2006 Yamaha 200 HPDI housing very warm after running on muffs

After changing out the Racor water-separator filter and the in-line fuel filter under the cowling...ran the engine on the muffs for about 10 minutes...checked for fuel leak. Good water flow from pee-hole and thru hub exhaust. Upon removing the muffs, happened to touch the housing just above the cavitation plate (where the plastic nut insert for the anode is located)-almost too hot to hold onto. I have never had the occasion to touch that area after running on the muffs...IS THIS NORMAL??? Thanking you in advance...John Castelluccio, Jr. Southeast Louisiana---Lower Bayou State

Muffs are for flushing only, not extended running. Your engine will eventually over heat on Muffs.

What Chris said. Never run an engine (especially that size) on muffs for more than 2-3 minutes and if you've loaded the boat on a trailer and towed it home, you can run it for 2-3 minutes on muffs but the engine has cooled to the point the thermostat has closed and it won't open again for a full flush on muffs. If you are able to put the engine on muffs within a few minutes of putting it on a trailer or hoisting it on a davit when the engine is still HOT, then it's worth it and actually better than any flush port it may have to hook a hose up to.