poppet or not

[coves]

96 225 efi. What happens if you run this motor with the poppet valve removed for a short (please define) time as an experiment looking for over heating problems?<br /><br />Thanks gang.

 

[dingbat]

Re: poppet or not

The poppet valve basically short circuits the cooling system to prevent an over pressure condition at higher RPMs. Taking the valve out will almost guarantee you overheat at lower RPM

 

[KCLOST]

Re: poppet or not

yep

 

[coves]

Re: poppet or not

OK, trying to get my head around this. The poppet restricts water flow at low RPM to establish proper running temp, right? As the RPMs rise, H2O pressure rises and opens the poppet, right? Now you have greater water flow to maintain proper operating temp as the engine is now running hotter, right? So if there is no poppet I would presume that you would be running to cool at low RPM and this might confuse things only at low RPM. You would not overheat, but probably run rough as the computer tries to maintain proper air/fuel mixture at the wrong temp. Whew, I need a beer....

 

[dingbat]

Re: poppet or not

The poppet is used as a constant flow device. Basically when the rpm is low it’s completely closed and all the water is circulated through the system. As the motor’s RPM rises, the poppet slowly opens in response to the pressure/ flow change and dumps the excess cooling water out through the prop thus maintaining a constant flow of cooling water to the heads which in turns mains a constant operating temperature. If you removed the poppet, you would in effect completely short circuit the cooling system at lower RPMs which would result in no cooling water being sent to the heads.

 

[coves]

Re: poppet or not

I get it! In a closed system (car) the thermostat is probably all that is needed to maintain everything, but with an open system we now have another variable. Interesting. So now why do I get an overheat alarm and response only between 3k and 5k? I thought for sure the poppet because it is suppose to respond at 3k. I can run at 5k+ all day with no problem and sometimes at anywhere in between with,again, no problem. But usually I will get the alarm in the 3-5 range. Hmmmmmmmm.....<br />Thanks,<br />CC

 

[dingbat]

Re: poppet or not

Try this. Unhook the temp sensor from the head and check it with a voltmeter to determine if it's a normally open or normally closed operator. Chances are it’s normally closed but you’ll need to find out for this test.<br /><br />Now take your old sensor and cut off the sensor so all you have left are the wires. If the sensor is normally closed, twist the wires together and replace the good sensor with this rig. This will fool the control module into thinking that the temps are OK. If the alarm goes off with this rig you’ve just eliminated a cooling problem and can start focusing on an electrical problem. Probably your control module when all is said and done.

 

[coves]

Re: poppet or not

Good idea. I have a four wire sensor that triggers both the alarm and the contol module to retard the rpms to 3k but this more things to think about. Hey! Just what I needed!

 

[dakk1]

Re: poppet or not

Nice one dingbat. I'm adding that to my library of outboard motor tests. Getting to be quite a collection. Maybe I can write a book someday. I sure as heck can't fix outboard motors! LOL.<br /><br />Dave...

 

[dingbat]

Re: poppet or not

Easier yet. Just remove the sensor from the block and let it hang there. If the alarm still sounds you've just eliminated overheating as the problem.

 

[AndyL]

Re: poppet or not

Would I be wrong in thinking that at less than 3000 rpm the boat speed through the water will not generate sufficient dynamic flow to supplement the water pump impeller if the poppet was leaking badly. However at higher rpm/ highr speed, sea water it being forcible driven through the system overcoming the wastage through a leaky poppet. Just my thoughts??<br />Andy

 

[coves]

Re: poppet or not

Well there's a thought. That would explain no overheat at 5K and above. Maybe the poppet is opening too quickly betwee 3k and 5k thus dumping too much cooling water. Now that would indicate the need for a stronger spring or a leak/poor seal somewhere. This is all so wierd. Isn't there an easier way to keep this puppy cool? Fill the engine cover with dry ice?

 

[achris]

Re: poppet or not

Originally posted by dingbat:<br /> The poppet valve basically short circuits the cooling system to prevent an over pressure condition at higher RPMs. Taking the valve out will almost guarantee you overheat at lower RPM

