Overheating Volvo Penta AQ125

[quantum]

Hi all!

Happy to say this is my first post on this awsome forum...sorry it has to be a hot question!

I have an 83 Bayliner Capri Bowrider, bought it last year for $1500.00 with the trailer and ran it most of last summer with no problems. This year it started overheating (225-240 degrees running hard) and pushing some antifreeze out of the radiator cap (heat exchanger?) I have read a quite a bit on the subject, but MAY have isolated it and wanted an opinion before I go tearing off hoses and such.

First we (me and the mechanic at the marina) thought it was weeds clogging the strainer which caused the overheating, lake is full of them on one end right now. So, I have been keeping an eye out for that. However, even when the stainer is clean, it runs good for a while then gets hot and won't run as fast. I can actually hear the engine back off about 300 rps at 3/4 throttle and sure enough the temp gauge starts climbing. Replaced the impeller, same thing happening.

Noticed water leaking from the fresh water cap with the strainer in it. We went for a ride with the doghouse off, and I noticed lake water leaking out of it at a pretty good clip.

Could that be a problem? Think a new cap would solve it? From what I read, if air is getting in it could cause overheating. Could it be as THAT SIMPLE as a cap? If so, why would the cap start to leak at all???

If not, my next step may be a new thermostat just for the sake of having a new one in there,

What else is there (besides the clear hose trick for air, which I don't quite understand 100% how to do).

Thanks for your help in advance, greatly appreciated.

 

[jerryjerry05]

Re: Overheating Volvo Penta AQ125

If your pushing water out the cap you probably need a manifold.Pull the manifold$$$$$ hook a hose up and check the flow.It should let as much water out as goes in. If that is ok then the next step is the heat exchanger$$$$.It can be back flushed.Or you can dip it in muratic acid for a SHORT time then flush with lots of water.Luck Jerry

 

[quantum]

Re: Overheating Volvo Penta AQ125

Hi Jerry,

Thanks for the reply,

With all those $$$$$ I am assuming you mean big bucks.

I know a guy that is parting out the same motor, so I can get the heat exchanger for about $25.00, and the manifold for slightly more.

My question is (since I am not looking at the motor) which part is the manifold? I am trying to think of it as a car engine, but I am used to V-8's LOL!

Is that the intake manifold, exhaust manifold, or a different manifold? Where is it on the engine? I gotta get me a manual one day real soon, but for now if you can point me in the right direction, that would be great!

Thanks!

 

[Hitech]

Re: Overheating Volvo Penta AQ125

The exhaust manifold. Assuming yours is like my AQ120 the exhaust is on the left side looking back from the front of the motor.

For a quick explanation of how these work, water is drawn in from the stern drive and pushed through the heat exchanger. From there it flows through chambers in the exhaust manifold and is mixed with the exhaust gases somewhere after the the manifold and the exhaust and water flow through a hose to the stern drive and exit through a port that is under water. There are "flappers" in the exhaust route to keep water from flowing backward and into the exhaust manifold an cylinders.

Hope that helps.

BTW, my cap leaks a little also. Key word there is little. If you find somehwere to purchase a replacement let me know.

 

[quantum]

Re: Overheating Volvo Penta AQ125

Hi Hitech,

Thanks for the explination, now it is starting to make sense!

So, the reason for the leaky cap may be because lake water is coming in faster than it is going out, thereby creating a back pressure, and escaping through the cap. OK, I think I can handle that.

This could also cause overheating, since the water isn't being refreshed fast enough??? I still may do the clear hose thing, just to see if there are any bubbles (air being sucked in).

With all those weeds, and this being a new thing, maybe something along the rest of the system is plugged? A hose? The intake? The flapper half shut? Like a said, a thermostat might be in my future, just for the hell of it.

I just want to make sure I know the proper terms...the heat exchanger is the part with the antifreeze in it? What is the other part called (the one with the tall plastic tube and the leaky cap)? Or is the WHOLE thing the heat exchanger?

I priced out a new manifold just in case, looks like about $300.00 shipped with the gaskets and bolts, good price?

I'll keep an eye out for a cap for you!!!

TY for the hand holding!

