Volvo penta overheating

I appreciate the site, due to the fact I am a new boater. I have a 1985 Renken 18 ft Volvo Penta AQ125A, 270. I have a problem with the boat getting hot while under throttle. If i pull back it cools down, but on throttle up it heats up again. I have replaced the manifold and cleaned all the cooling system parts. Replaced the impeller as well, Same problem<br /><br />Charly

Re: Volvo penta overheating

Look at the hose connection on the outdrive (the hose between the transom shield and the drive). It's made of aluminum and corrodes away. When at idle, it's under water, when you try to get on plane it sucks air because it's up out of the water.<br />It happens a lot in salt water.

Re: Volvo penta overheating

Is that the rubber hose between the two bellows. About one inch in diameter. If that is it how hard to fix?

Re: Volvo penta overheating

Yes, that's the one.<br />I don't think it's hard to fix, just remove the upper gear box, replace the fitting, and put the gear box back on with new orings.<br />That's how I do it, you may be able to get in there with a 3/16" allen wrench and get the old one off and new one back on, but if that is bad, what shape is the bellows in, and when was the ujoints and other things inspected.

Re: Volvo penta overheating

If it's not that water pickup pipe, and you can tell if it's leaking just by running it on muffs, it's quite likely a problem with debris on the raw water side (the inside) of the heat exchanger. They clog easily with cooked on vegetation that gets through the strainer. <br /><br />Muriatic acid will clean out the heat exchanger thoroughly and incredibly cheaply. It will also attack aluminum so take the heat exchanger out of the boat before pouring it in. It will bubble over with caustic foam and bits of green veggie goo when it starts to work (which is almost immediately) and you'll need to rinse that mess off the aluminum housing before it begins to dissolve it. This sounds worse than it is, just have a hose ready to keep the acid dilluted on the aluminum housing. <br /><br />Muriatic acid will burn your skin and eyes and ruin clothes so be sure to dress appropriately. You can buy the acid at any hardware store in the plumbing dept.