1989 Mercruiser Overheating

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Reel Antsy

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Looking for some ideas. I picked up a 1989 Sea Ray 23' with a 5.7 raw water cooled Mercruiser and Alpha One, Gen One outdrive, which overheats after getting up on plane. Not familiar with these I/O systems too much. Boat runs great otherwise, no water in cylinders or crankcase.

I have replaced the water pump in outdrive, new circulating water pump, new 142 degree thermostat.
I pulled intake hose and started the engine, it's getting good flow. It does not overheat at idle and runs 145 right in the middle of gauge all day long. The thing that bothers me is that when I pulled the hose off of the top of a riser, water and exhaust is coming from this hose, which goes to the thermostat housing where the spring loaded check valves (balls) are. Water should only flow from this housing to the top of the riser...Correct?

My thinking is that when the previous owner replaced the riser 3 years ago, he used a wrong gasket with openings in all 4 sides as oppose to the gasket with 2 openings and just the small bleed holes on the other side of the gasket. Also, the exhaust shutters have rotted away but am told this should not be an issue on this system? You can hear rattling every now and then from exhaust.
My friend is pulling risers off this week and will let me know if he finds an issue with the gaskets and or risers. I think there is a big issue with this causing the overheating and would like confirmation.

Can someone with this set-up enlighten me with a been there done that solution or idea of what else to check?

Thanks.
 
were all the blades from the old impeller intact?
did you replace the everything but the pump base or with a new pump base?
 
Impeller was intact. Impeller only I recall. As I mentioned, I get good flow from intake hose.

Thanks.
 
When your on plane the pump housing is above the water line and that part of the drive only has hot exaust water and gas in it
If the base is leaking(low pressure suction side) it will suck in hot gas and cause this type of hi speed overheat.
A way to test is remove the lower unit and put muffs on, water should not escape from anywhere.
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There are block drains. If you can get under there and open them you'll find all sorts of sediment I bet. You can stick a wire hangar up there a bit if they are clogged. I had a overheat issues with a big block mercruiser. I essentially did all you did but also would run the motor, drain block and repeat. alot of crap came out. I let it sit with radiator cleaner in it for a couple days as well before starting my draining cycle. I wish i could tell you exactly what fixed the issue but it stopped overheating.
 
The housing on the raw water pump should always be changed along with the impeller.

If you're sure it's exhaust coming out of the hose from the thermostat, it may be a bad head gasket. Hopefully not, but...

Funny thing, if the raw water flows out too fast from the manifold gasket, it can overheat. There can be an air pocket that forms. I guess there could be steam that's escaping the hose at the riser.

That hose at the riser is attached to the base of the riser, right??

And that part about hot gas and water that alien mentioned, if there isn't GOOD raw water flow out the system, the exhaust gasses get hot enuff to melt the plastic guide tube up from the raw water pump to the upper case. There are a lot of funny connections between one part of the cooling system that can effect another.
 
Charlie,

The hose I'm talking about is the number 6 in the below link. Water and exhaust is flowing out from it. It should only have water flowing to it, from the thermostat housing assembly. There is no steam, no indication of any head gasket, cracked head or water in oil. I don't have a fuel cooler, as it's carbureted. I do believe I have a power steering cooler, lower port side of engine though...but I have good flow after the cooler.

Can anyone confirm that water should NOT be flowing from top of riser back to thermostat on this set up? With this hose disconnected and clamped off and engine running, water does flows from the top port of the thermostat housing.

http://www.jamestowndistributors.com/userportal/show_product.do?pid=90426
 
If your trying these tests in the water ,your getting resistance from the water in the Y pipe. any water trying to get out thru the manifold into the riser gets blown back from the backpressure of the exaust. This could also be an indication that the exaust shutter is lodged in the bottom of the Y pipe.
 
quote:
Originally posted by jtybt15

The housing on the raw water pump should always be changed along with the impeller.

Click to expand...

Why? It's part of my PM to replace my impeller every other year (low hours per year). I only replace the housing if it is scored. The new impeller comes with new O-rings, and that's all that's needed for routine maintenance.

If you find that the housing is scored, then you buy the housing kit which also includes the wear plate. Promptly discard the bolts in the kit and replace with SS. Also remove the bracket and wire brush and repaint.
 
#6 and #14 are like bypass when the thermostat is closed. and water is circulating in the engine but not going out the exhaust. The check balls 'regulate' how much water runs out the riser from those hoses.

Hmmm, like alien says clogged exhaust Y pipe will create too much back-pressure. Along with poorly adjusted balls...low water going thru the #6 and #14, exhaust gasses can run back up the water passages in the riser...and so to those hoses.

Thing is, if that's happening, the risers should get extremely hot and clogged Y pipe should make engine run poorly.

See if them balls are sticking. If you have the original cast iron thermostat housing. They can rust up and collect on the spring and rod and affect the balls. I may be bass-ackward, but, weak springs allow too much water to bypass to the hoses so you may have springs forcing the balls outward to close off the hoses. It's very possible to have one side sticking and one side only getting low water flow.

BOY!! Is this getting confusing...
 
Just a guess:

If one or both your exhaust shutters have broken off but are jammed in downstream section of the exhaust there could be sufficient exhaust back-pressure on the port side to force exhaust and riser injection RW from that side back out the #6 RW injection hose on the stbd side when removed from the stbd riser. The back pressure can certainly contribute to over heat. I would want to find those shutter-flappers.
 
Jamie,
I think Sandy 'n me said the same thing in that back pressure could force exhaust back up the water jacket of the riser and out the #6 hose.

Stephen,
Geo used to say to replace the housing along with the impeller. I used to do as you until I was scolded by George. When my impeller was changed and an over heat still occured, changing the housing fixed it. Impellers may wear the end plate and housing differently.

The alpha I and earlier drives had pumps with high vane pressure on the housing. It could wear or blister the housing with little or no water flow.
 
Thanks for the feedback and helpful ideas all.

I will do a thorough flush and inspection and report back to you what I find, as soon as I can get back on it.

Much appreciated as always.
 
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