Air leak or blockage in raw water system?

[Capn_Kev]

2001 Bavaria 37 with a Volvo Penta MD2030.

I have a significant amount of air bubbles in my raw water system (clear hoses) that is causing reduced flow. Last year I replaced my heat exchanger housing, water pump">raw water pump, and associated parts. Kept the exhaust elbow and soaked in hydrochloric acid and wire brushes to clean it up and reinstall.

Since noticing poor flow and inability to reach normal cruising RPM's (2800-3200) I have done the following:

Cleaned the prop and shaft (was collecting plenty of hitchhikers)
Changed impeller, cleaned and reinstalled cover
Checked all hoses (sea cock to strainer, strainer to pump, pump to heat
exchanger)
Cleaned strainer
Changed oil and filter

Took it out after all the maintenance and the RPM issue was resolved (likely from the prop cleaning), but raw water flow seemed even more reduced.

I'm hesitant to pull the exhaust elbow, but could that be causing all the air bubbles inside the raw water system? The exhaust elbow is the last component of note (sea cock --> strainer --> pump --> siphon -- > heat exchanger --> exhaust elbow -- > muffler --> out the exhaust hose and loop).

I guess my question is could a blockage be causing the air bubbles, or should I be chasing an air leak/suction issue?

[Capn_Kev]

Anybody have thoughts? Or experience with what a blockage looks like vs. a leak?

I ordered a new stainless exhaust elbow that is on the way because who doesn't love spending money on boat parts, so I guess I'll find out soon enough if that had any part in the issue.

[Tetepare]

Clear hoses???


Sounds like it’s sucking air.

[tkeithlu]

Bubbles in the hoses means an air leak. Go backwards to the first place air is observed and start tightening the hose clamps. If that doesn't work, then it's time to take the upstream hoses off for cleaning and inspection. Fittings with bad gaskets and pipe threads without teflon tape could also be the source.

[catalystcat]

I'd start with the easiest- the seal on the raw water filter. One thing you can do is use a little seal lube (e.g., pool seal lube). Also, a cheat to check this is to wrap the top in clear wrap (kitchen type) to seal it up to see if the bubbles are reduced. Of course, this is for diagnostic or "get home in a pinch" only. (Oh yeah, don't forget to look for little chips or cracks in the raw water filter cover.)
Next would be the hose clamps. The double clamping is not really overkill.
Then, maybe open the lowest hose connections and see if some old impeller parts or some other junk got loose in the system.
After that, you get to the harder stuff - water pump O-ring, corrosion of water pump cover, etc.

[capt jgw]

I'd bet on the gasket in the water strainer, especially if it's above the waterline. Seal line or even Vaseline smeared on the gasket might stop it temporarily. If you can't find a replacement gasket, you can get rubber sheet at a hardware store and cut your own, and if it's an o ring they'll have those too. I always keep several different types of gasket material on hand and make my own as needed.