AQ125A iddles cool at 140 but overheats at high speed or RPM

nic420

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AQ125A iddles cool at 140 but overheats at high speed or RPM. I have replaced the following: water pump rebuild, water strainer housing, and the piece that connects the hose to the 270 outdrive. When I hooked up the muffs to it and run it at iddle speed it runs at 140 degrees all day long w/ no problem. I see water coming out from the outdrive exhaust and the water feels warm. When I took it out to the ocean same thing. But when a I go fast (35 MPH) it heats up to 260 degrees. Please help troubleshoot.
 

Maclin

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May 27, 2007
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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

Could be corroded/plugged exhaust riser or manifold. The cooling water has to go somewhere, any restriction in the exit reduces raw water flow, this shows up at the longer running times at higher rpms'.
 

Don S

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

Another place for an air leak on the suction side of the outdrive is the oring that seals the lower unit to the steering pivot tube up to the hose connection.
 

nic420

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

Don, I have replaced the hose connection part # 854031 if that is what you are refering to.
 

Mullin

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

I think Don is referring to the part #11 here, just below what you replaced:

http://www.volvopentastore.com/Inte...on_id.862275144--store_id.366--view_id.784589


You can back flush the system with a garden hose to see where any leaks are. Just disconnect the rubber hose at the back of the motor between the motor and outdrive and insert the hose to flush the outdrive from the top down.

Idles at 140? that's low, no thermostat? Mine runs like crap at that low of a temp.

I have replaced the following: water pump rebuild
Did you replace the raw water pump impeller? Not sure if you meant raw water or circulation pump.
 

nic420

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

I took it out last night and it overheats when I go above 1500 rpm or higher. Do you think if i retard the timing would it help? I have had the water pump impeller replaced during the rebuilt of the water pump already.
 

nic420

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

How do I troubleshoot for corrosion on riser or manifold? Water comes out at the exhaust for the outdrive when I hooked it up the garden hose but I do not know the amount it suppose to expell. When I turn up the garden hose the increased amount of water does not seem to get circulated. I just retarded the timing on the boat to see if it will help. Gonna try it out again this Sat
 

Maclin

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

When it overheats above 1500rpm, do you mean on the water in gear or just sitting still in neutral? If on the water is the boat trying to plane at that point, meaning is the top part of the drive out of the water at that speed?

Why do you suspect the timing? Do you think the timing procedure used was not correct? Even then, the cooling system should be able to keep up with timing-induced extra heat. If the timing is off too far the engine will have other driveability and starting problems before the timing can make that much difference in my opinion.
 

Mullin

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

^this.

The water from the garden hose is limited by the revolutions of the WP Impeller. The higher you rev the motor, the more water should flow.

I have had the water pump impeller replaced during the rebuilt of the water pump already.
Can you elaborate, because this sounds wrong. The circulation pump (the auto water pump) is not rebuildable, just replaceable. The sea water pump doesn't need a rebuild either, just an impeller change.

How do I troubleshoot for corrosion on riser or manifold?
Pull it off and look. You should do the same for the t-stat housing and the blocks water jacket.
 

Eddie Ray

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

I think your temp is too low to begin with. It should be around 180. As for the over heating.I have had the exact same problem with mine. I ended up changing the manifold. And also had the problem that Don is referring to. When the boat lifts on plane the o ring is out of the water and if not sealed it takes in air. Check to make sure you have a termostat,if one is there. Either test it,or replace it. You are for sure to cool at 140. Instead of taking the OD apart,I installed a brass water port with screen at the hose on the transom. It works really well. And it is easier to put a container there to flush the motor after boating.
Good luck
Eddie
 

nic420

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

It overheats when in gear. It's not the timing as I thought. It's probably the risers.
 

bruceb58

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

I am assuming you have a closed cooling system since you have an Aq125A. If so, you may have a clogged heat exchanger.

What happens to the coolant when it reaches 260? Does it boil out?
 

86 century

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Re: AQ125A iddles cool at 140 but overheats at high speed or RPM

I had this same problem several years back.
Ended up going to a through hull fitting as far back and close to center as I could worked great from then on.
 
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