Indigo Electronics Atomic 4 Temperature Control System

Indigo Electronics Atomic 4 Temperature Control System

Functional Description for Fresh Water Cooling ONLY

Original Design

As originally built, the Atomic 4 engine was equipped with a cooling system that controlled temperature by utilizing a thermostatic control valve (thermostat) mounted in the head of the engine. This control valve regulated the temperature of coolant in the head by controlling the amount of coolant passing through the head. During a cold start of the engine, essentially no coolant flow occurred through the head. Instead, a bypass arrangement (from the tee fitting on the side of the engine beneath the alternator to the thermostat housing on the forward end of the head) allowed all to the coolant to go around the block until such time as the coolant in the head became hot enough to open the thermostat. This thermostat would theoretically maintain the temperature in the 140° F range by opening further and further and eventually shutting off the bypass flow altogether if necessary.

The original system presents several issues with regard to proper engine operation and temperature control.

The design concept of "no flow until the thermostat opens" does not promote uniform temperatures within the engine and tends to cause the engine to go through significant "thermal trauma" each time it is started.
The bypass mechanism is prone to deterioration in performance due to wasting away of the "control boss" machined surface within the thermostat housing. This deterioration quite often leads to overheating as too much coolant is allowed to bypass the block.
The original thermostat is designed to maintain 140° F which is much too cold for optimum operation with fresh water cooling. Westerbeke has offered a 180° F unit but to date it has not performed well.

Indigo Design

The guiding principle behind the new Indigo design is more uniform temperature within the engine. This is accomplished by passing all of the coolant through the block at all times (no bypass at all and no thermostat in the head) and controlling the temperature of the coolant leaving the block. This is accomplished by utilizing a Thermostatic Control Valve (TCV) on the suction (inlet) side of the antifreeze circulating pump. The TCV controls the flow of antifreeze from it to either 1. Recirculate hot antifreeze from the exhaust manifold to the circulating pump or 2. Divert hot antifreeze from the exhaust manifold through the heat exchanger (thus cooling the antifreeze) and then directing the cold antifreeze to the circulating pump. By mixing these two streams of antifreeze, the TCV has the ability to control the temperature of the antifreeze coming from the exhaust manifold from about 130° F to 180° F. With the engine running at 180° F, the antifreeze entering the block from the circulating pump is about 150° F.

During cold startup, the TCV recirculates all of the antifreeze coming out of the engine (exhaust manifold) leading to a very uniform and fairly rapid warm up to operating temperature. Because all of the flow is recirculated during cold startup, it is critical that the initial filling of the system with antifreeze be carried out exactly per the installation instruction. The antifreeze pump has no source of antifreeze during cold startup other than that which comes out of the engine (the TCV only wants hot antifreeze at this time because everything is cold and will therefore not take any antifreeze from the heat exchanger even though it may be full). Thus it is most critical that the engine itself be completely filled with antifreeze when first putting the system into service.

With the Indigo System, there is no need to be concerned with the condition of the thermostat housing. As long as is does not leak antifreeze to the bilge, it is fine. Also, the operating temperature is adjustable over a range of about 130° F to 180° F by simply turning the knob on the top of the TCV. For this reason, the TCV should be conveniently located to allow easy temperature adjustment on those hot summer nights when you want to get some of the heat out of the cabin prior to shutting down for the night.

A rebuild kit is available for $35 which includes all of the internal pieces of the valve. Typically, if the valve overheats beyond about 220F, it will be necessary to replace these components (thermostatic element and shuttle valve, diffuser, spring, and o-rings) to get the valve operational again.

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