'78 Blackmax 150 Water Flow?

[bjperry]

So I've been reading up on water path and poppet valves and have a couple of questions. The way my motor is set up, and correctly according to the Merc manual, is to run my port t-stat to the starboard t-stat which then runs down and directly connects to the poppet. The telltale is supplied by a link coming out of the block on the port side and is not plumbed into the t-stat discharges at all.

So here's my question. If the poppet doesn't open until higher pressure, how does the water that's exiting the t-stats, and cooling the motor for that matter, actually circulate? According to the flow diagram the telltale is supplied by water that's actually circulating, ie water that has actually passed through the poppet. Thus, when no water is passing through, no water out of tell tale.

I'm alarmed because when I run my motor on muffs the heads get hot pretty quickly and the only water I'm seeing exiting around the prop is cold. No water comes out of exhaust relief ports and none is coming out of my tell tale. If I pull the hose running from the starboard t-stat to the poppet and just allow it to flow I get a lot of hot water and my heads stay cooler. This tells me there's a problem with the poppet but I've rebuilt all components in there and haven't seen any improvement.

Reading the forums it looks like a lot of people advocate plumbing the t-stat discharge into the tell tale and a lot of people also advocate supplying the poppet from the plug on the top of the block (behind flywheel). If I did that, where would I run the water that's exiting my t-stats?

I think it's currently plumbed as it's supposed to be but I don't see how it can function in this configuration. Please help my out as it's got me scratching my head.

 

[j_martin]

Re: '78 Blackmax 150 Water Flow?

So I've been reading up on water path and poppet valves and have a couple of questions. The way my motor is set up, and correctly according to the Merc manual, is to run my port t-stat to the starboard t-stat which then runs down and directly connects to the poppet. The telltale is supplied by a link coming out of the block on the port side and is not plumbed into the t-stat discharges at all.

So here's my question. If the poppet doesn't open until higher pressure, how does the water that's exiting the t-stats, and cooling the motor for that matter, actually circulate? According to the flow diagram the telltale is supplied by water that's actually circulating, ie water that has actually passed through the poppet. Thus, when no water is passing through, no water out of tell tale.

I'm alarmed because when I run my motor on muffs the heads get hot pretty quickly and the only water I'm seeing exiting around the prop is cold. No water comes out of exhaust relief ports and none is coming out of my tell tale. If I pull the hose running from the starboard t-stat to the poppet and just allow it to flow I get a lot of hot water and my heads stay cooler. This tells me there's a problem with the poppet but I've rebuilt all components in there and haven't seen any improvement.

Reading the forums it looks like a lot of people advocate plumbing the t-stat discharge into the tell tale and a lot of people also advocate supplying the poppet from the plug on the top of the block (behind flywheel). If I did that, where would I run the water that's exiting my t-stats?

I think it's currently plumbed as it's supposed to be but I don't see how it can function in this configuration. Please help my out as it's got me scratching my head.

That set of symptoms seems to indicate poor water supply. There is one way for water to get into the motor, from the pump. From there, some exits always-open ports in the exhaust plate, some goes through the poppit when the pressure gets high enough, some goes through the t-stats when the temp gets high enough. It all should be engine temp. It sounds like the water coming out the prop is exiting immediately, and the block is not filling up enough to properly cool the top.

That said, there are several ways that the hoses hook up, but I've never seen the one you describe. I think the t-stats, and the poppit should be connected together, and a T in the vertical hose supplying the tell-tale.

Here's a typical diagram.

Note that the hose from the t-stats, on most engines, goes to a fitting near the bottom that goes to exiit passages. If it goes to a fitting on the poppit, it's just an exit path that supplies a little pressure signal to the poppit from the t-stats. Don't know if it augments opening or closing, but it's a different poppit top casting when it's used.

Would help to get the maintenance manual for your particular engine and look up the hose routing. I suspect yours got boogered up by someone who doesn't know what he doesn't know.

hope it helps
John

 

[bjperry]

Re: '78 Blackmax 150 Water Flow?

John,

Thanks for the reply, but your diagram does not match what I've got in my Merc Shop Manual. There is no outlet my stats can connect to other than the poppet. That's why I'm confused. Even after my t-stats open at 143 degrees, if the only way the water can go is through the poppet which doesn't open until a higher pressure, then the water isn't going to go anywhere and the engine won't be properly cooled. I'm convinced that it's currently routed properly, I just don't understand how it can work. What you said about a certain amount of water by-passing the t-stats and circulating through the block makes sense. Why mine isn't I don't know. I suspect that I may have installed the wrong gasket when I put the new power head on and perhaps that gasket is blocking some of the ports that the water would otherwise by moving through. To be safe I'm ordering a new gasket and will replace that before proceeding further. That will also give me a chance to take a look at where the water should be going and perhaps I'll understand it a little better. I just thought someone on here might know exactly what I'm talking about and can break it down for me.

Benjamen

 

[j_martin]

Re: '78 Blackmax 150 Water Flow?

wrong base gasket is a common error. I've heard of the wrong gasket coming in the right bag from mercury.

The water from the thermostats actually doesn't go through the poppet valve. It bypasses it and goes to the base. The pressure of it modifies the operation of the poppet a bit.

If you take off the poppit and look in the hole you thus made, the round hole in the back is where water comes from the engine. The triangular hole in the bottom is where the water exits to the base/mid.

The diagram is a sample to show the muriad paths water takes through this engine, just a reference. Use the one for your engine.

hope it helps
John

 

[j_martin]

Re: '78 Blackmax 150 Water Flow?

Just a thought. A water pressure gauge would really help to sort it out.

John

 

[SANDYFLATS]

Re: '78 Blackmax 150 Water Flow?

I have the exact same motor 1978 Blackmax 150. I had the same problem with the water flow and was concerned about the t-stats connecting into the poppet valve. As you said, this is the correct plumbing on these motors. I believe that when water is flowing from the t-stats to the poppet valve at idle; the water flow from the t-stats eventually builds up enough pressure to push up on the bottom side of the black rubber diaphram which allows the poppet valve to open and water pressure to be released through poppet from t-stats. When the motors rpms increase, the water flow in the motor pushes the grommet open on the poppet valve which helps increase the water flow from the stats. The poppet valve is a pressure release valve. I know on my motor when running on muffs/garden hose, it normally takes about 1 minute before the motor builds up enough water pressure for water to start flowing out of upper exhaust and then about 30 seconds later, it will start to dribble out of tale end. When the rpms are increased just above idle, the water stream increased at the tale end. When rpms a decreased the water flow from tale in decreases. I believe this is how these old motors are supposed to work. When I run the motor on the lake, the water pressure builds up quicker and flows out the tale end sooner. One last thing I did was change out the water.

 

[Chris1956]

Re: '78 Blackmax 150 Water Flow?

I am not sure if this will help, but the water path on my '93 135HPV6 matches the diaghram presented. The output of the thermostats goes to the telltale and via a tee and to the exhaust extension. The output of the poppit valve goes to the top center of the motor and is dumped into the exhaust passage. The poppit pressurizes and recurculates the cooling water until the thermostats open and dump it. Esxcess water (or pressure) is released by the poppit into the echaust passage.

What I see in operation is that the telltale is non existant at idle, and has good flow at cruise. On the hose, the motor sucks in all the water it can.

I wonder if you could replumb your motor to match the later design?