Outboard motor water pumps

[Effie4Bass]

If I remember correctly, which at my age is always questionable, back in the late 80's or early 90's there was an article in a boating magazine about outboard motor water pumps.  It stated that the cooling stream coming from a running outboard was not a reliable indicator that the engine was being adequately cooled.

It seems they had tested the amount of psi it took to create a cooling stream and then the psi to actually run the cooling water through the water jacket of the engine.  I think there tests revealed that it took 3.5 psi to get a stream and approx. 7 psi to cool the engine.  This was some time ago and I'm wondering if things have improved to the point that the cooling stream is now a true indicator that the engine is actually being cooled?

Of course some engines had high heat warning horns but as in auto engine over heating warnings it comes to late to save the engine!!!

Any comments or knowledge of the topic?

Thanx in advance.

[Captain Phil]

I ran a 150 Yamaha on a Skeeter Bass boat for about ten years.  The only problem I ever had was an overheating issue.  Intermittently, the cooling stream would slow to a trickle followed by the alarm.  After many attempts, the dealer pulled the heads and found the water jackets were clogged.  They cleaned out the water jackets and I never had another problem. If you have a steady cooling stream, your water pump is working.  If you still have issues, you may want to check out the powerhead. I have seen boats where the engine mounting height or obstructions on the boat itself caused intermittent overheating.  

[Alex from GA]

Like you said the best way to know if the engine is being cooled is with a water pressure gauge.  All of the later engines have alarms if it's overheating.  Guys and girls that run hydraulic jack plates and run in skinny water will almost always have a pressure guage.

[Jig Man]

I had an Optimax that would overheat if I idled more than a few minutes.  We replaced all kinds of stuff even the head gaskets.  Nothing ever stopped it. I just had to be sure to run not idle.

[rejesterd]

The exit stream only tells you that water is being pumped by the impeller. It doesn’t tell you if water is actually going through the tstats and cooling the engine block. That’s what the cooling water temperature sensor and the overheat alarm are for. Some newer engines also have a water pressure gauge, which is nice. You can also point a temp gun at the block to check the temperature. 
 

But at the end of the day, you’re relying on sensors (whether it’s a sensor installed in the engine or a tool like a temp gun). If one of those sensors goes bad, you might not know it before it overheats and blows the head gasket. So as always, it comes down to simply doing the maintenance. If you flush the engine, test the tstats and sensors, and replace the impeller regularly (and the tstats as well if you’re in saltwater), you should be fine.