Silicone hoses are made with a liner layer to create a smooth inner surface for whatever media is passing through it. Which liner is right for your application will come down to what fluid will come in contact with the inside of the hose, as well as, what temperature your hose will need to perform at. For automotive and equipment applications there are a handful of different liners available, but we will discuss the 4 most commonly used.
Most silicone hoses simply use a similar silicone rubber compound for the inner liner as is used for the rest of the hose. Silicone rubber is a very versatile compound that is tough and resistant to many chemicals. It is the most cost-effective, while still being durable and having a high temperature resistance. It is great for air and Ethylene-Glycol coolants, but oil, fuel, and OAT coolants will degrade it. Therefore, regular silicone should not be used for crankcase ventilation or PCV systems, fuel systems, or oil lines. Even turbo systems with heavy oil blow-by can expose the silicone couplers to enough to oil to degrade them.
Flourosilicone is a modified silicone compound that is designed to resist oil and fuel vapor while still being able to handle high temperatures of up to 450 degrees F. When used as liner it can drastically increases the lifespan of a silicone hose that is exposed to fuel and oil. It is more expensive, so it is uncommon to see this liner on most hoses. Typically, this liner is only offered on specialty hoses but can be added to any custom hoses.
Fluorocarbon (FKM) Liners (also known as Viton) take the oil and fuel resistance even higher while also handling very high temperatures of over 900 degrees F. This is a very specialized liner material and it is the most expensive. Its applications are very specific and uncommon, but it can be offered on any custom hoses.
For OAT coolants, we work with a manufacturer that produces a proprietary liner specifically meant to handle the high acidity of OAT coolants. It maintains its high temperature resistance of 450 degrees F, but it is more expensive than the regular silicone liners. The added cost will pay for itself from the increased life you will get out of the hose. This is not offered on any of our standard hoses, but can be made into any hose on request.