Blueabyss

What year is the motor. Are they dry joint manifolds. Take a pic of the manifolds and post. If they are dry joint, I know what your problem is.

Chris

Blueabyss

Dry Joint Manifold and Risers that is.

muc

Might want to look at Service Bulletin 95-13 This bulletin talks about alpha gen 2 overheating and covers the paint issue BUP mentioned. It recommends replacing one of the water hoses with a clear hose to watch for air bubbles. Using a clear water hose is a very common troubleshooting technique when trying to track down overheating issues. And is one of the next steps you should take.

The engine serial number you posted belongs to an engine that was built August 1991. This engine has never been registered with MerCruiser. So if there are any recalls, you or the previous owner wouldn't have been notified. Suggest you contact a MerCruiser dealer or MerCruiser and get it registered into your name.

Is it possible the new thermostat was installed wrong? The plastic sleeve that holds the thermostat in has slots in it to allow water to the elbows. If installed wrong it could easily cause this problem.

Might want to post a picture of your engine so we can make sure you have the Design 2 cooling system on it.

Blueabyss

Also define overheating. Are you saying the risers are too hot or the gauge is above 190 or both.

Chris

AllDodge

iTrader: (1)

Bulletin 95_13 overheat above 3000 rpm
http://www.boatfix.com/merc/bullet/95/95_13.PDF

Gone Fishing

JUST TO RECAP GUYS (as a lot of questions and referrals are about things I've already addressed)

"...risers getting very hot, very quickly". "...impeller is good as new". ".. replaced the 160 stat and gaskets!. "...replaced both risers with new". "...removed circulation pump and checked (OK)" "...removed and checked PS cooler (OK)". "...replaced exhaust flappers". I have now narrowed the problem down to being OUTSIDE the boat (leg). No water coming in the boat. I rigged up a hose direct to the thermo housing inlet from the leg and the engine runs fine, risers warm/cool and engine running at around 165-170 constant.

Gone Fishing

Thanks - the risers overeat at idle, so the bulletin isn't relevant. The plastic sleeve i the thermo housing was inserted correctly (I defo wouldn't make a mistake like that). It s design 2 (as posted).

Gone Fishing

Risers and manifolds were ordered with engine number and are like for like.

Bobbyyeah93

iTrader: (1)

This may be a long shot but my neighbor had the same issue with his alpha set up, it ended up being a plastic tube that is inside the outdrive it melted and bent in the middle you couldn't tell until it was removed other than that Id look at corrosion where the hose comes off of the transom assembly they can corrode shut over time. You may want to remove the inlet hose coming off the drive to make sure the impeller is pumping water it may help you find the issue also be careful running it without water going into the drive the impellers can burn up quick. Wish you luck hope you figure it out

AllDodge

iTrader: (1)

To rule out the drive, could you swap the drives and see if the heat issue moves with the drive?