N

N62XS

Well Known Member
My new bird has an IO-360-A1B, Sam James Cowl, firewall mounted oil cooler that came with the engine(overhauled) with a 3" duct feeding the oil cooler from the rear right side baffle using Vans firewall mounting kit. On the third flight 1.5 hours, oil temps were in the 225 to 230 range, on a cool winter day(60 degrees). I think this is too high and fear that the summer temps will rise into the 250 to 260 range.

I am considering the following options:

1. Fabricate a larger 4" duct.

2. 9 rib larger oil cooler.

3. (Least desireable personally) Mount the oil cooler on the rear right baffle.

Any ideas/comments/recommendations are appreciated.

Thanks,
Robby Knox
 
Before doing a lot of revamping, check the accuracy of your temp probes. Just remove the sender and set it in a container of hot water on a hotplate with a thermometer. Use a jumper wire and ground to read the temp off your gage. If that checks out OK, then you need to take action.

Roberta
 
Oil Temps

I had the same setup on my 6A when I purchased it. I have a standard Van's cowl with a plenum. The builder ran a 4" scat duct to the firewall mounted oil cooler. My temps were pretty close to what you described.
I had to really watch it in the summer. :eek:
When I converted to a constant speed prop I had to move the oil cooler because it was in the way of the prop governor. I installed the oil cooler on the left side, not right side, behind the #4 cylinder and my oil temps improved immensely. No more oil temp problems! :)
 
Oil Temps

My set up is a firewall mounted Stewart Warner 8432R oil cooler with 3" Scat tubing. The only route that would work was to bring the tubing up and over the engine mount then straight down to the cooler. 4" tubing is not an option.

The first couple of flights had the temps in the 225 range. I boiled the probe and found the sensor was reading 5 degrees cooler than reality.

My next fix was to cut the exhaust tunnel to increase the exit air opening. I raked it forward 3" in front of the firewall. This opened the exit dramatically. The temps now run 198 at near full power. During touch and goes it will indicate 210.

Yesterday I built a ramp on the bottom of the tunnel to hopefully cause a low pressure area and help pull the air out. I flew it today and did not notice any improvement (or worsening). The ramp is one half inch high. I'm going to sand it down to reduce the size.

I'm also going to get some SCEET tubing that has a smooth inside wall and try that.

The 8432 is quite large and won't mount directly to the baffling. There on not many options. Others have said those temps are in line with theirs. The engine only has 14 hours on it so hopefully there will be some improvement as the engine breaks in.

Darwin N. Barrie
Chandler AZ
RV-7 N717EE
 
Your first option - enlarging to a 4" hose sounds like the way to start. The 1" increase in hose diameter will give you almost 80% more airflow to the oil cooler. That should help.

When I first flew my -6, I saw uncomfortably high oil temperatures for the first 100 hours. I tried lots of things, some of which helped in small ways, but the two things that really mattered were getting enough air to the cooler and letting the engine fully break-in.
 
I would try fabricating an exit air plentum that goes to louvers in the cowl, the idea would be instead of forcing the air through the front, to draw air through with low pressure from behind. If you combined that with adding the 4" scat, you might get the temps down.

Some of the fast glass guys here in Socal mount the cooler directly to the side of the cowl, right over the louvers they build for it. The do this buy riveting on then glassing in two piano hinges. They then rivet the other side to the oil cooler flange. This way you can simply pull two pins, and the cooler comes off. Then just run the scat from the baffle to the cooler. Not the most technically advanced method, but it seems to work fine for them.
 
Hummmm

As RV7 guy said he had a hard time fitting the 4", but 4" inch is ideal. However you no doubt have several other things working against you that can be improved. I did do the calculations on flow and duct and 4" is perfect, but 3" will work if all other factors are optimal. Options are use smooth bore hose or go to 3.5 inch might help. Now it is a matter of how you get air into the hose and out and into the cooler, these are called diffusers. Also you should have a SW cooler, there are no substitutes.

Van's oil cooler firewall air box kit SUCKS! There I said it. It is the key to high oil temps on many RV's. That little flat square sheet metal box in their kit, that bolts to the cooler is terrible. It should be shaped like a funnel and have gradual sloped sides. You could make one out of fiberglass fairly easily, even for a metal RV builder.

( Attached are some ideas, click to enlarge, notice the diffusers have have slope sides and the engine mounted cooler has a flex couple to the engine so the cooler is isolated from vibration. ):



The second part to the air going into the cooler is air going out of the cooler's exit area, which should be shielded and in an area of low pressure. Some ducting or baffle of the coolers exit may promote more flow thru the cooler. I personally don't like the cooler mounted on the firewall, but prefer it just off the firewall on the engine mount at an angle vs. perpendicular to the fire wall. I am assuming you are getting air behind the #4 cylinder baffle. Moving the cooler off the FW reduces the hose length. I am NOT a fan of direct baffle mounting of coolers because the baffle and cooler flanges often crack. Dan above experienced the cracking of his cooler. You can reinforce, brace the baffle and put fillers and spacers on the cooler to help, but to me it is a matter of when not if they will crack.


WHAT cooler are you using? The Stewart Warner (or now South Wind) is the most efficient and of course cost the most. All the other "want to bees" clone coolers are marginal to almost adequate but are not as efficient as the SW, for the airflow and oil flow we have. The SW 8604R is what you need.. If you have another cooler than this change will help tremendously. Here is RV-7 Dan's story: http://www.rvproject.com/20040519.html

Pacific Oil Coolers is a good place to call, Phone: 800-866-7335 their site is down? http://www.oilcoolers.com

Obviously your temps are way too high. I assume the engine is broken in? Temp Gauge is calibrated?


Good luck
 
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Robby's oil cooler

Hi guys,
Robby's oil cooler exit duct also goes to the heater box which may have an adverse effect on exit air. We have an 0-360 with the firewall mounted oil cooler and Van's square box with only 2" inlet ducting. Thanks for the info,
Pierre
RV6A 23.5 hours TTSNEW........YEEHAAAAA.........GGGRRRRIIINNNNNN

ps Robby's my buddy so I can talk about him!
 
pierre smith said:
Hi guys,
Robby's oil cooler exit duct also goes to the heater box which may have an adverse effect on exit air. We have an 0-360 with the firewall mounted oil cooler and Van's square box with only 2" inlet ducting.
Click to expand...

Please clarify. Do you mean:

1. The air exiting the oil cooler is then going to the heater box, through a 2" duct, or

2. The duct that takes air from the baffle goes to a "Y" that feeds both the oil cooler and the heater muff, or

3. Something else.

If you meant #1, it is no wonder that oil temperatures are high. All the air going through the cooler has to also go through that 2" duct to the heater box. The air coming out of the cooler is warmer than the inlet air, and has thus expanded. So a 2" exit duct is a huge bottleneck and would greatly limit the airflow. There is no point to going to a larger diameter inlet duct until you improve the ability to exit the air. That is where your bottleneck is right now. You would undoubtedly see some improvement just by removing the exit plenum (i.e. whatever it is that transitions from the cooler to the 2" duct) from the back of the oil cooler.
 
Either way, that sounds like Bad Idea? to me. Forcing exit air through another path is the last thing you want to do. You need at least a 3" scat (the size that you have going in or bigger) going to a low pressure area. Hence the Louver idea in my previous post.
 
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