1994 Johnson 90hp on 24' tri-toon Playbuoy

I recently purchased this 1994 Playbuoy 24' three pontoon Grand Tahoe boat with an excellent running 90hp Johnson.....except for one problem....After a couple of minutes of running at WOT ( 4600rpm ) the overheat alarm sounds (steady noise from controller). If I run it below 3500rpm it does not come on. If I run it at 4000rpm It will not come on for a while. Although I am unable to contact the previous owner now, I do recall him saying that he had a new water pump installed a year or so ago. A mobile mechanic came to my house and loaned me a water pressure gage to check at the lake. It revealed 2.5psi at idle and 22.5psi @ WOT. He thought that the prop (14x13) might be lugging it down or that cavitation from the middle pontoon could be causing the problem. I called the boat manufacturer to see if they had any problems with this arrangement and they said to check the motor better such as compression or water blockages.....I tested compression @ 130-133psi in all cylinders. The mechanic said that it was unlikely to have a blockage since it was kept in fresh water (wet slip). Bottom line: the mechanic says that he can tear it down and replace the water pump, thermastats, sensors ect. but it will be expensive and he feels the problem is in the set-up. What now??

Re: 1994 Johnson 90hp on 24' tri-toon Playbuoy

Howdy, 42nd.<br /><br />I agree with your wrench. I think you are overpropped.<br /><br />RPM at WOT should be 5,000-5,500. 4600 is lugging your engine and allowing it to overheat.<br /><br />Go down at least 2" on prop pitch and see what happens.<br /><br />Good luck.

Re: 1994 Johnson 90hp on 24' tri-toon Playbuoy

I agree with JB. I have a '91 Johnson 90hp, and it turns 5800 at WOT. I think the overheating is due to the engine being lugged down.

Re: 1994 Johnson 90hp on 24' tri-toon Playbuoy

Thanks for the support,<br />I bought a 14x11 prop and will give it a spin this weekend. Hope that does it!<br /><br />42ndavenue

Re: 1994 Johnson 90hp on 24' tri-toon Playbuoy

Thanks Guys,<br /><br />I finally got to the lake with the pontoon and it ran all day W.O.T. 5500rpm approx 23mph, 27psi water pressure and not even a chirp from the overheat horn. I guess my wrench (and you two) knew what you were talking about!<br /><br />Thanks again,<br />42nd