Overheating problems - but water pump is new

[Minus Alkohol]

Good morning Gentlemen, I'm new to the forum and new Aquasport owner.  I recently purchased a 1972 22-2 with a 1980 Evinrude 140.  After fixing my starting issue by cleaning the carbs and replacing the starter I have run into another issue.  The engine likes to overheat however I have recently replaced the water pump.  Yesterday I took her to the boat ramp to run her under a load while still on the trailer and this is what happened...she ran great, very strong for the year and size of outboard but after about 5-10 minutes the pee stream (which was previously very strong) stopped and I noticed that steam began to come out. No overheating alarm.

Now, I've been given some advise as to what I should investigate. First was the thermostat which I might try to purchase and replace today.  The next is to replace the head gaskets.

What are your thoughts and recommendations.  Would a faulty thermostat cause the pee stream to suddenly stop?  There was no visible blockage on the water intake and when I replaced the old impeller it was still intact so I no reason to believe that it caused any blockage further up the line.

Also, I am fairly novice to outboards so be gentle.  Also, note that the engine has been sitting before I bought it for several years (don't worry I changed the fuel lines, drained all the old gas and changed the fuel/water separater - I was actually running off a portable tank at the time).

Thank you.

[GoneFission]

Themostat could be the problem.  A stuck thermostat can cause the symptoms you are seeing.  The next likely thing would be blockage somewhere in the cooling system.

Fix the 'stats first - may be an easy fix!

[Blue Agave]

Themostat could be the problem.  A stuck thermostat can cause the symptoms you are seeing.  The next likely thing would be blockage somewhere in the cooling system.

Fix the 'stats first - may be an easy fix!

^X2 replace the thermostats (2).

The conditions of the thermostats will give you an indication if they are the problem. If the problem persists after changing the thermostats I would drop the lower unit and check the impeller to verify that something didn't go haywire.

[fitz73222]

Replacing the thermostats is a good idea anyway. But unlike the V6 Mercury fellows, this engine pees before the thermostats, right out of the back of the pot belly so there still may be a water pump issue. As we experienced with one of Scotty's 75 Mercs, we had an issue with a good water tube to plastic adapter fit and we had to put a bead of RTV to stop the water loss at the joint. One way to tell if this is an actual issue is run the engine on a flush attachment, fire it up and see if there is a significant loss of water coming out of the midsection drains. These are located higher up on the engine where the lower swivel pin joins into the lower engine mount assembly. The presence of excessive flow coming out of there means the water pump to copper water tube, plastic tube is leaking and the water isn't making it into the powerhead. Also disconnect the pee tube where it comes out of the block and look for a blockage in the elbow or hose. It's ok to fire it up with the pee hose disconnected to see if water is making to that point although a blockage there will not cause the engine to overheat; it's just an indicator.

[icemanbryan]

Well, I am not an expert on outboards.
A few years ago a buddy of mine did the impeller replacement, had your same type issue.
He did not install the keyway correctly.
I guess the impeller will spin and then the water acts as a lube.
Then the shaft spins and the impeller does not.
Sounds about like the same issue you are having,yeah?
Just a thought.
There are many here who know way more than I do.

[Bergertime]

I had an over heating problem that took me all over my engine but the culprit was a botched install.. The below is an excerpt from my thread where the problem was discovered.  Hope it may help.  Good luck.

6)Replaced the whole water pump - Here comes the culprit! Upon inspection after the new-old impeller and pump was removed we found that the floor plate of the existing pump was concaved down towards the prop. This prevented the impeller from creating the suction and water flow needed to push the water up to the top and cool the engine properly. When I observed the mechanic (Sunday) remove the impeller some force was needed to loosen the brass fitting which holds the impeller on which he applied horizontally to the drive shaft. The prior Mechanic (which I will never let touch my boat again) used significant downward force (hammer and screwdriver) to free the first impeller which forced the floor-plate to flex and bend downward. This was not evident until the floor plate was pulled and inspected holding it sideways. However, once viewed outside the pump the curvature was significant and obvious. Lesson learned there.

[Capt. Bob]

Just for future reference, look at your first pic. You'll notice the vents (3) just above the cavitation plate (they're on both sides).
When you start the motor cold, no water should exit these vents at first but after a short run time you should start to observe water flow (slow at first and then increasing). This indicates the opening of the thermostats as the motor moves to operating temperature. It's just an indicator while running on the muffs that the "stats" are not stuck closed or blocked (very low flow observed).

Also, remember that the water pump works two ways in your motor. When idling, the impeller acts as a displacement pump. Water is drawn through the intake vents (where you place the muffs when on land) into the pump body. The impeller is pushing (displacing) the water within the pump upwards into the motor. That's why it's important that as Fitz, BT and Ice mentioned, the pump must be properly assembled for it to function. While underway at speed, the water is forced into the vents with enough pressure to deform the impeller vanes now causing the pump to "circulate" the water flow. So at speed, with all other cooling system components functioning correctly (stats, pressure relief valve, block passages, gaskets) you will not get an overheat condition with a somewhat worn but undamaged impeller. The critical time is at low/idle speeds.

Changing the water pump out is not like rebuilding the upper or lower units but it still requires some skill and knowledge of what's happening. Improper placement of the internals and reassembly can result in conditions worse than just a tired pump. This is stated just to bring up the importance of this preventative/corrective maintenance no matter who performs it.

Good luck.

[Minus Alkohol]

I want to thank everyone who replied.  I will inspect the impeller to ensure proper installation and function and report back.