Second Oil Cooler Upgrade
Unleashed has always been plagued by one problem, high oil temperature. The original setup for racing in 2006 included a water spray bar on the oil cooler. This did help, but made it very difficult to manage. Nothing like one more quantity to maintain during flight! I have constantly been working to improve the oil temps, but nothing really solved the problem. I had it to the point where we could eliminate the water spray bar, but if you did a long climb, or the OAT was high, the oil temps would go to redline if not managed with power. The best thing I found was retard the timing on the engine. This did sacrifice some power but it was worth saving the engine in general. If we were going to race at Reno this year, this problem had to be solved.
The original oil cooler was only 9 rows and for most 180-200 hp engines that would work, but maybe not enough for UNLEASHED. In general it was thought that adding a bigger oil cooler would solve the problem. But, with the tight cowling I was unable to install a bigger oil cooler in place of the old one. So the next step was to add a second oil cooler, and just for good measure I would add 6 more rows of cooling capacity. In theory this had to solve the problem.
To be sure all of the oil was cooled, we plumbed the second oil cooler in series with the first cooler. The only space available was on the firewall in the same location the original oil cooler was located. Then we began the debate about bringing cooling air off the rear baffle or from the outside of the cowl with a NACA duct. In regards to CHT’s the engine is very cool and the plenum I made works very well. Sometimes CHT’s are not warm enough. So with all of that in mind, I thought it would be ok to use some of that plenum air to use on a second oil cooler with no noticeable rise in CHT’s. This second oil cooler would not need much air to provide that little bit of extra cooling we needed. For that reason we used a 2″ sceet tube from the #4 baffle. (#4 had the lowest CHT’s also)
So, how to get air from a tube 2″ in diameter to cover an oil cooler? Build another plenum.. again Your probably used to this part. Get some polypropylene foam, shape it up, cover it in glass, melt the mold, glue it on. Done. And for that first amazing test flight when all would be solved and oil temps would be in the green? Didn’t happen. Oil temps remained as high as before. That was a dream crusher, let me tell ya.. So now I knew something was very wrong. Next step was to remove the vernatherm to test that it was working properly and forcing oil to the oil cooler when needed. Well, that engine is so tight in that little Lancair that I couldn’t remove the vernatherm without taking off the entire oil filter adapter. 4 bolts, some oil lines, tach cable and a big mess later, adapter was out. First thing I notice is the gasket from the adapter to the accessory case is clearly not correct. I mean, it isn’t even close. And to top it off, that gasket is blocking 75% of the port that allows oil to flow to the oil cooler, as well as letting oil bypass the vernatherm. Amazing.. simply amazing.
So, $3 gasket later, oil temps are 40 degrees cooler. You can do a max power climb as long as you want and never see much over 200.