thermostats gone

[terryintexas]

My 84 235hp evinrude overheated at WOT. Bought the powerhead used. First time out had heating problems. Blew head gasket. Found the thermostats had been removed when I changed head gasket. Could running without thermostats cause over heat?<br />need help,<br />terry

 

[Beernutz]

Re: thermostats gone

Thermostats not only assist warmup. They regulate the flow of water thru your engine, and make sure that cooling water reaches every part of the engine that it's supposed to, thus maintaining the correct temperature throughout your block and heads. Youd on't want different levels of expansion in different areas. Water can actually move thru an engine too fast, failing to pick up enough heat on its way, and missing the heads altogether.<br /><br />Flush out the engine really well, and check the water pump, and install thermostats. Check your ignition timing as well.

 

[Dhadley]

Re: thermostats gone

Don't forget to change the deflectors while you have the heads off.<br /><br />Good luck!

 

[Beernutz]

Re: thermostats gone

One more thing.<br /><br />After you get it all back together, you should "read" your plugs. Install new spark plugs. Run the boat down the river at WOT for at least 5 min. (outside the manatee zone, of course). Shut her down, and pull each plug. The insulator on the center electrode should be a chocolate brown color. If one or more of them is still white or very light brown, you probably have a carburetor problem. A lean condition at WOT will really heat 'em up. Can also result in seizure.<br /><br />Also, it's surprising how many people think that increasing the oil content of pre-mix is good for a motor. Actually, it can cause overheating. Think about it. The main jet will only allow a finite amount of fluid (fuel/oil mix) to pass thru it. The fuel/air ratio is what controls the burn temperature in the combustion chamber. If you have more oil in the mix, then less fuel gets thru the jet orifice. This results in a "lean burn", just like a partially obstructed main jet would cause. This is especially dangerous at WOT.<br /><br />I don't know if you're running pre-mix, but thought I'd pass this along.

 

[terryintexas]

Re: thermostats gone

Thanks for the help guys. I will be sure to install thermostats when I go back together. Also this boat is equipped with a water seperator fuel filter. Don't know how old but could a partly plugged fuel filter cause cyl. to overheat at WOT? Motor ran fine at mid-throttle for more than 1/2 hour before found smooth water to open it up. Then it overheated in less than 5 min. at WOT. Lost power before it rattled and shut down. Alarms never sounded.<br />terry

 

[Bob_VT]

Re: thermostats gone

You stated you bought the powerhead "used" ... I would recheck all the water connections. Could you have blocked any passages when the powerhead was installed on the lower unit. (I know this is easy to overlook for example if the gasket was installed upside down) How is your impeller? Has that been changed lately too. I would examine the entire cooling system, ports and lines from top to bottom.<br /><br />I agree with Beernutz and it is important to run thermostats. Engines are designed to run at a specific operating temperature.<br /><br /><br />Good luck. Bob

 

[Beernutz]

Re: thermostats gone

Good point, Bob. <br /><br />It would help to know the history on both the "new" powerhead and the reason why you replaced it. If this is a continuation of prior problems, you should suspect parts that you are still using.<br /><br />If your alarm and sensors are operational, and it truly overheated, water is either not getting to the sensors (heads), or its going by too fast to pick up heat from the motor.<br /><br />Change the filter, but I doubt that it'll help. <br /> <br />It actually shut down? Was it temporarily stuck, or crank over slowly when you restarted it? Sounds like a seizure. I had a similar problem on a '78 Johnson 115 that I'd bought used. Seized it 3 times before realizing that it was a single cylinder seizure. As with yours, there were no overheating alarms. I pulled both carbs, and found that a previous "mechanic" had been into them. He hadn't installed the float correctly in one of them before forcing the floatbowl back on. He bent the float, resulting in a low float level and a lean mixture in primarily the #1 hole. I rebuilt the carbs, and the problem went away (except for that scuffed piston knock left over from the seizures).<br /><br />It's likely that the previous owner had some trouble. Otherwise, why did he remove the thermostats? If you replaced the entire powerhead (carbs & all), from what you've just told us, I'd suspect carburetor(s). Do you still have your old ones?<br /><br />Good luck!

 

[Beernutz]

Re: thermostats gone

OOps, make that an '88 Johnson 115 that I had trouble with. Fat fingers on the keys.<br /><br />Incidentally, I checked around and found that the previous owner of my motor had similar trouble. That's why she sold it.