Friend's 2000 jeep with straight six is losing coolant- have to add it every three-four days. Left it rinning for two hours once, not a drop on the ground. Oil is clean, carpet is dry. Any ideas where it is going? Thanks-

(1)out into the overflow jug then it evaporates away easily when hot or (2) combusted in a cyl & out the tailpipe. Borrow a stant rad pump kit & w it hot open the cap (carefully) & pump it to 15 lbs & see if you see/hear any leaks in the next several minutes & if none (& no more than a fraction of a lb of pressure drop) let it sit (overnight if need be) & if it looses it's pressure if you have emission testing down there let it idle/take of the rad cap & set the probe in the air space above the coolant and it'll detect combustion gasses in seconds. A new rad cap may fix this ASAP

A slow leak will evaporate. Check for white deposits from evaporated anti-freeze. My daughter's Jeep had a cracked thermostat housing whick leaked slowly... no drips.

Water pump. It wont leak when its hot or pressure in the system. Let it sit over night and check it when its cool not started as well as when its warming up.

yup. get a pressure tester. test it hot AND cold.

I had the same problem in my 383 block.

got a tester, and the darn cooling system held 15 psi overnight. didn't lose a single pound of pressure after a good 15 hours.

a week later I bent a pushrod as I hydrolocked a cylinder that filled with water after a 5 minute drive.

the #3 cylinder wall was cracked, and when it heated up, water would push into the cylinder and go out the tail pipe as steam. but when cold, the metal contracted and 'sealed' the crack so that it held pressure. no water in the oil either.

The factory radiator features plastic/composite upper and lower caps. With the age of the vehicle, the seals at the bottom are leaking and blowing coolant out over the hot block and and it is evaporating. This occurs when the engine is hot and driven for an extended time.

Jeep TJ and ZJ models are known for this leak. Go to radiatorbarn.com and order a new-aluminum/brass radiator for approximately $100.

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Water pump. It wont leak when its hot or pressure in the system. Let it sit over night and check it when its cool not started as well as when its warming up.

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Some of those had problems with the cylinder head cracking. If you take the oil fill cap off and shine a light in the hole you will see green coolant at the crack. I have seen several like this, it always cracks directly below the oil fill cap.

Thanks- we'll check it out this weekend-