Merc 850 pee hole

[jusfloatin]

Good day to all

I purchased this boat several years ago as a project.

When I pulled the motor off the boat to be painted, I had to unhook a oil pressure line ( 1/8 black plastic line ) which was connected in the same spot the pee tube would normaly be hooked to. ( the dash does have a oil pressure gauge )
The pee tube was not hooked up.
Anyways after doing the restore I hooked it all up the way it was and started it with muffs on. I did not know the history of the motor and I never did hear it run prior to this so I will admit I had concerns if the water pump was working as the gauge did not move and I was worried I would pooch the motor so I decided to shut it off.
After some help from this forum I was convinced to clean the pee hole change the fitting to accomodate the pee tube and try it again. Which I did and she peed like it had been holding it for a while.
I ran it the whole summer that way and no problems.

My questions is though, if I was to change it back to the way I got it, no pee tube but hooked to the oil pressure gauge.

1-What should the pressure be?
2-Would running it like that make the motor run warmer?
3-Can a tempature gauge be add and where would I connect it at?
4-What is a good running tempature?

This is a 74/75/76??? Merc 850 Thunderbolt

 

[Chris1956]

Re: Merc 850 pee hole

The telltale hose runs from the cylinder head to the bottom cowling. It is 3/8" ID neopreme. You cannot see it unless you remove the wrap cowl.

That motor has no thermostat, so water temp will vary a lot. A pressure gauge teed into the telltale line will show some water pressure, which is the best indicator of motor cooling you can get with that motor.

 

[jusfloatin]

Re: Merc 850 pee hole

Thanks Chris1956

I had and have it at the present time the way Merc indended to be and no problems what so ever.

The reason for my question as to what if and how can I is this boat will be used in a couple of mountain lakes in Alberta which are feed by Glaciers.
The water tempature even durring the hotest of times is barely above freezeing.

Like you said these motors have no thermostat which is is basical the question behind my original question.

 

[Moody Blue]

Re: Merc 850 pee hole

Good day to all

I purchased this boat several years ago as a project.

When I pulled the motor off the boat to be painted, I had to unhook a oil pressure line ( 1/8 black plastic line ) which was connected in the same spot the pee tube would normaly be hooked to. ( the dash does have a oil pressure gauge )
The pee tube was not hooked up.
Anyways after doing the restore I hooked it all up the way it was and started it with muffs on. I did not know the history of the motor and I never did hear it run prior to this so I will admit I had concerns if the water pump was working as the gauge did not move and I was worried I would pooch the motor so I decided to shut it off.
After some help from this forum I was convinced to clean the pee hole change the fitting to accomodate the pee tube and try it again. Which I did and she peed like it had been holding it for a while.
I ran it the whole summer that way and no problems.

My questions is though, if I was to change it back to the way I got it, no pee tube but hooked to the oil pressure gauge.

1-What should the pressure be?
2-Would running it like that make the motor run warmer?
3-Can a tempature gauge be add and where would I connect it at?
4-What is a good running tempature?

This is a 74/75/76??? Merc 850 Thunderbolt

If you've had the motor for "several years" and you don't know the history before that, then a waterpump impeller change is long overdue. Simple maintenance and cheap insurance.

The oil pressure line is actually a water pressure line. The gauge on the dash sounds like a unique approach to show water pressure. Points for creativity

To answer your questions,

1) Pressure at idle will be in the 2-3 PSI range and about 10-12 PSI at WOT with a brand new pump impeller. Not sure if you will see those readings at the telltale output or not. I connected direct to the port on the water jacket cover between plugs 2 and 3. I tried using the telltale line with very poor results.

2) No. The telltale output is only an indicator that water is flowing through the motor. The telltale output is plumbed in the discharge side of the cooling system so plugging it will not affect operating temp.

3) I have both temp and pressure gauge connected to the same port at a "T" fitting. I have a 60-100F gauge and it barely moves off the peg unless I'm running the motor hard. Cold blooded motors.

4) See 3) above.