Oil Cooler on Front Ramp...

A member friend has a PA-12 with a Pacer cowl and short engine mount on an O-320 which had a rear baffle mounted oil cooler that would just not work, probably due to very little spacing between the rear of the oil cooler and the firewall. The shop doing the conversion is now putting ramps on the front cylinders,(a good thing) and remounting the oil cooler on the left front ramp.
Has anyone done this before? And with what results?
I've seen other aircraft, like Comanches, with this configuration.
Anything that gets the cooler off the baffles is probably a good thing.....

I have a 160hp 12 with short mount and my cooler's on the rear baffle. Even now (summer) I need a strip of tape to block some flow so the oil temp will get above 180*.

Stewart

I did just that, and it worked well. I left the cooler on the rear baffle, and plumbed both coolers in series. It ran way too cold. I built a cabin controlled flap for the rear cooler, and only open it a little on a long climb on a hot day. It's nice to have control of the cooling.

Stewart, do you live somewhere at low altitude and high humidity?
Do you have a divider plate(vane) along the back of the #4 cylinder to divert cooler (top of cowl) air to the oil cooler? How much spacing between the rear of the cooler and the firewall? And, which brand of cooler??
Carey, how's your altitude and humidity? How well did the rear cooler only work?

Lake Hood Seaplane Base is about 75' asl.

I used a Niagara 20003 cooler. Yes, it's the larger than usual unit, but I may move someplace warm when I grow up. Clearance? 5-6 inches to the firewall off the top of my head.



I'm not savvy enough to enlarge this pic. Look at the photo gallery to get the big picture.

Stewart

I did this stuff when I went to a 160. The rear only cooler was marginal with the 150, not nearly enough when I changed engines. Straight and level at 1000' and 70 degrees OAT was about 210 oil temp at about 90mph with the rear cooler only. Now with the rear cooler flap closed, 90mph@ 90 degrees OAT gives me an oil temp of about 190-195. My flap is on the back side of the cooler, so the air is still hitting the front of the rear cooler.

Stewart, thanks for posting those pictures...I notice that the rear of your cooler has a lot more clearance to the firewall, and it appears that your baffles are the reason. I am presently of the opinion that the regular baffles extending too far to the rear are a major cause of inefficiency in cylinder head cooling. In addition, the way the baffles are sealed to the cowl, i.e. below the rocker covers, should allow for more oil cooling by airflow across the covers. Veddddy interesting.....
Carey, that is some real good performance. Normally(?) oil coolers are connected in parallel, but it would be a heck of a lot easier to do them in series....which cooler is upstream in the oil flow??

I think the front cooler is upstream. I didn't think it would make much difference. If I used a vernatherm, I probably wouldn't have to mess around with the cooler flap. But, I like the idea of forcing as much air over the rear cylinder as possible. I don't know if the rear cooler steals cooling air from the rear cylinder or not, but it's a thought.

Well, sure it does...up here in the high desert, cool wet air molecules are scarce, gotta practically count them by hand....if they go through the rear cooler, they can't go through the cylinder fins...things are bad enough with a front mounted cooler... :roll:

Hi Carey Gray.
Could you post some cooler flap photos, to watch position? tks

SOOOOOO. Before you look at oil temps the big question is what are the CHT'S??? You need to have all the information Oil and CHT/EGT temps of all cylinders. We are taking low HP aircraft and sticking high HP engines into them!!!!!! It is not a simple motor mount! Get some proper gauges/information and you will understand how to fix the problem it is that simple! DENNY

Salex,
This is what I did on a 180 hp Cub. It works, temperature never exceeds 190*. Tilted back at an angle to more align with the air flow. Open more on top than lower down for more efficient airflow. It's a fluid dynamics thing which I'm unable to explain clearly for you. The baffle is tight against the back of #4 cylinder extending above the cylinder with a lip bent forward to help scoop cool air into the cylinder fins. The cool air for the cooler actually passes over the top of the engine before being directed down into the front of the oil cooler. The cylinder baffle separates the heat from the cylinder from the oil cooling air. There are many more parts in the assembly which are holding the cooler than that which appears in the pictures. It must hold the cooler securely since it is subject to shaking vibration from the engine. Also, the attaching hardware for the cooler must carry loads from the aft flange forward to prevent the front flange from cracking. There is a thick strap in the first picture for this purpose. If you have a long bolt place a piece of tubing on the bolt between the flanges to prevent bending the aft flange.

Where’s your oil temp probe? If in the top of the engine case the temps will indicate 15-20° warmer than if the probe is in the oil filter adapter. Since we all compare notes on these topics it’s important to identify the probe location.

If you have a pacer cowl why not just put it up front in the stock location? DENNY

I mounted a lightweight Niagara to the rear baffle 2200 hours ago on my 160 Lyc. Shortly after I added a cabin adjustable flapper between #4 and the cooler to regulate temps. Bad idea! Overheated #4. Now I use an aluminum plate to close off the backside of the cooler in winter weather. That works great. My oil temps ( probe at filter adapter ) routinely run 110 degrees ( +/- 5 ) hotter than OAT.

I pretty much have the same setup skywagon used in post#13, only my cooler is straight up and down. I also use ramps on cylinders 1&2 and those are my coolest cylinders.....cylinder 4 is my hottest at 380 climb and about 340 cruise.
This is on a PA20 PACER with all new baffling.

