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Raw Water clear tube test - yields lots of bubbles

JackM

New member
Hello -

We are at our wits end trying to solve this problem

DP SM 1.78 with TSK SX MHP Transom shield (2001) - replaced risers and manifolds in Nov, this spring among other things replaced bellows (both) and shift cable. On muffs and in water at idle temp is fine, then under load at about 2500 rpm - temp starts to rapidly climb. Checked raw water pump (volume test good), checked lines for blockage - everything clear. Installed clear tubing on suction line up to T-Stat housing and legs feeding manifolds - sure enough as the boat is put under load - starts sucking air, lots of bubbles. Also, at dock increasing RPM and changing trim, yields bubbles which might hint at the hose connection.

Have pulled the boat and going to drop the outdrive this week. I have searched a bunch of forums and folks have indicated that the tube to outdrive connection is the likely culprit. I'm working with a very experienced mechanic - most of his experience is with Merc's and old OMC's. Recently we back filled the raw water suction to look for leaks and the only water came out was at the nipple which apparently is equipped witha a drain hole. So hoping the brain trust can help point us to steps to ID the source of the air leak. Should we just swap out the nipple or are there other tricks or ideas which should consider?

Thank you for any insight folks can offer
 
If you cannot find the leak, Block off the water feed from the drive inside the hull. Cut the hose in the transom assembly and install a thru hull with an eel grass strainer. Problem solved.
 
If you cannot find the leak, Block off the water feed from the drive inside the hull. Cut the hose in the transom assembly and install a thru hull with an eel grass strainer. Problem solved.

Many years ago I had a plastic bag wrap itself around inlet on the drive and engine overheated. Changed to thru hull with external wedge strainer and have since done this on several boats... PROBLEM free. Only difference, is I discarded the water line from the drive to the transom as well.

https://www.groco.net/media/file/file/e/x/ex-hull-strnrs.pdf

I use the APHS strainer. Others are problematic. This one is very maintainable.

Only caveat... it is advised to "toe in " the forward end of the strainer towards the keel on V bottom boats. As I recall, 50% of the deadrise hull angle is the recommended number.
 
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