5.7 Merc overheating- NEED ADVISE PLEASE

1990 233 XL Ambassador 5.7 Merc Sterndrive. Had motor replaced - who knows when? Casting numbers indicate 95-2000 Vortec, Gen 1, roller cam.

Long story short, Motor took on water into cylinders and crankcase. Going into reverse too hard, carb spit and died (assume flappers).

Drained oil and replaced, blew out cylinders, lubed & hand spun crank.

Started motor with muffs, outdrive looked like it was taking a ton of water.
ran fine, but after 8-10 minutes water temp gauge was getting high, shut down before it got too hot. Pulled plugs, DRY. Crankcase clear and no signs of higher levels. I let the motor cool down, and started again, heated again within 5 minutes all the way up to the first red line. I noticed that the exhaust man. had water droplets coming out of the 1/2 moon (casting) imprint located outside and above where the 2nd bolt from the front mounts to the head.

Couple of thoughts,
1. Was the garden hose enough or do I need to run it at the lake.
2. Where is the thermostat located and what degree to I use.
3. Is it OK to run it at the lake with the 1/2 moon crack on the exhaust.
4. Could the crack exhaust cause high temps.
5. No add. fluid in crankcase, no water in cyl.
6. What could be causing high temps.
7. Can exhaust be JB welded?

I appreciate all of your thoughts.
John

Re: 5.7 Merc overheating- NEED ADVISE PLEASE

I forgot to add that I did a compression check before I started it up and the numbers were good.

Re: 5.7 Merc overheating- NEED ADVISE PLEASE

I could use a little advise here?

Re: 5.7 Merc overheating- NEED ADVISE PLEASE

have ya replaced the impeller lately?
that's usually the first place to start at for overheat condition...

Re: 5.7 Merc overheating- NEED ADVISE PLEASE

Sounds like an impeller to me too...

Re: 5.7 Merc overheating- NEED ADVISE PLEASE

Impeller.... water won't work it's way into the engines water pump without some help.

Re: 5.7 Merc overheating- NEED ADVISE PLEASE

How hot, exactly, did it get? It sounds like maybe it just got a little hot, and you might be super sensitive due to your unfortunate accident. I know mine does not cool quite as well from the hose as it does with river or lake water.

Are you getting a good flow of exhaust water? Maybe the same thing that let the water back flow is now stopping it from flowing out?? Just guessing here.

Re: 5.7 Merc overheating- NEED ADVISE PLEASE

The temp. gauge needle got to the red dash line before the actual red line, which is the last line on the entire gauge. I wasn't being sensitive, actually I was waiting to see how far it would go, actually too risky. I'll be bringing it to the lake tomorrow. Any other suggestions?

Re: 5.7 Merc overheating- NEED ADVISE PLEASE

Sounds like you need a service manual, if you don't even know where the T-stat is.
I would start replacing things that you know are broken (manifold with crack???), replace impeller, might as well replace elbows, too, unless you know how old they are.