This is an in-depth analysis of why a cheap pattern-part Heater Control failed after a few months normal use. I’ve returned to the subject of Ford heater control valves (HCV) because it’s an important topic and one that affects several Ford models sold in the UK, Europe and in the US. Earlier this year I made several ‘how to’ videos on how to replace your Fiesta, Ka, or Puma heater control valve which are well known to fail in the closed position so no cabin heat or open position (full heat). There have been incidents where HCV failure has also been put down to fragments of the unit breaking up and clogging the cooling system but the common reason for HCV faults is seal failure which causes either coolant leak from unit ‘tell-tale’ hole or simple reluctance to work due to coolant leaking past seals into the solenoid and either corroding it solid or affecting ability for the coil to provide the magnetic field needed to move the plunger open or shut. Older HCV’s were sealed so even if it failed the coolant would stay in the system. Later units have a small hole which allows coolant to flow out if the seals have let go – which is what happened to my Fiesta a few months ago. This was the second HCV (bought from an online auction site for £14). In hindsight I should have bought a Ford or equivilent OEM part as the pattern-part was cheaply made. As you will see from this video the quality of the materials for the seals is dubious and the design is such that the main circular gasket or diaphragm incorporates a very thin extruded seal which wraps around the plunger stem. This almost paper-thin rubber has torn thus allowing pressurised hot coolant to flow into the solenoid body and out the drain hole. This hole is large enough to almost empty the car’s coolant tank in less than 3 miles. I only discovered it after suddenly smelling hot coolant inside the car while driving. Luckily I managed to top it up and limp home. The basic Fiesta doesn’t have a temperature gauge but it does have an engine overheat warning light. Luckily this didn’t come on as I spotted the leak in time. Incidentally this HCV is also used in the Mk I Ford Ka, the Puma and certain Fiesta models. My Fiesta was a 1999 1.3 Endura-E OHV unit. Several Ford based forums including the Honest John forum mention the HCV causing overheating. This is either down to the leaking problem I just described or it’s due to pieces of the valve or unit breaking off and clogging up the narrow radiator, matrix, or cylinder head coolant passages. In normal operation when the HCV is closed such as during the summer months, coolant doesn’t flow around the heater matrix. Because the system is in parallel the flow around the engine and radiator isn’t affected. When some owners have reported their heater has failed and the car has overheated, there are usually other issues with the cooling system such as; 1)Too low a coolant level caused by bad maintenance, or leak from HCV or other component of the cooling system. 2)Incorrect antifreeze concentration or system being filled with normal water, 3)Severe rust and limescale build up – especially in the iron block/head OHV Endura- E engine 4)Thermostat failure. 5)Hose collapse on low pressure side of the pump caused by old soft hoses. 6)Engine cooling fan failure. Normally spotted when stuck in traffic 7)Pump falt – impeller worn out due to cavitation, plasic impeller separating from shaft, pump drive belt snapping or slipping. When my car’s original HCV failed in the closed position, the car operated normally but the heater didn’t work. There was no overheating because the rest of the system was in good condition. Don’t underestimate how little it takes to clog up a cooling system. Think of it a bit like your kettle at home. Even a thin layer of limescale will reduce heat transfer from head and block to the water. Add some rust and and low antifreeze concentration and you can see why engines can overheat. Antifreeze not only protects against freezing but also from boiling. If coolant boils it produces air bubbles and vapour which leads to airlocks, lack of heat transfer and localised thermal stress – especially around cylinder head. Antifreeze also inhibits corrosion, helps lube the water pump seals. If you mix your own coolant, use de-ionised or soft water – never tap water except in an emergency – and aim for a 50:50 ratio of antifreeze to water. You can buy de-ionised water from retailers that sell car batteries. Halfords sell five litre containers of de-ionised water. They also sell ready mixed antifreeze/summercoolant so check your car handbook to see what type your’s needs. Most Fords need the long life red coolant. Dont mix red with the old blue or green antifreeze. It will gel up and cause flow and cooling problems. Anyway, thanks for watching and reading this, drop me a message or a comment, rate, and subscribe for more car related videos.
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