Losing Coolant

[quickv6]

I have a 94 2500 6.5 TD Truck has 402,000 miles. I am losing water about 1 gallon every 1800 to 2000 miles. I have had this truck about 100,000 miles. The water loss has been exactly the same since day one. There is no water in the oil via an oil sample check. The cooling system will hold 20 psi pressure over night. The is no visable leak anywhere. Where is this water going? Any ideas? I am not sure if the engine has ever been replaced. I am the 3rd owner and the 2nd owner says he never replaced it. The block casting number is 12555506. I cant find a date code.

Thanks
Lonnie

[john8662]

Check everywhere for an external leak, one main place to leak water is the quick connect on the water crossover that feeds the heater core. If it's got white crust or wet crust on it, it's probably leaking. You might also take the time to see if you have a radiator that's leaking slightly, but your pressure test should have seen that. With that casting number of a block, the engine has been replaced for sure. Thats a 97+ model casting number. For a 94 truck you'll typically only see 599 and 929 engines for originals.

What kind of oil analysis did you run? Since there isn't any coolant in the oil, you might be able to rule out a cracked block. It could also be a head gasket leaking, there have been a few head gasket leaks, mainly found on the passengers side, or a cracked head.

[quickv6]

The last oil change I pulled an oil sample and took to the local CAT dealer. They sent me a break down of what was in the oil. Antifreeze and water was 0 content. I am putting my money in the cracked head. No other way out than the exhaust and not be seen. Radiator is new and so is the heater hoses and fittings.

Where exactly is the date code located. Looked oposite the ser# number but cant see anything. I looked at some pics of an enhanced block and this does not look like one of those. Are the 506 blocks worth rebuilding or should I find another block.

[BBCB]

I too was having this issue - my problem boiled down to the sh*tty plastic "T" connector that splits flow for the rear heat. Granted, you don't have a Sub, but you may look. The coolant was dripping into the valley under the intake, sitting there to evaporate from engine heat. I could smell it, but never a drop anywhere.

Good luck.

BBCB

[john8662]

The date code should be located on the passengers side rear of the engine, just opposite deck as the side you fond your casting number on. If your 506 is not cracked on the bottom end or cracks coming from the oil cooling holes internally it's rebuildable. Whether it's worth rebuilding is up to you, if this engine is for stock performance, I'd say no problem, it's when you turn it up that problems seem to form (above the usual cracking of course). For the head work go ahead and pull the engine, it's not even close to worth working on in the chassis. This way you can pull your oil pan and carefully inspect the bottom end to determine where the coolant is going.

[victor50]

I had the same problem. This went on a year before I found the leak. I also tested everything possible. Getting ready to pull engine and found water coming out water pump weap hole. I had checked this many times before. I belive it was leaking at high rpm while towing and the clutch fan would engage. Pump was two years old with 40k.

[quickv6]

I am thinking about building a short block with splayed mains. I would like to make a little power with this truck. If this is not the best block to use I can purchase a complete 93 NA 6.5 that has the 599 casting number. What is the strongest block to use at this point? If the 599 is that block how much power can I make with one?

[quickv6]

Originally posted by victor50:
I had the same problem. This went on a year before I found the leak. I also tested everything possible. Getting ready to pull engine and found water coming out water pump weap hole. I had checked this many times before. I belive it was leaking at high rpm while towing and the clutch fan would engage. Pump was two years old with 40k. Did you have any signs of leakage? Antifreeze trail or rust anything? This is driving me nuts.

[victor50]

No,My system had no rust in it to see. The only sign was stain on lower rad hose,but it was never wet and could not tell if it was oil or water. This will drive you nuts!! If theirs no presure buildup in the system and no water in the oil and it runs good it almost has to be external. My water pump was tight and not very old.Was also OE GM.