I have followed this thread with some interest, as it was always said that Fiat motors overheated easily. The answer is yes and no.
WIth ANY cooling system you have to understand where you are starting from. This means the following:
A. Radiator (rear) that is sized for the job, clean on the inside and clean on the outside.
B. Hoses in good condition capable of holding 24 lbs of pressure.
C. High pressure radiator cap (15-24 lbs)
D. Thermostat that opens at the proper temperature
E. Coolant level
F. Proper working water pump
G. Proper working fan
H. Properly tensioned belt.
Now lets look at each of these items.
A .
Radiator - The standard radiator was for a 32 HP motor. A112 stock motors make 70 HP. So the radiator must be able to dissipate a minimum of double the heat. This means the standard radiator should have at least a core with one more row and it should be lengthened as much as the chassis will allow. Make sure that the top tank of the radiator is at least equal/above the thermostat housing, as the top tank should be the highest item in the cooling system.
B.
Hoses - If the hoses are more than 4-5 years old replace them.
C.
Radiator cap - A 15 PSI cap will raise the boiling point of pure water from 212 degrees F (100 C) to 249 degrees F (121 C). The same cap on a system with 50% ethelyne glycol/water will raise the temperature from 225 degrees F (107 C) to 263 degrees F (127 C). Running a 20 lb cap will raise the boiling temperature even further. If really high boiling points are required, then one would go for a 'waterless' cooling system. These liquids are capable of withstanding temperatures in excess of 400 degrees F (204 C) at 15 PSI pressure. While we are discussing boiling temperature we might as well talk about what happens inside a motor with cooling fluid and loss of pressure. When this happens steam is generated. First, steam is an insulator to the transfer of heat. So, wherever the steam is present the metal will become superheated. If this is an area in the head, then detonation can easily and quickly occur. Further, lower system pressures will also allow the pressure at the waterpump inlet to drop even further, thus creating steam at lower temperatures still. BTW - The radiator cap is the single most neglected item in the cooling system. If you do not know how old it is, or what pressure it is, get a new one and mark if with the installation date.
D.
Thermostat - ALL engines MUST use a thermostat or, in their place, some type of restrictor plate. Why? Well there are several reasons. First, the thermostat will allow the engine to come up to operating temperature faster, reducing wear. Second, the thermostat (or restrictor plate) will form a partial barrier to water flow, allowing the waterpump to build up pressure behind the thermostat to something like 30 PSI. This means that the boiling temperature of the fluid in the block will be even higher than in the radiator, approaching something like 300 degrees F (149 C) with a 50/50 water/glycol mixture. This will make steam pockets less likely to occur. Third, the reduction of speed of the water through the system by the thermostat will allow more time for the fluid to give off its heat while traveling through the radiator.
If you run a second radiator, it should be run in series to the rear radiator. So the water would flow form the pump into the block, through the block and head to the thermostat, to the top tank of the rear radiator, through the radiator and then from the bottom tank of the rear radiator to one side of the front radiator, and from the other side of the front radiator to the input to the pump on the block. The front radiator should, as a minimum, have a bleed valve on the top of the radiator to bleed off any trapped air. A better solution would be to have a small copper line going from the top of the front radiator to the top tank of the rear radiator. With this the system can bleed itself and purge itself of any potential steam pockets. There has been a lot debate about the proper diameter of the pipes leading to/from the front radiator. In my own car I have used AN-12 stainless lines for all of the flexible water connections. The internal diameter of AN lines/fittings is easy to calculate. AN uses a ratio of 16 per inch. So a AN-12 is 12/16 or 3/4 inch internal diameter or 19mm. Even accounting for some frictional loss in the pipes, I calculated that a 1 inch (25mm) tube would be more than large enough. In reality, the actual hole diameter in an open thermostat is probably less than 3/4 inch or 19mm. For a blanking plate this would be the equivalent of four 3/8 inch (10mm) holes.
E. -
Coolant level - Their should always be a small amount of air in the top tank of the rear radiator to allow for expansion. Remember that air can compress and fluid cannot. If you are driving on the street the best coolant/water mixture is between 40-50% coolant, the rest clean water. NO MORE coolant than this. The most efficient conductor of heat is pure water, but it boils easily. The worst conductor of heat is pure alcohol, but it does not boil easily. So a reasonable combination of the two is a good compromise.
F. W
ater pump - Make sure that the water pump is working properly. Most water pumps 'cavitate' above 6000 RPM. So, if you are running the motor to 8500 RPM, you must make sure that the pump is not over driven. When cavitation occurs, the impeller in the pump is turning faster than the water is capable of moving. This causes additional friction and air bubbles are produced, which are then pumped into the block. Across the inlet to the water pump the pressure is lower than the system pressure, add to this the additional heat generating friction of cavitation and the end result is steam. Not a good idea. Of course, it goes without saying that the pump should not leak. Almost any good mechanical or electronic pump can handle two radiators in series.
G.
Fan Assembly - Regardless of whether the fan is electrical or mechanical, the shroud around the fan MUST be in good condition if you expect to pull/push air through the radiator core. Without a fan shroud the fan's effectiveness is reduced by 50%. Air will go around the radiator, rather than through it.
H. Belt - The belt should be in good condition and sufficiently tight enough to not slip. Any further tightening will only decrease the life of the waterpump and the belt.
I hope this is of some help to those of you who are having cooling problems.
Paul Vanderheijden
www.scuderiatopolino.com
