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AQ131A 270 overheat

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Glasstream172

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So im kinda new to this boat thing i recently acquired a 1987 glasstream 172 cutlass with a AQ131A and 270 outdrive that s been overheating for multiple years now.usaully on a plane or pulling a tube or skier it runs around 240 then boils over. Ive replaced the rawpump, thermostat, exhaust manifold, and flushed and checked for good flow. I inspected the water neck down on the out drive and it looks to be in good shape but noticed it leaking from the seal or swivel bushing below it when running with muffs and wont draw any water. what do i need to do to change it and how hard is it to do.
 
Sounds like it may be the bushings for the pivot pin need replaced? Pull the water neck fitting and watch the pivot pin as you wiggle the drive up and down by hand. If it has slop you will need to pull the drive to replace the bushings. If its good replace the water neck fitting with a new beaded gasket.
 
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Glasstream172 said:
So im kinda new to this boat thing i recently acquired a 1987 glasstream 172 cutlass with a AQ131A and 270 outdrive that s been overheating for multiple years now. usaully on a plane or pulling a tube or skier it runs around 240 then boils over.
At 240 degrees, serious engine damage may occur. I would suggest that you NOT use this boat until this has been corrected!

Ive replaced the raw pump, thermostat, exhaust manifold, and flushed and checked for good flow. I inspected the water neck down on the out drive and it looks to be in good shape but noticed it leaking from the seal or swivel bushing below it when running with muffs and wont draw any water.
You must remove the water neck fitting in order to properly inspect it.
These are wear items, and require routine replacement.
A replacement is cheap insurance against over-heating damage!

what do i need to do to change it and how hard is it to do.
It is best to remove the transmission for this work. Watch for the shims that will be underneath the transmission..... they must all go back as they were.
At that same time, you can replace the bearing crosses and the drive shaft bellows.

Apply propane or map gas heat to the suspension fork area before attempting to remove the two water neck fasteners.
The bead of the beaded gasket faces down!
The bead requires water proof grease.


As Kim suggested, check the upper pivot tube bushing.
If the bushing shows signs of play/slop, it will cause the beaded gasket to fail, and that will create a seawater pump suction breach.
You will need to further disassemble the drive for a bushing replacement.

Do this now, and you won't have any trouble for a long time.
Click to expand...
 
RicardoMarine said:
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Click to expand...

..... or you can convert to thru hull with external strainer and never have to take the drive apart to replace a "wear item" again... An added advantage is that for a very few dollars more, you can install a "T" fitting and a garden hose fitting and have an EASY means to run on land/flush while in water the engine without "ears". Have done this to all my Volvo drive boats for many years. Never going back to thru drive water pickup.
 
sandkicker said:
..... or you can convert to thru hull with external strainer and never have to take the drive apart to replace a "wear item" again... An added advantage is that for a very few dollars more, you can install a "T" fitting and a garden hose fitting and have an EASY means to run on land/flush while in water the engine without "ears". Have done this to all my Volvo drive boats for many years. Never going back to thru drive water pickup.
Click to expand...

How do you do that is there like a kit you can buy or have any pics of the set up
 
While I appreciate what Bob is suggesting, there is nothing wrong with the OEM seawater system.
It does require that we stay on top of things, such as routinely checking/replacing the water neck fitting.

A thru-hull pickup draws seawater from just below the hull. There is a greater chance of picking up floating debris, plus the water is typically not as cold at/near the surface.
Whereas with the OEM system, there is a lessor chance of picking up floating debris, plus the water is typically cooler from 3 +/- feet under the surface.

It's your call...... I'm just making another suggestion to you.


As for a Thru-Hull pick up kit..... you would need to make this up yourself. It is not difficult to do.

Before cutting into the hull, make sure that your location (for the pick up unit) will not encounter any issues with trailer bunks or rollers.
Be sure to use suction hose at the seawater inlet side. In other words, hose that is collapse proof.

Shown here is a bronze ball valve. A Marine style seacock would be preferred.


 thru-hull pick up.jpg
 
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RE: picking up debris on the surface.... Not as I have it. I use a GROCO APHS series strainer on the hull.. No need for a strainer inside. Also picking up plastic bags on a leg mounted inlet and overheating is a thing of the past. I originally got the one with the smallest screen, but changed to the 0.125 hole one. Also used a standard mushroom raw water inlet instead of the scoop shown in Rick's photo. The openable port below ( which faces aft when installed) is a handy cleanout port if you ever get barnacles in the inlet line. The screen is held in with 4 nylon screws which allows removal and cleaning annually if necessary. I put a thin coat of zinc anti fouling paint on inside and outside of screen. In addition, in Ricardo's photo is a plastic fitting. At this point in my setup I have a "T" with a garden hose fitting screwed in for mid season flushing with salt away and to ease winterization. I should caution you not to hook this up directly to a garden hose, but rather let the hose free run into a 3 to 4 gal bucket with a short hose from the T into the bucket. To winterize my 5.7L FWC, I just dump 3 gallons of antifreeze into the bucket and start the engine, more than enough to fill my system including the mufflers and then some. The average garden hose flow rate just keeps up with the water demands of my 5.7 at idle for mid season flushing and testing. As a matter of caution, I replace this fitting every 3 to 4 seasons as they are not generally available in bronze.



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The argument that a break in suction force, resulting in loss of cooling water, is certainly valid for a stationary boat; however, consider the approximate condition for a moving boat with an outdrive:
Pressure exerted by moving water on a stationary structure (or equivalently, moving boat in still water): The force per sq in. is roughly given by: F=AkV**2.(NOAA technical report). The constant k is approximately 1.4 for a square surface pushed through the water. For a 16 sq. in. surface (roughly the surface area of the intake vents on my AQ131A) the resultant water pressure is approx. 9 psi at 5.5 mph. Bottom line: at any reasonable forward speed, there is considerable positive water pressure on the raw water inlets; the additional effect of the raw water pump suction is minimal. The positive pressure goes up as the square of the forward speed, so it seems to me that a small loss of suction at the various fittings on the suction side of the cooling circuit is greatly overwhelmed by the pressure generated by the water at any substantial forward speed. Food for thought...
 
re: "The constant k is approximately 1.4 for a square surface pushed through the water.".... except its not.
its a series of slits on the surface of a streamlined surface... at best tangential to a laminar/turbulent flow.
Regardless.... at a certain point, pinholes in this part DO RESULT in loss of effective cooling when the boat is on a plane... OBSERVED.... furthermore, when the boat is stationary or moving at very slow speeds, this part is submerged and any vacuum leak in this part sucks water, not air.
 
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A through hull pickup must have a scoop otherwise cavitation occurs from the negative pressure thats created from the water rushing past the hole.
 
djhinca said:
............... so it seems to me that a small loss of suction at the various fittings on the suction side of the cooling circuit is greatly overwhelmed by the pressure generated by the water at any substantial forward speed.
Click to expand...

Well, I can tell you first hand that a tiny suction breach (such as a corroded water neck fitting or failing beaded gasket) will indeed prevent enough seawater from entering the cooling system. I have repaired many over my 24 years of doing AQ series service work.


NOW..... I will say that the SR-71 had this down to a fine science! :D
 
.... the wedge strainer does yoman duty as a scoop... and on the subject of scoops, they should be installed with the open end forward... that may seem too obvious to state, but a good friend of mine had overheat problems at anything over dead slow... seems the YARD installed a raw water scoop with the open end facing AFT
 
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