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View Full Version : Merc200 overheating issues

westcoastv20
01-31-2012, 10:55 PM
Hey all, have a 1998 Merc 200. It had been sitting 2 years. Took out bad fuel. Rebuilt water pump and lower end, New plugs, new therms, good compression in all 6 cylinders. Left hand side runs at about 145 degrees. Right hand side runs real hot, and quickly gets hot. While running and the therms pulled, water flows easily out of the head on left side, the right side however kind of "burbles" out every other second or so. Doesn't take long til the temp is above 200 degrees. My mechanic is going to look to see if the cylinders are scored. ( Not sure how they would be scored if they have good compression.) ANY IDEAS OR SUGGESTIONS??
spareparts
02-01-2012, 06:44 AM
check the poppet valve, its located on the right side of the block down low , its designed to allow excess water to bypass the power head at higher rpms, if its stuck open or the diaphragm is torn, it won't hold enough water in the block. Did you replace the upper housing with the impeller?
randlemanboater
02-01-2012, 01:54 PM
Could be your poppet valve is full of seashells like this one was.

http://i145.photobucket.com/albums/r222/randlemanboater/101_0100.jpg
westcoastv20
02-01-2012, 04:55 PM
Gents thanks for your responses. Luckily the problem came down to the container we had the prop in. It was too small, causing the exhaust to be brought in through the water pipe. Once we put the muffs on it, engine ran great. Temperatures were between 143-155 at idle and up to about 1500 rpm. The things you learn when messing around with an outboard for the first time. Might be able to do our sea trial this weekend. Weather looks like mid 70's. might even go out and try to catch some ling cods.
lathehand
02-02-2012, 09:08 AM
Those big mercs or any bigger engins woun't run cool in a trash can.Just not enough circulation.Glad to here it was only that. :clap:
Destroyer
02-02-2012, 11:26 AM
Those big mercs or any bigger engins woun't run cool in a trash can.Just not enough circulation.Glad to here it was only that. :clap:

I use a fermentation tub (The kind you buy for making wine) for my testing. It's big, not to expensive, has a drain at the base, and there's never a questrion of will the engine fit into it. Got it off CL for $50. Look under wine making or under fermentation tubs. :party: