Pull the Head or Just Head Cover?

I am still having overheat problems. Overheats at idle and high speed. Impeller is new. Tested the T-stat and works fine. Yesterday, on the earmuffs I pulled the t-stat and actually left cover off. Ran motor with water spilling out t-stat holes. No over heating. Put t-stat cover back on (with NO t-stat) ran motor high speed....no overheating.......thought maybe I had blown some clog out! But then I throttled down and suddenly started overheating at both idle AND highspeed.

I think my only other option is pull exhaust cover and head to clean out water passages. I have NO idea what I'm looking for, or what to do once I pull the covers off. Never done this before.
1) Do I need to pull just the head cover OR do I need to pull the next set of bolts to remove the actual head?
2) What am I expecting to find? Open channels that water flows through? How do I clean them?
3) If I have to remove the head, am I going to have pistons and piston rings flying all over the place that I have to replace or can't get back in!! (sorry for the novice question).
4) Any advice to make sure I don't snap bolts when removing?
5) Anything special I have to do when installing new gaskets when re-assembling?

thank you so much.

[robert graham]

I'm no expert on this subject but I understand there's a poppet valve near the thermostat that shoul be checked for operation on these overheating issues...maybe check that before pulling the heads. Good luck!

thanks for the prompt reply, but no poppet valve on these guys. Sorry, should of said in my first post - this is a 90 hp. 1998.

[robert graham]

is your water pump impeller put in right, housing in good shape, aluminum tube/grommet running up to engine in good shape? if your engine has spent a lot of saltwater time then maybe a good idea to remove exhaust cover and heads to remove salt/corrosion deposits. be careful removing all those bolts not to ring one off in the block. Good luck!

[89 Grady White Project]

I would 1st take your thermostats out and verify in a pan of water on the stove if they are opening at the right temperature and opening all the way. I use a spare piece of wire to suspend the thermostats off the bottom and use a meat thermometer, so I'm sure of the temperature.

Another possibility: I have a pair of 2003 250HPDI's and I found a pressure relief valve at the base of the power head, so I removed it and there was a lot of trash, sand, etc. in there so I cleaned it out. It appeared to help, but it just took the engine longer to overheat. I did notice the grommet was very hard, so it may not be sealing good enough. Engine's too hot right now, but I'm going to double check later. A weak spring could be a problem too, but the manual doesn't give a oz/cm specification so I have no clue if its the problem unless I take the other motor PRV apart.

Hope that helped. Good luck.