The second most common telephone call that I receive from boaters having difficulty on the water arises from engine overheating. There can be numerous reasons why outboards overheat, the most common being a worn water pump impeller, but it's not the only reason.
Servicing the water pump once a year or every 100 hours of operation is important because you're doing much more than an impeller job.
The water pump impeller material is very tough and flexible when new but as time and heat take their toll the rubber becomes brittle, maybe even cracking, eventually unable to produce enough volume to counteract the heat of combustion inside the engine block. Basically, the more work the engine performs the more cooling water it requires.
When we do a water pump job, we begin by removing the propeller and lower drive unit. The fluid is drained and vacuum and pressure tests are performed to determine the integrity of the gearcase seals. These tests can detect a weak or leaking seal, preventing possible future damage, downtime and expense. The gearcase lube is examined for abnormal color and odor - signs of water contamination and/or overheating.
We also inspect the shift rod assembly for salt and mineral deposits that can place it in a bind and become hard to move or rotate, or in extreme cases cause it to become bent due to mineral getting up behind the motor mounts (common on Evinrude) and forcing them to change position by pushing mounts out and flexing the shift rod against the inside of the steering pivot tube.
Thermostats and bypass valves are inspected and the most important part of the operation is applying proper lubricants to the retaining ring, drive shaft, prop shaft, shifter rod and all water pump and gear case mounting bolts.
A tip for Yamaha owners: Receiving an engine over-temp alarm at idle or during a prolonged period of idling can be an early signal of a water pump problem. Ignoring it can lead to complete failure a long way from the dock. This can be found on even new or recently serviced engines. Quite often it is necessary to shave the water pump housing and liner just slightly to straighten and better match the sealing surfaces to increase the pump's efficiency. A quick way to cool an engine that has overheated at idle is to shift the engine into neutral and set the throttle to about 1500 RPM for a few minutes. This will temporarily increase the stream of cooling water but will not fix the problem. Do not ignore the symptom!
Here's wishing you a great Christmas and prosperous New Year.Coastal Bend Marine
Port O'Connor Texas
361 983 4841