Not Peeing at Idle Merc 40 1983

[JMMFIRE]

Alright so this is throwing me off a bit. I went out the other day and my Merc stopped peeing at idle. I brought it in immediately, pulled the lower off, back flushed it and attached the hose to the brass water pipe. Started her up and water flowed through fine.

I figured with those results it must have been my water pump. I replaced gaskets, face plate, and impeller. Did a quick test with the drill and bucket and it pumped fine.

I reattached the lower and put put it on muffs. Still nothin at idle. Only once I opened the throttle a little will it pump fine. It seems to be running hotter than normal.

I get either exhaust or steam (not sure which one it is) coming from the tell tale. The motor is stock with a thermostat bypass. I’m not quite sure where to go from here. I’m trying my hardest not to remove the powerhead as I just did so a month ago.

 

[tommarvin]

JMMFIRE you did all the right things, more than most people would.and you didnt burn your motor up,good for you.
Please do not remove the power head.
I think you sucked something in the intake /intake copper tube. Drop the lower unit, remove the motor,cover ,remove the stat 10mmbolts, pour water in the t stat hole through a funnel does it drain out the copper intake water tube? if not you need to clear the copper tube with something like wire till water drains out when you pour water in the t stat hole,thats it your done.
I lied were not done yet, put the stat in a pan of hot water does it open around 140 F and close?.

 

[JMMFIRE]

Nothing is jammed in the copper tube. Like stated before, I back flushed and it flowed freely. Also like stated before, I do not have a thermostat on this motor.

 

[racerone]

Model 40 in this case is a single cylinder 4 HP or a big twin cylinder 40 HP ?----Serial # is ?

 

[JMMFIRE]

Model 40 in this case is a single cylinder 4 HP or a big twin cylinder 40 HP ?----Serial # is ?

It’s a twin 40hp. Serial is 6279856.

 

[racerone]

The parts book does show a thermostat for this motor ?----Did you take it out ?----Launch the boat and see how it behaves.

 

[JMMFIRE]

The parts book does show a thermostat for this motor ?----Did you take it out ?----Launch the boat and see how it behaves.

There is also the option for one stock with a bypass. That is what I have. With it there is no poppet valve or thermostat.

 

[JMMFIRE]

The issue began as I was on the water. I’m uncomfortable launching it because it seems to be getting hotter than normal.

 

[schematic]

If you are sure the pump is fine....pull the powerhead. Likely a blown base gasket

 

[tommarvin]

Buy a IR temp gun at HF or better, put on the muffs where water goes in both sides of the intake.Turn on water,point the gun at the top of exhaust, how hot is it really getting
If it gets over 180F turn off the motor and report back with your findings.

 

[JMMFIRE]

Buy a IR temp gun at HF or better, put on the muffs where water goes in both sides of the intake.Turn on water,point the gun at the top of exhaust, how hot is it really getting
If it gets over 180F turn off the motor and report back with your findings.

It is indeed overheating.