lml@lancaironline.net Mailing List Archive

Good information Randy.

On this bird, the cylinder with the highest CHT (#3) has the least amount of exhaust piping in its vicinity. As you know the exhaust pipes are routed around the left side. Those side cylinders (#2, #4) have CHT's lower than #3. Also, the headers are heat coated on the inside. The engine has been sealed up with RTV at every opening. That was the first thing I did 10 years ago. The bottom wrap-under baffling on #3 was opened up then also. I have modified the rear baffling on #3 head so as to create an air space where there was none before (the rear of #3 has no cooling fins so the baffling is typically tight against the head). Removing the 4" exit scat tubing from the oil coolers did nothing to lower the CHT's or RAISE the oil temps. Bottom cowl rear exit area (sq. in.) was calculated and is equal to or more than standard 320 and RV cowls.

How do you do visual condition inspections on the headers with the pipe wrap on them? Of all the repairs I have had to do in the engine compartment, the most have been to the headers. Multiple cracks to weld - stainless headers.

Gary

----- Original Message -----

From: randy snarr

To: lml@lancaironline.net

Sent: Monday, March 09, 2009 10:41 AM

Subject: [LML] Re: oil cooling/ head temps

Gary, One side note on the head temps. I made my plennum similar to yours.
My head temps run within 6 deg of each other usually 310-360 F depending on power and temps.

One thing that I did was to shine a light up through the bottom of engine with the hangar lights out and found and sealed EVERY gap in the baffeling except where cooling air needs to go with high temp RTV.
I also opened up the gap on the bottom of each cyl to 2.6" times the dept of the cooling fins as I read somewhere NASA had done some testing and determined that was the optimum opening. I also radiused the baffeling exits inder the cylingers rather than 90 deg bends on the exits. I understand that helps flow as well.

I have also come to the conclusion that there is airflow coming into the cowl through the nose gear slot and bottom exit cowl area. I see this when I get an oil leak. the oil runs down and then blows forward. Weird. Ayway, you may need a small 45 deg lip on the bottom of your cowl exit like I probably do.

One last thing of note, in my pictures you will see the exhaust wrap, that did make a difference on head temps and it also evened them up. My exhaust wraps around the engine like yours does and runs close under the cyinders. I wrapped those areas with 4 layers of exhaust wrap and 2 or 3 layres everywhere else and have had good results lowering engine compartment temps-unmeasured but it appears to be so. I tested the heat wrap on my heat gun. With 4 loose layres I could hold my hand on a heat gun nozzle on the high heat setting. That sold me on that stuff.

FWIW...
Randy Snarr
N694RS

--- On Sat, 3/7/09, Gary Edwards <gary21sn@hotmail.com> wrote:

From: Gary Edwards <gary21sn@hotmail.com>
Subject: [LML] Re: oil cooling
To: lml@lancaironline.net
Date: Saturday, March 7, 2009, 6:33 PM

It seems that most temp issues are with oil. Mine are not with oil, but with CHT's.

As you know (you have seen pictures), I have 2 smaller (6" round) oil coolers, one on each side (mounted to the engine mount) with naca ducts and short 4" to 6" long straight 2" inch scat duct to them. The scat duct is connected via glass enlargers. On the outlet side, there are glass reducers down to 4" scat duct, with the duct routed down to near the nose gear front cover on the firewall. It as close to the lower cowl outlet area that I could get.

The oil temps. are too low, especially in winter. It is difficult to get the temp to 180. In summer, the oil temp is about 190 to 200 climb and cruise. I tried (for winter) closing off one cooler with duct tape over the cowl inlet to raise the temp and it didn't make any difference. Tried it on both sides. I also removed the 4" outlet duct (reducers left on), to let the outlet flow directly into the rear cowl area, with no change noticed. In only one case, have I had a high oil temp; in Bend, Or., giving a friend a ride after a previous flight. Outside temp in the '70's. Never has happened again.

Now, if I could just get my CHT's down. I have to step climb with that issue when at gross weight.

Gary Edwards

LNC2 235/320