Poppet valves

grbeasley

Seaman Apprentice
Joined
Feb 9, 2011
Messages
36
I have a 1994 40hp Mercury Tracker outboard 4 cyl. It runs fine, but when you get up in the RPM's, the overheat alarm sounds. When I get the RPMs down, the alarm quits. I have been told that I need to replace the Poppet valve, but when I look at various sources for the valve, it does not list one for my engine. I have looked at youtube videos showing replacing them, but can't seem to locate the valve on my engine. Do all outboards have Poppet valves? Thanks for all replies.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,046
Not all outboards have a poppit valve.----Is this a problem that showed up suddenly ?-----Has the waterpump been maintained ?
 

kmarine

Chief Petty Officer
Joined
Nov 5, 2010
Messages
581
Replacing the impeller regularly is as important as changing the oil in your car. Many boats are brought in with extensive overheat damage because they neglected to replace the impeller. It is one of the cheapest parts on the engine!
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
As already pointed out, the water pump is a critical part of the cooling system. The rubber impeller not only wears but the vanes take a 'set' curved shape and no longer pump near as efficiently as a newer impeller. For this reason many owners decide to error on the side of caution and replace the impeller every year. Personally, every other year is fine. While the pump is apart carefully inspect the stainless 'cup' and lower plate, if you find a line worn into one or both parts from the raise ring around the unside center of the impeller, then it is also time to replace those stainless parts as the side seal is not within tolerance.

You can use just a spot of grease to 'stick' the key into position during assembly but do NOT get any grease on the impeller vanes. If you want to pre-lube the vanes use either a silicone based lube or K-Y jelly.
 

grbeasley

Seaman Apprentice
Joined
Feb 9, 2011
Messages
36
Thanks to all. The water pump was replaced last year. When the alarm first sounded I did not even know what it was as it was my first engine with such alarm. If it does not have a poppet valve, what could be the problem? Water is streaming from the p-hole just like always.....nice steady, solid stream that I can put my hand under and not get burned. Could it be the thermostat?
 

grbeasley

Seaman Apprentice
Joined
Feb 9, 2011
Messages
36
OK, I am going out on a limb here, but if it does not have a poppet valve or thermostat and the water pump is pumping water, the only other thing it can be is a bad heat sensor. I am open to any other guesses as to what it could be. As a last resort, I guess I could take it to a marine mechanic, but I hate to admit defeat being the great diy'er as I am (tongue in cheek). I might replace the water pump again. Maybe it doesn't pump enough water at high RPM's to keep it under the heat sensor's tolerances. Thanks to all.
 

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,657
Motor may be mounted too high, or trimmed out too far, so that the water pick is slightly out of the water, sucking air into water pump.
 

grbeasley

Seaman Apprentice
Joined
Feb 9, 2011
Messages
36
Thanks for all the help. This is what I know.....no poppet valve and possibly no thermostat. I took the boat out last week for a spring check up run. After obtaining plane for a couple minutes, the alarm sounded again. I slowed down and it quit. Got back on plane and alarm sounded. Then I stopped and put the engine in neutral and ran it at planing RPM's (around 4,200) for a few minutes.....long enough for the alarm to sound and it never went off. I then got back on plane and the alarm did not sound after that. It chirped a couple times, but not a steady sound like it did before. I am going to change the water pump and see how that does before I take it to a mechanic. Any further thoughts would be greatly appreciated.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,046
All I am going to say is that it is a mistake to run a 2 stroke motor at high rpm in neutral !!
 
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