J

jimbower

Well Known Member
I apologize if there is already a thread for this topic, but I didn?t find anything I could use. After a long build (more than 11 years) my RV-6A took to the air in August (flown by my flight adviser). It sat for several weeks until I came back from getting transition training, then I started to fly off my 40 hours. For several reasons, my next few flights were of short duration (half hour to 45 minutes), so I never noticed high oil temps. However, I finally saw the oil temps climb to around 227 degrees, only decreasing as I pulled back the power and lowered the nose.

I am running an overhauled O-320 with a fixed pitch 3-blade Catto prop. Cooling baffles are from Van?s FWF kit. I have several penetrations in them: one 2? SCAT tube to the heat muff, two 1? SCAT tubes for cooling the battery and my one magneto, and a 3? SCAT tube from the back baffle to the oil cooler which is mounted on the firewall (again, using Van?s kit). All that air (plus what was flowing over the cylinders) is being routed to the back of the cowling.

I?m sure oil is being circulated through the cooler, so that leaves airflow as the culprit. It?s my semi-educated theory that all the air being dumped into the back of the cowling is not able to exit the cowl fast enough to allow a negative pressure area and permit proper airflow through the oil cooler. The exhaust pipes fill some of that rectangular opening, and the nose gear structure may block some air.

I have a set of louvers on order from Avery Tools, but have not received them yet. I am hoping they will contribute to a better airflow out of the cowling. Thoughts?

What puzzles me is that my configuration is not much different from those built by others, so why am I having this problem? I know of no way to observe whether sufficient air is flowing, so I really need some ideas here. As it is, I can?t fly the airplane very long until the oil temps reach unacceptably high levels. Lycoming recommends 180-190, with an absolute maximum of 245. My temps might get that high under sustained level flight, and I have no desire to damage my engine.

Thanks in advance for your help. I welcome any and all suggestions.

Jim Bower
RV-6A N143DJ
Flying (sort-of)
St. Louis, MO
 
Possible help

Jim, although I did not build my plane, I do recall having a conversation from the previous owner that I bought the plane from regarding the oil cooler. Like yours, mine was initially installed on the firewall with I assume scat tube directing air. The oil temp was high and the only way the previous owner could rectify the problem was to move the cooler to the back of the engine baffling. The previous owner is an AE with lots of homebuild experience.

Hope this gives you a direction to look.

Good luck, AL
 
Instead of installing louvers, we opened the cowling outlet 5/8 of an inch.
We don't have a oil temp issue, but had high CHTs. They dropped 15-30 degrees. The data seems to indicate that we also gained 3-4 knots:eek:

Our friend John found this article ( http://www.mnwing.org/Sept2011.pdf ) just as we were about to make the cowl exit increase final. We increased the opening at that time from 1/2 to 5/8 inch. W didn't go all the way to 3/4 as indicated in the article. It was nice to know that the test data was accurate.
 
Ken,

I'm using the one that was supplied in the Van's FWF kit...not sure of the brand. I've heard others have used bigger oil coolers...don't know if that's indicated here, but I'm open to anything.

Al,

I wanted to avoid the cracking baffle issues I've heard about so that's why I mounted it on the firewall. I have not ruled out moving it to the back of the baffle if I can't solve this problem any other way. Thanks.

Jim
 
The stock oil cooler in the Van's kit for the O-320 would typically be a 7-row Niagra (NDM), and is usually plenty big enough for a carbureted 320.

The 3" diameter SCAT tube from the baffle to the cooler is probably restricting airflow to the cooler too much.

Many folks here on the forums who've firewall-mounted their coolers say that you must use 4" SCAT along with 4" baffle flange to keep enough air flowing to the cooler.
 
Neal@F14 said:
The stock oil cooler in the Van's kit for the O-320 would typically be a 7-row Niagra (NDM), and is usually plenty big enough for a carbureted 320.

The 3" diameter SCAT tube from the baffle to the cooler is probably restricting airflow to the cooler too much.

Many folks here on the forums who've firewall-mounted their coolers say that you must use 4" SCAT along with 4" baffle flange to keep enough air flowing to the cooler.
Click to expand...

Maybe with stock VANS OC but with a SW OC a 3" scat works great with an O-360.
 
RE: High Oil Temp

Hi Jim

I am one of those other threads..............:confused:

My experience is start from simple and work out from there.

IF the vernatherm (if you have one) is OK, temp sender is OK, all baffeling is shut tight and solid, engine is timed correctly, the engine is healthy (compression is good), and ect.....................it is as you said not ejecting enough hot air or the oil cooler isn't keeping up..........

If it were me the simplest change would be to increase the airflow to the FW mounted oil cooler. I would order up a 4 inch scet tube ($$$$$$$$$$$$$$) from Spruces, (smooth air flow compared to scat tube)

http://www.aircraftspruce.com/search/search.php?query=sceet&search=1


build a 4 inch exit / inlet, install, go fly, and smile!!!!! Of course remember I am an old retired chemistry school teacher so what do I know? :eek:

Frank @ 1L8 ...RV7A... wait for the new heavy duty oil cooler from PAcific
 
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