250HP OX66 Overheating at Idle

[Reel1Fishing]

Good evening everybody,

Have had an overheating at low idle issue with my 2000 250HP OX66 since last season. Have done a ton of research and still can’t resolve it. Above 1,100RPM it doesn’t overheat (In water, not earmuffs).

First thing I did was replaced both thermostats and the poppet valve system. Replaced water pump and housing (twice). Still doing it. So I opened the heads and started cleaning all the water jackets/passages (on both sides). Even tried flushing with light acid mix. Hasn’t fixed it. I couldn’t find a diagram of how the water travels through the block. Maybe something is still plugged?

Last week I went out and noticed a lot of water coming out of the exhaust. I know water exiting through there is normal, but how much? I never opened the middle/exhaust part of block. Any suggestions will be appreciated. Thanks.

[99yam40]

maybe it is time to board scope the exhaust

[TownsendsFJR1300]

maybe it is time to board scope the exhaust

Board scope?

[Reel1Fishing]

Pretty sure it was typo and he meant borescope. I actually have one but will see if I can open middle exhaust portion on block. Was afraid of breaking a bolt but will hope for the best. Any other suggestions? Thanks.

[99yam40]

Board scope?

yep you and the correction system got me I think
.
op drop lower unit and shove it up there to look

[DennisG01]

Might try removing and taking a look at the temp sensor. Could be something in that cavity that's causing a disruption of waterflow around the sensor at lower flow rates. Especially if the overheat alarm goes away quickly upon increasing the RPM.