poppet or not

[KCLOST]

Re: poppet or not

That is a good possiblilty rocks... Another possiblity is a bad impeller... <br /><br />However some water should exit the tell tail even when the thermo's are closed.... You can probably look at the water lines and figure out how this happens....

 

[KCLOST]

Re: poppet or not

Assuming you have a good impeller/pump...

 

[AndyL]

Re: poppet or not

Just another thought. If the outlet tube that leads from the pump to the block is holed or not sealing properly at the junction of the powerhead or even at the pump, water will be being lost and not making it into the head and this could lead to your symptoms. I haven't got a diagram for your engine arrangement but would like to throw this open to discussion to those with more intimate knowledge of the motor.<br /><br />Andy

 

[coves]

Re: poppet or not

I just ran a compression test and all is well. At the time, since I had all the pulgs out I was going to change them out as they were still the originals! '96 with 315 hours and still the same plugs. Well they looked OK regarding wear but boy a couple of them were really "gummy". I replaced all six and now there has been no overheat alarm. What the ......!? Can a fouled plug still run the engine but cause just enough overheat to trigger the alarm? Was this never even a poppet issue? This is just too bizarre! And there still seems to be no aggreement on how this poppet thing really works. At high RPM, poppet open, are the thermos no longer in the system? If you're running in the winter, cold water, lots of pressure at high RPM, wouldn't the engine still need to maintain proper temp via the thermos? I can't wait to see the drawings! Place your bets everyone!

 

[heybaylor]

Re: poppet or not

thermos are always in the system..<br />you do need a picture

 

[dingbat]

Re: poppet or not

I'm sitting here looking at the diagram and it's quite obvious that the poppit is a pressure/flow control valve. <br /><br />Water flowing in equilibrium is at 0 psi. Once you restrict the flow of water in any way this restriction creates a back pressure which is what you see with a water pressure gauge. <br /><br />A poppit is used to regulate and maintain the back pressure in the system. At lower RPM the cooling water come in through the water pumps in the lower unit and is circulated around the block and up and out the thermostats at the top of the heads and the pressure you see on your pressure gauge is mostly the back pressure created by the passage ways in the thermostats. Since the diameter of the cooling passage in the thermostats is fixed, the coolant flow through the stats is limited. As the water flow increases the back pressure increases and thus the higher gauge reading you observe. <br /><br />An increase in water pressure will produce an increased flow only to a point. Once you reach the maximum fluid velocity the fluid will vaporize and you end up with cavitation at the thermostats. You need some kind of a flow diverter to exhaust the increased flow of water around the thermostats at elevated RPMs and the poppit valve was the solution. <br /><br />With the poopit open it creates a passage between the block and the prop discharge circuit that circumvents the restrictions of the thermostats and thus allows a greater flow of water though the cooling system in response to the higher heat loads at higher RPMs. A spring is used on the poppit to regulate the size of the opening at the poppit in response to the increased flow while still maintaining the back pressure necessary for the proper operation of the cooling system. <br /><br />

At high RPM, poppet open, are the thermos no longer in the system? If you're running in the winter, cold water, lots of pressure at high RPM, wouldn't the engine still need to maintain proper temp via the thermos?

The thermostats work by varying the water flow through the motor and are the main means of regulating the temperature of the system. When the stats open the flow restriction is decreased and the back pressure falls off so the poppit closes a little in response to the pressure change in the system. When the stats close back up the back pressure increases and the poppit opens up a little in response to the increased pressure in the system. In effect, the poppit mimics the actions of the thermostats and since the thermostats are regulated thermally and the poppit is regulated via pressure, the thermostat remains the main control of temperature in the motor. A damaged or malfunctioning poppit assembly may not mimic the thermostats and cooling issues will occur.

 

[coves]

Re: poppet or not

Well, this makes total sense to me, but I am curious to see AChris's rebuttal. I never thought I would open such a can of worms with this! But still an excellent learning exercise. <br />By-pass valve vs. pressure relief valve. Sounds like the poppet actually accomplishes BOTH! Very cool (pun intended).<br /><br />Did you catch the fact that changing the spark plugs seems to have aleviated the problem. Can a fouled plug = overheat or is this coincidental? I still have not run enough hours yet to verify all is normal now. We shall see.

 

[rocks]

Re: poppet or not

Coves,If you have a water pressure guage that should tell you if the pop-it is opening.I have been fighting this same problem with a 150 mariner for the last 6 months.At 3000rpm it over heats and the pressure pushes up to 20psi.I have replaced everything even the plugs,with no success.

 

[coves]

Re: poppet or not

I'm trying to figure where to install that on this engine. I think it would be important but at this moment have no idea where all the plumbing goes. Did you catch the thread about cutting a twist or two out of the poppet spring so it will open with less pressure? And why did this happen within just the last 6 months for you? Something in the water pathway? Do you boat where there is alot of debris in the water? and there is an unseen restriction? Thereis stuff where I boat all the time. At least every couple of weeks I have to clean out the speedo hole so who knows what else I am sucking up. YOur pressure rising would indicate the poppet not opening, as mentioned in this thread (which has become a rope), which would interefere with proper water flow (cavitation) around and through the thermos which would lead to increase temp. Did you change the spring? The dealer here mentioned vaguely about spring problems but he knows less than we do!

 

[rocks]

Re: poppet or not

I've tried new spring,new seat,diaphram,therms,plugs,water pump.I am going to try to clip the spring next,but with my luck it won't work.No restictions in flow,just a loud Beeeeeeeeeeee. I don't even need a stereo my engine gives me sweet music every time out.Good luck

 

[coves]

Re: poppet or not

BTW, as mentioned in all this, be sure your compression is normal and equal among all the cyls. I really still do not get it either. YOu have done the exact same as me. And still I don't trust it yet. What could have possibly changed within six months for your engine? Also, however odd this is, be sure all six are firing. I actually ran my boat an entire season before I realized I was only running on 5/6. At that time the overheat buzzer sounded very rarely exactly at 3K and at no other time. When that ignition was fixed, now running on all six, new water pump impellar, then the alarm went off every time out over 3K and under 5K. Just like you I changed out everything I could get my hands on with the spark plugs last. What, what, what???? Oh yea, it's a boat!

 

[LDS]

Re: poppet or not

I have a 200 merc (93) which is fine at idle but temp increases as rpm goes up. Water pump, housing, plugs, etc all changed with no difference. I tried new stats with no change. I pulled the stats out with no change. Now I am wondering about this poppet valve. If I have no stats in now, will the decrease in water back pressure cause this valve to close more...and if I can get to this valve(s) and remove or replace it, will I be better off running with stats or without.

 

[LDS]

Re: poppet or not

I have a 200 merc (93) which is fine at idle but temp increases as rpm goes up. Water pump, housing, plugs, etc all changed with no difference. I tried new stats with no change. I pulled the stats out with no change. Now I am wondering about this poppet valve. If I have no stats in now, will the decrease in water back pressure cause this valve to close more...and if I can get to this valve(s) and remove or replace it, will I be better off running with stats or without.