1994 Chevy 3500 Dually 6.5 litre turbo deisel.

Greetings,

Depending on how bad your symptoms are (power loss and overheating), I would have the fuel injection pump checked out - especially the fuel solenoid driver (FSD, aka the pump mounted driver or PMD) if you have the DS4 fuel injection pump (if you have the earlier all-mechanical DB2 FI pump then you won't have an FSD). A dying FSD will cause power loss and will only get worse over time to the point where your motor won't run. If you don't catch a failing FSD quickly enough it will take out the optical sensor inside the FI pump as well, and at that point you will need an entirely new FI pump to the tune of around $1800.00. If this turns out to be your problem, then I would suggest you remote-mount the FSD off the FI pump and onto a unit called an FSD Cooler to help head-off this problem from reoccuring. Heat transfer from the FSD to the FI pump body was the biggest killer of these units, and is aggrevated by heavy hauling and increased heat loads. Regardless of whether you have the DS4 or DB2 FI pump, the FI pump s always a good place to start looking on these motors.

There are a few things that you can do to help with your situation that are not FI pump related. The very first is to retrofit the cooling system with the newer style water pump and dual-thermostat set-up with crossover that GM went to back in '97 or '98. This was in response to an overheating issue that caused burn-through of the head gasket for the rear-most cylinders. This is a distinct danger for earlier 6.5's that are used for heavy hauling or towing. The new pump and waterways increased coolant flow and decreased engine temps to eliminate the problem.

The second item is an aftermarket downpipe from the turbo exhaust. The stock downpipe has restrictions at the bends which causes increased backpressure (and increased exhaust gas temps, or EGT). A mandrel bent downpipe with radius bends will greatly reduce backpressure and reduce EGT's which will help your motor under load.

The third item is an intercooler. An intercooler reduces the temp of the air coming out of the turbocharger making it more dense before it goes into the cylinders. While this doesn't help reduce operating temps for the motor under load, it does pack more air into the cylinders which increases performance by improving combustion. If you add an intercooler, you will also need to increase turbo boost, but a chip should help with that. Any company that makes the aftermarket intercooler will also have recommendations for other performance mods to get the most out of their product and your motor in general.

There are also some basic items you need to check, like the fan clutch, quality of the antifreeze in the radiator, and that the radiator is clean both inside and out for the best heat transfer. These are basic maintenance items.

The 6.5L turbo diesel wasn't the most competitive motor when it came to towing, and your '94 probably has plenty of use on it. I suspect that it's going to take more than one thing to help improve things, and unfortunately nothing that is going to help you much is going to be cheap, especially on an 11-year old motor.

Good luck- Jonathan