Introduction to Zetec Cooling Systems

Introduction

There is plenty of noise, on the Internet, describing apparent overcooling of Zetec engines fitted to Westfield’s.  Most of it is supported by experience of road use and the visual observation of the engine temperature gauge in both winter and summer driving. Verbal reports and e-mail postings describe engine temperatures struggling to reach an operating temperature of 80 °C.  Remedies include fitting radiator blinds, used during winter and summer, to re-plumbing the coolant system with a variety of “Tee” pieces to re-route the coolant system similar to Zetec engines used in Mondeo’s.  

The purpose of this paper is clarify, the apparent overcooling syndrome, and the variety of remedies implemented by owners, The paper provides information on the cooling system as used on the Ford Mondeo, and as implemented, by Westfield Sports Cars, with Ford approval.  EM Engineering has a Westfield SEiW 2.0L Zetec with a modified cooling system and this will be used as an example of owner implemented alterations. The modifications are not track tested and are for road use only. 

Ford Mondeo Thermostat Bypass Pipe

It is the pipe work of the Ford Mondeo cooling system that is the most interesting to Westfield owners. The first point to note is pipe number 17.  This is a metal pipe, of approximately 16mm diameter, which runs between the bottom hose, number 20, in the diagram, and the thermostat housing, numbered 19, in the diagram. This provides a path for coolant circulation prior to the opening of the thermostat. This assists engine and heater warm up.

Secondly the expansion tank, 3, main connection is connected via a relatively large bore hose to the radiator bottom hose, 20. The overflow connection is routed via a rubber hose, 21, and rubber hose, 14, to the top connection on the thermostat housing, 19.  The Radiator top hose, 16, is connected to the main outlet of the thermostat housing, 19. The Radiator bottom hose, 20, connects between the Water pump (not shown) and the Radiator, 1.

All Mondeo’s employ a pressurised cooling system with thermostatically controlled coolant circulation. A water pump mounted on the drive belt end of the engine, pumps coolant through the engine. Internal passages pass coolant around each cylinder, the inlet and exhaust ports, near the spark plugs and exhaust valve guides.

A wax pellet type thermostat is located at the transmission end of the engine, in a housing at the top the engine. During warm up the thermostat is closed preventing coolant circulation via the radiator. Instead, coolant is returned from the thermostat housing, thermostat bypass, via a metal pipe across the front of the engine to the radiator bottom hose and the water pump. The supply of coolant to the heater is made from the rear of the thermostat housing. As the engine nears normal temperature, at 88 °C, the thermostat starts to open and allows hot coolant to travel via the radiator, where it is cooled by airflow through the radiator, before returning to the engine via the bottom hose and the water pump.  As the thermostat opens to allow coolant to flow through the radiator it correspondingly closes the port to the bypass cutting off the flow through the bypass.

A pressure type filler cap, in the expansion tank, seals the cooling system. Operating at about 1.2 bars, the pressure in the system raises the boiling point of the coolant and increases the cooling efficiency of the radiator.  When the engine is at normal operating temperature the coolant expands and the surplus is displaced into the expansion tank. When the system cools the surplus coolant is automatically drawn back from the tank in to the radiator.

Under high temperature conditions, such as slow or stationary traffic in hot weather, cooling airflow is maintained through the radiator by a cooling fan. The cooling fan is operated by the ECU receiving coolant temperature information from a sensor in the thermostat housing. The fan may be either single or two speeds.

The Westfield Cooling System

Ford approves the Westfield cooling system. Any alterations undertaken by the owner may invalidate the warranty. The Westfield Zetec Cooling installation is characterised by the connection of the thermostat bypass via a rubber hose, to the main pipe joining the thermostat outlet and the radiator top hose. This provides coolant via the radiator regardless of the position of the thermostat.  The Westfield system is complicated by the detail changes of, ducted and non-ducted nose installations.  The following schematic diagrams show how the system is connected.

Non-Ducted Nose

The schematic diagrams below are largely, self-explanatory. 

Non-Ducted Nose Operational theory

In the non-ducted nose cooling system the coolant pump circulates coolant through the standard internal passages in the Zetec engine block.  With the thermostat closed coolant continues to flow via the thermostat bypass, the radiator top hose, to the radiator, where it is cooled by airflow through the radiator. Coolant returns via the bottom hose and the water pump to the engine.  On reaching operating temperature the thermostat opens and provides the main flow of coolant to the radiator, increasing the volume of coolant and superseding that being provided via the thermostat bypass.   In low air flow conditions, such as heavy slow moving, or stationary traffic, additional cooling air is provided by a thermostatically controlled fan. The fan switch is mounted in the alloy pipe connecting the thermostat housing to the radiator top hose, adjacent to the thermostat outlet. The fan switch sensor samples coolant temperature.  Two types of switch are provided “Red Top”, Ford FINIS No: 7001614  (88 - 77 °C) used on engines fitted with Carburettors and “Orange Top”, Ford FINIS No: 7001611 (106 – 92 °C) used in Fuel injected cars with a catalytic converter.  In high temperature conditions the fan switches on providing additional cooling air through the radiator until the coolant temperature falls below the switch off point.

Ducted Nose

There are detail differences between non-ducted and ducted nose installations. The non-ducted nose can be removed leaving the radiator and associated cooling pipe in place. In the ducted nose installation the radiator, cooling fan and associated ducting are mounted on the nose cone. Removal of he nose cone necessitates draining the cooling system.
 

