Interference May 12, 2015

By Stephen Horsfall
originally posted Sunday July 1, 2012


I have a problem with my boat’s VHF radio.  When I used my radio, my depth finder, which is mounted on the dash of my boat, goes wild.  The fish finder shows a lot of fish.  Also when I use the VHF radio, my regular AM/FM radio comes on very loud, like a power surge. This situation did not happen when the boat was new.

“Frustrated”, via e-mail


Assuming the problem only happens when you are transmitting, this sounds like a short in the VHF antenna or the antenna lead in.  You don’t mention if the VHF still transmits clearly.  If not, this is the first thing I would check.

If the radio is sending and receiving properly, then I would look for a break in the shielding of the depth sounder transducer cable and/or the regular AM/FM antenna lead in, assuming that none of the original wiring to this equipment has been changed or repaired lately.

Interference between the VHF and the regular radio is fairly common and usually results from the close proximity of the two units and their antennas.  There are filters on the market to eliminate this problem.  Some boats use the windshield frame for the antenna of the AM/FM radio and it is particularly susceptible to this kind of problem.

Interference on the depth sounder can often be eliminated completely if you use a separate power supply (2nd battery) independent of the boat’s electrical system.  This is especially effective in taking care of engine sourced electrical noise.

If all this checks out ok, I would make sure all ground wires for your electronics are in good condition and the connections are clean, tight and free of any corrosion or oxidation.


I have a Volvo Penta 4.3 GXIe.  At 160 hours it runs perfectly, but I was told by another boater it has an Achilles’ heel.  He said there is a bolt (I believe he said starboard side) that should be tightened annually as it can back itself off with vibrations and lead to expensive repairs.

Several marinas have winterized my boat over the years and no one else has mentioned it.  Do you know of any problem?  Do most marinas know what to look for and are they checking torque on bolts?  I tried once to get far enough in to the engine compartment to check myself but was not successful.

Thank you for any advice,

S. Gadzos, via e-mail


I have not heard of a specific problem with this unit in regard to a bolt working itself loose, though occasionally starter motor mounts will loosen up.  This is a more common problem on the 4 cylinder engines, due to their inherit vibration.  Loose starter mounting can cause damage to the flywheel ring gear and the starter motor itself, if left unattended.

Loose engine mounts can also cause some expensive damage, but they are not a common occurrence as they usually have lock nuts to keep them secured.  The steering system fasteners should be routinely checked for safety reasons, especially the steering cable connectors and the steering lever on the drive.

The fasteners that would likely cause the most engine damage are usually located internally and are not accessible from the outside, so there is no easy way to check these.  Most engine manufacturers apply Loctite or similar sealants during engine assembly to insure things stay together.

A mechanic doing a winterizing job, would not normally check the torque of fasteners, but he would usually be on the lookout for potential problems and loose fasteners usually cause irregular noises during operation.

As always, never ignore any different sounds or operational irregularities that occur during normal operation.


After a long winter, we had a 70 degree day and I got the boat out to get it ready.  I ran it with the ear muffs on with the hose.  I do this every year, but I never really looked at where the water exited.  The tell-tail stream was strong, but there were two other holes in the lower unit that water was exiting, and it was exiting around the shift shaft as well.  Is this normal?  Also there is a small plastic tube not attached to anything, is that normal as well?  

Name Withheld, via e-mail


The water that comes out the tell-tale hole is a very small portion of the cooling water that circulates through the engine.  The larger portion of the water is directed through the exhaust to cool this area as it gets very hot.  There are several exhaust relief holes to eliminate back pressure when the engine is idling and I suspect this is the reason you see water coming out other areas of the lower unit.

The small plastic tube that you found is a hook-up that can be used to attach a speedometer tube to a pick-up in the lower unit instead of using a transom mounted pitot device.  It is generally more accurate and less likely to be fouled by weeds etc,  Note if you decide to use this for your speedometer, the fitting (connector) must be cut open slightly for it to work as it is normally closed on the end as it comes from the factory.  Also, if you use this, the connection should be left off (open) for the winter to ensure that no water stays in the lower unit speedometer cavity during the winter.

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