See full version: Critical Note When Using; Ear Muffs; on Your Volvo Penta Outdrive
The reason why? To prevent air flowing into the cooling water that could lead to damaging the impeller. I've used a plastic golf tee to do the same thing but of course I've forgotten to do this and it certainly stands to reason it would be a good idea to eliminate static engine runs as a source of premature impeller wear or even failure.
Through the course of this, I've confirmed the supply from my water hose is not sufficient for the motor. I have to fill the bucket first and then keep the hose running while the motor runs in order to get a few minutes worth of time with the motor running. here
I've had bad luck with the muffs. I don't think I ever had enough water supply for the water pump, and water was always leaking out around the sides. I didn't try plugging the hole, but I did recognize the issue with not doing that. more
While OMC’s sterndrive competitors Mercruiser and Volvo mounted the rear of the engine to the inside of the transom and mounted the front of the drive to the outside of the transom, OMC took a completely different approach. They mounted the engine and sterndrive on the stringers of the boat; the drive was sealed to the transom with a large rubber diaphragm. The OMC stern drive was then referred to as the stringer mount drive or “stringer”.
The Mercruiser and Volvo sterndrive designs utilized U-joints to allow the drive to tilt and turn. The rather unusual approach that OMC took to allow the drive to tilt (for trailering the boat) was with a ball gear arrangement. For this reason, some people have also called the stringer mount drive the “ball gear drive.”
The only pieces to survive the OMC redesign from the stringer to the Cobra were the 400 and 800 lower gearcases. Other than minor differences in the shift mechanism, the stringer lower gearcases and the Cobra lower gearcases are virtually identical with many interchangeable parts, including the housing itself! here
i inexplicably let my engine freeze and replaced the lower pump, a damaged oil cooler, and two freeze plugs. i can't see or haven't been able to discern any other damage and the engine runs fine. there is no water in the oil and the fluid systems seem intact. i removed the thermostat completely (deducing that the the engine temperature wouldn't have rise in order to have flow)
in the past, i have been able to flush the system without problems but now, in order to get water to flow all the way to the exhaust ports, i have to hold the adapter 'ears' tight to the intake openings and eventually water will start to come out with the exhaust. the flow thru the exhaust stops when i release the pressure.
am i missing something, or should i assume there is a major problem, either with the main pump or with the interior coolant raceway and i should take it to an omc dealer for repair. truthfully, i hesitate to do that because of some past experience with boat repairs and i just don't want to be told i need a major part or repair from someone i have no trust in at all. here
Marine Closed "Freshwater" Cooling systems is a bit of a misnomer as they do not actually circulate freshwater but an antifreeze/water mixture. Unlike in a car where the antifreeze/water circulates through an air-cooled radiator, a closed cooling system uses lake or ocean water flowing through a heat exchanger to remove heat from the engines cooling water/antifreeze mixture.
The heat exchanger is the heart of the closed cooling system. It uses raw lake or ocean water brought in from the raw water pump to act as coolant for the engines circulating water. The circulating water runs in a closed loop through the engine only in a half system and in a full system, the exhaust manifold as well. The heat exchanger acts as a radiator does in an automobile, however rather than air the raw water is used for cooling the circulating water. The raw water is brought in an pumped through several small tubes inside the heat exchanger, this tubes will absorb and exchange the heat from the circulating water surrounding them and will exit the heat exchanger towards the exhaust risers to be dumped overboard. The hot circulating water runs thru the heat exchanger on different lines exchanging its heat thru the cooling tubes and exiting the heat exchanger back towards the circulating pump and the block. We carry a number of replacement heat exchanger tanks for a variety of stock applications:
The half closed cooling system is designed to circulate cooling water through the block only. As shown in the diagram below, raw water is picked up through the drive pickup or through a hull mounted pickup, if present it will pass through a sea strainer to clean debris out of the water. From there it will pass through the raw water pump. The raw water will be used with your Engine Oil and Power Steering Coolers as they will not be part of the closed circulating system. From Here the raw water will be passed into the heat exchanger tank and be pumped through many small tubes where it will exchange heat from the circulating systems water. The raw water then exits the heat exchanger to go through the manifold, into the riser and then exit the boat. As for the circulating water in closed cooling system, cool water will enter the engine through the circulating pump and circulate through the engine. Hot water will exit at the water outlet on top of the manifold and head to the heat exchanger to exchange the heat it's carrying with the raw water. After the exchange the cool circulating water exits the heat exchanger and returns to circulating pump to begin another loop. See below for a diagram of the half system operation: here