Mercruiser Alpha One LX 3.0 - Hot at low speed

[rstier]

Hi,<br />I have a 1993 Mercruiser Alpha One LX 3.0 liter (4Cyl) which I run in fresh water. This year it started overheating (180 degrees +) at low speeds (less than 10 mph). <br /><br />Water appears to be running fine through the engine and out the prop/lower unit. I pulled the manifold to thermostat hose and water pumps through there no problem. While I was there, I replaced the thermostat but that didn't help. Water appears to be pumping ok through the block as well since I opened the petcock drain in the block and water continued pumping through. What am I missing? There doesn't seem to be any leaks. I did replace the impeller and housing at the beginning of last season so I am guessing that is good. All parts including the o-ring were reinstalled properly. The oil level is perfect. At higher speeds it runs at about 160 degrees which is what the thermostat is rated at so that is not a problem. Maybe a circulator pump? Thanks in advance!<br />Ron

 

[Limited-Time]

Re: Mercruiser Alpha One LX 3.0 - Hot at low speed

Slow speed over heat still points to the impeller. The circulating pump can be pretty screwed up and still not cause a problem. I'm sure one of the Pros will chime in shortly. BTW welcome to iboats.

 

[Highalpine]

Re: Mercruiser Alpha One LX 3.0 - Hot at low speed

I too am interested in understanding what causes the overheating at low speed/rpm. I have an '89 Mercruiser/Alpha One. The problem has been coming on gradually over three seasons. It's now to the point where I need to dock quickly to keep the alarms from going off! Once I get the boat running at about 1800RPM, it holds its own.

 

[Limited-Time]

Re: Mercruiser Alpha One LX 3.0 - Hot at low speed

When was the last time the impeller was changed?? FWIW you would be better served starting your own thread concerning your problem. Oh, And welcome aboard.

 

[95yj]

Re: Mercruiser Alpha One LX 3.0 - Hot at low speed

Overheating at lower speeds and OK at higher speeds suggests the raw water pump. Just 'cause water is flowing doesn't mean it's adequate to cool the motor. Alpha I Gen II manual says to test by pulling the raw water hose from the engine while running at exactly 1000 rpm. Catch water in container for 15 seconds. Do this four times to verify consistency. Minimum water on each 15 second run should be:

Gear Ratio Quarts
1.98:1 = 3.0
1.84:1 = 3.3
1.65:1 = 3.6
1.50:1 = 4.0
1.32:1 = 4.5

Anything less than that means time to replace the impeller.