80's mercruiser antifreeze and seawater mixing

I have an 80's mercruiser 170 that is mixing antifreeze with seawater. My heat exchanger is good for sure. Whats the possibility the manifold is cracked internally? Nothing seems to be mixing with the exhaust. It wont hold antifreeze in the reservoir but sucks the reservoir full of seawater. .

Overheat? Anything is possible! Pressure test the cooling system, Cap good?, overflow reservoir intact?, Pressure test heat exchanger?, good gaskets?, Riser and gasket? Did you check your oil level? Is it high on the stick? Camshaft seals? Is the coolant leaking into bilge? It's gotta be going somewhere and you would smell it with the engine running on trailer coming out exaust. It has to be something that keeps coolant and seawater seperated. Also, the antifreeze would have to be going either out the exaust, in the bilge, in your oil, or worse into your cylinders. Did you run engine and detect the slightest smell of antifreeze? I don't mean to scare you but it could be a cracked head, blown head gasket, or even worse. That is why I asked if you had recently had an overheat. Need more info but start with the simple things and work your way into the job. all the best, Tom P.S. Before you do anything, do a compression test before you spend any money.

1st thing I would check real carefully is the heat exchanger / end cap gaskets. I know you said it's good, but aside from exhaust manifolds that are closed system cooled, any heat exchanger is the only place it can be mixing. There is no raw water in the intake / block of a closed cooling system. Just the exchanger (s) or (maybe) manifolds.

Not uncommon for the exchanger end plate gaskets to go bad (or be installed wrong) and leak between the raw water and coolant sides of the exchanger (if a tube isn't leaking).

It wont hold antifreeze in the reservoir but sucks the reservoir full of seawater. .
can you explain this better?
only 2 places where that could happen ,heat exchanger and riser gasket.

The boat sat unwinterized. The heat exchanger was busted. I changed it and made sure the new one is working proper. When i pour antifreeze in the reservoir it runs out the back of the boat. The same way that the seawater does. I started the boat with the muffs and the reservoir filled up with seawater. Im not sure what the gasket looks like we used liquid gasket with the intention of getting a new gasket.Im speaking of the gasket between manifold and reservoir. The reservoir doesnt leak if it is off the boat. I turned it upside down with the cap on and filled it. Engine has clean oil no water. No water in cylinders either.

the only way is a damaged/incorrect riser gasket. did you remove the riser ?

http://www.marineengine.com/parts/m...+MANIFOLD+ASSEMBLY+AND+EXHAUST+ELBOW+ASSEMBLY
http://www.marineengine.com/newparts/part_details.php?pnum=MER27-89657&ptype=&Engine=&Model=
the front half of the riser is the A/F side to fill the engine, the back half is the sea water side out from the heat exchanger.Correct gasket IS A MUST

Coolant and water lines switched?

"Im not sure what the gasket looks like we used liquid gasket"

Hoses are different sizes, guyig. looking at the manifold you would think all slots should be open but there not, 3 are sealed. 1 is open to connect the manifold with the fill/res section.
water exiting the HE goes to the rear of the rise and out the exauser. cant have A/F in the front and RW exiting the rear unless there are 2 seperate areas. having all 4 slots open will mix the A.F and exaust water

doug4320 said:

The boat sat unwinterized. The heat exchanger was busted. I changed it and made sure the new one is working proper.
When i pour antifreeze in the reservoir it runs out the back of the boat. The same way that the seawater does.

I started the boat with the muffs and the reservoir filled up with seawater. Im not sure what the gasket looks like we used liquid gasket with the intention of getting a new gasket. Im speaking of the gasket between manifold and reservoir. The reservoir doesnt leak if it is off the boat. I turned it upside down with the cap on and filled it. Engine has clean oil no water. No water in cylinders either.

Click to expand...

IMO, all that you have indicated, points to either the H/E, or a breach between the reservoir and the exhaust elbow or manifold.

Use the tried and proven P of E (process of elimination), one item, and one item only, until you find it.


Apparently there are several configurations to this.

It was the riser and gasket. All fixed now. Thanks for all the info guys