Aq125a engine looses sea water prime after 10 minutes - Help!

Hello y’all, I’ve spent a fair bit of time reading on this forum and now am in need of help! I have an aq125a that I just replaced thermostat, and impeller with gaskets... I ran the 270 sterndrive a couple different ways with both muffs and in a tub of water, put an earplug in the drain hole below the intake holes when using the muffs. She starts up fine, starts pumping water after about 30 seconds or so and life is good for about 5-10 minutes. It then looses prime somehow and as the temp starts to overheat I can remove the cap and strainer to the heat exchanger and there is nothing but steam and no water is pumping.... now the two obvious places I thought of is the rubber seal on cap which appears good and is tight and the outdrive water intake piece which is natorious for rusting out... visually this also looks just fine and I am in freshwater over here. Please advise if I am missing somewhere else that I may be leaking air or what may be causing this to loose prime? The alternator belt is new last year and has good tension and preliminary look at all the hose clamps looks fine as well. I am stuck now and don’t know how to go about troubleshooting this one as if it starts to pump water why would it loose prime and stop after 5 minutes?

Pull the S hose from the water necking and look for corrosion. Better yet.... replace it and the special beaded gasket!
The smallest suction breach will prevent the system from working correctly.

The water neck fitting is a "wear item" and should be routinely replaced.



When you remove the S hose, you will likely see corrosion underneath and around where the hose was making contact.
This corrosion can cause a suction breach that will KILL all incoming seawater flow.


The "bead" on the new gasket must face DOWN.


TIP.... mildly heat the suspension fork (in this area) before removing the two small cap screws.




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Visual inspection of this pickup looks very clean with very little corrosion however I will take off and replace gasket, any suggestion on where to buy the gasket that I could get shipped next day here in US?

Owarzecha said:

Visual inspection of this pickup looks very clean with very little corrosion however I will take off and replace gasket, any suggestion on where to buy the gasket that I could get shipped next day here in US?

Click to expand...

Better yet, has anyone had any luck using liquid gasket maker for this?

It appears I need to remove the outdrive housing in order to replace the s hose, is that correct? If so can you describe which piece I need to rget move, it appears maybe the Op shield comes off separate and would be just a couple bolts?

Owarzecha said:

Better yet, has anyone had any luck using liquid gasket maker for this?

Click to expand...

The gasket underneath the water neck fitting has a molded bead incorporated into it.
The special bead must face DOWN!
The flat surface of the gasket seals the water neck to the suspension fork.
The special bead allows for both a seal and for articulation between it and the top of the pivot tube.

This cannot be reproduced with a gasket-maker product!

Owarzecha said:

It appears I need to remove the outdrive housing in order to replace the s hose, is that correct?
I doubt that you will need to replace the S hose.
But yes...... the transmission (upper gear unit) must be removed in order to access this area.

If so can you describe which piece I need to rget move, it appears maybe the Op shield comes off separate and would be just a couple bolts?
The transom shield remains attached to the structural transom.
The transmission will be removed.

Loosen the drain plug and capture the gear oil. (loosen the dip stick to vent the area)
Loosen the helmet pin.
Raise helmet up and out of your way.
Remove the shift mechanism cover. (do not completely remove the top screw)
Loosen the band clamp from the AFT area of the drive shaft bellows.
Remove the vertical linkage rod from the eccentric piston. (leave the linkage rod attached to the gear yoke)
Remove the two vertical cap screws. (5/16" hex key wrench)
Remove the two 3/8" nyloc nuts. (9/16" wrench)
The transmission should now lift up, turn sideways and come out.

You will need four new OEM O-rings when going back together.

Click to expand...

While the transmission is removed, look to see if there is excessive play between the upper portion of the pivot tube and the upper suspension fork bushing.
If there is excessive play, a new beaded gasket will seal for a short duration only.
If so, it would be best to further tear into this and replace the bushing.


NOTE: Since the special bead moves against the pivot tube, the beaded area should be coated with a water proof grease.
The flat surfaces can be coated with a sealant.




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Rick, I have Sierra parts 18-2777, and 18-2775 for the s Hose and water neck pickup parts, can you advise the part number on the 4 oem o rings you mention in your posts so I can order those up? I appreciate your help

Owarzecha said:

Rick, I have Sierra parts 18-2777, and 18-2775 for the s Hose and water neck pickup parts, can you advise the part number on the 4 oem o rings you mention in your posts so I can order those up? I appreciate your help

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Go here and look under "transmissions" .

https://www.marinepartseurope.com/en/volvo-penta-cat-7742840.aspx

You will need to look at all 3 drive components in order to see the O-rings that you'll need.

The individual parts are tagged by SEQ #s ...... these SEQ #s may change from one schematic to another....... so do not confuse SEQ #s with OEM part numbers.

RicardoMarine said:

Go here and look under "transmissions" .

https://www.marinepartseurope.com/en/volvo-penta-cat-7742840.aspx

You will need to look at all 3 drive components in order to see the O-rings that you'll need.

The individual parts are tagged by SEQ #s ...... these SEQ #s may change from one schematic to another....... so do not confuse SEQ #s with OEM part numbers.

Click to expand...

update, this issue was inside a corroaded water pickup. Replaced this and everything runs fine with no overheating... engine temp gauge stays at 182 and doesn’t loose prime.

Owarzecha said:

update, this issue was inside a corroaded water pickup. Replaced this and everything runs fine with no overheating... engine temp gauge stays at 182 and doesn’t loose prime.

Click to expand...

What part was corroded?

The water pickup tube was corroded under the hose clamp so it looked good from outside but right on bottom was sucking air. Be extremely careful when taking the hex nuts out as per Ricks hint above... I snapped one off without much pressure and then spent the next couple hours drilling and tapping to get it.

Owarzecha said:

The water pickup tube was corroded under the hose clamp so it looked good from outside but right on bottom was sucking air. Be extremely careful when taking the hex nuts out as per Ricks hint above... I snapped one off without much pressure and then spent the next couple hours drilling and tapping to get it.

Click to expand...

The chrome water pick-up tubes rarely go bad. I think that you must be referring to the aluminum water neck fitting...... yes/no?

As for the two water neck fitting fasteners, these would be two small socket head cap screws.
Always apply heat to the suspension fork before trying to remove them.
When going back together, coat the threads with a thread sealant as to help prevent corrosion.


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Rick, you are 100% correct and yes I mean the neck fitting was the issue here. Thank you for your help on this one! Wish I was near you as I don’t have anyone near me here in mn that works on these older Aq125a to bring to.