#4 cylinder cooling

I recently completed an oil cooler airflow control door on my RV8, and immediately noted a reduction in #4 cylinder head temperature when the door is closed in flight. The oil cooler is mounted in the standard position aft of the #4 cylinder. Before the airflow control door was installed, the #4 cylinder has always been the warmest, sometimes 30 degrees higher than the coolest cylinder. With the door closed, the split is now 15-20 degrees warmer than the coolest cylinder (#2). It appears that the oil cooler "robs" enough air from #4 to make it run hotter. Has anyone developed a baffle system that causes the airflow to the oil cooler to be shared with all of the cylinders, and not "rob" it from just #4? Thanks for any suggestion!

Craig, when you're thinking about what might be happening, remember #4 has the exhaust port on the rear. I'd bet you can change the deltaT across that small section of critical fining with minor changes to the tinwork.

I agree with Dan.

But, it might be worth using a water manometer to check the Delta P in various places "above and below" the Cylinder and the oil cooler.

The minor changes Dan mentioned could be real minor.

mjb

The "trying to understand" is why I suggested studying the "problem" with a manometer set-up!

mjb

I have the same issue (RV-6A / IO-320 / std cowl). Since installing the larger cooler (larger cut out in baffle), my #4 runs about 25* hotter than the others. I put a small curved AL piece on the back wall to try and divert some air to the head fins near the Ex valve. I probably need a bigger piece or something to take a bit more air from the cooler. The previous cooler (#4 was only about 10* higher) sat a bit higher and likely stole less air from the #4 cylinder.

My climb temps top out at 400 in the worst of conditions (the end of a long climb) and cruise temps are under 350, so I haven't worked hard to address this.

Larry

#4 cylinder warm

Thanks, Dan, Larry and Mark, for your suggestions. I have daydreamed up some air directors to put more air on the exhaust side of #4. I'll report the results.....

I'm not sure what you mean by air directors, but it reminds me of the approach Jabiru takes. I wouldn't go there.

We may be speaking to the same point, but I'd focus on massaging the baffles for that cylinder rather than redirecting the air.

mjb