Volvo Penta AQ125/270 overheating raw water not pumping

[offshorejason]

Ok guys, I've read just about every thread I can find seeking solutions but I'm desperate and not finding a solution. I have an AQ125 with a 270 outboard and my engine is overheating. When I remove the cap on the heat exchanger, I never see moving water. Here's what I've done:
-Brand new impeller, turned clockwise and uniform.
-brand new connector (854031) at the top of the outboard with a new hose to the transom.
-removed and tested each piece from the transom to the impeller.
-removed and checked clear all connections to the heat exchanger.
-turned the motor with the impeller casing open to ensure it's spinning (it is).

I have had it out on the lake and initially, it stayed in the middle (temp) as long as I was at idle or a little above. Going above idle made it overheat. I figured the water level dropping while going above idle was what caused the sea water pump from catching a prime but changing the connector should have fixed it. Last time I took it out, completely overheated no matter what. I have been testing it with a large tub of water in the driveway but it's still not cooling. I'm out of ideas, please help. Any ideas are very welcome!!

 

[Fun Times]

Thinking you may have either a engine Circulation Water Pump issue such as possible worn pump blades inside or other issues of the pump or a broken coolant “thermostat” issue.

 

[dennis lintz]

I had this problem happen a few years ago. I cleaned everything. Changed heat exchanger and hoses after heat exchanger. It still over Heated. had my mechanic friend look at it and found pieces of the impeller in the inlet hose before the thermostat and filter basket. Not sure how it got in there, but it doesn't overheat anymore, although it does run high temp still.

 

[offshorejason]

Thinking you may have either a engine Circulation Water Pump issue such as possible worn pump blades inside or other issues of the pump or a broken coolant “thermostat” issue.

Thank you for the response. Wouldn't I be seeing water at the exchanger if everything to that was functional?

 

[offshorejason]

I had this problem happen a few years ago. I cleaned everything. Changed heat exchanger and hoses after heat exchanger. It still over Heated. had my mechanic friend look at it and found pieces of the impeller in the inlet hose before the thermostat and filter basket. Not sure how it got in there, but it doesn't overheat anymore, although it does run high temp still.

Awesome, I will take that all apart and check it out. Did you still see water moving in the exchanger?

 

[Fun Times]

Thank you for the response. Wouldn't I be seeing water at the exchanger if everything to that was functional?

The red tank heat exchanger with the radiator cap should have antifreeze inside vs water and the thermostat ought to be in the antifreeze side too… The engine block, thermostat, circulating water pump should be the coolant antifreeze side of the system.

External redirection

www.volvopentashop.com

Volvo AQ125 Engine Cooling System

As I understand it, the Volvo Penta AQ125 has 2 cooling systems. There is the fresh water system that by means of the impeller, draws water into the cooling system and discharges it thru the lower unit back to the lake. The 2nd system involves the antifreeze and the heat exchanger. I assume that...

forums.iboats.com

 

[offshorejason]

The red tank heat exchanger with the radiator cap should have antifreeze inside vs water and the thermostat ought to be in the antifreeze side too… The engine block, thermostat, circulating water pump should be the coolant antifreeze side of the system.

External redirection

www.volvopentashop.com

Volvo AQ125 Engine Cooling System

As I understand it, the Volvo Penta AQ125 has 2 cooling systems. There is the fresh water system that by means of the impeller, draws water into the cooling system and discharges it thru the lower unit back to the lake. The 2nd system involves the antifreeze and the heat exchanger. I assume that...

forums.iboats.com

Yeah, I have antifreeze in it. The radiator system is air tight, no leaks. I just rebuilt the fresh water pump and it seems to be good but I'm not seeing water at the exchanger (where the fresh water pumps to). I have no clue why it's not slinging water like crazy, it's all checked and rebuilt all the way to the outboard

 

[dubs283]

Volvo used/uses many different shapes/styles/sizes of sea water pumps and impellers. Best bet is to procure oem and verify by eye exact fit

As mentioned, check entire raw water side of cooling system for debris/blockage. Also, be absolutely positive about closed cooling water (circ) pump operation. Seems this could be a culprit in your situation based on provided info

 

[Scott Danforth]

Thank you for the response. Wouldn't I be seeing water at the exchanger if everything to that was functional?

