Internal Corrosion?

I have a 1992 Mariner 200 with low hours. It really runs superb, but recently I have been getting an overheat alarm. It has good water pump pressure and the pee stream is strong. I put an IR gun on the heads, and the top two cylinders on both sides are running hotter than the lower cylinders, the left side more so than the right. It has new thermostats, no change. compression is good on all cylinders.

Since the engine sits for long periods, I feel there must be some internal corrosion built up that is impeding the water flow. I would rather not have to disassemble the engine if I can avoid it.

My thought was to remove the thermostats and housings and pour several gallons of either a dilute acid or a dilute alkali into the engine to try and dissolve the deposits, then after a suitable time reassemble the engine and run it to flush out any remnants.

Does this sound reasonable? To anyone? If so, what substance should I use and what percentage strength?

Thanks.

Re: Internal Corrosion?

See the attached flow chart. If the water pump is good, sounds like you have a restricted flow to the heads. Water enters the heads from the exhaust divider plate area. I would remove the cover and plate(2 gskts) and clean the 1/4 inch supply holes.

Re: Internal Corrosion?

Check your poppit valve and make sure it is working correct. I would think any build up would be salt. Boaters World and other sell SALTAWAY, which is suppose to work well. I have never tried it. I know vinegar dissolves salt, may remove the stats and pour a gallon or so through each opening.

Re: Internal Corrosion?

The poppet valve was just rebuilt (by me, so I don't know if you can easily screw that up or not). I am not sure exactly what the poppet valve does, but the one in this engine is free, so I guess it is working.

With regard to the chart that Faztbullet sent. I couldn't really read the legend. I have the service manual for this motor, but couldn't find a waterflow chart in it. What plate are you talking about? Is it in the engine compartment or on the leg?

Thanks

Re: Internal Corrosion?

It is on rear of block. Numbers#'s 1-4. Will post better scan of water flow.