470 coolant leak

[magregor22]

I just bought a 79 sangster with a 470 merc and I noticed its leaking coolant into the seawater system. I can see it coming out of the leg when I presure test the cooling system. I removed the heat exchanger and tested it and it's O.K. I'm just wondering where else they could be crossing? I downloaded the cooling schematic and it almost looks like there is a plate under the exhaust elbow which could be the culprit but I figured I would post this question before pulling off any more pieces. I did some searches on this site but besides the heat exchanger i can't see any other possibilities. All help would be greatly appeciated. Thanks Gary

 

[a.d.mobile]

Re: 470 coolant leak

how does it run when the boat sits and started can you smell antifreeze? when you pressure checked with engine running did it smell like burnt antifreeze sweet smell behind boat? that plate is a good start but a head gask or cracked head will do this also and the 470 has been known for this...

 

[magregor22]

Re: 470 coolant leak

I must be missing something in the cooling system drawings. I know that when I presure test the cooling that the coolant is coming out the prop or leg so to me it seems that it must be crossing over into the seawater system and besides the heat exchanger that seperation plate is the only place I can see that the two systems come close to each other. If it had a blown head gasket or cracked head how would the coolant get into the seawater system? Am I missing something? Any thoughts or wisdom would be greatly appreciated, thanks

 

[beckerdg]

Re: 470 coolant leak

I am no expert, but what generally comes out the prop is the exhaust mixed with seawater. They mix at the riser. So the coolant could be entering your exhaust system then mixing with seawater at the riser. A head gasket problem would let coolant where it should not be and it could find an exit through your exhaust... The exhaust manifold on my 86 MCM 170 also appears to have a coolant jacket and could leak into the exhaust if it developed a leak.

 

[magregor22]

Re: 470 coolant leak

i see what you you are saying about the coolant mixing in the exhaust maifold with the exhaust gases and then being blown out through the prop. That all makes perfect sense. The problem i have with this is there is no water showing up in the exhaust manifold that i could see. when I presure tested the system I got water coming out the leg( I can't remember if it was coming out the prop when I presure tested or only when the motor was running but it was coming out of there someware) right away and I would think if I had a leak into the exhaust manifold that it would fill the manifold before it leaked out the leg or outdrive if the motor was not running. when i took the riser off the manifold was dry and when i took the heat exchanger off there was no signs off contamination with coolant in the sea water system which leads me to believe that it has to be between the seperation plate maybe coming up one of the bolts. I will do some more testing tommorrow, I just came off a 16 hour shift and can't find the energy to go out there tonight. but i appreciate all the advice i can get because this is the time working on any boat motor bigger than a 9.9 outboard. by the way the motor is a 1979 470 serial 5452486 170hp

 

[crazy charlie]

Re: 470 coolant leak

Do yourself a favor and change the manifolds if they are not current.I believe there are update kits for larger manifolds.This engine was notorious for failure due to manifold failure.Good luck. charlie

 

[magregor22]

Re: 470 coolant leak

I think I found the problem, The coolant jackets on the riser are rotten. And when I put a straightedge on the mating surface there is a hollow in the middle, also somebody stripped one of the bolts holding the riser to the manifold and drilled it out. I am pretty sure that the coolant was traveling up the bolt and out the seawater side. I guess I was lucky it did that and not the more likely thing, that is to fill the manifold and engine. Time to go spend some hard earned money. i will buy a manifold,riser,and end caps. Am i missing anything else? Thanks for the input it helped alot. gary