Boat Over Heating

[crzy2bealive]

My boat overheated on Friday while heading back from the channel and per the temp gauge I was climbing over 200 and smoking.

I got parts and replaced the thermostat, impeller, temperature sending unit.

The old impeller had all the pieces still attached.

I inspected the thermostat housing and no blockages.

I did find the source of the smoking issue and my brand new alternator was getting up to 400 degrees and started smoking. So I’ll swap that out.

Manifold, risers, temp housing reading 135 on the gun.

Exhaust water coming out around 120.

Maybe bad temperature gauge. I could throw another one on to rule that out.

No milky oil or water under the oil cap so head gaskets should be ok.

Any suggestions?

350 Mercruiser
Alpha One Drive

 

[HOOTER SLED-]

Maybe a booger in one of your hoses?

 

[monkeyswrench]

On my Alpha I had the same scenario...without the smoking alternator...and it was the sending unit. Also had one melt and stick a plastic washback flapper from somewhere in the Y-pipe. It was creating lots of backpressure.

 

[Fun Times]

What year?
Did the warning horn sound off? The horn should sound at about 196 degrees.

 

[crzy2bealive]

What year?
Did the warning horn sound off? The horn should sound at about 196 degrees.

1991 no horn

 

[River Runnin]

Plugged intake?

 

[Shlbyntro]

Sounds to me like your gauge was lying. Id replace the alternator and recheck everything before tearing it apart. if the alternator was throwing out odd voltages as it was burning up, it could have been skewing your gauge readings

 

[Sunny]

I literally just went through this. I had a bad alternator causing the gauge to read incorrectly. I replaced both water pumps, sending unit and thermostat, and was still showing that it was overheating on the gauge. Once I replaced the alternator all issues were solved.

 

[timstoy]

Mechanical gauges.

 

[lbhsbz]

Bad alternators can cause all sorts of weird electrical voodoo. Start there.

Back in the day when I was a Toyota dealer tech, the mid '80s cars would occasionally be towed in because all of a sudden EVERY light on the dash lit up and the gauges all went wonky....bad alternator.

 

[crzy2bealive]

Mechanical gauges.

I’m going to throw one on as a back up!

 

[crzy2bealive]

I literally just went through this. I had a bad alternator causing the gauge to read incorrectly. I replaced both water pumps, sending unit and thermostat, and was still showing that it was overheating on the gauge. Once I replaced the alternator all issues were solved.

That’s good to know! Luckily I have a warranty on the alternator.

 

[MooreMoney]

Did you run the boat after the new impeller? The bad impeller will look good but still be bad.

 

[lbhsbz]

Did you run the boat after the new impeller? The bad impeller will look good but still be bad.

This….at least in outboards. The vanes take a set and lose tension against the housing and just end up spinning in the water without actually pumping anything. If yore a cheap MF, you can flip ‘em over and get a couple more weekends out of an impeller. Lol

 

[MooreMoney]

This….at least in outboards. The vanes take a set and lose tension against the housing and just end up spinning in the water without actually pumping anything. If yore a cheap MF, you can flip ‘em over and get a couple more weekends out of an impeller. Lol

I replace mine yearly. No way I’m turning them over to save $50.

 

[crzy2bealive]

Y

Did you run the boat after the new impeller? The bad impeller will look good but still be bad.

Yup I did that’s when I discovered the alternator issue.