7. Optimum Temps
65C (150F): too cold. According to service manual, EGR valve is non-operational below 150F, "to improve drivability when cold."
82C (180F): getting warm. Thermostat begins to open, circulating coolant through the radiator. Some coolant is still bypassing the radiator.
95C (203F): fully warm. Thermostat is fully open, not bypassing the radiator at all.
100C (212F): boiling point of pure water at atmospheric pressure.
105C (221F): getting hot. Stock ECU will activate fans to cool the car down. Fan speed will be low, or medium (if A/C is already on).
108C (226F): hot. Stock 93-95 coolant thermoswitch activates, changing fan speeds from low>> medium (or med>>high if A/C is already on) (switching to an FC thermoswitch will change this temp to 203F)
115C (240F): getting dangerous. OEM temp gauge begins to rise.
117C (243F): dangerous. boiling point of pure water with 13psi pressure cap.
121C (250F): too hot. OEM temp gauge will point to white line. Boiling point of pure water with 16psi pressure cap.
124C (256F): way too hot. Boiling point of pure water with 19psi pressure cap. Boiling point of 50/50 coolant mix with 13psi pressure cap.
127C (260F): way too hot. OEM temp gauge will point to red line.
133C (273F): way too hot. Boiling point of pure water with at 30psi (2.0bar) pressure cap. This is what Carlos Iglesias is using on his track car. Many race cars use even higher pressures: I've heard rumors that F1 teams run their coolant (pure water for efficiency) at 50 psi or higher (boiling point would be over 290F).
FYI, a 70/30 mix of water/ethylene glycol (standard yellow-green coolant) will raise the boiling point by about 8 F compared to pure water, and a 50/50 mix will raise the boiling point by about 13F.
A Mazda competition preparation manual, dated 1980, gives the following recommendations. Note that this is for a non-turbo 12A motor in a racing environment:
Warm the engine up at an idle speed of 2000-2500 RPM, until the oil temp reaches 160F (70C).
Recommended coolant temperature (outlet side): 160-195F (70-90C).
Max coolant temperature: 205F (95C).
Recommended oil temperature (oil pan): 195-230F (90-110C).
Max oil temperature: 250F (120C).
8. Coolant Flow
Water Pump exit port pushes cold coolant directly into driver's side of the engine block (near intake ports), heated coolant returns to WP from the passenger side of the engine (after passing exhaust ports).
If the thermostat is closed, a bypass port is open and coolant goes back through the water pump again without flowing through the radiator or AST.
As the OEM thermostat opens, it closes the bypass port. Hot flow exiting the waterpump flows through the open t-stat, out the filler neck to upper rad hose, through the radiator where it is cooled. The water pump sucks coolant from the lower radiator hose. Warning: rumor has it that 'parts-store' brand thermostats don't close this bypass.
Regardless of thermostat position, the throttle body coolant line takes coolant from the passenger side of the rear iron, and is pulled back into the waterpump housing inlet.
Regardless of thermostat position, the heater core is fed by a large coolant line below the oil filter, and is pulled back into the waterpump housing inlet. It always has substantial flow, and always bypasses the radiator, decreasing cooling capacity. Turning the heater on, and running the cabin fans at full speed will dissipate some heat.
Turbo cooling starts at the return port for the wp, goes to turbos, returns at wp inlet pipe. Not much pressure drop, so not much flow, and flow reverses at shutdown, making t-stat housing gauges jump, but this is very local volume of hot coolant thermally siphoning through turbos.
AST is functional when thermostat opens, and flow goes across top of filler neck and drops to 10mm exit port. Then comes in a 10mm port to ast mid body, and lower hose feeds this flow to lower rad tank, then to wp inlet. To limit the amount of coolant bypassing the radiator, a .086" pill is intregrated to the lower nipple of the stock AST.
Coolant expands as it heats up, and pushes air and coolant through AST pressure-releif cap to overflow tank.
(description taken from KevinK2 ,
http://www.rx7club.com/showthread.php?t=465083)
With AST installed:
With AST removed and FC filler cap installed:
9. Links
Maintenance:
Coolant Flush How-To's:
http://www.fd3s.net/cooling_system_flush.html
http://www.robrobinette.com/flush.htm
Coolant Burping Tool/ Radiator Cap Funnel
http://www.rx7club.com/showthread.php?t=342309
Part Numbers for replacement Coolant Lines:
http://www.rx7club.com/showthread.php?t=331644
Replacing Turbo Coolant Lines:
http://www.robrobinette.com/turbo_lines.htm
Modifications:
Stock Water Temp Gauge Linearization:
http://www.rx7club.com/showthread.php?t=252334
AST Elimination
http://www.robrobinette.com/coolant_tank.htm
http://www.fd3s.net/coolant_tank_elimination.html
Fan Mod:
http://www.fd3s.net/fan_mod.html
http://rx7.voodoobox.net/howto/fanswitch/fanswitch.html
http://www.rx7club.com/showthread.php?t=462760 << electrical schematic of relay circuit, with description
Upgraded Water Pump
http://www.rx8club.com/showthread.php?t=116423
Electric Water Pump:
www.meziere.com << Meziere sells electric pumps and adapters for the 13B
http://www.rx7club.com/showthread.php?t=414533 <<example here
10. Misc / Unfinished Business
It would be nice to get some before/after temperature data for various mods, using the following test:
-Let the car sit at idle, measuring time from 180F >> 210F (stock ECU will activate the fans at 210F when the parking lights are on).
-Fans will turn on, then measure time from 210>> fans turnoff (180F).
Many people swear by Evans coolant. I haven't tried it. The advantage is it doesn't boil and doesn't require the cooling system to be pressurized. The disadvantage is it's expensive and doesn't transfer heat as efficiently as water.
I'd like to discuss coolant-seal failures further. I've begun gathering photos from engine tear-downs and it seems like the failures occur in the same general vicinity.
(figures 5d-9)
Thanks for reading,
-scott-