Hot Exhaust nozzle

This seems odd to me.......On my Cat 3116 starboard motor the exhaust elbow is nice and cool, but the black exhaust boot / hose is very hot. The heat is just after the clamps so I would think that the exhaust water flowing from the cool elbow would stay cool 3 inches from the elbow into the exhaust boot (if that is the correct terminology??) Any ideas ?? Could it be the transmission cooler water flowing into the elbow ?? The engine is running about 185-190 at high RPMS and appears stable........Thanks in advance.......

Thanks for the info......I did have the impellers replaced last November as well as the heat exchangers cleaned out. I thought I would remove the black exhaust boots and see if I can tell what the issue is in the elbow / riser. Always Something !! I am surprised that the engine temp seems OK though ??

Do I dare ask how much the "mixers" cost to replace??

OK......I finally ran the boat again. The black rubber exhaust hose appears to be 6" in diameter. The metal elbow / nozzle/diffuser that it is attached to is cool to the touch all around. The black boot is cool except for an area about 2" back from the clamps / elbow. for about a 3" area on the top half only of the boot it registers 220 degrees when operating the motors for a couple of hours at 1900 rpm's or so. The rest of the boot all the way to the fiberglass elbow is cool. It seems to have a "hot" spot.....the hose is labeled 250 degree limit but it just seems the diffuser might have an issue ?? Any info would be appreciated ...thanks in advance.

Thanks .....I will send Jorge a photo. Is the spray ring a part of the riser / elbow that the rubber boot connects to?? If so do I necessarily need to replace the entire elbow or can I just replace the ring ??

OK.....The solution. Thanks to Jorge I have a solution. I removed the elbow......Starboard side and solid brass so a pain in the neck.....2 person job. After removing it the mechanic took it to his shop and decided to weld a couple of fins on the stainless spray ring directing the water towards the top and so far running at 2000 rpms for about 20 minutes it stayed cool.....what a difference !! Another option was to weld a couple of holes on the bottom shut so more pressure on the top directing the water where the heat was.....same concept and it worked !!!! Thanks to all that helped me with this. I'm glad I didn't need any parts !!!!