Ok im a newbie to diesels and love mine but im having a problem with my truck... its a 1998 silverado with a 6.5 diesel turbo. i have replaced the themostates water pump and radiator over the last few months because the radiator wasnt in the best shape and age was unknown along with the water pump. and i figured while i was at it i did the thertmostates..but now for some reason im losing coolant and i cannot find out where its going.. i have pressure tested the system and it holds for a long time without any air loss. i can drive it for about a day and it loses around a cup or so of coolant. it doesnt overheat no bubbles in the tank and no coolant in the oil so im lost here, any help would be great

 

Do you have any drip traces around the T-stat housing?
Or around any of the hose connections?

Double-check all rad hose connections. Verify that all hose clamps are correctly placed and properly tightened.

Check overflow hose for cracks.

In the past, on one vehicle I owned, The rad cap went bad and was blowing too much antifreeze into the overflow tank and eventually on the ground. I replaced the cap to a 16 lb cap that was supposed to be on it. Doing so made the head gasket blow. But it didnt blow bubbles into the radiator. Weird, I know.

 

iv checked all the hose connections and had the line comming from the tank to the rad leaked a little when i moved it when the system was hot and at pressure so i replaced the spring clamp with a regular clamp. i had a shop test the sysem as well because i got a loan a tool to check the system myself and they found nothing. it totally has me at a loss here. its not overheating or anyting like that as it gets just over the first thick line on the gauge.i read somewhere that i should have gotten a dye test and have some of the coolant tested for diesel fuel .. any ideas on that and where would i even have that done

 

The heater quick connect fitting on the water crossover is a common leak place and a poor setup.
Many people replace the quick connect with a 3/4 hose barb and cut and clamp on a piece of heater hose to the stock pipe or replace it entirely with heater hose.

Most help sections of parts stores have replacement quick connect fittings,but they tend to break apart when trying to remove them so be prepared to have the threads gone through with a proper pipe tap.

 

If you are not not finding a visable leak, you are burning it. Most likely Headgasket time. GM cooling tabs can buy time.