volvo aq170 overheating problem

[bgbrds]

I have a 1973 volvo aq170a series engine with a 270 drive with a possible overheating problem. This is what I found or done so far. I replaced the seawater impeller I have removed the circulation pump and exhaust manifold side cover and end cap to flush out all the rust flakes that was causing poor water circulation. I now get good flow through the engine and the water temp going out the exhaust drain is about 130 degrees. The boat is a 19 ft reinell closed bow. When at crusing speed near w.o.t the temp rises above 200 degrees on the guage. as I decrease the throttle the temp will lower to about 150 to 170 degrees until I give it more throttle. Could this be caused by a wrongley matched prop? The current prop is a 14 inch diameter by 17 pitch. It also takes along time to get the boat to plane from dead stop.

 

[TowRoper]

Re: volvo aq170 overheating problem

test your t stat looks like the only thing you didn't do yet you may also be running to lean?

 

[Maclin]

Re: volvo aq170 overheating problem

The water intake on those drives can leak air in at several points from the drive on up to the transom. Most of the drive is underwater at slower speeds so the leak is not a problem, but once on plane the parts of the drive that can leak air in are out of the water and the raw water pump loses suction and an overheat condition is induced.

The water is drawn thru the grates on the lower drive then up thru some tubing into the intermediate section of the drive, then out thru a hose that goes up to the transom. The tubing and sealing between the lower and intermediate sections can leak, also the fitting that the hose connects to can corrode away, and the hose itself can leak or be attached to a very corroded and leaky fitting.

There is a test for this, basically removing the raw water intake hose at the pump, taping up the grates and plugging the drain hole on the front of the lower drive torpedo then running water under pressure from a garden hose back towards the drive to see where water may be forced out. This may be in the sticky at the top of the forum. Don S is usually kind enough to give a link to the testing procedures book he has online for us.

You can also search these forums and find other posts with the same problem and what they did to find/fix the problem.