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
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
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