Hi guys,
I'm new to the forums as I haven't owned a boat in years but picked up a nice clean circa 2001 19' bowrider with a 4.3 Mercruiser EFI and A1G2 outdrive a couple of weeks ago. This is a raw water cooled boat and has been used primarily in fresh water but occasionally in salt. From the outward appearance, it's been meticulously maintained - the engine looks like new, has new manifolds and risers, new hoses etc. It does not smoke, starts immediately, everything works.
On our first outing, I noticed that after about 5 minutes running, the temperature was up at around 160f according the gauge. A minute later, I looked again and it was back at 0 where it remained. I assumed a fault with the gauge but headed back to the ramp at idle speed anyway. I contacted the previous owner who said he'd had no such issues but it had been about 6 months since the boat had been on the water fro a decent run.
Once home, I read numerous articles on this forum where similar issues had arisen. I tested the gauge by grounding the signal wire and it "pegged full" and stayed there. I tested the sender, it was reading a resistance around 600 ohms as it should.
I then ran it up to temperature with ears and the hose while on the trailer. When reading the ~160f on the gauge, the thermostat housing was giving 100f (38c) via a laser thermometer, the front ends of the manifolds were reading 133f (56c) and the top of the risers were reading 122f (50c). The gauge then did the same thing, dropped to 0. I allowed it to idle for another minute or so and the recorded temperatures at the various locations remained the same, maybe 1-2 degree fluctuations. I then shut it down and ordered a new (160f) thermostat.
I replaced the thermostat last night - the old one was looking pretty sorry but not the worst I've seen however I doubt it was functioning properly. I replaced the gaskets in the housing as well and made sure to install it the right way round per the manual.
I ran the boat up to temperature today. The gauge went up to the usual 160f and stayed there for a bit. I thought I was free and clear but after a couple of minutes it dropped back down to about 100f - not 0 as it did before. I took some temperature readings at various spots on the engine again, the top of the thermostat housing, manifolds and top of the risers were reading the same as before. I took readings on the front of the heads at both sides and these were both 180f-200f (82-93c) between several readings over a minute or so but were going up and down. I shut everything down at this point.
I realised I had no "normal" reading for comparison. Wondering if anyone's taken readings from similar points on a "known good" 4.3 and whether the gauge moving up to 160 from cold and then dropping back to 100 might be considered normal for a raw water cooled unit. Ie the temperature drop is once the thermostat opens.
It's taken me about 15 years to convince SWMBO to allow me to buy a boat, if I destroy the engine within a month, I'll be in all sorts of trouble...
Cheers!
I'm new to the forums as I haven't owned a boat in years but picked up a nice clean circa 2001 19' bowrider with a 4.3 Mercruiser EFI and A1G2 outdrive a couple of weeks ago. This is a raw water cooled boat and has been used primarily in fresh water but occasionally in salt. From the outward appearance, it's been meticulously maintained - the engine looks like new, has new manifolds and risers, new hoses etc. It does not smoke, starts immediately, everything works.
On our first outing, I noticed that after about 5 minutes running, the temperature was up at around 160f according the gauge. A minute later, I looked again and it was back at 0 where it remained. I assumed a fault with the gauge but headed back to the ramp at idle speed anyway. I contacted the previous owner who said he'd had no such issues but it had been about 6 months since the boat had been on the water fro a decent run.
Once home, I read numerous articles on this forum where similar issues had arisen. I tested the gauge by grounding the signal wire and it "pegged full" and stayed there. I tested the sender, it was reading a resistance around 600 ohms as it should.
I then ran it up to temperature with ears and the hose while on the trailer. When reading the ~160f on the gauge, the thermostat housing was giving 100f (38c) via a laser thermometer, the front ends of the manifolds were reading 133f (56c) and the top of the risers were reading 122f (50c). The gauge then did the same thing, dropped to 0. I allowed it to idle for another minute or so and the recorded temperatures at the various locations remained the same, maybe 1-2 degree fluctuations. I then shut it down and ordered a new (160f) thermostat.
I replaced the thermostat last night - the old one was looking pretty sorry but not the worst I've seen however I doubt it was functioning properly. I replaced the gaskets in the housing as well and made sure to install it the right way round per the manual.
I ran the boat up to temperature today. The gauge went up to the usual 160f and stayed there for a bit. I thought I was free and clear but after a couple of minutes it dropped back down to about 100f - not 0 as it did before. I took some temperature readings at various spots on the engine again, the top of the thermostat housing, manifolds and top of the risers were reading the same as before. I took readings on the front of the heads at both sides and these were both 180f-200f (82-93c) between several readings over a minute or so but were going up and down. I shut everything down at this point.
I realised I had no "normal" reading for comparison. Wondering if anyone's taken readings from similar points on a "known good" 4.3 and whether the gauge moving up to 160 from cold and then dropping back to 100 might be considered normal for a raw water cooled unit. Ie the temperature drop is once the thermostat opens.
It's taken me about 15 years to convince SWMBO to allow me to buy a boat, if I destroy the engine within a month, I'll be in all sorts of trouble...
Cheers!
