1990 88 SPL Heat Alarm Issue WOT > idle

[crappie14]

I recently installed a "new to me" 88 SPL on a 20 foot toon. On the first trip out it became apparent I had a prop mismatch and ended the trial run rather quickly, 4200 rpm at WOT. I ended up with a 13 pitch prop and had 5200 RPM WOT with what I would consider a medium load of passengers/gear. Day one consisted of 4000 RPM (15 mph) just moving around and enjoying the new ride. I couldn't have been more pleased with the speed/noise and fuel usage of the motor. Day two started out with a WOT run about 3 miles across the lake to test the motor (roughtly 6 minutes of WOT) 5200 RPM (25 mph) and again no problems until I backed off the throttle when the heat alarm started to sound. I checked the stream and immediately shut the motor off. It took about 45 minutes for the alarm to clear. Once it cleared, I started the motor and headed back in at the 4000 RPM pace from day one. I continued the 4000 - 4500 RPM pace for the next five days of my trip with no other heat issues putting several hours on the new to me motor.

The motor supposely had a new water pump installed just prior to purchase however I have no way short of dropping the lower unit and replacing it to know for sure. The stream coming out is steady however is is much less pressure than my other motor however brands and years are different.

Question 1, how strong of a stream does this V4 88 have at the tell tale? If it was directed horizontal should it spray 3 feet or 30 feet?

Question 2, I had run the motor hard about 6 minutes at WOT. Dropping the throttle back quickly to an idle did I reduce the water flow to the point that the sensor gave a "false" signal and if I had increased the engine speed would it have cleared? Needless to I am content with running the engine in the low to mid 4000 RPM range to conserve on fuel knowing I can get off the water quicker in case of an emergency. I don't necessarily want to try to fix something that isn't broke but I don't want to overlook a problem that needs to be addressed either.

Question 3, Has anyone ever added a real heat gauge to this motor where one can see the temperture as opposed to having to rely on the alarm and not really knowing what is going on? I have a water pressure gauge on the pontoon from the prior motor however the motor did not have a plug dedicated for the connection and I had doubts as to whether a "T" in the Tell Tale line would give an accurate reading.

Thanks in advance for your thoughts.

 

[emdsapmgr]

Re: 1990 88 SPL Heat Alarm Issue WOT > idle

That engine has two aspects to the cooling of the powerhead. When idling, the water pump impeller in the lower unit provides the water to cool the engine. It should be a strong stream out of the telltale. If it is a weak stream, it is suspect. When you get the engine on plane, or at least moving quickly through the water, the onrush of water into the lower unit water pickup will force extra water into the powerhead. When this occurs, two pressure relief valves will open and will permit this extra water to circulate throught the block. Once you get the boat moving through the water quickly, it is less likely to overheat due to the pressure relief valves being open. If you pull the throttle back to idle, the valves will close and the block will have to depend only on the impeller for cooling water. Based on the above scenario you have presented, I'd consider replacing the impeller. Your engine should idle all day long between 143 and 155 degrees. Cooler when you are going faster. Overheat horn activates at 212 degrees-then silences when the powerhead cools to 175-which is still too hot for normal operation.