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Discussion Starter #1
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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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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Discussion Starter #3
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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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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Is it possible to have water leaking around the intake gaskets?
 

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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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Discussion Starter #7
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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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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Would that cause water in the oil?
I'll give it a shot when I get back home.
It would cause coolant to mix with the oil in the oil pan.How does the oil look?Is it way over full?
 
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Discussion Starter #12 (Edited)
I have already replaced the quick connect, and it is not leaking now. My oil level never goes up, I usually add a quart every time I fill up my truck and it has never had any milk ish looking color. I actually changed my oil Friday and it looked fine, just black as usual. I'm wondering if my heater core could possibly be leaking. Also, there is no coolant in my transmission fluid. I just did a flush Friday as well.

Thanks for the ideas, keep them coming!
 

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You just have to trace all the coolant lines to make sure that they are not leaking with a good flash light.

The leaks can evaporate very fast, so if there is a leak, you probably can see a big glob of white/coolant colored powder.
 
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You just have to trace all the coolant lines to make sure that they are not leaking with a good flash light.

The leaks can evaporate very fast, so if there is a leak, you probably can see a big glob of white/coolant colored powder.
I don't think it is any of my lines. They are all new and have not been leaking since installed. I will look over everything again when I get home. Is there any dye that I can put in my coolant?

this is a very big leak, I am adding a gallon of water every 5 hours of drive time...
 

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At the hose coming out of the expansion tank near the radiator cap, (should be about am 8" section that will drain down the inner wheelwell.... put a small container (odwalla bottle or water bottle etc) around the drain hose. Drive it, when you are done with your drive, hop out and check it, if there is water in there then it is coming out the cap/overpressurizing/weak cap. It can be pretty hard to spot the evidence without catching it red handed like this.

If it is managing to burn that much water without pushing it somewhere else then I would think cracked head mostly behind an intake valve?
 
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I don't think it is any of my lines. They are all new and have not been leaking since installed. I will look over everything again when I get home. Is there any dye that I can put in my coolant?

this is a very big leak, I am adding a gallon of water every 5 hours of drive time...
Does your upper rad hose stiffen up after starting? Sorry if it's already been mentioned, or you've done it...
 
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Discussion Starter #17
I will check the radiator hose pressure and the overflow after my next stop. I did notice some coolant dripping down through the transmission inspection cover and some coolant splatter on my transmission pan.
 

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I will check the radiator hose pressure and the overflow after my next stop. I did notice some coolant dripping down through the transmission inspection cover and some coolant splatter on my transmission pan.
Smoking gun.

Check the rear block off plates at the rear of the engine; adjacent to fuel filter manager

Check the coolant crossover quick connect VERY carefully. Once it gets hot any leakage there evaporates quickly. Check for residue. Also check AFTER its cooled down. When it will become visible. During the cool down period.

If its neither one of those then its surely a failed head gasket. Either beginning to fail/slight leak on the deck area/seam
 

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Did you replace the quick connect with another quick connect? or Barb and hose?

When I replaced the quick connect with another quick connect, for some reason, it was still leaking or never stop leaking. The fix did not last.
Even the barb and hose fix last for about 10 years so far.
I did maintained the barb connection by replacing it around 10 years to minimize corrosion.
 
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I used the 6.2 cooling crossover hose fitting. Works like a champ. Regular hose.

The trick is forming the hose around the exhaust and turbo using some good ole fashioned exhaust heat and zip ties. :hehe: I have my lazy moments where I dont feel like dragging out tube forming dies and heat guns and such too :hehe:
 
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