Sooooo, oil lubes and helps too cool an engine. Now oil temps do not directly reflect what you CHT'S are but there is a relationship. I have seen a Pacer with a new engine have high oil temp issues until it was discovered that one cylinder had a rocker shaft issue causing extreme high temps. You have a plane that has greater HP than stock with a bastard cowling, and now you have moved the oil cooler out of direct airflow (anything else like advanced cam timing, high compression pistons, pepperbox jet, or electronic mags???). You have no clue as to the cause of the problem because you have no information as to what the engine is doing other than burning gas. A hint is if you can not lean 150 degrees before any cylinder hits pitch of peak you are too lean from the start, that may be why you have such high temps in the winter. As far as adding weight you must be one hell of a pilot to notice a flight performance change from one gallon of gas (about the weight of a cat/egt system). I know I am sounding like a hard ass but just saying my oil temps are high does not help find the cause. Post some pict of the baffling/cooler/cowling bottom and any non stock 160 mods. What prop are you running? Did you change the carb when you went to 160 hp? DENNY

salex, This is correct.

DENNY said:

A hint is if you can not lean 150 degrees before any cylinder hits pitch of peak you are too lean from the start, that may be why you have such high temps in the winter.

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The actual EGT number is not relevant as there are no high or low limitations. You are only concerned with the total number of degrees difference between low and high ... full rich and lean. The original Alcor EGT instrument didn't have any temperature numbers on them at all. Only markings for temperature differential.


The rich to lean/temperature curve looks something like this. As the mixture is moved from full rich (left side of chart) toward full lean (right side of chart) the temperature rises then falls. As DENNY mentioned, the height of the temperature curve wants to be a minimum of 150 degrees.

Salex,
This is from the engine's type certificate E-274
NOTE 1. Maximum permissible temperatures are as follows:
Cylinder head 500°F (well-type thermocouple)
Cylinder barrel 325°F
Oil inlet 245°F

I consider 400°F CHT as my personal limit. Only on very hot days does the CHT ever want to exceed 400. In which case I richen the mixture to bring it down.

Your maximum oil temperature being 200 is still below the limit by 45°F. Any of the engine manufactures never seem to mind the oil temperatures being at or near the top limit. Actually being hot helps in "boiling" off any water condensation in the oil. It's better than being on the cool side. (engine will last longer)

One thing which is important is to ensure all the air entering the nose cowl intakes is forced around the engine cylinders and oil cooler as intended. If there are any gaps between the baffles which allows the air to bypass, that air is lost. Some of it can go around the nose of the engine behind the ring gear. One thing to check is the felt baffles which you just installed new actually do seal what is intended. When the engine moves around they need to maintain 100% contact. Do they? It's difficult to know since everything is closed while your flying. In my opinion those felts never did seal very well. They just seem to be there to keep the metal baffles from wearing on the cowl.
This is an optional baffle seal which I used in my Cub. https://www.aircraftspruce.com/catalog/appages/cowlseal06-02461.php?clickkey=50593 It forms a smooth curved tight seal between the engine baffles and the cowl all the way around. The incoming air pressure forces them tight against the cowl. You can see it in the pictures in post #13. I used this type of baffle seal in my 185 also, with positive results.

Another thing you can try for oil temperature control is to place a baffle tight against the back of the #4 cylinder as is shown in this picture. This will keep the heat from #4 from warming up the cooling air before it enters the oil cooler. Notice the forward facing lip at the top which directs air into the cylinder fins. The oil cooling air passes over the top of the entire engine without being heated. You could bend up a temporary baffle similar to this one, just wedging it in place for a test prior to making a permanent fix. Bend the sides back to force the baffle tight against the cylinder. Remember you want the cooling air to go between the cylinder fins, not around the outside.



Your oil temperature probe location is correct.

Sounds like you are running lean. How does your oil temp respond if you do not lean? How much RPM drop do you get when you pull carb heat at 2400 RPM on a 60 degree day? I have a rear mounted oil cooler with the baffle like the picture above. Mine works fine, but I have spent a lot of time with ramps and getting a tight seal also have seaplane lip. I will mention it once again. The question should be why is my oil getting so hot? not why is my oil not getting cooled enough? I believe you are chasing the result of a hot running engine. Getting the oil temp down will not fix the root of the problem. Yes I know everyone ran cubs and Cessna's for years without a CHT/EGT However, that was low power aircraft with stock cowling!! That is not what you have. I can assure you a lot of custom cub builders would love it if a CHT gauge was never invented. SQ and Carbon cubs had lots of temp issues. A few other things to check are the mag timing and primer system. I had a buddy chase a high CHT problem for two years until they found a small hole on the inside of the stainless primer line where it went around # 3 interesting thing is #2 was always the hottest cylinder. Still runs somewhat warm but much better, it is a 0360 with Charley Center cowling. DENNY

If your leaning authority is 100° you’re almost certainly running scary lean in winter. And as Denny says, lean will make cylinders hot, and hot cylinders make oil hot. I shoot for 200° of leaning authority and would rather miss higher than lower.

PS- a typical Alcor EGT gauge does indicate degrees accurately. 25° per mark, if memory serves (I went digital long ago). It doesn’t indicate a value for high temperature. The asterisk is there for you to adjust the needle to indicate your peak EGT or another value you choose.

DENNY said:

SQ and Carbon cubs had lots of temp issues.

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CubCrafters seem to have worked that out on the later models. I have no concerns about CHT or oil temperature operating my FX-3 down here in Arizona. FX-3 has very tight cylinder baffling and the oil cooler is mounted on top at the rear of the crankcase.

I did look back at a few recent screen shots and I couldn't find one with oil temperature lower than 190 deg F in cruise. Highest about 208 deg F I think. It warms up quickly and clears all the moisture out of the oil. Who wouldn't want that?

"The desired oil temperature range for Lycoming engines is from 165˚ to 220˚ F. If the aircraft has a winterization kit, it should be installed when operating in outside air temperatures (OAT) that are below the 40˚ to 45˚ F range."

ref https://www.lycoming.com/content/operating-cold-weather

It's a bit warmer that 80 deg F here in the summer. That would be a very welcome night low temperature at the moment.