CHTs too high

We have CHTs that average well over 400 deg. on our Lycomig 180 hp carburated engine. We have an aluminum film on the inside of the cowling;bafflling is good as far as we can tell, magneto timing has been checked. We are considering using RV-10 lower cowl vents to allow for more outflow from the cowling. It appears that we have about 10 or 12 square inches less outflow area than we have inflow area. Should there be a positive presssure in the cowling? Is there any drawback to providing increased outflow capacity? Thanks.

HIGH CHT's

You haven't given many particulars here. How hard are you running your engine? How many hours? Do they improve once you settle in to cruise, 24 squared?
The film you mention in your cowling doesn't do anything for CHT. It helps from scorching your cowl surface next to a hot exhaust mostly.
The louvers you mention really helped my CHT's from going over 400 during climbing to cruise altitude.
The over 400 CHT, does it occur even when you're at cruise and 24 squared and mixture leaned out?

hot?

Please search for this on forum, been discussed several times. Best answers come from oil cooler type, location, opening baffeling on left front cyl( just move it out with a washer) same on right rear. The lower price oil cooler Van's sells did not do the job. These minor changes lowered my temps 40 degrees.

CHT's too high

This is usually not oil cooler related however it is true most RV8's with an 0360 will require a large oil cooler to keep oil temps down especially if your engine has piston oil squirters installed. The CHT problem is almost always poor baffle installaton. The washer offset on he back of the baffles should be done. Also look at the markoff on the upper cowl, it will tell you if you are getting a good seal. ON the -8 cowlings, the past few years VANS has increased the lower cowl exhaust area to help with CHT cooling. If you have an older cowl it may require vents. Call Vans and find out what vintage cowl you have. Put the vents on as a last option as they are ugly. Make sure your baffleing is seated tight around the engine and sealed with high temp sealer and that full contact is being made with the upper cowling. The fwd baffleing is one of the places I see done poorly on alot of airplanes.

My -8 has the piston oil squirters so I have very low CHT's 290-330 however the heat removed from the pistons/CHT's with the squirters transfers heat to my oil so I have a very large oil cooler.

CHT's may also be a little high during engine break in. Also the foil tape is needed more on the lower cowl in the exhaust stack area and Im not sure adds any value on the upper cowl.

My 2 cents.

Pat

Chts too high

If the high chts are too high only in the climb, check to see what carb you have ? The 10-3878 doesn't supply enough fuel in the climb and you can modify it or switch to a richer carb.
Good Luck

Quite a few engines have a lot of casting flashing between the fins in the cylinder heads. Look down between the fins, while shining a flashlight up from below. I pulled out a bunch of loose flashing pieces using a piece of stainless wire with a hook bent on the end, and I removed a lot more with a needle file.