The history: I own a boat with a raw water cooled Volvo 4.3GL PLKD with an SX outdrive that I bought new in 1997. The boat is used 100% in fresh water and used only 2-3 times a year for maybe an hour or two per use. I live in Southern California, so when it's not being used, the boat is garaged and is never exposed to extreme temperatures. For the first couple of years when everything was new and exciting, I had the boat professionally serviced when I knew it wouldn't be used through the winter. I then felt I could save money by doing the oil changes and winterizing myself. So for many years I would follow the directions in the owners manual for end of season storage. As time went on I began questioning why I even needed to winterize a boat that will never be exposed to freezing temperatures or even change the fluids every year if it is only being run maybe 4-6 hours a year. I know I will hear some harsh words from the experts, but for the last several years, the boat has gotten an oil change every third year or so. Now before you start the bashing, I did check the fluids before each use and they would always be full, very clean and viscous. I would say that it always looked as fresh as brand new oil.
The problem: Late last year I noticed the temperature gauge at about 2/3 (about 200) when running on plane. When I brought it back to idle, the temperature would come back down to under 175. The two times I was out this year it did the same thing. It had been about 5 years since the raw water impeller was replaced, so I just replaced it along with a complete service: new oil & filter, outdrive oil & lube, fuel filter, plugs, cap, rotor and for good measure; a new circulating pump. When I removed the old impeller, it was in pretty good shape considering, with all but a very small amount of material attached. I just had the chance to get the boat on the water again and it ran silky smooth....right up to 2/3 on the temp gauge again when on plane.
The hypothesis: I'm pretty sure the small amount of material that wasn't attached to the removed impeller is still in the cooling system and causing a restriction
The forum search results with a lot of unanswered questions: 1) I know I need to remove the thermostat housing and clean the passages. I've ordered a new thermostat, o-ring and gasket (I needed the new gasket to check the housing so I thought I might as well replace the 12 year old thermostat while I'm in there even if it's good) What is the most efficient way to flush the engine block and manifolds when the housing is removed? Where do I backflush from? What hoses should be undone and left on? How much or little water pressure should be used? Should I use compressed air at all? 2) I've read that the power steering cooler is where things collect as well, but according to the cooling diagram for my engine (thanks for the engine manual pdf files), the cooler comes before the raw water pump. Would I expect to find anything in there? 3) When backflushing from the raw waterpump to the intakes, should I remove the power steering cooler and backflush from there instead, or as well? Should I remove the water passage plate in the outdrive when backflushing or will any debris exit the intakes easily? (I don't have a new gasket for this seal) 4) I've read that running hot on plane and not at idle could be the result of air intrusion in the water intake, so I know I would need to do the clear hose check to determine if that's the cause (thanks for the overheat diagnosis pdf file). Is it possible that a keel guard installed a couple of years ago might be causing uneven waterflow at the intakes? I wouldn't think so, but I think it might coincide with the timing of the temperature problem. 5) Knowing that the cooling system hasn't been completely drained in about 5 years, is it possible that keeping fresh water in the system without circulation for months at a time is causing "clogging of the arteries"? Wouldn't the passages be less likely to rust or corrode if there was no air in the system?
The appreciation: Thank you for reading this long post and thank you in advance for your expert answers.
The problem: Late last year I noticed the temperature gauge at about 2/3 (about 200) when running on plane. When I brought it back to idle, the temperature would come back down to under 175. The two times I was out this year it did the same thing. It had been about 5 years since the raw water impeller was replaced, so I just replaced it along with a complete service: new oil & filter, outdrive oil & lube, fuel filter, plugs, cap, rotor and for good measure; a new circulating pump. When I removed the old impeller, it was in pretty good shape considering, with all but a very small amount of material attached. I just had the chance to get the boat on the water again and it ran silky smooth....right up to 2/3 on the temp gauge again when on plane.
The hypothesis: I'm pretty sure the small amount of material that wasn't attached to the removed impeller is still in the cooling system and causing a restriction
The forum search results with a lot of unanswered questions: 1) I know I need to remove the thermostat housing and clean the passages. I've ordered a new thermostat, o-ring and gasket (I needed the new gasket to check the housing so I thought I might as well replace the 12 year old thermostat while I'm in there even if it's good) What is the most efficient way to flush the engine block and manifolds when the housing is removed? Where do I backflush from? What hoses should be undone and left on? How much or little water pressure should be used? Should I use compressed air at all? 2) I've read that the power steering cooler is where things collect as well, but according to the cooling diagram for my engine (thanks for the engine manual pdf files), the cooler comes before the raw water pump. Would I expect to find anything in there? 3) When backflushing from the raw waterpump to the intakes, should I remove the power steering cooler and backflush from there instead, or as well? Should I remove the water passage plate in the outdrive when backflushing or will any debris exit the intakes easily? (I don't have a new gasket for this seal) 4) I've read that running hot on plane and not at idle could be the result of air intrusion in the water intake, so I know I would need to do the clear hose check to determine if that's the cause (thanks for the overheat diagnosis pdf file). Is it possible that a keel guard installed a couple of years ago might be causing uneven waterflow at the intakes? I wouldn't think so, but I think it might coincide with the timing of the temperature problem. 5) Knowing that the cooling system hasn't been completely drained in about 5 years, is it possible that keeping fresh water in the system without circulation for months at a time is causing "clogging of the arteries"? Wouldn't the passages be less likely to rust or corrode if there was no air in the system?
The appreciation: Thank you for reading this long post and thank you in advance for your expert answers.
