Frequently Asked Questions - FAQs

Q: You seem to offer nothing but "high temperature" thermostats but I like to run my engine cool. Where can I get a "cooler thermosat"?

A: Running your A4 below 140F is really a bad idea. The lower the engine temperature, the more trouble the engine has with the combustion process. The fuel does not vaporize as well and the resulting air/fuel mixture is harder to ignite and once ignited, burns less completely. This shows up as fluffy carbon deposits within the combustion chamber and on spark plugs. Additonally, unburned fuel collects around the piston on top of the uppermost piston ring. This excess fuel can wash away lubricating oil on the cylinder walls and lead to stuck rings. There is really no good reason to run any internal combustion engine below 140F.

Q: My engine overheats and I know my pump impeller is OK and I have plenty of water coming out of the exhaust. Is my thermostat broken?

A: Possibly, but more likely the thermostat housing on top of the thermostat is very corroded. This is a very common problem. There is a "control surface" in the housing that is supposed to allow the thermostat to close off some or all of the water which bypasses the engine. If the thermostat cannot reduce the bypass flow then there is not sufficient coolant flowing through the engine to control the temperature.

Q: I see a lot of comments about putting a valve in the traditional bypass hose between the water inlet to the engine and the original thermostat housing to control engine temperature. Is this a good idea?

A: Not really. It is kind of an interim step. By manually controlling the bypass flow, you can indeed control engine temperature. However, you have to be sure to keep the valve open sufficiently during start up in order to provide adequate flow through the manifold and exahust system. Also, as engine load and raw water temperatures change, the valve will have to be adjusted.

Q: I am going to convert to FWC. Can I use the same Indigo Thermostat with FWC?

A: Yes with just two minor changes. First, you will need to eliminate the bypass hose that goes from the raw water pump discharge to the Indigo Thermostat housing. You can simply install a 1/4" NPT pipe plug in the housing. Secondly, you will need to purchase a new 180F thermostat from NAPA, Part No. THM138. They cost about $10.

Q: What makes the Indigo Thermostat Kit different from what I already have? My current thermostat seems to control the temperature just fine.

A: First, replacement thermostats are about $10 for the FWC version and about $17 for the Raw Water version. Second, the Indigo Thermostat housing is cast from Silicon Bronze and will not corrode and deteriorate like the current thermostat housing. Third, the recirculation feature on the Indigo Thermostat is like that found on most modern automobiles and does a much better job of reducing the temperature differences in the engine coolant from entrance to exit. Your current thermostat may make the engine temperature gauge read 140F but all it is doing is making sure the water leaving the engine is 140F. A good part of the rest of your engine is much cooler, down near the ambient raw water temperature. Specifically, the areas back about cylinders 3 and 4 (the cylinders away from the flywheel) stay much colder than the other parts of the engine. That is where the re-circulation feature comes into play because it helps keep the traditionally cold areas considerably warmer.

Q: Where do I mount/attach the Indigo Thermostat?

A: The easiest installation, depending on your engine compartment, is to mount the Indigo Thermostat housing on a 1/2" x 6" long pipe nipple threaded into the right angle pipe fitting currently mounted on the transmission end of the manifold. This is where the engine coolant currently exits the engine. Unless you manifold is really rotten, it can easily support the weight of the new housing mounted on the nipple. If you prefer, the new thermostat housing can be mounted on the flywheel end of the manifold. Currently, coolant from the original thermostat housing enters the manifold here. In order to perform this installation, you will have to install a longer hose from the existing thermostat housing to the transmission end of the manifold and introduce the coolant into the manifold there. You can then install a right angle pipe fitting in the flywheel end of the manifold and mount the new Indigo Thermostat housing on a shorter 1/2" nipple. Yet another option is to mount the Indigo Thermostat Housing on a vertical surface near the engine and run hoses to and from it. Mounting brackets are available.

Q:You say the Indigo Thermostat kit utilizes readily available thermostats. What are the Part Numbers for the thermostats?

A: The thermostats are available at NAPA Auto Parts Stores. For Fresh Water Cooling, the 160F thermostat is Part No. THM38. The 180F thermostat is Part No. THM138. For Raw Water Cooling, the only thermostat is a 140F model and it is Part No. SME18-3551

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