Raw Water System

[JVS]

Has anyone run across this problem?  I have bubbles in the clear hoses between the heat exchanger and exhaust riser.  When I raise the engine rpm I lose the raw water all together and the engine will over heat..  I have been through the raw water system from the intake up and can't seem to find anything wrong..   It's a d2-55 volvo.  I'm pretty frustrated !!!!

[Odysseus]

I am assuming it's the raw water side of the cooling, (this may not be the case) but 4 things to check:-

Take water intake pipe off turn engine seacock on and blow down pipe, do you get bubbles going out under the boat. You will know if you have.

Have you replaced the impeller if so did it have any bits of the blades missing?? they are a good source of blockage.

Check the pump is working, this is a messy job but you have to do it, take output pipe off pump into a bucket and look at how much water is coming through, should be a good flow.

Next, the heat exchanger, you may have a blockage there. This is a disassemble job by taking the end plates off and checking all the pipes inside. A pig of a job on some boats. no room.

Come back when you have checked.
Odysseus

[JVS]

  Like I said in my original post, I have been trough it from one end to the other!  I'm frustrated and can't see that I've missed anything...

[Odysseus]

Well clearly you have missed something, one of the less obvious things is the raw water pump although it's should be run off a geared drive (not sure on your boat) the drive may be broken and runs only at low revs through friction, so as soon as the back pressure from incleased revs cut in the drive slips. 

As I said before check the flow of water with the pipe off, also if its a jabco pump put a screw driver on the impeller shaft slot and see if you can turn it. If it turns then the drive is an issue.

Odysseus

[JVS]

The pump gear was my thought also, so that's what I'll try today!

Thank you for your help, I'll let you know..

[Still Sailing]

I had exactly this same problem back in 2009, and after 3 weeks trying everything and almost resorting to drink permanently I eventually disconnected the clear inlet pipe at the raw water strainer, connected up a freshwater hosepipe, opened the saildrive seacock, turned the hosepipe on full and left for 30 minutes or so.   The bubbles had completely disappeared when I reconnected the pipe, opened the seacock and restarted the engine. As a matter of routine I take the opportunity to flush the saildrive when in a marina or harbour....

[JVS]

It's certainly worth a try, I can't wait to get back to St. Thomas, where alcohol is much less expensive!!  Thanks, I'll let everyone know the results..