul problems show in a few hours [10 to 40 odd for brake in goofs] that's what time Harry had his temps went wild [40+], or very quick like blown jugs and pieces littering the taxiway...
we did a quick top end and normal brake in and he flew for years until he got a Gruman Cheater .
His Chinese CJ 6 was awesome
 
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Victor Bravo

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SSSsooooo.... back to the OP's cooling issue. My offer still stands, that if you post some good, detailed photos of the bottom of the cowl, air intakes, bottom of the firewall, etc. that myself and others here might have some good suggestions to reduce your temperatures and increase the safety margin related to the oil temps.
 

Marc W

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Thanks, but since it isn't my airplane or my project, I think my involvement is about at an end.
 

Skippydiesel

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That is not correct. The by-pass valve prevents oil starvation when cold, thick oil is clogging the cooler. It also prevents oil starvation if the cooler becomes clogged with debris/sludge. Dependant on the susceptibility of the cooler to these issues, the latter functions can be vastly more important than a fast warm-up. The by-pass does need to be checked, including for correct orientation. Removal for test purposes is reasonable. However, the first priority in this instance is check and calibration of the instrumentation - replacing the instrument does not in itself assure that the temperature data is correct.
1660811391108.png
Diagram from Dan Thomas - Engine Oil Design thread on this Forum.

Sure the bypass will do just that in the unlikely event of the oil cooler getting blocked but its main purpose is to open when the oil temperature reaches a predetermined point, thus allowing hot oil to go through the cooler/be cooled.

Without the bypass the oil would go through the cooler at all times, this would slow engine warm up, increase engine ware and fuel consumption and may lead pilots to ask for full power before the engine oil gets into minimum flight temperature, causing other damage.
The bypass/verntherm has greatest application in cold climates/conditions and is less relevant in the opposite.
 
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