Aq131 overheating on load

"AQ131a Overheating

Hi ,
I

"AQ131a Overheating

Hi ,
I know that overheating problem was on forum 1000000 times
I did read most of posts but couldnt find answer for my problem.

I have got two Aq131a on boat.

Portside engine is overheating when is on load at 3000-3500 rpm .

When boat is not moving I can rev 4500, keep it for long time
and engine will not overheat.


Starboard engine works properly.


What I did:

1) water passage between sterndrive and raw water pump is clear.
2) I changed water hose connector on sterndrive for new one.
3) impeller on raw water pump looks very good.
4) I checked heat exchanger , exhaust manifold, there is no blockage
5) Fresh water pump looks good.
6) Installed new thermostat.

Is anything else what I can check? where can to be problem?



Sebski"

"It might be multiple problems

"It might be multiple problems, and twin installations gives a few more.
Have You cross-changed/checked instruments and senders to eliminate that option?
Have You synched the tachs to be sure not one engine is pulling the load and thereby gets overheated?
(Do they reach same rpm at full throttle?)
Check if exhaust manifolds have the same temp when under load. If the one getting hot is hotter -You have a raw water cooling flow problem.(Put Your hands on them, if smells bacon far too hot!)
If Manifolds have the same temp, ok to touch, take both oil-coolers and heat exchangers to a radiator shop and have them acid-treated/cleaned, or do it Yourself.
And finally check fresh water circulation pump for impeller wear/cavitation damage. (Distance from impeller to housing).

This should keep You busy for some time."

"I have cross-checked instrume

"I have cross-checked instruments and senders, they are fine.
Tachometers are fine.
Exhaust manifolds - I can put my hands on them

The only one thing is fresh water pump.
I did check and couldnt see any rust or broken parts. But distance from impeller to housing, maybe there was something wrong and I just didnt notice, is any way to check it ?

Anyway, I have ordered new circulation pump, I will change during weekend and will see.

Sebski"

"You can install the automotiv

"You can install the automotive circulating pump in your engine and save a few bucks: it is virtually identical to the "marine" pump in your engine model. By the way, make sure the alternator belt is not loose, as that would give the symptoms you are experiencing.

Now that you are at it, I would dismantle all the copper pipes and give them a good blow with water and see if the flow is restricted. Same with the exhaust manifold. One easy thing you could do is swap exhaust manifolds between engines (you will just have to buy new exhaust gaskets, and the automotive type will work), and if the problem is cured but moves to the other engine, then you know where the problem is. The same could be said about the raw water pump (make sure the Woodruff key is correctly installed between the impeller and the pump shaft)."