50hp merc bigfoot 2001 model overheat

[rob johnson]

I just thought I'd redefine the problem I mentioned earlier in hopes that some more information might help. This is a 2001 50hp 4-stroke mercury bigfoot that has been setting off the overheat alarm and I tried to fix by replacing the t-stat, water pump and backflushing, all no improvement, infact, worse. Now the alarm happens more frequently and the tell tale stream still isn't producing like it should. The owner also complains of loss of RPM. Almost 1000 RPM at WOT. When I changed the spark pluggs they were light chocolate brown on one side of the insulator, and crusty black on the other side of the insulator. That is to say, dividing the insulator into 2 semi circles; one half black, the other half normal. Does anyone have any ideas that can help? Maybe the RPM loss and overheat are connected? I appreciat any and all suggestions. Someone in the other string suggested the poppet valve, but I have no idea what that is or where it is. Does anyone have a picture of this? or a location? Thanks for reading!!

Rob

 

[bgbass.1]

Re: 50hp merc bigfoot 2001 model overheat

i dont think you have a poppit valve i dont see it on the pics. try taking thermostat out and see if that improves water flow I know its new but somtimes there no good

 

[gibbyman]

Re: 50hp merc bigfoot 2001 model overheat

Hello, I have a 2000 50 hp bigfoot merc I had a similar problem last year. I was cruising the lake one day when the motor gave a little hiccup and then overheat alarm went off. Didn't do it at idle though. Still peeing fine at idle. It was late in the season so I put it away for the winter
Spring rolls aroung and I pull boat out of storage put in new impellor run in yard fine. Take down to the marina drop it in and go for test drive .Idle out runs fine get ready to do a couple of fast gas laps, alarm goes off. Back her down idle in haul it out back to the garage. Drop lower unit again impellor and pump look fine. Decide to change thermostat. take it back down to marinia and repeat same thing happens.Load back up back to garage. Replace alarm senders .back to the marinia you guessed it same scenario. Back to the garage. Eveybody is baffeled. Guy at local shop/parts store makes a call to Merc. finally gets hold of a guy willing to listen. He nails it on the head. It was a $4.50 rubber grommet gasket where water pickup enters engine.Only way to change is pull power head ,replaced gasket put back together and problem solved. Way to go merc. relying on a $4.50 gasket

 

[longshanks]

Re: 50hp merc bigfoot 2001 model overheat

Hey guys,

for what it's worth, I remember reading on here about this problem, happening to Merc 4 stroke 40/50/60s, about that vintage. As Gibby describes, where the water pickup enters the engine, there is a small passage where water passes through, which apparently becomes constricted, leading to overheating motor. My understanding is that corrosion builds up on a metal plate, constricting the rubber grommet that water passes through. Try doing a search on 'Mercury four stroke overheat', and I believe you will find others who've had this problem. Hope this helps, and good luck to you.

Shane