Overheating Issues: New Thought?...

[TXTripper]

So I have a 86 bayliner capri with a Volvo Penta aq125A and a VP 270 outdrive. I have explained that under a load, the engine overheats when run over 3000rpms, but never overheats in Neutral- nor will it overheat if just kept slow all day. Well, I know this could be one of about 15 different things, but if its a problem of getting water from the outdrive intakes, could I disconnect the water tube from where it meets the outdrive, extend the tube and run it straight into the water? In theory, this would at least tell me if the problem is within the seals of the outdrive wouldn't it? I would imagine if this tube is secured then it would suck even more water into the engine providing a better cool. Please give me thoughts, pros/cons, to running this tube and bypassing the outdrive. I am getting to my witts end with this issue!!!

 

[Chris1956]

Re: Overheating Issues: New Thought?...

TXT - Your problem sounds like you have a low volume of cooling water. My Alpha 1 outdrive has an impeller to supply cooling water to the engine. If I was to disconnect this as you had suggested, my motor would get no water. (Note: Bravo drives do not have an impeller. I do not know about Volvo Penta)<br /><br />Have you checked the water intake grating on the outdrive. Barnacles clog mine up late in the season. Also, they get inside the water passages under the water pump impeller and I need to clean them out every year.

 

[Blk-n-Blu]

Re: Overheating Issues: New Thought?...

TXT, Have been following your posts on this subject but being a Merc guy doesn't lend me information on the Volvo Penta.Here is a list of possible overheating causes.It could be a "lugging or propping issue"<br /><br /> http://www.marinemechanic.com/site/page85.html <br /> hope it helps.

 

[TXTripper]

Re: Overheating Issues: New Thought?...

I didn't think of that- thats right, to save myself from sounding like a complete idiot-- Pentas have an impeller in the engine, not in the outdrive- The water is "sucked" through the engine, not "pushed" as an impeller in the outdrive unit would do. Sorry, I should have clarified that. The fact that it is sucked in from the engine through the outdrive leaves me to believe that I could bypass the seals in the outdrive this way...sorry-<br />thanks for the link!

 

[fish393]

Re: Overheating Issues: New Thought?...

What could be happening is that when you are on plane the 270 water tube conection is on top of the intermidate housing in the rear of the drive.Thus it and would be exposed to air and not under water and that could be why under 3000rpms fine and over,sucking air.Remove the two screws on the water hose going into the stern and make sure the water tube has not shifted and if it has reposition it and reseal with a good gasket sealant.Recomended to replace the impeller every two years.good luck

 

[TXTripper]

Re: Overheating Issues: New Thought?...

Fish393-<br /> Can you explain a little more about this water tube shifting? You are talking about INSIDE the 270 outdrive housing right? This sounds interesting and is a new thought. Thank you-

 

[TXTripper]

Re: Overheating Issues: New Thought?...

Oh yeah- the impeller was changed in April...

 

[fish393]

Re: Overheating Issues: New Thought?...

The water tube runs from the lower drive to the imtrmedate drive and the top I am talking about is were the hose goes into the drive from the engine.Just make sure the hose is inline with the conection and that the seal is good.You could also run a sream of water though it with a garden hose to make sure it is not cloged.if the seal is dry rot or cracked thier it will suck air when on plane.It is just a precaution to make sure the tube and conection are inline the most important part is the seal.It does not take much I have learned to affect these volvos cooling systems.Also if their is a leak in the exsaust that will affect how much water is circulated as well on these systems. Check and tighten all connections. good luck

 

[doman]

Re: Overheating Issues: New Thought?...

check the black plastic housing on top of the heat exchanger ...there should be a plastic plate inside when you lift the cup up that splits it in half so water actually goes trough the heat exchanger before exiting...<br />if the plastic plate is gone and they do break easily it will overheat in higher rpms and run normal at idle ...i had the the same problem few years ago when i had my previous boat couldnt figure out what it was untill i remebered about the plastic piece that broke but i could find where it came from so untill i realised it came from there i was looking for problems everywhere<br />if your impeller is good and your thermostat is good and manifold is not clogged this is your problem there isnt nothing else that would cause this<br /><br />hope this helps<br /><br /><br />Dom

 

[TXTripper]

Re: Overheating Issues: New Thought?...

