mystery coolant loss

[evso]

my l400 diesel is losing coolant, but their is no leak under my vehicle, the oil is clean, no sign of water in oil. no moisture in cab.
any ideas?

[negativentropy]

I recently was loosing coolant as well. It was a little bit difficult to diagnose because it was a crack in the expansion tank, above the "min" line, but below the "max" line.

What this resulted in was when engine was cold, and the coolant was unexpanded, it sat below the min line, and thus didnt leak. As the engine heated up, the coolant expanded, reached the crack and under pressure was leaking out in a very fine spray.

I just kept topping up the coolant and it would disappear but only to the min line, I never ran out of coolant, even though I was definitely having to top it up regularly.

Anyway, replaced the expansion tank, problem solved.

[VanVonVan]

I would second the expansion tank, if nothing else is noticeable. Its a common failure. There is a overseas guy making aluminum ones. The price seems high but, well worth it.

http://www.tigweld4u.com/delica-expansion-tank.htm

I've had one installed for 6 years and its been amazing. I always seem to forget how hot it gets though.
Cheers,
Russell