Was out for a nice ocean cruise in my SeaRay Sundancer 290, with single Mercruiser 454 Magnum and Bravo 3 outdrive, yesterday. All was well during my ocean run. She cleaved the waves easily at 32-35 mph @ 3600 rpm, and made good time from Fort Lauderdale to downtown Miami.
Later that day, as I made my way up the Intracoastal back to Fort Lauderdale, the engine suddenly and mysteriously shut down. I attempted to restart, but the starter was unable to move the engine. I know from experience what a seized engine sounds like, and I raised my engine hatches to investigate. I immediately noticed the engine bay was completely covered in what was obviously gear oil. That stink is unmistakable. The Mercruiser High Performance Gear Oil, that had been ejected was not its usual snot green, but a disgusting black. That alone told me it was not my engine oil, which stays clear for the entire OCI. I looked over to the previously full drive oil reservoir to find it empty and ruptured. I knew at that point that it was not my engine that was seized, but rather the outdrive it is connected to.
I was not exactly shocked or amazed at this. The Mercruiser Bravo 3 is one of the hottest running outdrives in the business; well known to exceed 300°F oil temps during operation. In spite of this, most do run correctly for their lives. However, a great many, especially those under the greatest load, do not. A Bravo 3 pushing a heavy load (like an 11,000 lb. Cruiser) places incredible thermal load on the little bit of gear oil (3 quarts) held inside the drive. The worst spot is the upper gear case, which runs completely out of the water when a boat is on plane, leaving it with zero water cooling.
Does not really matter what gear oil you use. At 350°+, things aren't going to survive for long.
Solutions? There are two. The hard way, or the easy way. The hard way is by a company has actually put together a drive oil cooler that uses a 12v pump that circulates the drive oil into a raw water cooled heat exchanger. Addition of a filter, magnet, and temperature probe are options available. Fluid condition can be monitored at the circulating reservoir (overheated drive oil blackens within a couple of hours of an event). This is the most effective solution, proven to bring drive oil temps town by 100-140°. Cons? Expensive, more holes need to be permanently drilled into the hull, more stuff to go wrong, more stuff to look after.
The easy way is the tried and true drive shower. This consists of external piping bolted to the outside of the outdrive that has pickups down on the cavatation plate that face forward into the water stream and direct that water up toward the upper gear case, where it is directed at the upper gear case, showering it with raw water. Requires absolutely no drilling, and has no moving or electronic parts to fail. Costs 1/5 of the gear oil cooler. Cons? It's like any water intake. It can become clogged. The same sea life that attacks anything else in the water will also bond to the stainless drive shower. Gear oil temp reductions are 45-60° at best.
Fortunately my outdrive supplier is honoring their warranty on my drive. It was only 58 hours old when it self-destructed. We also had a long conversation about their previous assurances that a 45mph cruiser would not need any drive cooling.
I've decided to go with drive showers, and add temp probes and gauges to my Sundancer and my Nova's outdrives. The showers should stabilize things, but if they do not, then I'll have to look into the drive oil cooler.
I've also gotten their blessing to convert the next outdrive to Amsoil gear oil, as opposed to the semi-syn MHPGO. I should be back on the water next week.
Later that day, as I made my way up the Intracoastal back to Fort Lauderdale, the engine suddenly and mysteriously shut down. I attempted to restart, but the starter was unable to move the engine. I know from experience what a seized engine sounds like, and I raised my engine hatches to investigate. I immediately noticed the engine bay was completely covered in what was obviously gear oil. That stink is unmistakable. The Mercruiser High Performance Gear Oil, that had been ejected was not its usual snot green, but a disgusting black. That alone told me it was not my engine oil, which stays clear for the entire OCI. I looked over to the previously full drive oil reservoir to find it empty and ruptured. I knew at that point that it was not my engine that was seized, but rather the outdrive it is connected to.
I was not exactly shocked or amazed at this. The Mercruiser Bravo 3 is one of the hottest running outdrives in the business; well known to exceed 300°F oil temps during operation. In spite of this, most do run correctly for their lives. However, a great many, especially those under the greatest load, do not. A Bravo 3 pushing a heavy load (like an 11,000 lb. Cruiser) places incredible thermal load on the little bit of gear oil (3 quarts) held inside the drive. The worst spot is the upper gear case, which runs completely out of the water when a boat is on plane, leaving it with zero water cooling.
Does not really matter what gear oil you use. At 350°+, things aren't going to survive for long.
Solutions? There are two. The hard way, or the easy way. The hard way is by a company has actually put together a drive oil cooler that uses a 12v pump that circulates the drive oil into a raw water cooled heat exchanger. Addition of a filter, magnet, and temperature probe are options available. Fluid condition can be monitored at the circulating reservoir (overheated drive oil blackens within a couple of hours of an event). This is the most effective solution, proven to bring drive oil temps town by 100-140°. Cons? Expensive, more holes need to be permanently drilled into the hull, more stuff to go wrong, more stuff to look after.
The easy way is the tried and true drive shower. This consists of external piping bolted to the outside of the outdrive that has pickups down on the cavatation plate that face forward into the water stream and direct that water up toward the upper gear case, where it is directed at the upper gear case, showering it with raw water. Requires absolutely no drilling, and has no moving or electronic parts to fail. Costs 1/5 of the gear oil cooler. Cons? It's like any water intake. It can become clogged. The same sea life that attacks anything else in the water will also bond to the stainless drive shower. Gear oil temp reductions are 45-60° at best.
Fortunately my outdrive supplier is honoring their warranty on my drive. It was only 58 hours old when it self-destructed. We also had a long conversation about their previous assurances that a 45mph cruiser would not need any drive cooling.
I've decided to go with drive showers, and add temp probes and gauges to my Sundancer and my Nova's outdrives. The showers should stabilize things, but if they do not, then I'll have to look into the drive oil cooler.
I've also gotten their blessing to convert the next outdrive to Amsoil gear oil, as opposed to the semi-syn MHPGO. I should be back on the water next week.
