Cooling Systems

The Physics behind a Stern Drive Cooling System:

Where does the heat come from?

     Before you can begin to design a stern drive cooling system, you first have to understand what is causing the heat. If you can start a fire by rubbing two sticks together, it must be true that friction causes heat. If the faster you rub the sticks together the more heat you create, then it’s the speed or the RPMs, which is causing the greater heat. How does that equate to a stern drive? There are many heat sources including clutches and universal joints, but most of the heat is caused by the bearings which allow the shafts to spin. On the top half of the drive, there are two main bearings, one at the front, and one at the top. They share an equal load with one exception; depending on the type of drive you have, the front bearing is spinning 1.5 times faster for most Bravo 1s, and 1.83 times faster for Bravo 3s. It doesn’t take a physics professor to figure out that most of the heat generated by a stern drive comes from the FRONT Bearing. This led us at Simrek to ask, if the front bearing is responsible for generating 1.5 to 1.83 times the amount of heat of the top bearing, why do most drive cooler manufacturers target the top bearing cap? This increased RPM, along with the amount of extra components that it takes to spin a second propeller in the opposite direction is why the Bravo 3 is the hottest running drive in the MerCruiser line up.

What should you be cooling and why?

     The component inside the stern drive that is most susceptible to abuse from heat is the oil. It begins to break down at about 300 degrees. The metal components inside the drive can reach temperatures of at least three times that amount before they become affected. The only way the drive components can reach those temperatures is if the oil has broken down and the heat generating friction builds up. If you cool the oil and keep it from breaking down, it will cool and protect the components inside the drive. Now you should be asking, why do most drive cooler manufacturers target the top bearing cap? There is still one more reason to ask the same question.

What is the best way to cool the drive oil?

     Think of it like this; if you wanted to boil water in a pot, would you rather use a pot that is one inch thick or 1/8 of an inch thick. Obviously the water would be heated much faster in the thinner pot. The same principals are true when it comes to cooling something. The top bearing cap is over an inch thick, the sides of the drive are less than 1/8th of an inch thick. The thinner the material, the easier it is to wick the temperature of the drive oil inside through the casing. So the most efficient cooling system would be one that targets the sides of the drive. So again, why do most drive cooler manufacturers target the top bearing cap? The other component that is critical for cooling the drive is the amount of water the system can process and apply to the drive casing on a continuous basis. Click here to see how much water it takes to cool the drive by 65 degrees.

About Us: Simrek® Corporation specializes in external stern drive cooling systems for your high performance or pleasure boating needs. Composed of high-grade  stainless steel, the Simrek® Multiport Drive Shower® can add years of life to your Alpha and Bravo drives

Copyright © 1999-2012 Simrek Corporation, 764 Eagle Point Drive, Kernersville, NC 27284   Phone: 352-729-3093
The new: “No Drill Brackets” and the new “Max Pick-up Port System” are both Protected by US Patent #7,666,042 B2, Issue Date Feb. 23, 2010. 90 Degree Pick-Up Ports US Patent number 6,241,566 Issue Date June 6, 2001.The words: “Simrek”, “Multiport Driveshower” and “Halo” are all Registered Trademarks of Simrek Corp. and may not be used anywhere in print without written permission from Simrek Corp.