Greg Moss' cooling mods / Drystacking the 2 piece plate

[O/B Dude]

It is very important that the water jacket on the starboard side not be damaged when drilling. See attached text and photos below.



Most people mistakenly believe that like the engine in your tow vehicle, the Mercury V6 outboard expels cooling water from the thermostats after the water has circulated through the entire motor. This is false, as the thermostats are not last in line in the cooling water route of travel. In actuality, the water flow through the heads is from top to bottom, with the thermostat housings acting as a fork in the road. Half the water exits via the thermostat hoses while the other half continues down the head through the cooling passages and into the exhaust adaptor to be dumped into the driveshaft housing. I have never felt that pulling water off at the heads is a good idea. It only lets it do half the job of cooling the motor.

I like the idea of passing all of the cooling water through the heads. I feel there is a good chance of steam pockets forming in the head without sufficient water pressure to collapse them. There is more of a chance of detonation due to hot spots in the portion of the head adjacent to the combustion chamber. To rectify this, I plug the thermostat housings with pipe plugs. Cut the center out of the thermostats and reinstall them in the housings. This is necessary to hold the thermostat housing‘s rubber gasket in place. An appropriate sized washer would serve this purpose as well. Remove the fittings for the hoses from the thermostat housings and install 1/4" pipe plugs in their place. This will direct all cooling water through the heads before it can exit the motor.

Next I work on the exhaust adapter. On the two-piece adaptor plate, there is a 1/8" drain hole in center of the plate. Its main purpose is to allow the motor to drain any remaining water once the boat is back on the trailer. Without it, water could stand in the copper pipe and freeze in cold weather. It will also bleed off some of the water pressure. I like to seal it either with Marine-Tex or a short screw and red Locktite. After cooling water has passed through the motor, there is a triangular cavity that directs water to exit motor. This cavity splits into two passages. One expels water into the mid-section and is mixed with the exhaust. The other allows water to pass to the area behind the tuner. There are 4 holes in this area behind the tuner. These allow water to spray onto the tuner and provide some level of cooling as well as a path for spent cooling water to exit the motor.

Fill the water passage that leads to the mid-section. You must be careful and not fill the passage adjacent to this passage that directs water to the previously mentioned tuner cooling holes. Water will need to be able to flow through there. This passage is on the starboard side of the adaptor plate. Then, using Marine-Tex, fill the 4 holes that direct water onto the tuner. Next, drill two 1/8" holes on either side of the tuner. These must be angled downward and pointing at the water pump housing. This is very important as failure to do so will result in a melted water pump and may ultimately require a very expensive engine overhaul.

Now, drill and tap for the water hose fittings. Do this on both sides of the adaptor plate. Use 1/4" NPT pipe elbows with 3/8" hose. These fittings are available at Ace Hardware and other retailers. See photos for drilling locations and be careful not to drill through the raised water passage on the starboard side of the plate. Tap the holes and install the hose fittings with Teflon tape.

For the 1-piece adaptors, drill and tap the sides of the plate and drill for water pump cooling in the same way as the 2-piece plate. See photos of the 1-piece plate for drilling locations. The factory drain holes need to be plugged. These can be tapped and pipe plugs can be installed. The 1-piece plate in the photo is a Land and Sea unit but is similar in design to the factory Mercury unit. On this plate, 2 slightly oversized stainless steel bolts were used to plug the factory drain holes. Epoxy was applied to the threads to assure the bolts remain in place. Tapping the holes was not required. This was done so that the plate could be returned to stock by removing these bolts and installing pipe plugs in place of the elbows, then filling or plugging the holes that were drilled to cool the water pump.

Next, the block itself should be addressed. The factory casting leaves a bit to be desired with regard to the water passages. The two passages coming into the bottom of the block at cylinders 5 and 6 generally have more casting flash than what would be considered ideal. These need to be cleaned up. I have a long die cutter bit that I use to clean up the area in the water jacket so the water will flow more freely. Some motors have a drain hole with a brass set screw and a hole drilled into the screw. This needs to be plugged. Remove the poppet valve from the poppet cover and install a dump hose onto the poppet cover fitting. There is a small hole on the long type poppet cover that must be filled or plugged with a screw and red Lock-Tite. On motors that do not have a poppet valve, use a cover plate from a Hi-Po motor. Check the water passages that come in from the exhaust divider plate and make sure all of the passages are open and will flow freely, as this is another area where Mercury falls short. On my motor I had Jay Smith slot the water passages in the block from the exhaust divider plate. This plate is located between the cylinder banks and should not be confused with the exhaust adaptor plate. Instead of just having two or three holes, it is instead slotted open the whole length.

