Overheating Still..........Completely Puzzled

[niedmanns]

I am new to the site and to repairing boat motors so any help would be greatly appreciated. I tried referencing previous overheating questions from the site, but still can not figure out what the problem is.<br /><br />I have a 1985 Glastron/Conroy cuddy with a Volvo Penta AQ 125 A motor. The boat was used only twice over the past two years and was well maintained by the previous owner. <br /><br />When put in the water it begain overheating (temp gauge at 240 degrees). I spoke to the previous owner who said that the normal temp reading per his marine mechanic (after working on the boat) should be between 210 to 220 degrees. I disagreed and even so 240 degrees was way to high, so I began trying to locate the problem. <br /><br />I replaced the impeller (impeller looked good) & thermostat and it still overheated. <br /><br />I then found that the heat exchanger was completely plugged (water coming out of the top of the heat exhanger unit) and cleaned it so that it was operational again. We took the boat out and still it overheated. <br /><br />I removed the outdrive and found that the raw water intake housing (attached to the outdrive) was severely corroded (bottom portion of neck missing) and replaced it. It still overheated.<br /><br />So the new thermostat was tested and replaced (opening between 200 to 210 degrees as rather than the recommended 180 to 190 degrees) and the motor still overheats (temp gauge 210 degrees). <br /><br />Now when running the motor on the lake for 30 minutes, I took temp readings with a meat thermometer and the coolant box was 180 degrees, the block was 162 degrees and the heat exhcnger after removing cap and letting water flow out was 100 degrees.<br /><br />Although the timing has not been checked as of this time, I am assuming that if it was advanced to far that I would have difficulty starting the boat after it heated up (boat starts fine after runnign in water for several minutes).<br /><br />The only thing I can think of is perhaps there is a faulty temp sending unit or recirculating pump.

 

[Colorado Boat Nut]

Re: Overheating Still..........Completely Puzzled

if you start the boat on muffs are you getting water recirculating out the back of the boat?<br /><br />im not sure about your's, but mine should have water flowing back out if not there is a flow problem <br /><br />you can test your sending unit with an ohm meter <br />check your manual it will have the instruction's<br /><br />hope this helps<br />CBN

 

[Juancho]

Re: Overheating Still..........Completely Puzzled

niedmanns,<br /><br />I think I maybe of some help. I just had the same thing happen to my Bayliner with an '84 Volvo AQ125. First off, never in the history of boat repair has a thermostat or water pump impeller ever fixed an overheating problem. This is a slight exaggeration, but there is more truth to that statement then you might realize. <br /><br />First hook the boat up to earmuffs in your driveway. Startup the engine. Unscrew the cap on the black cylinder that sits on top of the Heat Exchanger. Does water come flowing out all over the place with the engine running? It should. If it does, you have pretty much eliminated everything from that point of the cooling system back to the intake on the out drive, including the water pump impeller. Also, make sure plenty of water is coming out the exhaust flap on the out drive.<br /><br />Secondly, let the engine warm up and then feel all around the exhaust manifold. Regardless of what anyone else says, the exhaust manifold should feel cool to the touch. Even if the rest of the motor is overheating. If it hot to the touch, or even too hot to touch then it is toast, and needs to be replaced.<br /><br />Thirdly, and most importantly, these motor/outdrive combinations have a little know quirk, which is super easy to fix, but cause serious overheating if gone unchecked. Check the lake water inlet neck for air leaks. The inlet neck I am referring to is on the outdrive between the two rubber billows. A black rubber hose is attached to it which routes lake water back to through the transom and to the water pump. On this neck there is a gasket. That gasket is leaking air and overheating the engine. There is a simple way to verify this. You splice in a piece of clear rubber tubing on the water pipe just before the pump. Air bubbles will be very easy to spot. I wouldn’t even bother personally. I would just replace the gasket, and make sure there is a real good seal between the inlet neck and the rubber hose.<br /><br />Finally, this is what was wrong with my boat, however I think it might be kind of rare. Remove the black cylinder that sits on top of the Heat Exchanger. This is the same black cylinder I referred to earlier that has a cap on top. Once you remove it take a good look at the bottom end. The cylinder should have a wall in it, which separates cold water coming in from warm water exiting the heat exchanger. This piece on plastic broke on mine, allowing cold and hot water to mix, effective killing engine cooling. Check the Heat Exchanger for the broken piece. While you are at it check the Heat Exchanger and make sure the passages between the cooling plates are nice and clean.

 

[skelly]

Re: Overheating Still..........Completely Puzzled

Hello Niedmanns, Like Boat Nut says, Your problem is likely flow, I had an over heating problem and it about drove me crazy!!! did everything you did and more, The problem turn out to be ( A Clogged exhaused elbow. )This is near the end of the system ,Exhaused & Sea water mix causing some serious corrosion, Think of it, If water can't get out, it can't get in .I hear that they should be replaced about every 5 years, check it out, I hope this helps you. Good luck Skelly.

 

[Lou C]

Re: Overheating Still..........Completely Puzzled

And another thing, your closed cooling thermostat should be a 160, not 180-190. Most raw water cooled boats use a 145, and FWC 160. My RWC OMC Cobra has a 160 in it from the factory, it opens at about 160 and is fully open at about 175 or so.

 

[niedmanns]

Re: Overheating Still..........Completely Puzzled

Thanks for all the input. I will get back to the wrenches this weekend and see if I can resolve this problem. I will keep you all posted.<br /><br />Thanks Again