Merc 200 overheating but pumping water perfectly

[Mackesson15]

I have a 1982 (maybe an 86 if the casting on the heads is any indication) 200 Mercury 2 stroke that has an overheating issue. It is pumping water perfectly and very strong out the back, When just sitting there idling the temperature is fine. As soon as I put it under load the temperature gauge shoots way up in a hurry. Water pressure at idle says 5-8 pounds, which I feel is way way too low. I've worked on this thing for 3 summers now and can't seem to get it right in the small window of time I have, and this summer's weather in New England has been horrible. It will idle all day long and the temp stays down, minute I put it in gear the temp rises as fast as I put the peddle down. There is water coming out the pisser at idle and in gear, can idle and watch the temp come back down. I looked back and when I have it revved up driving it, the water streaming out the back is even stronger. New thermostats, new poppet valve, new impeller, and housing x3, checked motor compression also for a blown head gasket- same compression on all 6 cylinders. Still can't locate the problem. Has low water pick up- of note the low water pickup hose is hot to the touch after trying to run her. Has anyone ever encountered this issue and if so what fixed it for you? Starting to lean exhaust divider gaskets, or exhaust leaking into the leg somewhere, only had this boat and motor for three years and have been working out the "bugs" since I got it I'm just tired of guessing at this point. I just want to fly this boat! Any help would be appreciated. Thanks.

522365

[tlwjkw]

put up a picture of tha power head.. mainly tha heads.. '82 is first gen.. '86 is second gen..

pressure at idle is fine.. whats your pressure at speed?.. have you checked t stats?.. have you checked poppet?..

[skialot2]

Has low water pick up- of note the low water pickup hose is hot to the touch after trying to run her.

The low water pickup hose should not get hot. It pulls in fresh raw water and should always be cold. Check for an obstruction in the pickup or a collapsed hose. Check all connections for leaks. If you have a leak when you are idling the leak will be under water and it won't matter. But when you plane off it will suck air and not pump enough water.

[Baker343]

I would start with the water intakes, critters love to take over small places. If you feel good with a new impeller and housing then I would drop your LU and back flush and/or try another proven LU, before you start chasing problems in your blocks cooling system.

[FMP]

Merc pump or knockoff internet box store junk.
Upper waterline/tube seal good?

[Fishwhisper]

I would recheck thermostats, make sure they aren’t stuck shut, 5-8 psi at idle i great. Also, did you check/replace the gasket hidden under the water pump base?