Ineffective Oil Cooler on O-200

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Marc W

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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.
 

TFF

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If the air comes from a scat hose, does it go into a defuser or is it just a hose pointed at the cooler?
 

rv7charlie

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Well, if the claim of 118 HP is legit, then according to most opinions about an O-200's real HP, that's at least 25% more power than stock, and quite possibly a lot higher percentage, if the engine was 'tired' when originally installed. Did he increase the total cooling inlet or outlet areas? If not, the oil cooler is just robbing some of the original cooling air.

And SCAT hose is really draggy. And a 2" hose is ~3.14 sq inches. Sounds a lot smaller than the face of a 9 row cooler. And like TFF just posted, without a proper diffuser, its effective area is even smaller due to turbulence.
 

Marc W

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They made a rectangular air box to run the scat hose into. He claims the oil temps were OK in Alabama with the new engine. He did replace the 2" hose with 3".
 

Pops

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I use two 2" dia scat tubing to the oil cooler on my little 1835 cc engine with a box the size of the face of the oil cooler and about 3" high. Almost works to good. If the OAT's are 70 deg or below I unhook one of the hoses. Need to make a cable operated valve.
 

Dan Thomas

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What does the backside of the cooler encounter? Is it getting airflow off the engine or anywhere else that inhibits the airflow though it?

Is the cooler new, or some old thing? These coolers get varnished up inside. That insulates the oil from the aluminum passageways. Some accumulate a lot of sludge and filth in them, blocking some of the passages.

The pressure relief should be checked to see that it's working properly. It might be relieving all the time, bypassing the cooler. Lycoming uses a temperature-sensing valve for this.

Is the air off the plenum being heated by a cylinder?
 

TiPi

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Start troubleshooting with gathering numbers:
fit 2 thermocouples to the inlet and outlet fittings of the oil cooler (junctions only, wrapped with plenty of electrical tape to the oil cooler connection boss). Then record the in and out temps at different flight conditions. Once you have real numbers, the next step(s) will be revealed.
 

wsimpso1

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"Doesn't help at all" is not data. Data is:
With no cooler oil temp was Tsump1 when ambient was Tamb1;
With a cooler and 3" scat tube, sump oil temp was Toil3 when ambient temp was Tamb3. Oil into cooler was Tin3, oil out of the cooler was Tout3.

If the difference between sump and ambient is the same with all versions, then the cooler really is doing nothing. Only really possible with zero flow of either air through the cooler or oil through the cooler or both very small.
Temp sensing (already suggested) of the oil fittings on the cooler are important to finding what needs fixing. Temp sensors of air ahead of and behind the cooler may also be useful.

If the difference between sump and ambient gets smaller with mods, the cooler is doing something, but maybe not enough. Temp sensing of oil in and out of the cooler will again indicate if you need better oil flow or better air flow or even both. Again air temps across the cooler may also be useful.

Data takes the problem out of guesswork and into diagnosis. There are a bunch of possible scenarios, so let's get a little data so we can both know what needs changing and how much change is needed.

Billski
 

Marc W

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It's not my baby. All I can do is make suggestions. Just looking for possibilities that might have been overlooked.

I don't know the history on the cooler. The outside is clean and I assumed it was new but you know how that goes. They claimed they checked the valve but I guarantee they didn't check it like I would check it.

However, I am wondering if there something that could have happened inside the engine to dump more heat into the oil?
This is really my question.
 

rv7charlie

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Related to Bilski's comments, how about some numbers?

What were the environmental temps in the SE before moving west, and what are the environmental temps out west? It would be reasonable to see some correlation between changes in environmental temps and changes in various engine temps. If he was in the SE in winter, and the SW in summer....

If CHTs haven't changed, it seems curious that oil temps have changed significantly, since all the heat loads should be related in a fairly consistent way. I didn't see any mention of checks on the gauge itself. If the gauge has developed issues (grounding of the gauge, for instance), he might be chasing a ghost.
 

Marc W

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Yes, numbers would be nice but I haven't heard any. They did put something that changes color on the cooler outlet side that showed 220 degrees. It doesn't really tell anything since the temps inside the cowl are probably that hot. I don't know if he checked the gauge. It has a Dynon efis.
 

TFF

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If you happen by, get pictures. Sometimes planes get flown different when they move across the country. If the flights are longer now, he might never have got it hot enough. Alabama gets pretty darn hot. Density is different but flow direction inside the cowl should not be different.
 

Skippydiesel

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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.
 

BBerson

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With high compression pistons it will need higher octane fuel to avoid entering detonation. Probably around 8.7-1 for aircooled. Might need to lower the timing.
 
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wsimpso1

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It's not my baby. All I can do is make suggestions. Just looking for possibilities that might have been overlooked.

I don't know the history on the cooler. The outside is clean and I assumed it was new but you know how that goes. They claimed they checked the valve but I guarantee they didn't check it like I would check it.


This is really my question.
Helping a friend might mean educating on the importance of having data to assist in troubleshooting. In the case of heat sources rejecting heat to the atmosphere, temperature of source and sink matters.

If this O-200 is being operated at higher horsepower than before, sure, heat rejected to air through oil and through head fins will be higher. Unless the owner went to a different prop, operating at higher horsepower is only achievable through running at higher rpm. Did the owner change the prop or run higher rpm for the various phases of flight?

Steady state temps at the Sump, HX In, HX Out, and Ambient tell the story;
  • Ideal world: HX In really close to Sump, HX Out is lower than HX In, and they all go up and down with Ambient;
  • If HX In and HX Out are close to each other and close to Sump, then oil is flowing but little heat is going to the air - little or no air flow through HX or HX is insulating the oil from the air;
  • If HX In and HX Out are near Ambient, little or no oil is flowing through the HX, but airflow is occuring;
  • If HX In is close to Sump, and HX Out is close to Ambient, oil flow through HX is low and air flow through the HX is good.
Each of these scenarios has different things to fix them. This is why data is so important.

Billski
 
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Toobuilder

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... Unless the owner went to a different prop, operating at higher horsepower is only achievable through running at higher rpm...

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.
 

rv7charlie

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Oh Oh Oh, ask me! ;-)

The prop-a/c combination is the dyno. The engine makes X HP at a particular condition of flight. If it makes X+Y HP on that same a/c, the prop turns faster and the plane moves faster. This obviously assumes a fixed pitch prop. With a c/s prop, 'it depends'. At what point on its efficiency curve was the prop operating before the increase in HP?
 
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