Cooling issues...penta 270.aq125

[2stroke1971]

Ive got an '84 bayliner with the AQ125B and the 270 outdrive. Ive been running it all season. Ive been through the classic "gets hot when up on plane" issue already, of course, the elbow neck was rotted. So I replaced that and that seemed to do the trick for a while.

However the problem seems to have crept back only its not nearly as bad. Before I replaced the neck, all it would take is 30 seconds at half throttle and the nose up and up the needle would go.
Now, I can go half throttle for half an hour and the temp stays ok...

HOWEVER, getting past half throttle, it starts to get hot now, but I will say that I am starting to hear the exhaust when this happens, and I dont remember the boat doing this before. Somewhere above half throttle, the exhaust port comes out of the water. I had my better half drive while I leaned over the back and looked down. It seemed like more of the drive was out of the water than I thought it should be. Lots of turbulence.

Now, when it gets hot, if I throttle down just a bit, she cools down right away.

I have got a feeling that the intake slots on the bottom of the drive are sucking air at some point! maybe not totally dry of course, but all it would need to do is get a little bit of air, and it would make things get hot I think.
They are not really that much below the exhaust.

Is this possible, and if so, what is the remedy? I dont need to be pulling water skiers, but on a good day I like to get to and from my fishing grounds quickly.

Wonder if one of those plane fins things would help....

Any ideas would be appreciated!

Oh yeah, the water pump was rebuilt this season, new impeller, new seals etc...
Thanks,
Neil

 

[captmello]

Re: Cooling issues...penta 270.aq125

Is this a salt water boat? If so, it may be time for a new exhaust manifold. If the old manifold isn't flowing properly, it can overheat. are you confident you got the new intake fitting gasket installed correctly, with the oring down and in the groove? I've always found it a bit tricky to get the gasket to sit properly when installing, especially when the upper is not removed.


I'm not sure about the exhaust noise, or why it would be louder. Might want to check the rubber fitting between the exhaust manifold and the exhaust pipe. If that is bad it will sound different, but would also leak a bit of water I would think.

 

[Don S]

Re: Cooling issues...penta 270.aq125

I have got a feeling that the intake slots on the bottom of the drive are sucking air at some point! maybe not totally dry of course, but all it would need to do is get a little bit of air, and it would make things get hot I think.

Wonder if one of those plane fins things would help....

You have a cooling problem, that "Fin Thing" is not part of the cooling system and your exhaust and water pickups have always been in the same place.
You are grasping for straws in the wrong places.

The reason your exhaust sounds louder is lack of water in the exhaust which muffels the sound. Either the manifold is getting plugged up, or you aren't getting the flow from the pump, or your heat exchanger is plugging up.

 

[occarvers]

Re: Cooling issues...penta 270.aq125

You can install a clear hose on your sea water inlet. This will tell you what flow you have going to the motor. If you are sucking air you will see bubbles. Is this this a closed system? If so maybe a clogged heat exchanger,

 

[2stroke1971]

Re: Cooling issues...penta 270.aq125

Ah, yes, now i remember why I love and hate this board. Some good advice, along with some crappy sarcasm. Good day gents!

 

[2stroke1971]

Re: Cooling issues...penta 270.aq125

I tried to stay away, but I couldnt resist a follow up.

More of the drive WAS coming out than normal, the reason? The lock mechanism was failing. Of course, the thrust of the motor would tend to keep the drive against the boat, but at some point if you reach enough speed, the drive will start pivoting up. The intake slots were sucking air at some point and there it went. Cooling system starts to dry out, the exhaust is noisy for lack of water AND the fact that its up in the air... Thats my theory and Im sticking to it.

Repaired the lock and viola. Had a 15 minute run at 25 mph yesterday and she didnt even crack 180. No loud exhaust noise either. Peeked over the transom at speed and things looked much better.

I understand the same questions get asked hundreds of times here, but the answer is not always the same....having become FAR too intimate with my cooling system than I ever wanted to be, the fact is I did start to think of weird reasons for my boats symptoms.

Thanks again everyone.

 

[captmello]

Re: Cooling issues...penta 270.aq125

I'm not sure I'm buyin' it.

I just don't see how the outrive could tip up while running. Thats where all the pushing force is coming from, unless it's happening when you are slowing down.

Whatever the case, thanks for updating your thread.

Why stay away? there's still so much to learn.