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6.5L Diesel Engine Discuss the 6.5 GM diesel engine & associated components. Automatic transmission questions & problems belong in the 4L80/85 - 4L60E - 6L90 Transmission Forum

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Old 03-23-2020, 12:05 AM   #1 (permalink)
asm225
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Disappearing coolant

My 1996 6.5 turbo diesel has always mysteriously disappeared coolant. My truck currently has 420,000 miles on it and I drive cross-country regularly.

It has a new all aluminum radiator, new water pump, and all new coolant hoses. There is no puddling under the truck, and I cannot spot any leaks. There is no coolant in the oil and no bubbling in the coolant reservoir.

However, it disappears a gallon of coolant between fill-ups (5-6 hours on the interstate).

Please help and send suggestions!?

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Old 03-23-2020, 01:16 AM   #2 (permalink)
MojaveMuse
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maybe the cap isn't seating right allowing the coolant to boil off and escape?

you already said no milkshake or drips. are you smelling coolant at all when you walk in front of the truck when warm?

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Old 03-23-2020, 02:00 AM   #3 (permalink)
asm225
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Quote:
Originally Posted by MojaveMuse View Post
maybe the cap isn't seating right allowing the coolant to boil off and escape?

you already said no milkshake or drips. are you smelling coolant at all when you walk in front of the truck when warm?
The cap is seating properly and is only a few years old. I do not smell any coolant. And that would be a lot of coolant to evaporate. The thermostats are new also, 190
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1994 EC 6.5L stock Dually
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Old 03-23-2020, 02:02 AM   #4 (permalink)
asm225
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At this point, I mostly fill with water, but I have noticed orange dexcool drips on the transmission pan and rust around the starter. All freeze plugs are visually intact
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1994 EC 6.5L stock Dually
1996 EC 6.5 GMC C2500 Kojo tune on stock vacuum controlled turbo actuator, Bosch boost gauge with Glowshift Boost Bolt, 409K miles on stock engine, smokes like a steam boat since I purchased with 300k miles. Still running
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Old 03-23-2020, 02:03 AM   #5 (permalink)
asm225
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Is it possible to have water leaking around the intake gaskets?
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Old 03-23-2020, 07:46 AM   #6 (permalink)
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With nothing on the ground and your loosing coolant I’d pull the oil pan and pressurize the cooling system.Then get under the truck and see if coolant is dripping while the system is under pressure.The 506 engine block would develop hair line cracks from the oil jet orifices under the upper main bearing and would spread to the cylinder walls.I don’t mean to alarm you but it’s just something to keep in mind if no leaks are present externally.
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1996 Chevy K1500 Z71.....with '99 6.5 506 goodwrench van engine,88-93 6.2 diesel Napa y-pipe,'87 700R4,acdelco TP630F/Racor 20S fuel filter setup,Bosch non-turbo injectors,stanadyne blue tag 5088

1993 Chevy K1500 Z71...with 97' 6.5 TD 506 block,82' 6.2 rocker arms,stanadyne injectors,stanadyne blue tag 4911,DSG girdle,reman 89 700R4,Banks boost/pyrometer gauges,acdelco TP1069/TP943 fuel filter setup,4 diamond eye exhaust/2 piece crossover

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2013 Volkswagen Passat 2.0 TDI

Last edited by dieselolds; 03-23-2020 at 07:46 AM.
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Old 03-23-2020, 01:05 PM   #7 (permalink)
asm225
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Quote:
Originally Posted by dieselolds View Post
With nothing on the ground and your loosing coolant I’d pull the oil pan and pressurize the cooling system.Then get under the truck and see if coolant is dripping while the system is under pressure.The 506 engine block would develop hair line cracks from the oil jet orifices under the upper main bearing and would spread to the cylinder walls.I don’t mean to alarm you but it’s just something to keep in mind if no leaks are present externally.
Would that cause water in the oil?
I'll give it a shot when I get back home.
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1994 EC 6.5L stock Dually
1996 EC 6.5 GMC C2500 Kojo tune on stock vacuum controlled turbo actuator, Bosch boost gauge with Glowshift Boost Bolt, 409K miles on stock engine, smokes like a steam boat since I purchased with 300k miles. Still running
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Old 03-23-2020, 03:34 PM   #8 (permalink)
mp06011999
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Is the 6.5 like the LBZ where the tranny fluid runs thru lines in the coolant flooded cooler? And thus, if there's a seal issue, coolant could be getting into the tranny?
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Old 03-23-2020, 06:09 PM   #9 (permalink)
JMJNet
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Check the coolant crossover quick connect on top of the engine.
That crossover is famous for leaking without notice and just show white powdery coolant residue.

Moral of the story, that leak will never shows up on the floor because it is so high and will evaporate in a few seconds.
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Old 03-23-2020, 08:48 PM   #10 (permalink)
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