Merc 200 making no Heat

Hi Randy,

I have not been able to make any heat all summer. Both temp gauges show 120* or below. Both gauges have been checked for accuracy.

I have run with all possible combo's throughout the summer, (poppet, thermo's, different size washers, no poppet, diverters) the water temp in the river was as high as 86* in the middle of the summer, still only 125*.

The mid plates have not been modified, (no dry stacking etc.) I am running stock compression and porting, with only exhaust chest work, timing is at 25*.

I am however running .082 or .084 main jets, but find it hard to believe that they would make the motor run so cold.

Also, I have a crack that just showed up in the corner of my splashwell, and am worried I will have to put a new transom in this winter, what is the best way to go about it without removing the top deck?

Thanks for the input,

John Mason



Sounds like you are reading the temp of the water and not the block. Most engine block or head temps sit around 150'. Get some new probes that read the metal parts temp. (ie: surface mounted head temp). The cracks in the corner appear in about every Hydro I have ever seen. Not much more you can do as the cracking is just cosmetic. If you fix them, they will come back as the flex pattern of the boat is such. Not to worry about.




Please submit whatever questions you have to  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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