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Dula737

I'm New Here
I have a RV-6A that has an 8 Row Stewart Warner Oil Cooler mounted on the firewall behind the #3 cylinder. I use a 3" scat tube to run air to the oil cooler. Every summer I have issues with oil cooling and am looking for a good solution, especially since I live in Las Vegas!
I use a plenum for cylinder cooling so mounting behind the #4 cylinder is not an option.
My question is: does anyone have experience with using a NACA duct to route air from the side of the cowling to the oil cooler. Or using a duct/vent on the bottom of the cowl to help draw air more efficiently. Looking for ideas and pitfalls to watch out for. Thanks.

Mark DuLaney
RV-6A
 
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How are your CHT's. If #1 is low, a cylinder blocker in front of #1 will direct a surprising amount of air elsewhere.

<edit> Many years ago, Van's wrote something in the RVator saying that a 3" SCAT tube is inadequate for feeding the oil cooler. A 4" hose will feed 2x the air. You should try upsizing there. My experience with the standard baffle kit was that once I got the hole feeding air to the cooler large enough, oil temperature stopped being a problem.
 
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Cooling

What steps lead you to the oil cooler being the cause for your temp issue?

A good friend of mine has a RV6 with a plenum cooling system and his oil cooler mounts on the back of the plenum with a sliding door that he opens and closes. Why can't you move your cooler to the rear of the plenum?
 
Dula737 said:
I<snip> 8 Row Stewart Warner Oil Cooler mounted on the firewall behind the #3 cylinder. I use a 3" scat tube to run air to the oil cooler. <snip>Looking for ideas and pitfalls to watch out for. Thanks.
Click to expand...


I'd try to upsize to a 4" SCAT tube first. That will flow a lot (77%) more air through the cooler and is probably the easiest single change you could make.

James Freeman
 
The increase due to the larger diameter assumes that all the loss is in the SCAT tube, which is not correct. The larger SCAT may or may not make a difference. I run a 3" line on my 6A O360, and do not have oil temp problems. I might see 200F in level flight at low altitudes with OAT of around 90F.

What sort of a transition do you have from the round SCAT tube to the oil cooler? A smooth expansion there may be more important than the size of the SCAT tube. Also, is that area well sealed against air leakage?

Knowing what your CHT's are doing would help the group also, as has been mentioned already.

Good luck, keep us posted.
 
Thanks for the inputs. My CHT's run around 380-390 on #3, that is normally my warmest cylinder. Oil temps typically are 210-220 at cruise with OAT of 85 or above. If I slow down, even at a lower power setting, they will get on up towards 230. Interesting enough, when running lean of peak at cruise the oil temps will start to come back towards a normal range 190-200.
The SCAT transition to the oil cooler is pretty good. It goes into a molded aluminum transition "box" that sits on top of the oil cooler. It is all sealed very good.
The 4" SCAT is a good idea. We (my mechanic and I) have looked at putting a 4" line in, however, it would be an extremely tight fit through the engine mount braces and would take some rework on the plenum. One of my ideas is to add a 2" line on a NACA Duct on the side of the cowl to the oil cooler to go along with the 3" line. However, not sure how pressure differentials would interact. Does anyone have any experience or knowledge of how a NACA duct might work for providing air to the oil cooler. Thanks for all the inputs, I am just trying to gather as much knowledge as I can before I start cutting holes.
 
The best location is behind the #4 cylinder for the oil cooler. With my engine, IO-360 A3B6D, the plumbing for the oil return lines are all on the #3 side. That would be my first choice but would require major rework. Thought about adding a secondary smaller oil cooler in that location, but was advised against it.
 
Adding a 2" line might help some, but not much, because it won't generate much airflow volume. In rough terms, a 2" SCAT tube has a cross section of 3 square inches, a 3" tube has an area of 7 square inches, and a 4" tube has a cross section of 12.5 square inches. You'd need your 3" tube and two more 2" tubes to more or less equal the cross sectional area of one 4" tube. In addition, due to the way air moves, you'll get less airflow per square inch in a smaller tube than a large one, so the three tube combination won't really flow as much as the big one even though the net cross section is roughly the same.

This retrofit may seem like a real pain, but you'll be happiest if you simply deal with it instead of making half steps. I used short cuts to try and reduce oil temperatures for the first 6 or 8 months with my airplane. I spent much more time on all of my ineffective fixes than it took when I finally took 2 or 3 hours and fixed the problem by enlarging the baffle hole feeding the cooler.
 
Kyle
I also have a 6A with firewall mounted oil cooler and 3" hose. My oil temps have been a little high (210) lately. You said in your post that you made the hole in the baffle larger. What size did you start with and enlarge to. I currently have only a 2" hole in the baffle and have been thinking of making it bigger. Thanks in advance. Randy
 
I have an O-320 (170hp) with the SJ plenum and used the Van's FW mounted oil cooler setup with a 3" tube. With the plenum, the 3" outlet sits almost directly behind that #4 cylinder with only a small portion stickin up above the cylinder. I've had no problems with oil temps at all.... even on 100+ degree days. Highest I've had is 195 and usually runs around 185 in cruise on warm days.

I know this probably doesn't solve your problem but I think it would be OK to have you scat tube behind the cylinder. What about oil cooler quality, I know there are different brands and have heard there is night/day difference. Is the SW the better brand?? I can't remember...
 
The hole in my #4 baffle is the width of the cooler ( maybe 3" - 4"?). I'm not sure how tall it is, but its bottom is even with the top of the cylinder and rises to about 1" from the top of the baffles.

The hole is roughly 75% the size of the oil cooler, which is mounted to the baffles with a 1/4" standoff.
 
Oil Temps

Hey Dula, (how about putting a signature box at the bottom)

I went through the same thing with my 7 and ECI IO 360 here is the Phoenix area. I had a Stewart Warner 8432R mounted on the firewall, left side. The 8432R is the dual pass expensive unit. I made a tapered flange for the cooler and mounted a flange on the back of the baffling above the #4 cylinder. Even in the winter I was above 200 degrees. I tried re-routing the 3" SCAT tubing (reduced the bends) with minor positive results. There was not enough geography for 4" SCAT.

Finally, I utilized a special offset box that Robbie Attaway developed on the back of the baffling behind the #4 cylinder. The box allows the larger coolers to be used on the stock baffling systems.

Now, even in the peak of summer my temps rarely rise about 200 in flight. I'll get a peak of around 210 when taxiing back to the house. The temps in cruise will consistently sit at around 178.

The temps are so low I'll probably have to block some of the intake to the cooler when winter hits. Now all I have to do is monitor the CHT's when climbing. I will occasionally hit 430 on the #4 requiring a stepped climb on the real hot days.

I'll get some photos and post.
 
I'm going through the same thing with my IO-360-A1A (200 hp) Lycoming on my RV8. I had a firewall mounted oil cooler and the 3" scat coming from the rear engine baffle behind the #4 Cyl. This summer I was seeing oil temps between 225-230 degrees on hot days out here in Denver in climbs. They also wouldn't cool down very quick or much when I transitioned from climb to cruise.... They might drop to 218 or so, but it took a long time...

I'm started "Experimenting" (Hey, its an experimental afterall :)) and recently built a temporary bracket and moved the cooler off the firewall between the engine brackets so I could increase the amount of airflow that exited the cooler. I also enlarged the opening behind the #4 cylinder to a 4" hole so I could increase the airflow to the cooler... My oil temps have dropped significantly! I now see about 190 in cruise and about 200-205 in climbs and in this is still in a hot (97 degree) Denver day. The Density Altitude on my last flight when I took off at airport elevation was 9000 feet (field elevation of about 5883) So the air was hot and thin.. The cooler seemed to be working much better. I should also mention that once I transitioned from climb to cruise that the oil temps would start dropping MUCH faster than the would before... This tells me that airflow was the answer to my problem anyway.

Now I just need to get a better mounting bracket and make things look nice and neat...

BTW, anyone know where I can get a 4" flange for Scat tubing? I made one, but I dont like it. Aircraft Spruce has a 3" (part 10350-12) but they dont have a 4" that I could find.
 
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