I Think I've Finally Figured Out The Cooling Problem

After changing the water pump on my 1970 Evinrude 4hp, the engine began to overheat but was pumping the correct amount of water. The water was just coming out ice cold and you couldn't even touch the cylinder head. I believe that the culprit is the water tube that was bent slightly more than was meant to be, and thus isn't going fully into the water pump housing. But to test this theory, would it be possible for me to run the engine with the lower unit off, and if I just hooked the water tube up to the garden hose? The engine is a no-shift model and I'm afraid of getting a run-away because there won't be any load on the motor. The driveshaft won't even be in the powerhead. Would it be safe for me to do this? When I hook the water tube up to the garden hose with the engine not running, the water pisses out in a good strong stream from a hole near the driveshaft and water tube.

Re: I Think I've Finally Figured Out The Cooling Problem

Yes you can do that. The motor will not run away as long as you keep the throttle just above idle. Good plan.

Re: I Think I've Finally Figured Out The Cooling Problem

There are a couple of things to check on that motor when it overheats. This requires pulling the powerhead of the exhaust housing as the square rubber gromment that holds the copper water tube to the powerhead to base gasket junction can melt or defrom and block the flow of water to the cylinders. Also sand, salt, and mud can get packed into the water cooling passages on the bottom of the powerhead and in the exhaust cooling passage to block or restrict the flow of water thru the engine.

Re: I Think I've Finally Figured Out The Cooling Problem

I pulled the powerhead, straightened the water tube to make it longer, and added a little bit of RTV to the end of the water tube so i created a tight seal on the pump housing. Now the water comes out of the exhaust hot, and I can hold my hand on the cylinder head for a few seconds. Now to boat test it.

Re: I Think I've Finally Figured Out The Cooling Problem

If you can touch the cylinder head without burning yourself, you're likely good. Be warned that head runs pretty hot on those 4hp though. I like to feel around the top of the block, just before it turns into the head, or the side of the top cylinder water jacket bulge (which is a little safer since it's further from the flywheel). Those locations should always be warmish.