BarFlyFisherman
NAXJA Forum User
I wanted to share my thoughts about the stock cooling system, and the reasons for making various modifications.
Please, not debate the benefits of Aluminum VS Copper. That horse has already been beaten to death, buried, dug up, and the skeleton beaten some more. Go read the archived thread about that debate.
Stock cooling system limitations/ parameters/ assumptions:
1. The XJ was not designed for creeping along at low speeds in high temperatures.
2. The primary engine cooling fan is RPM dependent: low speeds = low rpm/slow fan & low CFM = HIGH TEMPS & OVERHEATING!
3. Driving slow also means that the velocity of the incoming air is slow: low speeds = low CFM = HIGH TEMPS & OVERHEATING!
4. The output of the OEM water pump is RPM dependent: low speeds & low rpm's = low flow = HIGH TEMPS & OVERHEATING!
Other influencing factors:
1. There might be an optional A/C condensing coil in front of the radiator core. This coil "pre-heats" the air passing through the core, reducing it's effectiveness.
2. Adding an after market transmission cooler or power steering cooler in front of the radiator, further restricts the airflow through the core. These also "pre-heat" the incoming air, reducing the effectiveness of the radiator core.
Issues:
1. We need to move more water (gpm's) at lower rpm's.
2. We need to move more air (cfm's) at lower speeds & rpm's.
3. Using the A/C causes the condensing coil to add SUPER-HEATED air directly in front the radiator core.
4. OEM fans do not move a sufficient volume of air at low speeds. These were designed for stop & go city driving. At idle in trafffic, you don't have much load on the XJ. But climb hills, full of gear, with the A/C on, at >5 mph & you have an overloaded system!
Solutions:
1. Move more water at low RPM's:
a) Electric water pump - this is why these are so popular. They are not to save HP (pure fiction), but to ensure a stable GPM output across the broad RPM range.
b) Any of the high-flow aftermarket water pumps. Look for one that has a pump curve that will increase the flow at lower RPM's (where you need it), and levels out at the higher RPM's when you don't (higher RPM's usually means you're going faster).
2. Move more air at lower MPH/RPM's:
a) Increase the capacity of the stock fans. Install a higher CFM electric fan &/or a more efficient clutch fan.
b) Remove the OEM fans all together. Remove the radiator shroud, engine fan clutch & fan, and remove the stock electric fan (You're also removing the load on the water pump shaft & bearings!) AND REPLACE THEM with an aftermarket electric fan system.
I used (3) 9" ƒƒDynamics 1100 CFM fans that all kick on together. I used the old A/C trigger, to override the new fan relay, regardless of the temperature. I drilled & tapped the flat spot on a new high flow aluminum thermostat housing with a 1/4" pipe tap. Then I installed a 1/4" MPT X 3/8" FPT brass adapter (hardware store) to adapt the new threaded water temp sensor to the housing for the fans. I like this better that the probe set up, as it is the most accurate.
3. Cooler Air to the Radiator Core:
a) We must face reality... we just do not have that much room to work with. To that end, we simply cannot eliminate the added coolers in front of the radiator. Personally, I used the integral transmission cooler within the radiator, to cool the power steering fluid instead of adding one more thing in front of the radiator. I've got a Hayden 1405 (aka: 405) cooler on front for the automatic transmission fluid ($35 EBay).
b) With those limitations accepted, we must provide a means to dissipate the additional heat, as the incoming air, just is not as cool as we need it to be. Increasing the CFM of the puller fans, does help - A LOT! Higher wind velocity (unlike water higher velocity) cools things off much faster (convection)!
c) Another solution is to provide a larger radiator. With the removal of all of the factory fans, there is now the room to install a thicker core (3 CORE vs the OEM 2 CORE). And there is more room to work in there without scrapping up the knuckles!
Benefits of a 3 core radiator:
1. Metal end tanks - enough said. Whatever you do, get rid of the crimped on OEM plastic tanks. Even is you're staying with a 2 core radiator. The crimps do come loose from vibration & wear. Plastic & metal just don't bond together!
