THERMOSTAT AS 4N0236 - Caterpillar

All 3208, 3304, 3306 Engines Equipped With Sleeve Metering Fuel SystemsPlease put a mark through the article "Do Not Use Plastic Tubing With Brass Couplings As A Fuel Supply Line" in the September 28, 1977 Engine News on page 2, and add a note to see this article.
The use of plastic tubing and "compression fittings" without inserts as a fuel supply line on the above engines can cause air leakage into the fuel system. Air in the fuel system will cause difficult starts, rough operation, low power and too much white smoke on start-up.
In applications (usually Original Equipment Manufacturer's product) where plastic tubing and "compression fittings" are used for fuel supply lines, it has been found that the plastic tubing can hold a vacuum in the line as the temperature increases. But, as the temperature decreases, pressure decreases, and the tubing and the compression fittings become loose. Air then leaks between the fittings and the tubing and enters the fuel system.
Some manufacturer's, such as Ford Motor Company, use plastic tubing with a fitting that has a stem or insert that supports the inside of the fuel line at the connection. This is the only acceptable way to use plastic tubing for a fuel supply line.
If plastic tubing is used with compression fittings, make a replacement of the compression fitting with fittings that support the inside of the fuel line. Steel tubing or reinforced flexible hose and high pressure fittings can be used instead of the plastic tubing and compression fittings.