Coolant leaking into upper unit???

[Doug Redinger]

I was servicing my lower unit last night with a new pump impeller and lower unit lube when I noticed a small of amount of engine coolant dripping out of the hole in the bottom of the upper unit. I have a 1987 Mercruiser 3.7L inline 4 with an Alpha 1 outdrive and the closed cooling system. I know all about the infamous history of the 3.7's and in all fairness it has been a very good engine to me the last 4 years!! After looking at the drained lube from the upper and lower units, I can tell that there is a small amount of coolant in the old lube as well as a few drips of coolant coming out of the upper unit. What could explain this other than a bad exhaust riser or a bad heat exchanger?? Are there any other possible explanations?? How difficult a job is replacing the exhaust riser. Aren't the upper and lower units sealed from anything else?? If so does this indicate a bad seal between the upper unit and gimbal somewhere as well?? I just don't see how the coolant could be getting into the upper unit!!! Could the coolant be coming from a winterization done years ago and somehow it got trapped somewhere in the outdrive? This is the first time I have seperated the lower and upper units for service. I have always stored the boat in a heated garage and have never done a winterization on it!!

 

[nola mike]

Re: Coolant leaking into upper unit???

are you losing coolant? only place i can think of would be coolant leaking into your raw water exhaust from your riser/exhaust mani or gasket. it would probably be a pretty big leak for you to notice it in your exhaust though, and i don't see how it could get to your gear lube unless you have a separate lower unit seal leak. but for that matter, i can't see how you could tell the difference between coolant and raw water in your gear lube...

 

[zbnutcase]

Re: Coolant leaking into upper unit???

I have seen heat exchangers leak and coolant dribble out the water pickups on the drive, but have never seen coolant IN the drive.

 

[solar7647]

Re: Coolant leaking into upper unit???

After looking at the drained lube from the upper and lower units, I can tell that there is a small amount of coolant in the old lube as well as a few drips of coolant coming out of the upper unit.

How do you know that there is coolant in the lube? It would be milky and look like split pea soup if ether water or coolant were in the lube. I would be more apt to beleive that is water.

What could explain this other than a bad exhaust riser or a bad heat exchanger??

I dont think they are the issue it would be a pretty good size leak and you would have noticed that loose of coolant first.

Are there any other possible explanations??

Not to insult your abilities but this sounds like mistaken identity and it water getting in there and not coolant.....if you have a bad gasket allowing water into the lube, the lube can very well comeout the same spot and because the color that the lube turns when mixed with water it could be mistaken as coolant. If color is how how you came to the conclusion that its coolant.

How difficult a job is replacing the exhaust riser.

Both are pretty easy but I think your barking up the wrong tree with that one.

Aren't the upper and lower units sealed from anything else?? If so does this indicate a bad seal between the upper unit and gimbal somewhere as well??.

I would say that you have a bad seal for the raw water intake at the bellhouseing but thats a shot in the dark since I cant see what you dealling with I am sure its possible that it could very well be someplace else.

I just don't see how the coolant could be getting into the upper unit!!! Could the coolant be coming from a winterization done years ago and somehow it got trapped somewhere in the outdrive? This is the first time I have seperated the lower and upper units for service. I have always stored the boat in a heated garage and have never done a winterization on it!!

No that coolant would have been washed out the firtine used after winterizing.

The way i look at it is that keeping the drive sealed and lubed is regular up keep so if you do all the seals and gaskets and still have the issue it wont feel like such a wast of money but if you replace the riser or exchanger and still have the issue, that will hurt the wallet.

 

[Doug Redinger]

Re: Coolant leaking into upper unit???

The reason I know it was coolant was that the drained lube had a yellowish green cast to it. And after I seperated the lower unit from the upper unit, drips of flourescent yellow green coolant dripped out of the bottom of the small o-ring hole in the upper unit which connects the lower and upper units. I haven't run the boat for a year as I wanted to service it before I took it out the first time this year. The lower unit lube was not milky like you would expect; it is almost like the coolant got in there, but since i never ran the boat it never mixed the coolant with the lube. I just don't see how coolant from a closed cooling system could make it all the way into a sealed lower unit!!!

 

[stonyloam]

Re: Coolant leaking into upper unit???

OK, you did not winterize, so try this: Pull the aft plug on the heat exchanger, that is the seawater water side. See if there is antifreeze mixed with the water there. Could explain how the coolant got into the outdrive (not into the lube). Would indicate leak in exchanger.