Rupunzell
Bernice Loui
Design of the coolant pump is more than adequate for the cooling requirements in the exxe. What often happens today, the gap between pump impeller and housing is excessive resulting in poor coolant flow at low engine RPMs. This is the reality of replacement parts today. Many of them are not OEM Fiat quality or any where near the OEM spec. There is a drawing in the Fiat Service manual that illustrated this gap and it's specified limits. Sort of remember the gap being 1mm, BUT this must be confirmed. The surface finish of the pump impeller also has an effect on coolant pump performance. It should be noted the OEM Fiat coolant pumps have a precision machined surface near the coolant pump housing area. The impeller surface while cast is smooth enough to meet the needs of what this pump does.
On the endurance race Lampredi SOHC, the coolant pump housing and pump front was checked for clearance and housing surface where the housing meets the pump front surfaced on a milling machine to achieve the Fiat spec for gap between the impeller and housing. It has been so long since that was done, no longer remember how much material was removed to achieve the specified gap.
The other significant modification was the under drive crank pulley. This modification is a non-option for a endurance race engine due to the near constant operation above 5,000 RPM hour after hour. Running the coolant pump at these RPM's can easily result in pump cavitation which significantly reduces coolant flow. The alternator also suffers as they are simply not designed to run at sustained high RPMs.
When the LeMons exxe was converted to a Mazda 12A PP race rotary, the stock coolant pump was used as is with under drive pulley. The radiator and associated cooling system remained in the front stock position. Coolant temperatures were quite acceptable. Oil temperatures were a completely different kettle of oil.
As for the box behind the radiator at the front of the exxe, it's shape and configuration has been specifically designed to produce air flow and plenum effect to aid cooling at speed (this design is the result of a LOT of wind tunnel testing and engineering work). Removal of this box has consequences for the stock cooling configuration. Cooling at idle depends on a OEM spec correct coolant pump (impeller to housing gap and proper impeller design and construction) the thermostatic switch and cooling fans.
Over the decades of exxe ownership since the late 70's, cooling or over heating was never a problem. They have been run over the hill into SoCal on over 100 degree F days at near full throttle with zero cooling problems. Stuck traffic in over 100 degrees F days with no cooling problems, endurance raced in over 100 degrees F summer Buttonwillow race track heat with a modified performance engine and zero cooling problems.
What is important, the cooling system in the exxe must be of OEM configuration and specification for the cooling system to function properly. Anything less is not gonna work.
Problem areas today due to sub standard parts and degradation of the cooling system are likely going to be, non-spec coolant pump, leaks in the cooing system due to pin holes in the main coolant pipes and other areas, steam erosion of the cylinder head resulting in pin holes between the combustion chamber to coolant passages, air in the cooling system, clogged radiator, questionable thermostat, non functional cooling fans and switch, slipping drive belt... any single one of these items can easily result in cooling system problems.
Bernice
On the endurance race Lampredi SOHC, the coolant pump housing and pump front was checked for clearance and housing surface where the housing meets the pump front surfaced on a milling machine to achieve the Fiat spec for gap between the impeller and housing. It has been so long since that was done, no longer remember how much material was removed to achieve the specified gap.
The other significant modification was the under drive crank pulley. This modification is a non-option for a endurance race engine due to the near constant operation above 5,000 RPM hour after hour. Running the coolant pump at these RPM's can easily result in pump cavitation which significantly reduces coolant flow. The alternator also suffers as they are simply not designed to run at sustained high RPMs.
When the LeMons exxe was converted to a Mazda 12A PP race rotary, the stock coolant pump was used as is with under drive pulley. The radiator and associated cooling system remained in the front stock position. Coolant temperatures were quite acceptable. Oil temperatures were a completely different kettle of oil.
As for the box behind the radiator at the front of the exxe, it's shape and configuration has been specifically designed to produce air flow and plenum effect to aid cooling at speed (this design is the result of a LOT of wind tunnel testing and engineering work). Removal of this box has consequences for the stock cooling configuration. Cooling at idle depends on a OEM spec correct coolant pump (impeller to housing gap and proper impeller design and construction) the thermostatic switch and cooling fans.
Over the decades of exxe ownership since the late 70's, cooling or over heating was never a problem. They have been run over the hill into SoCal on over 100 degree F days at near full throttle with zero cooling problems. Stuck traffic in over 100 degrees F days with no cooling problems, endurance raced in over 100 degrees F summer Buttonwillow race track heat with a modified performance engine and zero cooling problems.
What is important, the cooling system in the exxe must be of OEM configuration and specification for the cooling system to function properly. Anything less is not gonna work.
Problem areas today due to sub standard parts and degradation of the cooling system are likely going to be, non-spec coolant pump, leaks in the cooing system due to pin holes in the main coolant pipes and other areas, steam erosion of the cylinder head resulting in pin holes between the combustion chamber to coolant passages, air in the cooling system, clogged radiator, questionable thermostat, non functional cooling fans and switch, slipping drive belt... any single one of these items can easily result in cooling system problems.
Bernice
I still say the biggest problem that Xs have with cooling is the fact that the water pump, which is really designed for the 128 has to struggle to push coolant the whole length of the car and back and further the metal pipes in the box under the car are enclosed and instead of acting like radiators, they just trap the heat in the coolant. Much like a 124 spider, if everything is functioning perfectly (rare in these old cars) then overheating should be rare.....there is just no margin for error.
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