Hello all. Wondering if I could get some ideas here. I recently (last Friday) picked up a 85 wellcraft 248 that has a single Merc 5.7 I/O. Got it for cheap, engine needed a bit of work. I was told by the previous owner that the engine overheated two seasons ago, he shut it down, had the impeller replaced and blocked it up from then on, never saw water again.
Before i purchased it I was able to get the engine running but it overheated. I planned to do some major work to get it in shape again.
I think it's around an 1988 5.7. Serial starts with 0b9
Here's what I found. Compression was good on all but #1, it was at 225. No water in oil. # 1 exhaust port had a crack, allowing water in, as a result I pulled and replaced both heads. Piston tops and cylinder walls in good shape.
Before replacing the heads I removed a bunch of scale from the block by way of screw driver, air compressor, water, and time. Pretty clear in there now.
List of new items.
Heads
Risers and manifolds (GLM)
Thermostat housing (GLM) and check balls
Thermostat
Circulating pump (MES)
Ignition, cap, rotor, wires, plugs but not relevant here
After putting the engine back together I got it running to find the same overheat scenario on muffs.
When the thermostat is out the engine runs cool, 120 ish. With it in the guage shows between 160 and 240, probably around 220.
this is a 140 degree thermostat and I've tried a few different ones, including different styles. Wide base and narrower spring base types.
The engine itself doesn't seem too hot. Risers are cold, manifolds cool. Hoses to risers cold. Hoses to manifolds warm, Large circulating pump hose, very warm, Thermostat housing very warm/hot.
I pulled the lower unit off and checked the water pump, seems like it was new, as the previous owner stated.
The Temp Sending unit seems to show everything from cold to hot but I don't know if it's accurate, and not sure how often these fail, or what the symptoms are of failure.
I disconnected the water hose at the transom (inside) ran engine and saw water coming out but not a hard pressure stream, more like a basic flow. Not sure what it should be.
Couldn't get the inlet side of the hose off the power steering cooler yet. I did back flush it from the circulating pump hose to the transom hose when I had it off. Seemed ok.
I've never had a 5.7 Merc before so I don't know what to expect here.
Can I expect it to run cool off of muffs?
Could having the thermostat in place coupled with limited water pressure/volume of a garden hose offer enough restriction to have the engine over heat?
Left over possibilities as I see it.
Garden hose/muffs, not ample
Water pump wasn't working properly (haven't put the new one in yet)
Bad Temp sending unit
Bad Guage
Restriction in oil cooler, though it back flowed pretty well.
Block restricted, Although I cleared it out pretty good.
I can't get it in the water yet to test. Rather have it running well in the driveway frst anyway.
Any thoughts greatly appreciated!
Before i purchased it I was able to get the engine running but it overheated. I planned to do some major work to get it in shape again.
I think it's around an 1988 5.7. Serial starts with 0b9
Here's what I found. Compression was good on all but #1, it was at 225. No water in oil. # 1 exhaust port had a crack, allowing water in, as a result I pulled and replaced both heads. Piston tops and cylinder walls in good shape.
Before replacing the heads I removed a bunch of scale from the block by way of screw driver, air compressor, water, and time. Pretty clear in there now.
List of new items.
Heads
Risers and manifolds (GLM)
Thermostat housing (GLM) and check balls
Thermostat
Circulating pump (MES)
Ignition, cap, rotor, wires, plugs but not relevant here
After putting the engine back together I got it running to find the same overheat scenario on muffs.
When the thermostat is out the engine runs cool, 120 ish. With it in the guage shows between 160 and 240, probably around 220.
this is a 140 degree thermostat and I've tried a few different ones, including different styles. Wide base and narrower spring base types.
The engine itself doesn't seem too hot. Risers are cold, manifolds cool. Hoses to risers cold. Hoses to manifolds warm, Large circulating pump hose, very warm, Thermostat housing very warm/hot.
I pulled the lower unit off and checked the water pump, seems like it was new, as the previous owner stated.
The Temp Sending unit seems to show everything from cold to hot but I don't know if it's accurate, and not sure how often these fail, or what the symptoms are of failure.
I disconnected the water hose at the transom (inside) ran engine and saw water coming out but not a hard pressure stream, more like a basic flow. Not sure what it should be.
Couldn't get the inlet side of the hose off the power steering cooler yet. I did back flush it from the circulating pump hose to the transom hose when I had it off. Seemed ok.
I've never had a 5.7 Merc before so I don't know what to expect here.
Can I expect it to run cool off of muffs?
Could having the thermostat in place coupled with limited water pressure/volume of a garden hose offer enough restriction to have the engine over heat?
Left over possibilities as I see it.
Garden hose/muffs, not ample
Water pump wasn't working properly (haven't put the new one in yet)
Bad Temp sending unit
Bad Guage
Restriction in oil cooler, though it back flowed pretty well.
Block restricted, Although I cleared it out pretty good.
I can't get it in the water yet to test. Rather have it running well in the driveway frst anyway.
Any thoughts greatly appreciated!
That's a new one on me, what manual is that?