Diagram 51 Courtesy of Westfield Sports Cars	Diagram 52 Courtesy of Westfield Sports Cars
(Click on the diagram or here for a full size picture).	(Click on the diagram or here for a full size picture).
Like the non-ducted nose, the thermostat bypass is connected to the radiator top hose. However the radiator cooling fan switch is repositioned in to the radiator.  Additional pipe work is provided to connect the expansion tank overflow to the radiator top hose. See diagram above.	The diagram above shows the ducted nose radiator top hose connections. Note the small bore pipe provided to connect the expansion tank overflow to the radiator. This feature was not incorporated in to the non-ducted nose.
	Ducted Nose Diagram 53, (left) completes the picture, showing expansion tank and heater connections.  In the ducted nose, the header / expansion tank overflow is connected to a “tee” piece and then to the thermostat housing and the radiator top hose. The Westfield expansion tank is considerably smaller than the one fitted to the Mondeo.
Diagram 53 Courtesy of Westfield Sports Cars	(Click on the diagram or here for a full size picture)

Ducted Nose Operational Theory

Since there are only detail differences between them, the theory of operation should be the same as the non-ducted nose. Greater cooling is achieved by ducting hot air out from the radiator to the exterior of the car, rather than exhausting it in to the engine bay as with the non-ducted nose installation. 

Operational Performance

The Standard installation for the Zetec engine is routinely the subject of reports of low operating temperatures from both non-ducted and ducted nose installations. This manifests itself in reports of the engine never getting to operating temperature on a cold day (often not achieving a temperature greater than 50˚C) except in a traffic jam. Even in summer the reports continue with, “The engine is slow to warm-up and often fails to reach 65 – 70 ˚C”.  The cause would seem to be that by connecting the thermostat bypass to the radiator top hose, the Westfield system is too efficient. The Most common remedy amongst customers, to reduce the efficiency of the system, and increase operating temperatures is with some form of radiator blank or blind, to restrict the cooling air passing through the radiator.  Many Westfield customers find that to achieve anything like normal operating temperatures of 80+ °C the blind must be used winter and summer.   The implication of this is that, in normal use, the thermostat rarely opens and the majority of the cooling is taking place via the thermostat bypass pipe.

Chart, Courtesy of Steve Richards

The situation is illustrated by the graph (left) of an 1800 Speed Sport, ducted nose car. The graph shows, temperature / time of a test, conducted on a customers, stationary, vehicle in still air, and an ambient air temperature of 16 ˚C.  It took 6 minutes for the temperature gauge to register a minimum 40 °C, 17 minutes to reach 88°C and 24 minutes for the fan to come on. Following on with a 5-mile drive the temperature settled to a stable 70 °C.   The blue line shows temperature indicated by the VDO temperature gauge and the Red line temperatures as reported by a Laptop PC.  There is a considerable discrepancy between the temperatures recorded on the gauge and the Laptop.  Subsequent tests have shown that the gauge is accurate

Whilst radiator blinds may have been acceptable in the 1950’s, they are not acceptable on a modern day sports car, doing little to enhance its image.  This is why customers have adopted alternative solutions. Most of these are modelled on the Ford Mondeo cooling system and involves re-routing the thermostat bypass

Increasing the Operating Temperature.

The task is to increase the operating temperature, by reducing the cooling efficiency of the Westfield, using a standard, well engineered, solution. Using the Ford Mondeo as a standard, the most significant difference is the routing of the thermostat bypass. The Westfield cooling system installation connects the thermostat bypass to the radiator top hose; the Ford Mondeo connects the thermostat bypass to the bottom hose. The Westfield system increases cooling efficiency, by sending a supply of coolant via the radiator irrespective of the thermostat position. With the thermostat closed the thermostat bypass simply acts as a restrictor in the flow of coolant to the radiator.  In worst case, low ambient temperature, it is possible that sufficient coolant will flow via the bypass and the radiator, that the engine will never reach thermostat-opening temperature. By contrast the Ford Mondeo system splits the coolant circuit in to primary and main coolant circuits The primary circuit, via the thermostat bypass to the bottom hose, assists warm up and coolant circulation until the thermostat opens. Once the thermostat opens, coolant flows via the radiator. Opening the thermostat correspondingly closes the thermostat bypass. The engine temperature is then controlled  by the thermostat via the radiator.  Emulating the Mondeo would reduce the efficiency of the Westfield system and provide a solution stop the overcooling syndrome. However increasing the operating temperature will cause increased coolant expansion.  The smaller size of the Westfield expansion tank is a potential problem. 

There are other minor differences between the Westfield and Mondeo installations but these will have little effect on the overall operation of the engine.  The Westfield shares the heater feed with the expansion tank. These are separate in the Mondeo.  The Westfield build manual (certainly for the 1800Q) wrongly indicates heater inlet and outlet.  The heater inlet is fed from the back of the thermostat housing and the outlet is shared with the expansion tank. This is probably a drawing error with no operational effect. 

The Mondeo and the non-ducted nose installation connect the expansion tank overflow to the top of the thermostat housing. The ducted nose installation also connects the overflow via a “Tee “ piece to the top hose of the radiator. This would have a beneficial effect on hot coolant expansion in to the tank by providing a bleed path via the radiator thus and reducing coolant expansion.