the check light means to SCAN it. (all cars, 1987 to now)
All posts are USA,
the water, coolant does lose coolant in 6 months of driving
but does not fast. so i presume you mean fast loss. like 1 day.
there are on 3 ways, (but inside leaks or outside are the 2)
so if no green AF on the ground nor on passengers toes (foot well)
then its internal.
way 3 is out exhaust tip. (seen as steam on a hot engine
and said steam , smells sweat (glycol stench)
way 3 is just one more external leak , as steam>.....
that leaves, milky engine oil or the A/T (AUTO? TRANNY) the dip stick shows milky. (not pink/red. and clear but muddY)
the engine is first.
transmission is useless to any blown engine.
some newer cars the trans, has overtemp sensor that can force it to limphome, mode. 210 is not hot. some cars run 200f thermostats.
first off stop using the side expansion tank for diagnoses.
some lie. (eg. dip tube in tank bad,)
use the RAD cap test method., look into the RAD cap filler well.
is it REALLY full , dead cold ?
if not , bingo. huh? (my guess is you did this already) methods?
fiddle the side tank later, find out if you have air in the system.
the tests for lost water are (no signs stated above)
1: RAD leak down tester
2: RAD green /blue die tester
a new rad cap is cheap, me i just inspect the gasket, like this guy.
see 17 signs of coolant lost there. and 24 causes.
some cars have 2 failures. a partial clogged rad.
then one more failure, breaks the camels back (heat load)
One other way to lose coolant is that it only loses it driving
and you missed that?
are you checking the ground at each trip, end? and after coming back.?
i bet the 17 ways to leak finds its.
but the system holds about 12psi hot. if not , fix that first.
we just grab the top hose on rad,and go to self, yah got full pressure.
if it does hold pressure, and there is a breach idling hot.
its easy to see, it will leak now at 12psi , so look/
if its not leaking externally then its inside the engine or out the exhaust tips.
and if it overheats idling, all cars do of the fan is dead.
if it overheats, the fan must be active. if not fix that now.
the FSM book covers most the tests.
napa sells this ( finds cracked heads. or gaskets in head) or worse.
same with this too