2. 33% more water jacket volume. NOTICE: I did not say cooling capacity... here's why:
a) The first 2 rows pre-heat the incoming air before it reaches the new 3rd row. So claims of 33% extra cooling is misleading. It is probably more like 28-30%.
b) Any added after market coils & the factory optional A/C coil pre-heat the incoming air, so that there just isn't the ability to effectively dissipate heat by the time the air gets to the 3rd row. Adding these coolers in front of the core lowers the additional cooling capacity to about 22-25%.
c) Still 25% an additional cooling capacity is nothing to laugh off. That, along with the 3300 CFM's from (3) fans, will bring the added cooling capacity right back up to 33%+!
3) Personally, I chose a 3 Core, 100% aluminum radiator (radiatorbarn.com $175). I do come from a family of rocket scientists... they insist on aluminum cores, primarily for the weight savings over the copper equivalent. They are ever so slightly more efficient that copper. The key when selecting a radiator is the density of the fins. The more fins per cubic inch, the greater the surface area in which to dissipate heat. But too dense does restrict the air flow....
Thermostats:
I've played around with many different configurations of temperature settings. I've tried high-flow models & lower temperature settings (180ºF). Things acted all haywire.... the check engine light came on with both styles of thermostats - here's what I surmise:
a) The high-flow thermostat does not create any back pressure in the system. The water just flows through the engine block too fast for the efficient transfer of heat to occur.
b) The lower temperature thermostat prevented the engine from getting up to the correct operating temp (210ºF!). The 210ºF was selected, as this operating temperature results in the cleanest emissions. Because this optimal temperature is programmed into the computer (ECM), the engine freaks out when it sees anything less for a substantial period of time (normally the stock temp would close to help raise the temp).
I went back to the stock temperature thermostat, but selected a HIGH quality calibrated thermostat (Mr Gasket/Stant). Everything's working great since.
I only installed a new high flow thermostat housing, so that I had a pristine surface when it came time to install the new gasket. I also wanted the larger sweet spot to drill & tap, that the aftermarket casting provided.
Please, not debate the benefits of Aluminum VS Copper. That horse has already been beaten to death, buried, dug up, and the skeleton beaten some more. Go read the archived thread about that debate.
Stock cooling system limitations/ parameters/ assumptions:
1. The XJ was not designed for creeping along at low speeds in high temperatures.
2. The primary engine cooling fan is RPM dependent: low speeds = low rpm/slow fan & low CFM = HIGH TEMPS & OVERHEATING!
3. Driving slow also means that the velocity of the incoming air is slow: low speeds = low CFM = HIGH TEMPS & OVERHEATING!
4. The output of the OEM water pump is RPM dependent: low speeds & low rpm's = low flow = HIGH TEMPS & OVERHEATING!
Other influencing factors:
1. There might be an optional A/C condensing coil in front of the radiator core. This coil "pre-heats" the air passing through the core, reducing it's effectiveness.
2. Adding an after market transmission cooler or power steering cooler in front of the radiator, further restricts the airflow through the core. These also "pre-heat" the incoming air, reducing the effectiveness of the radiator core.
Issues:
1. We need to move more water (gpm's) at lower rpm's.
2. We need to move more air (cfm's) at lower speeds & rpm's.
3. Using the A/C causes the condensing coil to add SUPER-HEATED air directly in front the radiator core.
4. OEM fans do not move a sufficient volume of air at low speeds. These were designed for stop & go city driving. At idle in trafffic, you don't have much load on the XJ. But climb hills, full of gear, with the A/C on, at >5 mph & you have an overloaded system!
Solutions:
1. Move more water at low RPM's:
a) Electric water pump - this is why these are so popular. They are not to save HP (pure fiction), but to ensure a stable GPM output across the broad RPM range.
b) Any of the high-flow aftermarket water pumps. Look for one that has a pump curve that will increase the flow at lower RPM's (where you need it), and levels out at the higher RPM's when you don't (higher RPM's usually means you're going faster).
