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Overheat Problem
bigut	#1  Posted on 03/06/08 - 8:51 AM
Member Personal Page Posts: 21 Comments: 0 Joined: 03/06/08	I have a 13' , 1970 sport, at medium throttle the boat runs great and cool, as soon as I go full throttle the alarm goes off. I have a 40hp mercury that has a dolphin fin on it. I am thinking I should remove the fin. Any suggestions or any one who has had the same problem.
Blue_Northern	#2  Posted on 03/06/08 - 10:06 AM
Member Personal Page Project Albums Posts: 532 Comments: 5 Joined: 09/04/07	I had a similar case last year it turned out to be the thermos. I had replaced them the year before but one was not opening at the right temp causing the alarm to sound at higher RPMs. There are only e few things that can cause this to happen: 1 - You have a bad water pump or impeller. Drop the lower unit and inspect the impeller to see if it is worn or lost its flex. This can easily happen if you crank your motor without water. I replace mine about every 2 years if needed. 2 - You have a bad thermostat. You can pull them out but be careful when removing the covers they are brittle and can break easily. Boil them using a thermometer to see at what temperature they are opening. 3 - You have a bad heat sensor sending a false alarm. There are a few easy diagnoses when looking to target the problem. The first is to make sure you are pumping water good and strong when the engine is running. A lack of pressure would indicate water pump or impeller. If you have a strong flow you can pull the thermos and run the engine with none to see if they are the problem. All this does is keep plenty of water flowing through the block the entire time you are running. If the alarm does not sound it is a fair deduction to say you need new thermos. If the alarm still sounds and you have verified good flow and no thermo problem check the sensors. The dealer told me you could run till the alarm sounds -- unplug one at a time. Mine has 2 and if the alarm shuts off you have targeted the side that is failing. Good Luck! Edited by Blue_Northern on 03/06/08 - 10:08 AM
MW	#3  Posted on 03/06/08 - 5:19 PM
Member Personal Page Posts: 1827 Comments: 10 Joined: 01/08/06	When was the last "Change out" of the water pump ? was it a complete "Change out" or just the impeller ? mw
bigut	#4  Posted on 03/10/08 - 7:23 AM
Member Personal Page Posts: 21 Comments: 0 Joined: 03/06/08	I have had the impellar replaced but I do no know if he did the hosing to it. I will check with the service place. So you don't think it could be the foil sucking water from the intake?
Blue_Northern	#5  Posted on 03/10/08 - 8:14 AM
Member Personal Page Project Albums Posts: 532 Comments: 5 Joined: 09/04/07	Highly unlikely -- most foils I see are mounted behind the intakes. Do you have some pictures? Is it pumping strong at idle? I still think you are going to find out you have a thermostat issue or sensor going out. Rob
MW	#6  Posted on 03/10/08 - 12:46 PM
Member Personal Page Posts: 1827 Comments: 10 Joined: 01/08/06	check the "Wear" plates on the water pump housing, they should be changed out when doing the water pump. mw
bigut	#7  Posted on 03/14/08 - 11:27 AM
Member Personal Page Posts: 21 Comments: 0 Joined: 03/06/08	Blue_Northern wrote: Highly unlikely -- most foils I see are mounted behind the intakes. Do you have some pictures? Is it pumping strong at idle? I still think you are going to find out you have a thermostat issue or sensor going out. Rob How do i pull the thermostat out, it is a brass fitting on the top of my cylinder head.