Update and still rying to solve a problem on my boat now going on for over 1 year so I thought I would put this out there and see if any of you have an idea.
Boat is a 2015 350 CBR. Engines are 8.2L ECT Mercruisers with Closed Cooling. I have 203 hours on the engines, and I boat in salt water. All maintenance is done by Formula service dealer who is a Mercruiser dealer.
Background: June 2018---After a day of boating, open bilge to do my religious post boating fresh water flush and see puddle of orange coolant in the bilge on starboard side. Call dealer---he says it’s the thermostat so we replace thermostat on Starboard engine. Their diagnosis was “Coolant Discharge from excessive heat build up causing expansion tank to overflow. R/R Thermostat and Coolant Sensor Cap.”
Summer of 2019 I start noticing that my starboard engine temperature ranges while boating between 147 degrees and 178 degrees, while port engine is steady at 163 degrees. I take videos and send to my dealer. On starboard, you can see the temp climb, and then somehow/somewhere a valve (or thermostat?) opens and the water temp drops back to 147ish and then starts the process all over again. It is a steady climb, fall, and reclimb all while underway—and the port side is perfect at 162 degrees
With dealer, we plan for late fall / early winter service which was impellers, fuel filters, and oil & filters. Dealer says, “The problem on the starboard engine is Poppet Valves.” In January 2020, we change the poppet valves and also new exhaust elbows. Checked the heat exchanger and the heater exchangers are clean as a whistle since I flush with SaltAway after every use. Water pressure is fine.
In February, we test it and determine that the problem still exists.
Covid hits---and not much happens.
During Spring boating with just my wife and me, I am still noticing the temperature fluctuation on starboard engine while port holds extremely constant. (This is annoying.)
I had a haul out this week (July 2020) for bottom paint and for drive service. Given the number of hours I boat, we do outdrive service every other year. And it was 3 years on the bottom point since last update. Since boat is 6 years old, I ask my dealer to check about Bravoitis and inquire to Mercury. So, we planned to take off drives anyway for spline greasing, and we checked gimbal bearings. Since the gimbal bearings were good, dealer says we should take off the water inlet houses from Bravo 3X drives and inspect and install new hoses (there is a Merc upgrade he tells me).
I am at the boat in the boat yard for the last 2 days while on the hard. I am watching the entire process of disconnecting the drives and I see the water hoses come out of both outdrives through the transom. Both look fine with no corrosion, no clogging. Updated water hose kits are installed in both drives
Dealer calls Mercury. Mercury says to check the 22-8M0045363 hose bib assembly
https://www.mercruiserparts.com/bam/subassembly/31939/16012/115 which I find out is underneath the engine (and a PITA to get to) which is prior to the Cool Fuel Module. They suspect that there might be some blockage/obstruction in there. My dealer says we can tackle that repair when back in the water (which I don’t know since I always think it is easier to do some of this on the hard when water doesn’t come through the lines into the engine. ) I don’t have through hulls on my boat for raw water cooling as the raw cooling water does come through the outdrives. There are no clogs nor obstructions observed in the outdrives.
Dealer surmises it might be the Cool Fuel Module. He says when we run the boat we can touch the back of the cool fuel module and see if hot which he says will tell him if the cool fuel module is failed (but I have never gotten any codes on any issues from the starboard engine on fuel temperature.) IF, and if it is a Cool Fuel Module, those run about $1300 for the module alone.
So sure, it would be easy to throw parts at it---which I don’t want to do---I want to know why I have this fluctuation. It will be easy to run up the engines in throttle mode at the boatyard when back in the water when they complete bottom paint and outdrive paint on Tuesday and at that time check the Cool Fuel modules to “see if they are hot.”
One friend suggested maybe I have wear in the back of my OEM raw water pump and we should change to the newer style that has the wear plate so the impeller doesn’t wear the housing. (One friend swears by the Stainless Hardin Aftermarket Stainless Steel water pumps.) None of the dealer service techs ever mention wear of the housing so I don’t know if the temperature fluctuation is due to cavitation at the back of the housing.
I don’t know if I have a bad thermostat again.
Looking for any insights that others may have since we have changed a thermostat, poppet valves, and water intake hoses through the transom, and we now are on a hunt and see expedition.