cutwater
07-02-2008, 03:08 PM
I have collected some good posts regarding crossovers from a thread I have bookmarked. This should help for future reference since the search feature is broken and only works for 2008 posts and posts from 2004 and prior. I found most of these things to be true in my recent adventure with installing the SM crossover - especially the part about expecting uneven water flow and having the bottom riser water dumps closed off when using the drive impeller. Just thought I'd share.
Joe - on running a crossover using only the Alpha's impeller...
Personally, I don't think an Alpha will pump enough water. I know that Budman had a sea water pump installed on the engine he just had made. Seems to me that every Alpha has steam coming from one side, which I would attribute to lack of cooling water, but I could be wrong. Gcarter has a crank mounted sea water pump, but I don't remember if he kept the circ pump or went with a cross over.
BigGrizz - on water pressure regulation - it's why I use a relief valve...
As for crossover causing problems is not BS. Anything over 35psi in the block is detrimental to head gaskets. It just happens to be more prone to the problem then circ systems, circ systems have it too just not so much due to application Race boats have relief valves for this reason. think about this the first place the cold water hits is the front of both heads than block then t-stat. if the state is open, takes a while to close, then the exhaust. Garry Grimes designed the one tat Mercury sells. If you look at some engines and you see rust from the head down the block this was probably the cause. This is especially true on blower and high compression engines. with a circ the impeller restricts the flow of warer. Now in most applications that the average 65-70 mph unit it is on the verge, especially with hull pickups and re entry. My Criterion would surge upto 32 psi at 78 untill i put on the closed system. I won't go into the temperature differential thing because have done this on the net before. Believe me it does exist.
Brownie - multiple:
The alpha pumps enough for a small block, probably not for a big block. If you have that combo, you may need to weld up some of the bottom holes on the riser dumps to force the cooling water to the top when idling (to keep your skin from sticking to it)
No matter what you do when you remove the circ pump, you must introduce the water into the same two holes that the circ. pump did.
If you run a thermostat on the crossover application (a must to me), you must drill 3 5/32" holes in the crown of the thermostat to allow water to bypass at all times. All thermostats are automotive based, and are expected to have the same (more or less) temperature on both sides of it. If you install a standard thermostat, the temperature will spike LIKE CRAZY.
The circ. pump belt is a fractional horsepower belt. How long do you think it would last on a 20HP Go-Kart?
BigGrizz - on why you should listen to Brownie :wink:
My suggestion is listen to Brownie. I have know him a long time and as of yet have never found him wrong. When he says I prefer, that means you should do it, when he says a must to me that means do it or pay the concquences.
Mario - GREAT POST!!! Where have you been?
Thermostats . . a few things seem to be getting missed here . .
They maintain a constant engine block temperature . . atleast they are supposed to
Holes are drilled in the top to maintain flow but most of all to bleed out air, as air pockets restrict water flow and a thermostat will not open unless it is submerged in water . .
As Brownie stated, an Alpha water pump is inadequete at idle to create enough water pressure or flow to push all the air through the bleed hole that should be in every thermostat . . and these need to be installed with the bleed hole at the top. Drilling a larger hole reduces the back pressure on the Alpha drive pump, allowing full water circualtion before the engine overheats. Restricting the risers ensures water is everywhere it needs to be.
Mercruiser 260 HP Alpha set ups come with a circulation pump . . for a reason. Service is easier with stock off the shelf components versus modified t-stats and welded risers . . .plus the pumps help to balance the flow to both sides of the V8. Cross over tubes, especially those where the inlet comes from one side, will not have a balanced flow.
In a marine application with fresh water cooling . .or sea water cooling a thermostat is still essential . . you do not want to inject 55 degree water into an engine at one end while it exits at 160- 180 some where else . .
Know that the block temperature at the inlet will barely rise above the inlet water temp, while the temp at the exit, or close to that will exceed 160, especially at the heads on top of the combustion chambers. This is not a good thermal equilibrium for the engine . . and can lead to headgasket failure . .especially with aluminum heads . . .
Gcarter, on your picture you show a crank driven pump. Please watch out for the front cover. The gasket is teflon or plastic, and when run at high rpms the pump will create enough pressure to push the gasket out. It is only clamped between two flat surfaces. I have the same pump, BTDT 2x and am now getting a cover made with an O-ring seal.
Mario
Brownie - on cooling systems...
The mission of the cooling system in a marine engine is is to keep the block at the CORRECT temperature. The word cool does not figure into the equation. The engine in your vehicle runs 200+ degrees at high output. They could make it run cold IF THEY WANTED TO. Clearances, evaporation and other factors make the engine want to be WARM. If you think that the mission is to run as cool as possible, you are waaaay off base. Some Gorilla motors have such a heat rejection problem (related to fuel consumption) that they keep all the obstructions out of the cooling path, and the BTU from burning 100 gallons per hour of gasoline keeps the motor warm. You must have seen the ads that claim that 75% of engine wear occurs at start up. When I worked for Tom Gentry on the "Gentry Eagle", We had to warm the 3600 HP MTU Diesels for 5 hours BEFORE WE COULD START THEM. Why do you think that was?
