The GMC 6.5 Turbo refers to a line of engines made by General Motors for pickup trucks they made starting in 1982. These lines of trucks were used primarily for hauling and towing. The engine was a V-8 Diesel. The turbocharged engine allowed for increased torque output. This is a common way for manufacturers to add power to a diesel engine while keeping the costs of production down. The turbo recycles exhaust gases back through the turbocharger and then back into the engine to generate more power than would ordinarily be available from the engine. Over time, these 6.5 L Turbo engines made by GM would fail due to common and persistent problems with the engine design. Before having your engine fixed, troubleshoot the problem.
Check the main bearing or have it checked for you. The main bearing webbing is notorious for cracking in the 6.5L Turbo engine. Although newer engine designs made after 2007 have an improved higher nickel cast iron alloy and lower block redesign, the 1998 model year had no such improvements. Have this problem serviced by a professional mechanic with extensive knowledge about the GM diesel engine.
Check to see if your engine starts and runs normally. The GMC 6.5L Turbo suffered from premature crankshaft failure. You'll know if your crankshaft fails because your engine won't run. This is one of the main causes of engine failure on these particular engines. The harmonic balancer that is supposed to prevent this problem doesn't do its job very well and fails prematurely itself. Once your crankshaft breaks, have your engine overhauled by a professional engine rebuilder.
Check for rough idle and fuel pump related problems. If your 6.5L Turbo GMC is having trouble running smoothly, it may be due to the faulty pump driver installed on this engine. The pump driver is installed from the factory in a high heat area (the intake valley). The driver can be relocated by a professional mechanic to a low heat area so that the pump does not fail. However, if the driver does fail, you'll need to have this, and the fuel system checked and serviced.