This is not quite right. The poppet doesn't 'dump' excess pressure, it uses the pressure (a direct relationship to engine speed) to control whether the engine is under thermostat temperature control or the engine is cooled using ALL the water supplied by the water pump. <br /><br />In previous years engines were either not temperature controlled or completely controlled by thermostat(s). If the enigne had no temperature control then they tended to run very cool at low speed, which lead to cold-fouling of the spark plugs. Owner of these engines were all too familiar with the need to give the engine a hard run if they'd been idling (trolling) for any length of time. <br /><br />Engines with thermostats (pre-poppet) tended to run nicely at lower speeds, but were prone to being a bit hot at high speed, because the thermostat tended to reduce the flow too much. <br /><br />Mercury's (rather clever) solution was a system that uses thermostats at low engine speed and full flow at high engine speeds. Hence the poppet valve system was born. At lower engine speeds, usually up to about 3000 rpm the water pump produced only low pressure, not enough to push the poppet off it's seat. This means that all water must flow passed the thermostat(s), thus they can controll the engine temperature. Once the water pressure reaches the poppet spring pressure it will push the poppet off it's seat and allow ALL of the water from the pump to flow through the block and heads, thus giving the greatest cooling flow. <br /><br />There is NO excess water pressure. All the water from the pump is used to cool the engine once the poppet opens. The only time excess water is 'dumped' is when the thermostats are closed, it is pushed into the exhaust system to cool the gases so they don't burn the driveshaft housing, water pump and gearhousing. when running under poppet control or the thermostats are open the water from the cooling system is used to cool the exhaust gases.<br /><br />If you run without a poppet valve you will probably run too cold at low speed and the EFI will over-richen the fuel mixture, fouling the plugs even quicker.<br /><br />Chris................<br /><br />P.S. This thread is very close to the other one you have running.

 

[KCLOST]

Re: poppet or not

"If you run without a poppet valve you will probably run too cold at low speed and the EFI will over-richen the fuel mixture, fouling the plugs even quicker."<br /><br />Not the case with a normal carbed V6 however, and for an EFI I don't understand your theory...<br /><br />And I find that hard to believe regardless, With the poppet gone the water is exited from the block before it should in relation to the water pressure...There is no correlation with the poppet to engine temps, and there is no correlation to the stats with water pressure.. They are completely seperate units that are designed to work at different instances...<br /><br />The spring is designed to open at a specific pressure, with it gone the water will exit at lower rpms, especially when the stats are closed (assuming water will even reach up to them when the poppet is gone)! It doesn't matter if the water dumps out the exhaust ports or wherever... But I does dump out the block through the path of least resistance "so to speak" and if that path creates low water levels at the top of the block you have a problem!!!!!. <br /><br />To make a long story short, a poppet removal can or will dump water from the system, preventing the stats from even becoming part of the cooling equatione. No or little water will get to them (this is at lower rpms of course!)..

 

[achris]

Re: poppet or not

What do you mean by 'dump' the water? The poppet does not dump water, when it opens the water moves through the block and heads WITHOUT control from the thermostats. Remove the poppet and you have all the water from the pump moving completely through the block and heads, causing too much cooling.<br /><br />When I get back home, I'll post one of two things, either the water flow diagram, or an apology to you (if I'm wrong ).<br /><br />Chris.............

 

[heybaylor]

Re: poppet or not

hmm this is gonna be interesting ..<br /><br />By bet on the poppit is that it ."opens a hole for the water to go out..and if there is is not enough water "flow/volume" to sustain water to the top of the heads . (poppit is at the bottom of the cooling chambers.....hmm they will get hot ..<br />at low rpm's the water flow aint enough ..so>><br />slam shut the poppit .and guess what the water has to go thru the thermo's to get out ..hmm that is real near the top of the cylinder heads..<br />after rpm builds .. the poppit opens with full pump "flow now cooling the entire shebang ..lotsa water ,and lotsa flow through the heads

 

[KCLOST]

Re: poppet or not

"Remove the poppet and you have all the water from the pump moving completely through the block and heads, causing too much cooling."<br /><br />No way.... That is not how a poppet is supposed to work... Unless they designed something new for his year of motor...<br /><br />It is basically a "pressure relief valve" and it is called so in the mercury parts listings.... NO water going through the poppet goes to the water jackets, it just speeds up flow through the jackets when it opens..

 

[KCLOST]

Re: poppet or not

Heybaylor is right on the money... BTW...<br /><br />Except that the poppet does not prevent any water flow to the water jackets when closed, It just seals the system off until high enough water pressure requires it to open... When opened, It increases water flow through them at higher rpms... The excess is dumped through the exhaust...

 

[AndyL]

Re: poppet or not

Thats the way I thought it worked too. When mine was leaking, the water pump at low RPM especially with XL shaft, could not maintain enough water in the top of the head to satisfy the alarms/ Temp sender as there was too much leaking past the poppet. I could rum the motor at idle with the thermostats out and nothing came out of the holes. At higher rpm /water speeds the pump could cope with the losses and the temperature was normal. Below 2500 rpm in gear and temps rose rapidly although the lower part of the block felt OK.

 

[rocks]

Re: poppet or not

So if the popet is leaking you would not see any water from the tell tale at low rpm's,because all the water would be passing through the popit and not up to the therms,which in turn open and give water to the tell tale????Am I right?