I am not a fan of water diverters in the cooling jackets. I have tried them and haven’t seen any difference in cooling, so I leave them out. I prefer not to have anything blocking the flow of water.

This cooling system expels water at 5 points. 2 holes to direct water onto the water pump, 2 water dump hoses installed on the sides of the adaptor plate, and a water dump hose exiting off of the poppet valve cover. Now you have what is known as a dry stacked exhaust. Without all that water exiting onto the tuner and into the exhaust housing, you should in theory see an increase in top end RPM due to a more favorable environment with respect to reversion. The pulses generated by exhaust reversion will draw on exhaust gasses only rather than pulling on the much heavier expelled cooling water, as happens with the original configuration.

This modification really is very simple to do and has worked very well on everything from 2.5 high performance motors to 150 hp recreational outboards. The high performance 1-piece plate is somewhat different but modification is very similar to that of the 2-piece plate. Always allow the motor to warm up and make sure to have engine heat before running it hard. Here in Texas with water temperatures in the summer reaching up to 95 degrees, I get 130 degree engine temperatures at WOT. Running on the hose I use a laser sighted temperature sensor to read the temperature of the spark plug bases. They all read very close to one another. If I am running in cooler water I will restrict the poppet cover dump hose. A telltale insert, the small plastic fitting at the end of the fishing motor type dump hose, works well here. It will still provide good water pressure at WOT and at idle.

I install the fitting for the water pressure gauge on the exhaust cover if it is tapped for one. For motors that aren’t, drill and tap it as needed on the top of the block behind the divider plate.

[O/B Dude]

Correct drill location for 2 pc plate. Use great care to avoid drilling thru the water jacket indicated by the white arrow. Drill the red dots only.

[O/B Dude]

Plug tuner cooling holes and drill water pump cooling holes as shown. Waterpump cooling holes should be drilled at an angle and aimed toward the water pump housing. Be carefull not to drill through the tuner flange or tuner bolts.

[O/B Dude]

Plug this hole.

[O/B Dude]

1 Pc plate dry stack drill locations. Drill the waterpump cooling holes at an angle toward the water pump. It is not necessary to install tubing to direct water there as long as the holes are drilled "aimed" at the pump.

[O/B Dude]

This is a land and sea 1 pc plate.

[snowmanmtl]

this system and this one?
http://forums.screamandfly.com/forum...t=dry+stacking

[O/B Dude]

Yes, some differences. Gregs mods are less work, use less hardware, dont have the possibility of the 1/16" nozzles clogging with the debris I sometimes find in my cooling system, and at least one water dump location is different. (Starboard side) Comp Kings will spray the tuner and the insides of the drive housing and may help with the white residue that forms, but I have found that the residue generally forms no matter what you do. Also, Gregs mods block flow from the t-stat housings and force all water thru the heads for extra cooling. I just now skimmed thru Comp Kings thread but I think I remember it pretty well from when I read it some time ago. The only other thing I can add is the possibility of water atomization with four 1/16" knozzles vs. two 1/8" holes. Gregs mods have 2 streams striking the pump only, Compkings has a smaller stream richocetting around the tuner and drive housing. May create for more water mist being pulled by reversion, but not sure.

[vintagevector225]

I have amid 80,s two peice plate.What about the water fitting on the top plate port side?Do Iplug it?Where is the water diverter?Can I tee the poppet valve dump to the starboard side dump so i only have two dumps exiting my cowl ?Here in michigan the water temps are a cooler than in texes.