No. You are looking into the expansion tank

 

[Scott Danforth]

Are you running on muffs, or with the boat in the water?

 

[offshorejason]

Are you running on muffs, or with the boat in the water?

I typically run from a large tub full of water. I have another question (sorry if I am frustrating you guys, I am very much big on learning and DIY).

I took off the expansion tank and the thermostat the other day and the thermostat is brand new. Should there be coolant behind the thermostat (in the engine?) Should I fill that spot below the thermostat if not? I dumped all the coolant when I took it apart and would like to flush it and replace it. I am weary of filling it if it is not supposed to be for obvious reasons.


Next step plans: I will look into the circulation pump next as I haven't done so yet. Also, I see on the original diagrams there is supposed to be an oil cooler and I do not have one. The out side of the heat exchanger runs straight into the exhaust bellows.View attachment Question.jpg

 

[Scott Danforth]

I typically run from a large tub full of water.

STOP.

Unless that tub is big enough to submerge the whole drive, the pump can not prime

You toasted your impeller.

Impellers do not "suck", they only push fluid and must be submerged to prime.

So replace your impeller and use a set of muffs

 

[offshorejason]

Unless that tub is big enough to submerge the whole drive, the pump can not prime

The tub covers the outboard and all it's suction points. I have checked the impeller three times and it is in fantastic shape. I just replaced it to be safe and the old one looks brand new. The ears I used previously didn't work well as there is a hole on the bottom that needs to be plugged and the slits for the suction are at a pretty sharp angle. I retrofitted the tub because of this.

Do you know if the area beneath the thermostat should be full of coolant (see my picture please)?

I think you were right about the circulating pump, that is my next venture. The lack of an oil cooler worries me too but one problem at a time. I removed the expansion tank, thermostat and housing, top of the heat exchanger, and the tubing running from the impeller housing to the top of the exchanger and flushed everything. I refilled the expansion tank with coolant but noticed the section beneath the thermostat didn't have fluids (hence my question).

I couldn't drain the exhaust manifold because the fitting is rust-welded but I will do so, and flush it, after I check the circulation pump and figure out the fluid levels beneath the thermostat.

I really appreciate your help!

 

[Scott Danforth]

You need water over the top of the drive to flood the impeller to prime it.

That is 18" higher than tou can get with a tub

 

[offshorejason]

You need water over the top of the drive to flood the impeller to prime it.

Ok, I will transition back to the ears and get an expanding plug for the drain hole. still wondering about coolant.

 

[offshorejason]

After doing some deep YouTube research, none of the other AQ125A engines have the oil cooler installed. I will be filling the manifold beneath the thermostat with coolant and checking on the circulation pump. *fingers crossed*

 

[kenny nunez]

You can also remove the suction hose from the through transom fitting in the boat then submerge it in a bucket of water. That way you will know if the pump is working.

 

[offshorejason]

Ok, double feed ears, new hoses and connections all the way to the heat exchanger, still no water out of the exhaust. Removed the exchanger and cleaned it. The only thing I haven't done is remove the circulation pump but that's on the coolant side and it wouldn't stop fresh water from making it's way through the system and out of the exhaust (I haven't taken apart the exhaust manifold either). I can't see any way to check the inlets on the outboard without removing the entire thing and I don't want to do that till this winter. Frustrated is an understatement

 

[kenny nunez]

Try what I mentioned, by submerging the suction hose in a bucket of water or just stick a garden hose in it. If the pump does not pull water then I bet either the 1/2 moon key somehow slipped out or the pump drive coupler is not turning the pump shaft.

 

[offshorejason]

Tried again and it failed again. Anyone ran theirs without a t-stat installed? It ran great as it heated up, and at one point I could tell the thermostat opened because it cooled rapidly, and then it stopped cooling again.