Dan Thomas
Touchdown! Greaser!
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Dan Thomas
It IS an oil leak, and it's why the cooler is wet there. It's seeping oil. Those ridges are welded together to form the cooler channels, and that chafed area has worn though the weld. That oil cooler was junk a long time ago.Looks a lot like an oil leak
Cessna wants oil cooler on their airplanes to be flushed every 1000 hours. Crud builds up inside them. And even with flushing, varnish gradually forms on the inside surfaces, insulating the hot oil from the cooling metal. We once had a 172 that ran hot right after we installed a new engine. Hotter is normal, but redline is not, and I had to keep terminating the test flights due to redline oil temps. The gauge checked out accurate. The oil cooler airflow was right. The engine oil system plumbing, internally and externally, was all right. The cooler had been flushed at engine change, and flushing it again made no difference.
A new oil cooler fixed the problem instantly. Varnish in the old one. Look inside an engine's crankcase sometime; if it's got lots of hours on it, it's all nice and brown inside. Varnish.