AQ140a Engine Overheating Issues - Frustrating!

This is my first posting on this site so please bear with me. I did not see any existing thread for this problem I am having. If I missed it, please let me know.

I have acquired a 22' Sissu work boat with an AQ140a I/O. The boat is to be used as a safety/tow boat for a Highlander racing fleet in Cleveland, Ohio on Lake Erie. I think it has a 270 or 280 drive on it.

Since we first got it started (it sat for several years in a heated dry stack building), the engine has always run hot and overheats.

1. I replaced the raw water impeller and raw water shaft seal. There are no visible leaks in the cooling system.
2. I had the heat exchanger checked out by a radiator shop and it is clear.
3. I rodded the oil cooler with hanger wire and found some few bits of zebra mussel debris but nothing serious. One of the tubes looks to be soldered shut but all others are clear.
4. I put in a new thermostat - 180 deg F. I tested the old one. The old one would not open until water in the pot on the stove got to 200+ degrees. Hoped that was the problem but it wasn't.
5. While I had the thermostat housing unbolted from the engine, I turned over the engine and a large slug of water belched out of the thermostat orifice so that tells me that the circulation water pump is working. I just did this for a second or two and stopped. I can't tell if the circulation pump is providing the proper flow though.
6. I replaced the exhaust manifold with a new one thinking this was the problem. The original one had the internal baffle corroded away and appeared to have a lot of internal corrosion.

With the new 180 deg F thermostat, it overheats quickly. I removed the thermostat and ran it without a thermostat and still have an overheating issue.

The engine overheats at anything between 1500 to 3800 RPM. At 4000+ RPM the temp holds steady on the high side but does not go to the 245 deg. mark or red area on the water temp gauge. Once overheated, the temperature comes down at idling or in the range of 1000-1500 RPM while in gear.

When the engine overheated with the water temp gauge needle in the red area the pressure relief cap on the expansion tank released pressure. At the same time I felt the raw water pump and it was hot to the touch. Is that just from the friction of the rubber paddles scraping the sides of the pump housing - is this normal or is that a sign that the raw water side is starved for water?

At idle, I loosened the cap on top to the heat exchanger where the strainer is and water overflowed out into the bilge.

Thinking that the problem is at the raw water pick up side of the system, while the boat is in the water at the dock, I took the rubber hose connection apart where the raw water pick up tube connects to the sterndrive at the rear of the engine and hooked up a fresh water hose to it and back flushed it and saw bubbles coming up from the grid on the front of the drive. I suppose there could be zebra mussel debris inside of the intake water ports in the sterndrive but I never saw any debris behind the grid when I repainted the drive unit. I then hooked up the raw water intake to the sterndrive again and went back out and it still overheated.

This Spring I replaced the universal joints in the sterndrive and noted that the raw water connection elbow on the out drive was in good shape and the rubber hose was good as well.

At this point I am stumped!

I was thinking that I would disconnect the raw water inlet hose at the sterndrive water intake at the back of the engine and hook up a reinforced rubber hose to the raw water pick up hose taking it over the transom to a borrowed strainer that I would fix in a position where it cannot move under way and run the engine in open water to isolate the stern drive from the equation to see if it still overheats.

Since I have had everything apart several times, I am running the engine without antifreeze, just water in the internal side.

Does anyone know what the flow rate is supposed to be for the raw water pump at some designated RPM?

Other than that, any ideas????

Gary

This may help.

http://www.marineengine.com/boat-forum/showthread.php?401384-need-help-with-volvo-penta-aq131a

el_pescador,

WOW, thanks for the quick response!
Since my raw water hose connection elbow on the sterndrive is not the issue, it can only be the 'O'ring at the end of the pick up tube inside the sterndrive, right?

This means I would have to tear apart the stern drive to get at the o-ring, correct?

To be sure the O-ring is the issue, couldn't I by-pass the sterndrive entirely by connecting a temporary hose to the inlet side of the raw water pump at the rear of the engine taking the hose over the transom and connect to a temporary sea strainer that I can affix to the transom several inches below the bottom of the hull? Then run the boat on a plane to see if the overheating issue goes away. If the problem goes away, then I can order the O-Ring(s) and new seals from you guys.

What do you think about that approach?

Gary

Gary, I think you should start looking first at the beaded gasket below the raw water hose connector in the outdrive. If that gasket is not sealing properly around the water tube, then the raw water pump will suck air.

How do you know the intake gooseneck is in good shape? Did you remove it and inspect it as El_Pesc suggests? Have all your tests been in the water or on the hose on a trailer? More info would be helpful.