For those of you that have been helping me with this, thank you. The problem still persistss. I removed the heat exhanger and cleaned the element inside, I replaced the impeller, I put new 50/50 coolant in the engine, I have tightened all water hose connections as best I can. I have replaced the resevior cap. I don't know what else to do. About the cap- I noticed that coolant was boiling over, through the cap last time I ran the engine hot...should this happen? Is the seal tight enough? would that effect the overheating problem? I just want the thing to STOP OVERHEATING! Thanks

 

[Peter J Fraser]

Re: Overheating Issues: New Thought?...

Are you sure that your head gasket is not leaking? <br />If it is constantly blowing water out of the pressure cap then this may be your problem.<br />If the coolant tank is filled to the top you will see water displaced as the system heats up to temp. This is normal and if you refill the tank each time out with the same amount of coolant all it is doing is returning the level of coolant to normal. If however you did not top up the tank and you continue to lose coolant then suspect a head gasket leaking into the cooling system. Usually this can be seen as a stream of air bubbles rising out of the coolant when the engine is running under load.<br /><br />If your seawater pump is sucking air in around the seals in the water tube on the leg you may be able to detect this condition by replacing the rubber hose where the water comes into the engine bay with a plastic hose that will enable you to see any air that is flowing with the water stream on its way into the pump.<br /><br />Good luck,<br /><br />Peter

 

[imported_Mike_M2]

Re: Overheating Issues: New Thought?...

Trip, here's what i do. To check if the "straw" is sucking air, i apply duct tape to the inlets on the sides of the lower drive to block them off. Then i plug that stupid pickup hole on the bottom. Remove the inlet hose from the raw water pump and stick your garden hose on it at low volume. The hose pressure will show you if your drive seals are leaking by the water squirting out. Fix those spots. I have also permanently installed a clear hose as Peter suggests, and since it's your own boat you may want to consider that. Have you checked to make sure your manifolds aren't clogged?<br />Also, i had a guy once who didn't want me to fix his leaky drive, so he installed a thru hull pickup and ran it to the pump. Never had a problem since.

 

[TXTripper]

Re: Overheating Issues: New Thought?...

First off, Peter- If I understand you correctly, I think that it was just levelling itself off causing the spillover...it was just topped off with coolant before the last run.<br />Ok Mike, I think that the "thru-hull pickup" is what I was talking about in my first message. I am talking about where the hose (that eventually goes to the pump) meets the drive. At that connection I want to disconnect it and run it straight down into the water. If it is leaky seals in the outdrive, then this should eliminate the water going through them. So this worked for a guy that you know? Never to have a problem again? Seems like its worth a try...what do you think?<br />Thanks for the info-<br /><br />Geoff

 

[TXTripper]

Re: Overheating Issues: New Thought?...

Oh yeah one more thing- <br />what is the best way to check the manifolds for a clog...please be specific, I ain't that smart!!

 

[imported_Mike_M2]

Re: Overheating Issues: New Thought?...

Remove the manifold and inspect it where the exhaust exits. Around the edge you will see slots, this is where the cooling water ends up mixing with your exhaust. These slots get clogged, sometimes corrode completely thru. <br />If you remove the manifold and blow into the place where the tube connects on the bottom, there should be no resistance, showing no clog.<br />As for the intake hose, if you mean just running a hose overboard and letting it suck from there i don't think it would be a good test of the "straw" affect. When you go on plane, the water gets forced up the drive by the speed of the boat, that's why they put the inlets wher they do. A thru hull has a scoop on it that does the same thing, the faster you go the more the water gets pushed up the intake.