Ok so my little brother's D15B VTEC motor has been throwing codes 6 (ECTS) and 14 (IACV). Bought a used-but-working IACV and swapped it in and code 14 disappeared. Yay. Anyway, two days later on his way home from work, and also when I test drove after he told me about this, the water-temp needle starts skyrocketing and hits red (Hot). The car drove just fine all the way back to the garage.

Checked the coolant...and there was nothing in the resevoir...still coolant in the radiator, but a near-empty resevoir. No wet spots in the engine bay...no hole in the resevoir...no moisture around the outside of the radiator, no puddles on the ground.

Where'd the coolant go?
Anyway, so we just filled it up again because he needed the car...Came back home and the coolant was gone again. Engine bay still dry, still no puddles/drips on the ground. I refilled it again drove 8 miles, parked, checked coolant...AND IT WAS ALL GONE AGAIN.

No smoke, no smell of burnt coolant, no drips, no puddles.
Where is my coolant going?

Engine is stock except for an intake.

 

Pull the plugs. Is it showing up in the cylinders? Wet carpet? Any coolant droplets around the front pulley?

 

Nope, nope, and nope.

 

my bet is your head gasket is shot that why u dont see it going anywhere like out the exhaust and no leaks

 

If your water pump is leaking it will only do so while running (generally) ... so you take if for a drive and it leaks out then you stop and no drips...

Plus if it's only a minor leak it will probobly only leak at higher rpms or under heavier load.

 

could be the water pump like he said. but it could also be a blown headgasket. look at the oil, does it look like thick choclatey color? does it smell like rotten eggs? try checking compression too.

 

Blown head gasket i would say