The Temp is a killer, also creates moisture traps.
The second stage (high pressure) piston composite ring goes first.
Adding those PC fan cooling to the compressor steel tubes won't do much. With a same effort you shall increase the water flow instead.
I am copying my post from AGN from a while back.
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About heat on cylinder heads...here are 3 readings on a freshly rebuilt first+second stage from a kit. The pressure is about 250 bars in this picture after some 15 minutes run time.
The Temp #1 probe is attached to the most highest point on first stage = low pressure cylinder ribs deep to the main body;
The Temp #2 probe is attached to the most highest point on second stage - high pressure cylinder - aluminum cap;
The original YH Temp sensor shows the water flow going back to the bucket.
Here are the addon Temp sensors attached. Also notice the addon - high flow air fan.
The Temp readings are after I changed the water flow...
- re-drill the waterlines (in aluminum cylinder head) to larger flow
- replaced the barb fittings to larger flow
- replaced the water pump to 4-5x larger pressure/flow.
I just feed the bucket continuously from a garden hose in my garage and the overflow is a collateral damage

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Last I checked about 67 hours on this YH, with regular maintenance, some rebuilds and some updates. I have not ran it this year yet.