Refer to the download link below to obtain a manual for your 2002 Dodge Ram 1500 pickup. Actually I posted two links; one link is for a downloadable factory service manual and the other link is for an aftermarket repair manual. 

Link For Service Manual

Link For Repair Manual

The service manual was produced by the Chrysler company primarily for use by Dodge and Chrysler dealers and their qualified mechanics. There is a lot of technical jargon in the service manual because it is assumed that anyone who uses the book of instructions to perform maintenance, repair and overhaul already has a advanced understanding of mechanical ideas and the procedures of Dodge Ram repair. 

If you’re a novice mechanic then consider getting the repair manual. The Dodge Ram repair manual is a book with instructions written in laymen’s terms on how to keep the Ram pickup working problem. It contains much of the same repair instructions as the factory service manual but written in easy-to-understand directions. Actually, if you’re a novice mechanic then consider getting both manuals if you plan to overhaul something complicated like the engine or transmission. 

In your case, both manuals should have a cooling system description, flow chart diagrams, diagnosis and testing guide, refiling coolant procedures, step-by-step draining procedures, part removal and specifications. 

Anyway, if your Ram 1500 temperature gauge is reading high then be sure to check the coolant reserve in the radiator and overflow tank. Make sure the. Pressure cap is tight and that the cap seals are not leaking. Make sure you have the correct coolant concentration and that coolant is flowing through the radiator cores as it could be corroded. Also make sure the Radiator or A/C condenser fins are not clogged or dirty. 

Make sure you have sufficient motor oil and be sure the cylinder head gasket is not leaking. A lot of other problems can cause your 2002 Dodge Ram 1500 temperature gauge to read high.