Overheating 2001 Mercruiser 5.0

[WhataBunch]

I have a 2001 Mercruiser 5.0 EFI with a alpha 1 gen 2 that I purchased last year. It is fresh water cooled and has always been in fresh water. It was serviced when we bought it and had a new impeller installed. The boat ran great last year and was winterized before storage for winter. I serviced the fluids before I took it out the first time this year and it ran great. But on the second trip, right after leaving the dock, it was running right around 150-160 degrees which is normal. A few minutes later it began to run hot , around 200+. I got it home and replaced the thermostat and started it up with the muffs in my driveway. I have water coming out of the transom and it appears the impeller is working but I'm still overheating. I am not familiar with the cooling system components and looking for suggestions.

Thanks!

 

[alldodge]

If you picked up plastic bag which covered the intake ports on the drive it can burn the impeller. Not saying this happened, but folks loose them in the water all the time.

What is your engine serial number and do you have a 1, 3 or 7 point drain system?

 

[WhataBunch]

If you picked up plastic bag which covered the intake ports on the drive it can burn the impeller. Not saying this happened, but folks loose them in the water all the time.

What is your engine serial number and do you have a 1, 3 or 7 point drain system?

Engine Serial is 0M042851. It has 5 drain points if I remember correctly.

 

[alldodge]

You can have two clog points, the power steering cooler and cool fuel. The PS cooler is the one which would clog up first with pieces of the impeller or other items. Take the hose off the power steering cooler on the back of the motor. Look inside the cooler and see if any pieces are in there.

 

[WhataBunch]

You can have two clog points, the power steering cooler and cool fuel. The PS cooler is the one which would clog up first with pieces of the impeller or other items. Take the hose off the power steering cooler on the back of the motor. Look inside the cooler and see if any pieces are in there.

[/QUOT

Because it's a tight fit, I was having trouble getting the intake side hose off, so I pulled the exit side hose on the PS cooler and started it up for a couple of seconds. There was immediately a good flow of water from the PS cooler and didn't appear to have blockages.

 

[alldodge]

Did the water come out before you started with water turned on the muffs?

If not suggest working your way through the hoses checking flow

 

[WhataBunch]

Did the water come out before you started with water turned on the muffs?

If not suggest working your way through the hoses checking flow

It didn't come out before I started it. When I pulled the exit hose form the PS cooler, it had some vacuum because I could heard it releasing when I broke the seal. What are your thoughts on the circulating water pump on the block? I was thinking about that, but the fact there was a vacuum on the hose makes me think it was trying to pull water.

 

[alldodge]

Water should not be coming out the hose with the motor not running. It might very slowly come out if the impeller vane is in the right spot, but most often there should be no water. I'm thinking your impeller is burned up.

Don't see any issue so far with the circulating water pump. I'm also thinking it was pressure and not vacuum.

 

[WhataBunch]

Water should not be coming out the hose with the motor not running. It might very slowly come out if the impeller vane is in the right spot, but most often there should be no water. I'm thinking your impeller is burned up.

Don't see any issue so far with the circulating water pump. I'm also thinking it was pressure and not vacuum.

If the impeller is bad, would it still be pulling water from the muffs and have some water out of the transom?

 

[alldodge]

Muffs will push water thru the motor, the impeller will pull the water thru. If some of the impeller vanes are damaged, the hose pressure will still push it thru and out. Just depends on how much is coming out

 

[WhataBunch]

Muffs will push water thru the motor, the impeller will pull the water thru. If some of the impeller vanes are damaged, the hose pressure will still push it thru and out. Just depends on how much is coming out

Thanks for your advice. It appears that I'll soon get to know more about my lower unit. I'll let you know what I find.

 

[WhataBunch]

I pulled the lower and the impeller doesn't seem too bad. It's pretty obvious that the last time the impeller was changed, the old gaskets were reused and were dried out and crumbled. I'll update after testing.

 

[WhataBunch]

No Title

 

[alldodge]

Should do much better once replaced. Look at the housing real close for scratches and such, along with the lower wear plate

 

[WhataBunch]

I cleaner everything and installed the new impeller today. I put the muffs on and after about 5 minutes of running it started getting hot again just as it did before. New impeller and thermostat, but still overheating. Any thoughts?

 

[Bt Doctur]

pull the drive and insert a washing machine hose cut i half into the water inlet opening , and retest and report back

 

[WhataBunch]

pull the drive and insert a washing machine hose cut i half into the water inlet opening , and retest and report back

Just to make sure, are you saying use the hose to flush inlet?

 

[Bt Doctur]

Ignore the red arrow, The hole with the O ring

 

[thumpar]

Have you tested the thermostat to make sure it is opening? You can make sure there is no junk in there when you have it off too.

 

[WhataBunch]

Have you tested the thermostat to make sure it is opening? You can make sure there is no junk in there when you have it off too.

I tested the thermostat and it opened but I installed a new one anyway.