Diesel World – October 2019

(Jacob Rumans) #1

Q&A| DIESELWORLDMAGAZINE BYJIMBIGLEY Q&A


IN TOUCH
I’m the original owner of a 1998 6.5L 3500 truck
with 410,000 miles. That’s a lot of experience with
this truck, so I can hear or feel everything. Over the
years my transmission has been revving out of gear
while on the highway. It’s usually fixed by discon-
necting both batteries for five minutes to reset the
computer controls. If it happens again, I have my
batteries tested. A bad battery is usually the cause.
Another issue involved my radiator thermostat
running my truck too cool. A new thermostat fixed
it. Now it drops out of overdrive randomly and then
goes back in. My batteries are good—I’ve done the
disconnect trick. My thermostat has me running at
a good temp. I know it’s got 410k miles, but could
it be the transmission module? I’m open to any
suggestions. Thanks, John Williamson

Hi John, Two things you can do today:


  1. Have the trouble codes read, and then let
    me know what codes (if any) are being set.

  2. Service the transmission if it's been a
    while—say more than 50,000 miles since
    the last fluid and filter change. Look for
    a more than normal amount of sediment
    or metallic/friction disc particles in the
    transmission oil pan. There will be some,
    but the amount is the issue. If you’re in
    doubt about what amount of sediment
    might be normal or abnormal, send me a
    photo if you can.
    If your transmission oil pan still has the
    original factory gasket, don't throw it away
    because it's reusable, and it is much-much
    better than the gaskets used by the after-
    market or nearly any mechanic's garage.
    Let me know what develops.


HEAD GASKET FAIL
If you recall I have talked to you about R&Ring my
1993 6.5L engine for a rebuild or simply replac-
ing it with the ’96/’97 engine that I bought from
a guy in Portland. I removed the heads from my
original ’93 engine to send to the machine shop
to be tested for cracks. We could not see any
obvious head gasket failure, but that might not be
definitive. The quoted price for a complete rebuild
of my cylinder heads is so high that I want to go
ahead and install the newer engine in my truck. In
looking at the ’96/’97 engine, it does not appear
to use the dual thermostat and high-output water
pump modification that I have on the ’93 engine,
so I want to switch those parts over to the ’96/’97
engine. I also want to install a new timing set and
roll in a set of rod and main bearings.  What I have
been able to determine is that there are differences
between the ’96 and ’97 year engines. Is there a
way to tell for sure which version that I have? The

only casting numbers that I see on the back of the
block are 10237141 and J215.  I would hate to
order the wrong parts. Any suggestion would be
very helpful. Cheers, B.J. King

Hi B.J., The four-digit J215 date code
decodes to July 21, 1995, so it’s an engine
likely installed in an early 1996 model
year vehicle. The seven-digit block casting
number of 10237141 also indicates a mid
1990s GM casting—not the best, but also
not the worst of the GM castings. If it is
crack-free, I’d consider it fit for any duty
for which these engines were designed.
The GM 6.5L diesel main/rod bearings
almost never wear out if the engine was
reasonably maintained. I would not mess
with the bearings unless there's a good
reason to do so. These engines utilized
“select-fit” main and rod bearings, mean-
ing there could be slight variations in sizes
of bearings to produce the factory-spec-
ified clearances. This requires a careful
measurement of the rod and main journals
and casting bores to know for certain what
size bearings to use. I would, however, look
for main web cracks in the block. These
cracks, if they are present, will emanate
from a main cap bolt hole (center 3 mains)
and extend upward toward a cylinder—the
worst cracks can sometimes reach a water
jacket or cause a main web failure.
Look for head cracks in the space between
the valves that sometimes appear in the
end cylinders of each head. If you can't
find any cracks, I'd just clean the cylinder
heads, prep the deck surfaces using 80-
grit wet/dry paper on a flat sanding block,
and then reinstall them.
Incidentally, your original 1993 engine’s
seven-digit casting number should end
with the numbers “599.” If yours does,
know that that could be the best cylinder
block GM produced, because it has the
lowest incidence of cracking.

GASKET LEAKS
I’ve recently read about head gasket leaks. This
led me to the conclusion that my Duramax had all
the common symptoms.
I have the heads off now, but I am not enough
of a diagnostician to determine where or if the
gasket is leaking. I can see a gasket break on the
left bank, but the right bank had water filled in the
exhaust manifold, so water ran out when I loosened
the three-bolt flange bolting the manifold to the riser
pipe on the RHS. I could not tell if there was a leak
on the right side head gasket. Anyway, have you
heard of the CO or carbon dioxide test for radiators

138 OCTOBER I 2019 • DIESEL WORLD http://www.dieselworldmag.com

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