2. Move more air at lower MPH/RPM's:
a) Increase the capacity of the stock fans. Install a higher CFM electric fan &/or a more efficient clutch fan.
b) Remove the OEM fans all together. Remove the radiator shroud, engine fan clutch & fan, and remove the stock electric fan (You're also removing the load on the water pump shaft & bearings!) AND REPLACE THEM with an aftermarket electric fan system.
I used (3) 9" ƒƒDynamics 1100 CFM fans that all kick on together. I used the old A/C trigger, to override the new fan relay, regardless of the temperature. I drilled & tapped the flat spot on a new high flow aluminum thermostat housing with a 1/4" pipe tap. Then I installed a 1/4" MPT X 3/8" FPT brass adapter (hardware store) to adapt the new threaded water temp sensor to the housing for the fans. I like this better that the probe set up, as it is the most accurate.
3. Cooler Air to the Radiator Core:
a) We must face reality... we just do not have that much room to work with. To that end, we simply cannot eliminate the added coolers in front of the radiator. Personally, I used the integral transmission cooler within the radiator, to cool the power steering fluid instead of adding one more thing in front of the radiator. I've got a Hayden 1405 (aka: 405) cooler on front for the automatic transmission fluid ($35 EBay).
b) With those limitations accepted, we must provide a means to dissipate the additional heat, as the incoming air, just is not as cool as we need it to be. Increasing the CFM of the puller fans, does help - A LOT! Higher wind velocity (unlike water higher velocity) cools things off much faster (convection)!
c) Another solution is to provide a larger radiator. With the removal of all of the factory fans, there is now the room to install a thicker core (3 CORE vs the OEM 2 CORE). And there is more room to work in there without scrapping up the knuckles!
Benefits of a 3 core radiator:
1. Metal end tanks - enough said. Whatever you do, get rid of the crimped on OEM plastic tanks. Even is you're staying with a 2 core radiator. The crimps do come loose from vibration & wear. Plastic & metal just don't bond together!
2. 33% more water jacket volume. NOTICE: I did not say cooling capacity... here's why:
a) The first 2 rows pre-heat the incoming air before it reaches the new 3rd row. So claims of 33% extra cooling is misleading. It is probably more like 28-30%.
b) Any added after market coils & the factory optional A/C coil pre-heat the incoming air, so that there just isn't the ability to effectively dissipate heat by the time the air gets to the 3rd row. Adding these coolers in front of the core lowers the additional cooling capacity to about 22-25%.
c) Still 25% an additional cooling capacity is nothing to laugh off. That, along with the 3300 CFM's from (3) fans, will bring the added cooling capacity right back up to 33%+!
3) Personally, I chose a 3 Core, 100% aluminum radiator (radiatorbarn.com $175). I do come from a family of rocket scientists... they insist on aluminum cores, primarily for the weight savings over the copper equivalent. They are ever so slightly more efficient that copper. The key when selecting a radiator is the density of the fins. The more fins per cubic inch, the greater the surface area in which to dissipate heat. But too dense does restrict the air flow....
Thermostats:
I've played around with many different configurations of temperature settings. I've tried high-flow models & lower temperature settings (180ºF). Things acted all haywire.... the check engine light came on with both styles of thermostats - here's what I surmise:
a) The high-flow thermostat does not create any back pressure in the system. The water just flows through the engine block too fast for the efficient transfer of heat to occur.
b) The lower temperature thermostat prevented the engine from getting up to the correct operating temp (210ºF!). The 210ºF was selected, as this operating temperature results in the cleanest emissions. Because this optimal temperature is programmed into the computer (ECM), the engine freaks out when it sees anything less for a substantial period of time (normally the stock temp would close to help raise the temp).
I went back to the stock temperature thermostat, but selected a HIGH quality calibrated thermostat (Mr Gasket/Stant). Everything's working great since.
I only installed a new high flow thermostat housing, so that I had a pristine surface when it came time to install the new gasket. I also wanted the larger sweet spot to drill & tap, that the aftermarket casting provided.