[merc326]

Thanks for the update.
Merc326

[vintagevector225]

I am not clear on what you do with the factory dump on the port side of the two peice plate that goes to the tattel tail. My waterpump guide tube is distorted from heat with no cooling mods is this normal?could i drill two 3/16 holes aimed at the waterpump instead of the 1/8?Could i connect the poppet valve to the starboard side dump so i only have two hoses exiting my cowl?Any information from you or any one else would be much appretiated.THANKS VINTAGEVECTOR225

[NZ Sidewinder]

Interesting old thread.
My stats don't pass water at cruising speed and the water temp gauges placed just behind the Stats tell the story why.
No heat in that water up there.
Don't ask me how this is possible but it's what I see.

[wogi]

It is very important that the water jacket on the starboard side not be damaged when drilling. See attached text and photos below.



Most people mistakenly believe that like the engine in your tow vehicle, the Mercury V6 outboard expels cooling water from the thermostats after the water has circulated through the entire motor. This is false, as the thermostats are not last in line in the cooling water route of travel. In actuality, the water flow through the heads is from top to bottom, with the thermostat housings acting as a fork in the road. Half the water exits via the thermostat hoses while the other half continues down the head through the cooling passages and into the exhaust adaptor to be dumped into the driveshaft housing. I have never felt that pulling water off at the heads is a good idea. It only lets it do half the job of cooling the motor.

I like the idea of passing all of the cooling water through the heads. I feel there is a good chance of steam pockets forming in the head without sufficient water pressure to collapse them. There is more of a chance of detonation due to hot spots in the portion of the head adjacent to the combustion chamber. To rectify this, I plug the thermostat housings with pipe plugs. Cut the center out of the thermostats and reinstall them in the housings. This is necessary to hold the thermostat housing‘s rubber gasket in place. An appropriate sized washer would serve this purpose as well. Remove the fittings for the hoses from the thermostat housings and install 1/4" pipe plugs in their place. This will direct all cooling water through the heads before it can exit the motor.

Next I work on the exhaust adapter. On the two-piece adaptor plate, there is a 1/8" drain hole in center of the plate. Its main purpose is to allow the motor to drain any remaining water once the boat is back on the trailer. Without it, water could stand in the copper pipe and freeze in cold weather. It will also bleed off some of the water pressure. I like to seal it either with Marine-Tex or a short screw and red Locktite. After cooling water has passed through the motor, there is a triangular cavity that directs water to exit motor. This cavity splits into two passages. One expels water into the mid-section and is mixed with the exhaust. The other allows water to pass to the area behind the tuner. There are 4 holes in this area behind the tuner. These allow water to spray onto the tuner and provide some level of cooling as well as a path for spent cooling water to exit the motor.

Fill the water passage that leads to the mid-section. You must be careful and not fill the passage adjacent to this passage that directs water to the previously mentioned tuner cooling holes. Water will need to be able to flow through there. This passage is on the starboard side of the adaptor plate. Then, using Marine-Tex, fill the 4 holes that direct water onto the tuner. Next, drill two 1/8" holes on either side of the tuner. These must be angled downward and pointing at the water pump housing. This is very important as failure to do so will result in a melted water pump and may ultimately require a very expensive engine overhaul.

Now, drill and tap for the water hose fittings. Do this on both sides of the adaptor plate. Use 1/4" NPT pipe elbows with 3/8" hose. These fittings are available at Ace Hardware and other retailers. See photos for drilling locations and be careful not to drill through the raised water passage on the starboard side of the plate. Tap the holes and install the hose fittings with Teflon tape.

For the 1-piece adaptors, drill and tap the sides of the plate and drill for water pump cooling in the same way as the 2-piece plate. See photos of the 1-piece plate for drilling locations. The factory drain holes need to be plugged. These can be tapped and pipe plugs can be installed. The 1-piece plate in the photo is a Land and Sea unit but is similar in design to the factory Mercury unit. On this plate, 2 slightly oversized stainless steel bolts were used to plug the factory drain holes. Epoxy was applied to the threads to assure the bolts remain in place. Tapping the holes was not required. This was done so that the plate could be returned to stock by removing these bolts and installing pipe plugs in place of the elbows, then filling or plugging the holes that were drilled to cool the water pump.

