Soulshine
Well-Known Member
First some background:
Merc. 454s w/ fully closed cooling systems. Serial numbers indicate ‘81 - ‘87. Boat is an ‘83 that was repowered, but not sure when.
I sprung a leak in the port side thermostat housing gasket last weekend. Took it apart to find very little of the upper gasket intact and a generally crusty situation.
Got parts cleaned and painted and was told at my marina that this serial number called for 140 thermostats, so I bought two kits even though there was a 160 in there.
Up to this point the port side always ran at about 155 and the starboard at 170 or more, so I planned to do both.
After buttoning up the port side and warming it up, I noticed that it ran at about 135. The dash gauge was surprisingly accurate as an IR thermometer found the areas around the thermostat housing and sensors to be just that.
Upon taking the starboard side apart I noticed something that slipped by the previous day. In the pic below you’ll see a notch (in this case full of gunk still) that lines up with a groove in the lower part of the housing that seems designed to allow a small amount of coolant into the manifolds prior to the thermostat opening. Trouble is that the gasket in the kit did not have this notch, but as I said, I hadn’t noticed it since the old gasket was in pieces.
So I cleaned the gunk out of the notch seen in the pic, cut the notch in the gasket and put the starboard side back together and got the identical results as on the port. Same temps and both are running very well, if a bit cooler than before.
So my questions (finally) are:
Should I replace the gasket with one with the notch on the port side and am I correct in my assumption of its purpose as a bypass of sorts?
What are your feelings about running at sub 140 temps?
I did tune ups at the same time and have never seen these engines run so well and so consistent to each other.
One other odd observation was that after the thermostat replacements, both engines ran exactly 200 RPM faster at idle than before.
I didn’t touch the carbs, but did adjust them back down.
Could the lower operating temps cause such a change? How and why?
It’s true what they say about the only thing working on an old boat is it’s owner.
Merc. 454s w/ fully closed cooling systems. Serial numbers indicate ‘81 - ‘87. Boat is an ‘83 that was repowered, but not sure when.
I sprung a leak in the port side thermostat housing gasket last weekend. Took it apart to find very little of the upper gasket intact and a generally crusty situation.
Got parts cleaned and painted and was told at my marina that this serial number called for 140 thermostats, so I bought two kits even though there was a 160 in there.
Up to this point the port side always ran at about 155 and the starboard at 170 or more, so I planned to do both.
After buttoning up the port side and warming it up, I noticed that it ran at about 135. The dash gauge was surprisingly accurate as an IR thermometer found the areas around the thermostat housing and sensors to be just that.
Upon taking the starboard side apart I noticed something that slipped by the previous day. In the pic below you’ll see a notch (in this case full of gunk still) that lines up with a groove in the lower part of the housing that seems designed to allow a small amount of coolant into the manifolds prior to the thermostat opening. Trouble is that the gasket in the kit did not have this notch, but as I said, I hadn’t noticed it since the old gasket was in pieces.
So I cleaned the gunk out of the notch seen in the pic, cut the notch in the gasket and put the starboard side back together and got the identical results as on the port. Same temps and both are running very well, if a bit cooler than before.
So my questions (finally) are:
Should I replace the gasket with one with the notch on the port side and am I correct in my assumption of its purpose as a bypass of sorts?
What are your feelings about running at sub 140 temps?
I did tune ups at the same time and have never seen these engines run so well and so consistent to each other.
One other odd observation was that after the thermostat replacements, both engines ran exactly 200 RPM faster at idle than before.
I didn’t touch the carbs, but did adjust them back down.
Could the lower operating temps cause such a change? How and why?
It’s true what they say about the only thing working on an old boat is it’s owner.
