Mercruiser 5.7 Pink antifreeze in oil

Brentpit

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Apr 24, 2010
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8
I have a 87 Wellcraft St. Tropaz that has 2 Mercruiser 5.7 Stern Drives. The motors have a half enclosed cooling system. Last fall I removed the boat from the water and ran 6 gallons of Pink antifreeze through the intake hose by running the motor and pouring the antifreeze in the hose that attaches to the strainer basket. then I checked the antifeee in the cooling system. it looked good and tested good.

This spring I went to change the oil and it looked milky (bad news) the starboard motor (other looked fine). The oil I drained settled and the bottom on the jug was all pink antifreeze. After scratching my head for an hour or so. i asked the boat shop where my boat is stored. They said check the oil cooler. I looked and no oil cooler just a transmission cooler. the green Antifreeze is fine and it is full to the correct amount. I started the motor with a hose in the water intake and it ran just fine Pink antifreeze came out if the exhaust when I first started it as expected. Driving the boat last fall did not get any water in the oil I checked oil in both motors when we pulled it from the water (not milky). The motor does have an exhaust leak that is noticeable by sound and fumes in the boat on one of the exhaust manafolds Gaskets have been ordered. Any help appreciated.
 

Bt Doctur

Supreme Mariner
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Aug 29, 2004
Messages
19,092
you say you have a half system so that would mean you have regular AF in the motor and heat exchanger and raw water in the manifolds and risers.
Running pink thru the raw water side without draining them first could result in a freeze crack in the exaust manifold or elbow.
 

Scott Danforth

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I would still go with a bad oil cooler. its a 2" diameteter heat exchanger.
 

Brentpit

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Apr 24, 2010
Messages
8
Yes it has raw water through the Manifolds and Risers but AF in the motor. The Heat exchanger seem to be functioning and it does not have the Pink AF in it It's is green. I did did remove the drain plugs and drain the water from the Manifolds before running the antifreeze through the motor plus put six gallons of antifreeze in each Motor. If there is a crack in the manifold that would allow water in the Oil?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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no, in a half system, you could remove the manifolds completely and still run with the glycol in the engine.

the ways for AF to mix with oil on a half system are bad intake gasket, bad head gasket, cracket block, or in some instances where the oil cooler is glycol cooled, the oil cooler.

however that would be green antifreeze.

to get pink AF into the oil on most engines with a half system, is the raw water cooled oil cooler. hence my post above. check the oil cooler. 99% of the time, the oil cooler is not drained, and gets busted at the first freeze.
 
Last edited:

stonyloam

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Mar 13, 2009
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5,827
I believe the oil cooler is a power steering fluid cooler, same part number as the one on my 470.
 

Bt Doctur

Supreme Mariner
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Aug 29, 2004
Messages
19,092
If pink AF was put in the manifolds and risers and some is now found in the oil you have a crack in either the exaust manifold or riser. It entered the oil pan by getting past the piston rings in a cylinder. Unless your running inboards you have a power steering cooler not a trans cooler..
Best thing to do is remove the risers and look at the inside. Almost sure you will see a hole.
 
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