I have a 2001 Sea Ray 185 with Mercruiser 4.3L mated to Alpha One, Gen Two outdrive. The engine is new (remanufactured from Mercruiser, with about 20 hours on it). The problem described here pre-dates the new engine, so I don't think it's related to the engine itself, rather to the drive, which is original.
The boat was originally a saltwater boat (prior owner) - only in fresh water the last 5 years (when we bought it used).
Symptom: Temp gauge after warm-up is rock-solid at just under 170 degrees until the boat starts to plane. After about 20 seconds on plane, the temp gauge fluctuates wildly. It will swing from 100 degrees to 200 degrees in about 3 seconds. Sometimes the alarm starts to buzz, which I believe is an overheat alarm. It seems physically impossible for cooling water temperature to fluctuate that quickly, leading me to believe that there is air in the cooling system when that occurs. Coming off plane, it takes about 30 seconds and the temp reverts to 170 degrees and stays there until you go back on plane. I can drive around all day with no problem, as long as I don't get the boat up on a plane.
When we first bought the boat used, our lake mechanic pulled the drive off and said that the mating surfaces between the drive and the bell housing, specifically around the cooling water passageway between those two surfaces, are VERY corroded. So much so that the circular channel for the sealing O-ring had basically corroded away. I have had two different mechanics use their best efforts to mickey-mouse something to seal up that water flow interface between bell housing and outdrive - they have used various epoxies and a dremel tool to recreate the circular channel to hold the sealing O-ring. This has worked temporarily, but the problem always comes back.
As far as I can tell, this water passageway seal is under lake water when the boat is still (so even if there is a leak at the interface, there is still lake water outside and inside the water passage - so no air can get in the cooling system), and remains under water at low speed until the boat gets up on a plane. At that point, the drive comes up out of the water somewhat and I think that any leakage where that O-ring is (which is now above the lake water level) could result in air getting into the cooling water flow, which I believe is what causing the temp gauge to swing wildly.
My questions are:
1) I can buy the explanation that air is getting into the cooling water system when this failing seal is no longer under water - but that seems to be most likely if the raw water pump is PULLING water up the leg of the outdrive from the lake (I think this may be the basic design in some older Volvo outdrives), so an air leak would allow air to get sucked in. But in the case of a Mercruiser Alpha One Gen Two drive, the water pump is always under water (since it's at the very bottom of the leg) and it PUSHES water up. If there is a leak in the water passage on its way from the pump to the engine (even if that leak is above the lake water level when the boat is on plane), then wouldn't water just leak OUT at the failure point, rather than air getting sucked INTO the water passageway (after all, it's on the pressure side of the water pump, not on the suction side)? I could see this result in lower water flow in the cooling system (and higher engine temp), but not the wildly fluctuating temp gauge that I see (which I really believe can only be due to air in the system)?
2) Assuming that the root cause of the problem really is an improperly sealing cooling water O-ring at the bell housing / outdrive interface (because the two mating surfaces are so corroded), is the only solution to get a new bell housing and outdrive? I've been trying to avoid that large expense for this boat (hell, when we bought the remanufactured engine, it was almost equal to what we paid for the boat used in the first place!). Would you consider used (non-saltwater) bell housing and outdrive as a solution? Any thoughts on what that might cost?
Thanks in advance to anyone that reads this entire post.
Here's a link to a video of the temp gauge swinging wildly:https://www.youtube.com/watch?v=APJ6ytYmokw
The boat was originally a saltwater boat (prior owner) - only in fresh water the last 5 years (when we bought it used).
Symptom: Temp gauge after warm-up is rock-solid at just under 170 degrees until the boat starts to plane. After about 20 seconds on plane, the temp gauge fluctuates wildly. It will swing from 100 degrees to 200 degrees in about 3 seconds. Sometimes the alarm starts to buzz, which I believe is an overheat alarm. It seems physically impossible for cooling water temperature to fluctuate that quickly, leading me to believe that there is air in the cooling system when that occurs. Coming off plane, it takes about 30 seconds and the temp reverts to 170 degrees and stays there until you go back on plane. I can drive around all day with no problem, as long as I don't get the boat up on a plane.
When we first bought the boat used, our lake mechanic pulled the drive off and said that the mating surfaces between the drive and the bell housing, specifically around the cooling water passageway between those two surfaces, are VERY corroded. So much so that the circular channel for the sealing O-ring had basically corroded away. I have had two different mechanics use their best efforts to mickey-mouse something to seal up that water flow interface between bell housing and outdrive - they have used various epoxies and a dremel tool to recreate the circular channel to hold the sealing O-ring. This has worked temporarily, but the problem always comes back.
As far as I can tell, this water passageway seal is under lake water when the boat is still (so even if there is a leak at the interface, there is still lake water outside and inside the water passage - so no air can get in the cooling system), and remains under water at low speed until the boat gets up on a plane. At that point, the drive comes up out of the water somewhat and I think that any leakage where that O-ring is (which is now above the lake water level) could result in air getting into the cooling water flow, which I believe is what causing the temp gauge to swing wildly.
My questions are:
1) I can buy the explanation that air is getting into the cooling water system when this failing seal is no longer under water - but that seems to be most likely if the raw water pump is PULLING water up the leg of the outdrive from the lake (I think this may be the basic design in some older Volvo outdrives), so an air leak would allow air to get sucked in. But in the case of a Mercruiser Alpha One Gen Two drive, the water pump is always under water (since it's at the very bottom of the leg) and it PUSHES water up. If there is a leak in the water passage on its way from the pump to the engine (even if that leak is above the lake water level when the boat is on plane), then wouldn't water just leak OUT at the failure point, rather than air getting sucked INTO the water passageway (after all, it's on the pressure side of the water pump, not on the suction side)? I could see this result in lower water flow in the cooling system (and higher engine temp), but not the wildly fluctuating temp gauge that I see (which I really believe can only be due to air in the system)?
2) Assuming that the root cause of the problem really is an improperly sealing cooling water O-ring at the bell housing / outdrive interface (because the two mating surfaces are so corroded), is the only solution to get a new bell housing and outdrive? I've been trying to avoid that large expense for this boat (hell, when we bought the remanufactured engine, it was almost equal to what we paid for the boat used in the first place!). Would you consider used (non-saltwater) bell housing and outdrive as a solution? Any thoughts on what that might cost?
Thanks in advance to anyone that reads this entire post.
Here's a link to a video of the temp gauge swinging wildly:https://www.youtube.com/watch?v=APJ6ytYmokw
