So how is the Indigo RWC Thermostat different? As can be seen in the drawing to the right, the Indigo Thermostat includes both the actual thermostat, a re-circulation control valve stem and spring, and a totally separate thermostat housing. This kit utilizes a "single-action" thermostat with the additon of the re-circulation control stem and spring to provide "double action" control. However, in this case, the "double-action" aspect controls raw water that is re-circulated to the engine instead of controlling raw water that is by-passed around the block as the original thermostat does. The housing assembly can be mounted in several locations depending on your engine compartment layout. The easiest location is where the raw water exits the manifold (typically the end near the transmission but it can go on the flywheel end with a little re-routing of hoses) or on a bulkhead near the engine. With this new thermostat installed, the original one, either the "Dole" or "Holley" model is removed. In the case of the "Holley", the existing thermostat housing is reused (even with a corroded control surface) and the original bypass hose is plugged.

For a RWC engine, some new plumbing is required to properly configure the Indigo Thermostat. The first is the "re-circulation" connection. When the engine is running, a portion of the raw water flow (controlled by the re-circulation valve stem in the bottom of the housing) passes through the block, head and manifold and then back to the suction side of the raw water pump. A hose must be run from this re-circulation connection to a new tee which must be installed at the suction or inlet side of the raw water pump. The second change is that a "bypass" hose must be installed between a new tee installed at the raw water pump discharge and the Indigo Thermostat housing. The connection on the thermostat housing cannot be seen in the above drawing but it is a tapped hole with an orifice machined in that is just "behind" the outlet connection shown. This bypass provides cooling water to the exhaust system at all times to keep the exhaust system below 145°F. An Installation Hardware Package (see below) is available which provide all of the necessary fittings for making the plumbing changes described above. You will still need to provide the hoses.

Raw Water Cooled System Performance

Thermostat control in a Raw Water Cooled application is a much more complex engineering problem. The guiding criteria for thermostat control are: Exhaust temperature below 145°F at all times, Engine temperature between 145°F and 155°F, and raw water inlet to the engine (via re-circulation) above 85°F. In order to provide control over a raw water temperature range from about 55°F to 90°F (what our customers are likely to experience), the basic thermostat design parameters were established for the worst case scenario of full power (Wide Open Throttle-WOT) operation at 90°F raw water temperature. Two aspects of the RWC model make it different from the FWC model and able to accomplish these objectives: 1. There is bypass flow from the raw water pump to the exhaust system controlled by an orifice to always provide cooling water to the exhaust system 2: A 316 Stainless Steel valve stem and spring are installed below the "single action off-the-shelf" thermostat to control re-circulation flow. With the addition of this valve stem and spring, the "single action" thermostat has essentially "double action" capabilities.This combination of features allows the RWC thermostat kit to properly control engine and exhaust temperatures at all power levels, regardless of the raw water temperature. The following data shows thermostat performance at various conditions:

NOTE 1: As of this time, the above data is all that is available. It is expected that Exhaust Temperatures will be lower with lower raw water temperatures and the other readings will most likely be a few degrees cooler as well.

NOTE 2: An interesting observation was made during testing. The temperature read by the traditional "in-head" sensor (shown in above chart as "Temperature Gauge Reading") was always several degrees higher than the temperature of the actual coolant. The difference is a function of engine load and is most likely attributable to heat being transferred through the metal of the head directly to the sensor. A significant benefit of the Indigo Thermostat Kit is that it allows the traditional temperature sensor to be re-located to the coolant entrance to the new thermostat. This not only gives a more accurate indication of engine coolant temperature but it also frees up the "in-head" connection for the installation for a high temperature alarm sensor. Check out our Alarm Kit which is a great addition for peace of mind when motoring. Having each of the two temperature sensors in an active coolant flow area is a far superior installaton as compared to the common practice of installing the two in a "dead ended" tee on the head.

A Complete Retrofit Package including:

• Step-by-step instructions
• Precision cast and machined Silicon Bronze housing
• Drilled and tapped connections to:
  
  1. Mount housing on manifold.
  2. Accept re-circulation hose.
  3. Accept by-pass hose.
  4. Accept exhaust coolant hose.
• 140F Thermostat for Raw Water.
• Gaskets, housing fasteners, and existing bypass blank-off fitting included.

Installation Hardware Packages

RAW WATER COOLING - Late Model: Includes one 1/2 NPT street ell to attach thermostat housing to manifold, one 90° hose barb fitting for the thermostat re-circulation connection, one 3/8 NPT street tee for the raw water pump suction, one hose barb fitting for the re-circulation connection at the previous tee, one hose barb fitting for the bypass connection on the thermostat, one 3/8 NPT street tee for the raw water pump discharge, one hose barb fitting for the bypass connection at the previous tee, one hose barb fitting for the exhaust connection on the thermostat, and five all stainless hose clamps. No hose is provided. PRICE: $25.00

RAW WATER COOLING -Early Model: Includes one 1/2 NPT street ell to attach thermostat housing to manifold, one 90° hose barb fitting for the thermostat re-circulation connection, one 3/8 NPT street tee for the raw water pump suction, one hose barb fitting for the re-circulation connection at the previous tee, one hose barb fitting for the bypass connection on the thermostat, one 3/8 NPT street tee for the raw water pump discharge, one hose barb fitting for the bypass connection at the previous tee, one hose barb fitting for the exhaust connection on the thermostat, and five all stainless hose clamps. No hose is provided. PRICE: $29.00

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