Next, the block itself should be addressed. The factory casting leaves a bit to be desired with regard to the water passages. The two passages coming into the bottom of the block at cylinders 5 and 6 generally have more casting flash than what would be considered ideal. These need to be cleaned up. I have a long die cutter bit that I use to clean up the area in the water jacket so the water will flow more freely. Some motors have a drain hole with a brass set screw and a hole drilled into the screw. This needs to be plugged. Remove the poppet valve from the poppet cover and install a dump hose onto the poppet cover fitting. There is a small hole on the long type poppet cover that must be filled or plugged with a screw and red Lock-Tite. On motors that do not have a poppet valve, use a cover plate from a Hi-Po motor. Check the water passages that come in from the exhaust divider plate and make sure all of the passages are open and will flow freely, as this is another area where Mercury falls short. On my motor I had Jay Smith slot the water passages in the block from the exhaust divider plate. This plate is located between the cylinder banks and should not be confused with the exhaust adaptor plate. Instead of just having two or three holes, it is instead slotted open the whole length.

I am not a fan of water diverters in the cooling jackets. I have tried them and haven’t seen any difference in cooling, so I leave them out. I prefer not to have anything blocking the flow of water.

This cooling system expels water at 5 points. 2 holes to direct water onto the water pump, 2 water dump hoses installed on the sides of the adaptor plate, and a water dump hose exiting off of the poppet valve cover. Now you have what is known as a dry stacked exhaust. Without all that water exiting onto the tuner and into the exhaust housing, you should in theory see an increase in top end RPM due to a more favorable environment with respect to reversion. The pulses generated by exhaust reversion will draw on exhaust gasses only rather than pulling on the much heavier expelled cooling water, as happens with the original configuration.

This modification really is very simple to do and has worked very well on everything from 2.5 high performance motors to 150 hp recreational outboards. The high performance 1-piece plate is somewhat different but modification is very similar to that of the 2-piece plate. Always allow the motor to warm up and make sure to have engine heat before running it hard. Here in Texas with water temperatures in the summer reaching up to 95 degrees, I get 130 degree engine temperatures at WOT. Running on the hose I use a laser sighted temperature sensor to read the temperature of the spark plug bases. They all read very close to one another. If I am running in cooler water I will restrict the poppet cover dump hose. A telltale insert, the small plastic fitting at the end of the fishing motor type dump hose, works well here. It will still provide good water pressure at WOT and at idle.

I install the fitting for the water pressure gauge on the exhaust cover if it is tapped for one. For motors that aren’t, drill and tap it as needed on the top of the block behind the divider plate.

OK, knowing that this post is over 20years old, I'm sure that quite a few have tried this on their engines.
With this said, can anyone on here give me input on the pros and cons that one may have encountered running this cooling system mod. Any and all input on this matter will be very appreciated. Asking because I'm contemplating doing this to one of my engines, and would like to know what others have experienced in doing it. Thanks

[NZ Sidewinder]

Hi Greg
I can't claim to have actually duplicated your system but have done some work in the area of 2.5 cooling.
Reading your post, I did get de railed at the part about the stats being half the flow.
On a 225 Promax I put a temp sender unit directly behind each Stat.
So close that when the Stat opened it almost touched the sender.
At WOT the water temp there is 80 or 90F.
The states stay closed at that temp.
A Stat would bleed air even when closed.

Then the diverters.
Imo it's unlikely that diverters will show much effect on overall engine temp because they only work to keep the cylinders at a more even temp across individual cylinders, or in other words, they help keep each cylinder round in shape and therefore sealing better.

Water pumps.
I have semi dry stacked that Promax.
That is by using a water jacketed tuner.
However imo the only benefit of that system is that the tuner doesn't get cooked.

That motor also has a small water bleed that fills the water pump pocket with water full time.
In a full dry stack system that bleed which comes from the LWP maintains the pump in a pond of water.
The slotted exhaust cover sounds interesting.

Footnote.
My prized std 225 Promax is now on a display rack and to replace it I built a junkyard carbed fishing 2.5 which turns 500 rpm more than the Promax did with the same prop and boat. (Both racing)
The Promax ran a 1 piece exhaust plate which was modified to behave just like a 2 piece.
That thread is on S&F somewhere.
The junkyard motor runs std 2 piece plate but has diverters.
Both have stats and poppet installed.