Raw Water System Cap Leaking

[Mbcarter967]

I have a Volvo Penta AQ125B in my Bayliner Capri. I’ve only had it a few weeks, so I’m still working some bugs out of it. Last weekend, when I had it out on the lake, it started leaking water out of the raw water system cap when I went to a high throttle setting. It didn’t leak at lower throttle settings. The cap was secure, so I began looking on the internet and found a thread where people were saying that was indicative of the exhaust manifold being blocked with rust. The thread sounded exactly like my problem, so I thought that must be it. After taking the exhaust manifold off today and running water through it, there seemed to be no problem with a blockage. The water was flowing through fine as high as the pressure of my water hose (which is pretty high compared to other places I’ve lived). Are there any other possible problems this could be caused by? The cap appears to be in good shape overall and fits tightly

 

[dubs283]

When you say "raw water cap" are you referring to the closed cooling/heat exchanger cap or the cover on the raw water pump?

 

[kenny nunez]

If you are loosing anti freeze coolant from the heat exchanger side then get a 125 Volvo service manual. You have a leaking head gasket. When the cap starts leaking does the temperature go up?
When the boat is on plane at full throttle there is more water flowing through the exhaust manifold than a water hose can provide. The other problem might be the heat exchanger itself. You will be surprised how much crud can get in between the segments of it.

 

[captmello]

sounds like it's the cap on top of the strainer to the heat exchanger. keep in mind that the higher the rpm, the more water will be pumped, so maybe it's just a leaking cap or missing gasket on the cap.

 

[Mbcarter967]

When you say "raw water cap" are you referring to the closed cooling/heat exchanger cap or the cover on the raw water pump?

It’s not the heat exchanger. It’s the cap that goes on top of the chamber holding the strainer basket

 

[Mbcarter967]

If you are loosing anti freeze coolant from the heat exchanger side then get a 125 Volvo service manual. You have a leaking head gasket. When the cap starts leaking does the temperature go up?
When the boat is on plane at full throttle there is more water flowing through the exhaust manifold than a water hose can provide. The other problem might be the heat exchanger itself. You will be surprised how much crud can get in between the segments of it.

No, I’m not loosing any antifreeze. I’m actually thinking now that it might be the exhaust manifold after all. When I looked at it closer, there is more rust in it than I originally thought.

 

[Mbcarter967]

sounds like it's the cap on top of the strainer to the heat exchanger. keep in mind that the higher the rpm, the more water will be pumped, so maybe it's just a leaking cap or missing gasket on the cap.

I thought the same at first. The cap is good with a solid gasket. I’m leaning more toward the exhaust manifold after closer inspection now

 

[Horigan]

Another way (better) to measure exhaust manifold/riser flow is to measure the temperature with an IR gun after getting fully warmed up and running on plane. They should be 110F to 120F, definitely under 140F. If one or both is hotter you have a flow issue. Others may chime in on what the max allowable temperature is, but measuring temperature is a better way to assess cooling flow through the manifolds.

A flow restriction could result in higher than designed for pressure at the strainer.

 

[Mbcarter967]

Another way (better) to measure exhaust manifold/riser flow is to measure the temperature with an IR gun after getting fully warmed up and running on plane. They should be 110F to 120F, definitely under 140F. If one or both is hotter you have a flow issue. Others may chime in on what the max allowable temperature is, but measuring temperature is a better way to assess cooling flow through the manifolds.

A flow restriction could result in higher than designed for pressure at the strainer.

Yeah that’s what I’m leaning toward. Any suggestions on measuring flow without putting it back on the boat? I’m a little wary of putting it on just to take it off again with all the old connections on the adjacent parts

 

[Bondo]

It’s not the heat exchanger. It’s the cap that goes on top of the chamber holding the strainer basket

Ayuh,.... Welcome Aboard,..... Isn't that Before the raw water pump,..??

 

[Mbcarter967]

Ayuh,.... Welcome Aboard,..... Isn't that Before the raw water pump,..??

I don’t think so. It looks to me like the water from the engine is pumped up into the strainer basket, then through the strainer and into the exhaust manifold. Am I wrong on that?

 

[captmello]

was the bost used in salt water?

 

[Mbcarter967]

The previous owner told me that it wasn’t, but he did live close to the ocean so it’s quite possible. I’m trusting him less and less as more issues arise.