AQ125/270 Still overheating (PLEASE HELP)

[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).
-pushed water from the impeller back towards the outboard and it flows without issue out the intake (just to make sure it isn't clogged).

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, it completely overheated no matter what. Replacing the connector didn't fix the issue.

The engine side is filled with antifreeze and is air tight, no leaks. The issue is on the fresh water side. Given that I have replaced each hose and connection, the impeller, the connector to the outboard, I see no reason why it shouldn't be pulling fresh water to run through the heat exchanger. running the boat in the lake, in a tub, with muffs, doesn't matter, there is still no water making it to the heat exchanger. I am to the point of considering buying a marine air conditioner pump to bypass the impeller system and just pump water through but that comes with it's own bag of issues (flooding the exhaust, etc). I would rather fix what I have and I'm out of ideas, please help. Any ideas are very welcome!!

 

[Scott Danforth]

since the cap is on the expansion tank portion of the heat exchanger. you would never see water moving in it, its not like the top tank of a radiator

you could remove the raw water pump and hook a hose up to the line to the heat exchanger as a test.

did you use a clear piece of hose between the raw water pump and the heat exchanger to check for bubbles in the cooling system indicating a leak?

did you verify the raw water pump was plumbed correctly?

did your old impeller have missing pieces? did you find them?

did you flush out the power steering cooler?

never run the drive in a tub unless the water level is higher than the drive like it is when the whole boat is in the water

 

[offshorejason]

Thank you for the reply! I appreciate you! I have read that people open their heat exchanger and get water flowing and I have not ever seen any coming from it. I have not used a clear tube for any of it. I would have to find some large diameter clear tubing... The plumbing is straight forward as it is all outside of the motor, none of it hidden anywhere. The tubes are straight from each component and obvious. I don't think it could be plumbed incorrectly. My old impeller looked great but I replaced it anyway to be safe. Every component of the system was removed and inspected and the fresh water side wouldn't be stopped if pieces of the impeller broke off. There is no power steering cooler or oil cooler on it. I don't have power steering and the out side of the fresh water, that goes through the heat exchanger, goes directly to the exhaust manifold.

 

[offshorejason]

please forgive the crudeness of this but it really is this simple of a system. The coolant side is separate from the fresh water side and it is clear that the problem is the fresh water side not pulling.

 

[Lou C]

Is the exhaust manifold & elbow clear? They get clogged with cast iron flakes over time. Water has to enter & exit the raw water side of the heat exchanger. Disconnect the feed hose from the heat exchanger to the exhaust manifold & hook up a garden hose to it to test; you should get good flow out of the exhaust housing on the transom mount.

 

[captmello]

while running on muffs, there should be water flowing under the cap of the strainer, lots of water. pull the cap and see. if you've got good flow there, I'd suspect the exhaust manifold is clogged.

 

[kenny nunez]

Sierra #18-3888 lower gear unit seal kit.
You need to drop he lower gearcase and replace these seals. Anytime an overheat occurs above planing speed this must be first addressed. It is a common problem with AQs. All needed tools are fractional, the oil needs to be drained and refilled after reassembly. Hopefully you have an AQ service manual. The job is easy, tilt the drive up, drain the oil and start unbolting.
You will need to refill the drive from the bottom up with one of the pressure pump gear oil kits. 30weight motor oil non detergent is recommended.

 

[QBhoy]

Hi. If you are suggesting that there seems to be no flow evident in the header tank…that’s the closed cooling system being suggested at fault.
How is the water pump for that ?
Is the cap definitely holding pressure ? If it doesn’t, your coolant will boil or close. Are you losing any coolant out the cap ? Is there any water in the oil or sign of exhaust in the coolant ?
I’d try proving that you have flow on the raw and closed side. Just to see where you are.

 

[offshorejason]

@Lou C thank you for that! I have run a hose directly into the exchanger and it flows out of the exhaust making me believe the line to, and through, the exhaust is not clogged. I don't think the closed loop side has any issues at all. The raw water side seems to be the issue. I am simply not getting anything to the exchanger when in normal configuration.

@kenny nunez I have not considered this actually. I will look into this. Would that keep it from getting prime even if the water level is higher than the outboard's intake systems? Meaning; if when in the lake, it sits low enough to cover the all of the components that feed the raw water side, wouldn't this be a non-issue?

@QBhoy my closed loop side is great, never noticed an issue on that side. Coolant is clean and the thermostat functions well. To my knowledge the closed loop side is working well, just not getting water to the exchanger from the raw water side to cool the closed loop side.

@captmello when running on muffs, I still don't get water to the exchanger...are you saying the cap of the exchanger?

 

[kenny nunez]

When the drive is submerged below the swivel joint no air can enter the incoming water. When on plane the joint is above the water line allowing air to enter. No matter what, this area should be addressed.

 

[captmello]

@captmello when running on muffs, I still don't get water to the exchanger...are you saying the cap of the exchanger?
[/QUOTE]
I'm referring to the strainer cap that is part of the raw water side, not the expansion tank cap that acts like a radiator cap. I mentioned muffs because I assumed you were working on land.
has this boat been used in salt water? if so, the exhaust manifold could be rotted out, retricting flow. follow Kenny's advice as well. there can be a big difference between overheating at idle speed in the water or overheating while on plane. if it overheats while in the water at idle it could be a different set of issues to check. if it only overheats while on plane, it usually is an air leak in the outdrive.

 

[offshorejason]

@captmello The boat has never been in salt water (that I know of) and shows no signs of it. I have run with muffs and in the water and get nothing to the heat exchanger (raw water side). It overheats while at idle. I just cant seem to get it to pull water through the raw water system. I have run water from a hose through the exchanger which comes out the exhaust just as quick as I fill it so I don't think the issue is the exhaust.

 

[Scott Danforth]

@captmello The boat has never been in salt water (that I know of) and shows no signs of it. I have run with muffs and in the water and get nothing to the heat exchanger (raw water side).

This says you have a blockage or the raw water casting has rotted off the pivot shaft

 

[kenny nunez]

On the suction side of the raw water pump remove that hose, get a piece of hose connect it to the suction side and submerge the other end in a bucket.
If the pump still does not pull water then the raw water side of the heat exchanger is blocked. You did say before that the exhaust manifold flowed water through it so it should be not the problem.