Re: 1986 Mercruiser 170hp 470 3.7 over heating problem
^^Hopefully not....DONT attempt to convert to raw water cooling. Sure it will work fine.....until it doesnt (google "galvanic corrosion"). A properly functioning 470 cooling system will not overheat. Fix the problem, dont DYI-engineer a new one.
Only leak found was a small one on the front of the heat exchanger.
How did you fix this? A slight water leak around the gaskets is a lesser concern, but any antifreeze (if thats what it was) coming out of the heat exchanger is a definite problem. Cracked tube inside the heat exchanger..?
Pulled raw water hose off the fitng at idle speed no water rev it up then alot of water
This is a big problem. No water at idle= kinked hose or a problem with the pump. Check the hose under the bellhousing. If its not situated correctly, it can kink, depending on how far up or down the drive is. Look at it with the drive up, down, halfway, etc. Next check the hose (inside the boat) from the transom to the heat exchanger. Very easy to get this 3 ft hose kinked, depending on how its routed. I've personally been down that road before...
Pulled hose conection for raw water to front of heat exchanger was geting water but i was hot as hell and seemed like it was boiling and trying to go back threw the intake hose in.
Was the hot water coming out of the heat exchanger, or the raw water hose from the drive? Hot water from the exchanger is plausible because the hose from the exchanger plugs into the riser and dumps the lake water into the exhaust, and the exhaust pressure is pushing back the water. In and of itself this isnt a problem. Unless the exhaust flappers are stuck shut, or installed wrong, not allowing exhaust pressure and the water to exit. You might want to revisit this area.
If you meant you were getting hot water and exhaust pressure from the raw water hose coming from the drive, then the drive needs to come off and you need to check the water pump/tubes/pocket cover. You'll have to separate the drive halves to do this.
Also blowing coolant out over flow bottle.
Que scary music NOW....This is big problem. You are getting pressure into the antifreeze side, and that has several sources.
Head gasket or problems with the head/block mating surface is always a possibility.
Another would be the riser to manifold surface; either the surfaces arent flat (or they are corroded), or the gasket is wrong one/defective/bad.
Holes or cracks in the heat exchanger would allow water pressure from the raw water pump to cross over into the coolant side. This would allow intermixing of the two waters but I dont know if enough pressure would build up to push water around a new coolant cap and out of the tank. Maybe, I dont know. I doubt it.
Another possibility is a cracked head or exhaust manifold. If your exhaust manifold is cast iron, these were prone to cracking, in the area of the #4 and up near the riser mating area. The later style ones ('85-'89) were aluminum and less prone to this. Pull the riser off and shine a bright light down into the abyss. You might need to pull the manifold off and clean it up to see whats going on. Mine had a big old crack (I have pictures of it somewhere, if I can find them, I'll post). Upgraded to a later style aluminum manifold. Not cheap.
Good luck, keep us posted. If you dont find the problem, consider dynamite...
