AQ313A OVERHEATING

"I have twin 131's in my v

"I have twin 131's in my vessel both rebuilt 2yrs ago and have about 250hrs on them. I have performed a block test that was fine,new raw water impeller,new hose conector on outdrive,and switched heat exchanger from other motor and still overheats under load only above 2500 rpm.Copper intakes are ice cold and exhaust manifold is not any hotter than the starbird side motor."

"To a limited degree, the free

"To a limited degree, the free flowing ability of the exhaust manifold "sea water" port is going to have an effect on the amount of BTU's that the H/E can remove from the engine coolant. Although you do say that the copper tubes are cold to the touch, this may still be a factor.

Have you by chance checked to see if the drive itself has any sea life (crustaceans) growing within the water pick up areas... including the "S" hose?

For years I kept a plastic bag of these odd findings around to show people just how much growth and restriction these can casue.

."

"Dale, you may want to check t

"Dale, you may want to check these old threads

http://www.marineengine.com/discus/messages/12487/151259.shtml

http://www.marineengine.com/discus/messages/12487/215701.shtml

http://www.marineengine.com/discus/messages/12487/80294.shtml"

"Just put a new hose connectio

"Just put a new hose connection on and examined the hose,looked clean.I also have a typo on the motor model it's a AQ131.I have also replaced the T-stat."

"El Pescador,thank you for the

"El Pescador,thank you for the info from the old threads.I pulled the exhaust manifold and it didn't look so good so i replaced it.The motor still overheats over 3k on rpm.do you think it's possible that it is sucking air in the outdrive assembly below the hose connector?Do you have a exploded view of this area you could send me?This seems to be where it has to be sucking air since I have ruled out any connetions that may leak on the motor."

"Have you tried to plug with d

"Have you tried to plug with duct tape the intake grids and to put a plug in the drain hole, the pressurize the raw water cooling pipes with a garden hose from inside the boat? If there is a leak, you will see where the water comes from.

Have you also followed Ricardo's recommendation and check for barnacles inside the grid and the cooling tube below the hose connector?

"

"El,to do the test you have de

"El,to do the test you have described I will need to haul out.What do you think about a clear hose on raw water intake inside the boat? When I changed out the hose connector I checked for obsructions in the places you and Ricardo have mentioned."

"Dale, these most always work

"Dale, these most always work well if all components suggested have been examined to be in good working order.
The clear hose may give an indication, but I'd rather see you spend this time on going over your system once again.
The water neck fitting (hose connection) is a critical component... that and the proper installation of it's gasket and the S hose connection.
There is an "UP" side to the installation of this ribbed gasket, and it must be installed correctly.
Any corrosion powder within the S hose (from the previous water neck) must be cleaned from it.
Any loose suction hose clamps must be addressed.
Any bad copper tubing gaskets must be replaced.
The lower pivot tube O ring must be in excellent condition and in place.

I'd also suggest that pressurizing a suction system to detect leaks may not be the best approach. Pressure can sometimes "mask" a suction leak.... or even offer a "False Positive".
I'd still do it, but just be aware!
You could also connect a shop vac to the inboard side of the system and see if you can test via some method....... You'd have to get creative, I suppose.
Maybe this is where your "Clear Hose" idea, my shop vac idea, El P's masking tape idea and some colored soapy liquid may work!??? Starting from the drive, brush the liquid on... look for bubbles in the clear hose. I actually like that idea!

I still think you'll find the problem if you are vigilant in your pursuit by just going over the system once more..... and this would include the engine Circulating pump, Sea Water pump, T stat, Heat Exchanger, etc."

"I have been through the follo

"I have been through the following components.New impellor kit installed correct,new t-stat,new rubber gaskets on all copper connections,new exhaust manifold,new hose connector,checked S hose,new alt belt, and new hose clamps.What about the circulating pump?How do you make sure it operates correct?How about that O ring on the bottom of the intake tube?"

"The engine circ pump would ne

"The engine circ pump would need to be removed and inspected.... this is true!
The lower unit would need to be removed to replace the Pivot Tube O ring!

Are you certain that your temp gauge is reading correctly?
Do you actually have a high temp reading?
Have you checked temp with a Lasor Temp sensing gun?

If you have twins, perhaps you can swap temp senders and possibly even sender connections at the gauges....... and fairly easily.

I'd recommend using the good ole "P of E" (process of elimination) ... One item at a time until you find the source! It will make you a better trouble shooter for next time!"

"Put the clear tube on and the

"Put the clear tube on and the cooling system pumped lots of water with no air in line.Brought the rpm up to 3500 and the system did nothing but suck air.Is there a connection nipple that I cannot see on this drawing where the S hose goes through the transom shield,I believe that's the problem and will arrange a haul out as the vessel is large."

"Another place where air infil

"Another place where air infiltration can occur is through the key 11 flanged plastic bushing between the key 9 joint fork and the key 1 intermediate housing. In the picture above, this is in the area just below the key 28 hose nipple, but is not visible. The flange of this bushing must seal between the joint fork and the intermediate housing. The flange was broken and no longer attached to the bushing and mine leaked there. Very difficult to diagnose. Made the entire drive operate with less vibration and improved the steering response as the bushing was also worn since it can't be lubricated."

"Gary,
The flange of that bu

"Gary,
The flange of that bushing is actually between the Main Suspension fork and the Intermediate housing. However, I do follow what I think you may be seeing here..... but it should be a non-issue at this location.
So, I must respectfully disagree with that as a potential for a suction leak!

Reason: The special "O" ring embossed, or "Raised Bead", water neck gasket is intended to seal against the "Pivot Tube" top outer diameter! And of course, this pivot tube is part of the water pick-up system.

Now, if this seal were to fail, I'd agree with an air leak of sorts at/near this bushing location. Maybe that is what you are referring to!


."

"Ricardo,

You are correct;

"Ricardo,

You are correct; the o-ring on the gasket failed because the bushing was worn and allowed the pivot tube to move which caused that seal to leak, at least in my case."