Joe - on running a crossover using only the Alpha's impeller...
Personally, I don't think an Alpha will pump enough water. I know that Budman had a sea water pump installed on the engine he just had made. Seems to me that every Alpha has steam coming from one side, which I would attribute to lack of cooling water, but I could be wrong. Gcarter has a crank mounted sea water pump, but I don't remember if he kept the circ pump or went with a cross over.
BigGrizz - on water pressure regulation - it's why I use a relief valve...
As for crossover causing problems is not BS. Anything over 35psi in the block is detrimental to head gaskets. It just happens to be more prone to the problem then circ systems, circ systems have it too just not so much due to application Race boats have relief valves for this reason. think about this the first place the cold water hits is the front of both heads than block then t-stat. if the state is open, takes a while to close, then the exhaust. Garry Grimes designed the one tat Mercury sells. If you look at some engines and you see rust from the head down the block this was probably the cause. This is especially true on blower and high compression engines. with a circ the impeller restricts the flow of warer. Now in most applications that the average 65-70 mph unit it is on the verge, especially with hull pickups and re entry. My Criterion would surge upto 32 psi at 78 untill i put on the closed system. I won't go into the temperature differential thing because have done this on the net before. Believe me it does exist.
Brownie - multiple:
The alpha pumps enough for a small block, probably not for a big block. If you have that combo, you may need to weld up some of the bottom holes on the riser dumps to force the cooling water to the top when idling (to keep your skin from sticking to it)
No matter what you do when you remove the circ pump, you must introduce the water into the same two holes that the circ. pump did.
If you run a thermostat on the crossover application (a must to me), you must drill 3 5/32" holes in the crown of the thermostat to allow water to bypass at all times. All thermostats are automotive based, and are expected to have the same (more or less) temperature on both sides of it. If you install a standard thermostat, the temperature will spike LIKE CRAZY.
The circ. pump belt is a fractional horsepower belt. How long do you think it would last on a 20HP Go-Kart?
BigGrizz - on why you should listen to Brownie :wink:
My suggestion is listen to Brownie. I have know him a long time and as of yet have never found him wrong. When he says I prefer, that means you should do it, when he says a must to me that means do it or pay the concquences.
Mario - GREAT POST!!! Where have you been?
Thermostats . . a few things seem to be getting missed here . .
They maintain a constant engine block temperature . . atleast they are supposed to
Holes are drilled in the top to maintain flow but most of all to bleed out air, as air pockets restrict water flow and a thermostat will not open unless it is submerged in water . .
As Brownie stated, an Alpha water pump is inadequete at idle to create enough water pressure or flow to push all the air through the bleed hole that should be in every thermostat . . and these need to be installed with the bleed hole at the top. Drilling a larger hole reduces the back pressure on the Alpha drive pump, allowing full water circualtion before the engine overheats. Restricting the risers ensures water is everywhere it needs to be.
Mercruiser 260 HP Alpha set ups come with a circulation pump . . for a reason. Service is easier with stock off the shelf components versus modified t-stats and welded risers . . .plus the pumps help to balance the flow to both sides of the V8. Cross over tubes, especially those where the inlet comes from one side, will not have a balanced flow.
In a marine application with fresh water cooling . .or sea water cooling a thermostat is still essential . . you do not want to inject 55 degree water into an engine at one end while it exits at 160- 180 some where else . .
Know that the block temperature at the inlet will barely rise above the inlet water temp, while the temp at the exit, or close to that will exceed 160, especially at the heads on top of the combustion chambers. This is not a good thermal equilibrium for the engine . . and can lead to headgasket failure . .especially with aluminum heads . . .
Gcarter, on your picture you show a crank driven pump. Please watch out for the front cover. The gasket is teflon or plastic, and when run at high rpms the pump will create enough pressure to push the gasket out. It is only clamped between two flat surfaces. I have the same pump, BTDT 2x and am now getting a cover made with an O-ring seal.
Mario
Brownie - on cooling systems...
The mission of the cooling system in a marine engine is is to keep the block at the CORRECT temperature. The word cool does not figure into the equation. The engine in your vehicle runs 200+ degrees at high output. They could make it run cold IF THEY WANTED TO. Clearances, evaporation and other factors make the engine want to be WARM. If you think that the mission is to run as cool as possible, you are waaaay off base. Some Gorilla motors have such a heat rejection problem (related to fuel consumption) that they keep all the obstructions out of the cooling path, and the BTU from burning 100 gallons per hour of gasoline keeps the motor warm. You must have seen the ads that claim that 75% of engine wear occurs at start up. When I worked for Tom Gentry on the "Gentry Eagle", We had to warm the 3600 HP MTU Diesels for 5 hours BEFORE WE COULD START THEM. Why do you think that was?