 

[jerryjerry05]

Re: Overheating Volvo Penta AQ125

The cap can be had at Florida Boat Sales,Pasadena,Md. 410-255-4365 ask for parts.They usually have these things.
The tall thing with the big cap is part of the raw water side.Called a raw water strainer.If you run in a lake with a lot of weeds and sand/mud you might want to put in a second sea strainer. It will save your waterpump and the heat exchanger.
I wouldn't change things unless you know for sure.
Flush the exhaust manifold(black thing right side of motor)To see if it's clogged at the end where the exhaust goes out.Luck Jerry

 

[quantum]

Re: Overheating Volvo Penta AQ125

Hi jerry,

Once again, TY!

Do I need to remove the manifold to flush it, or can it be done while still on the motor? Is it as simple as taking off a hose and running water through it with a garden hose or something?

Or, even better, is there a procedure posted somewhere on how to flush a manifold?

I like the idea of another strainer. Going to look into that.

 

[quantum]

Re: Overheating Volvo Penta AQ125

Well, the marina pulled the motor yesterday and took the head off. Turns out there was one cyl that was running at about 30psi compression, all the others were in the 160-170's.

Upon removal of the oil pan, there were pieces of the ring for the bad cyl laying in the bottom, which explains it. There is also a mark on the piston top, but the cylinder wall is not damaged or scratched.

They did this to solve 2 issues. One was the overheating, the other was the lack of power and hesitiation.

I figure now that the thing is out and apart, it would be a good time to flush the cooling system (hoses, heat exchanger and exhaust manifold), drop in a new thermostat and give the carb a good thourough cleaning. The timing belt was changed at the beginning of the season, along with the points, rotor and impeller.

I can get just the 1 piston and its rings, wrist pin etc (kit) for about $65.00 shipped from an online shop, or I can get the whole set for about $250.00 shipped.

1. Should I replace them all or just the one?

2. Should I do anything else besides what I mentioned to it while it's out and apart?

3. Think this will solve the problems (overheat and hesitiation)?

TY guys!

 

[Coors]

Re: Overheating Volvo Penta AQ125

If I had broke rings, I would have micrometers all over my engine, checking everything.

 

[quantum]

Re: Overheating Volvo Penta AQ125

Thanks for the advice, Coors.

The mechanic did just that, and he said everything looks OK. The cylinder wall is even in good shape, maybe I got lucky???

BTW, the price for the piston kit was $250 EACH! And here I thought I was getting a deal.

So, piston is on order, just waiting for the UPS guy. We're gonna backflush the heat exchanger and the exhaust manifold since it's off already, check the hoses for air and HOPE I can get it back in the lake before July 4th. I just won a new wiring harness on e-bay, so we'll put that on.

Just as an aside, has anyone repowered their AQ125 Penta with something else on an 83 Bayliner 1950 BR? I didn't see any threads on it. IF I did that, I'd probably want to still use the 270 drive, so what motors would work? Again, just thinking toward the future and weighing my options.

 

[quantum]

Re: Overheating Volvo Penta AQ125

The outcome...

Figured it would only be fair to post it.

First piston I got (shipped overnight) was for a 125B not 125A, plus is was .060 over, so that's a no go. They'll take it back but no credit on the shipping, which is normal. OK...so I send it back.

Go to order the right one, no longer available. I found a marina with it on the shelf, $345.00 (damn!). Had that shipped overnight too.

Sure enough, it was the right piston. Mechanic goes to hone the cylinder, and there's a hairline crack about 2" long running down the now-shiny wall. UGH! That might answer some questions right there as to the overheating and general sluggishness I had.

Makes no sense to repair a cracked block, and the second marina will take the piston back (again, no credit on shipping). Sent that back too.

Start calling boat yards in NJ, and found one close by with a complete 125A. When I say complete, it was complete, bolt in motor, for $1000.00. Rented a truck, picked it up and bought it over to my mechanic.

They put it in today. Used my old starter, alternator, wiring harness, and a few other misc parts.

Took it for a little test ride tonight as soon as they were done. What a difference!!! Started right up. It's faster, compression is in the 160's across the board, and temperature was stable at about 185 or so. I didn't want to beat on it, since we need to adjust and tweak some things, but it ran good!

So, fingers crossed, it looks like I'm back in business. Now on to the interior work again!

I was really hoping to get it in the water for 7/5. They have a nice fireworks show right ON the lake, and I promised my 8 year old we'd hang on the boat at night and watch them.

The things we do for kids, right?

The other cool thing is now I have some spare parts I can keep handy if I need them, like 3 good pistons, heat exchangers, etc.


TY for the advice guys.