Toyota Trucks: 1985 22R loosing coolant

My 85 22R 4x4 extracab is loosing coolant, but its not apparent to me where
it's going.
To start, I thought I would replace the radiator cap. Is there some issue
with after market caps? I remember some discussion about do not use after
market ________ in the cooling system.
I guess several things could be wrong; head gasket could be leaking ,
maybe pin hole in radiator or bad hose.
Would a water pump going bad consume water? What are water pump symptoms?

What's the best way to check the cooling system for leaks, can it be
pressure tested ?

Thanks in advance!

Scott
82 Yamaha Virago XV 750
85 Toyo Hilux 4x4 extra cab
01 Taco V6

I finally got a chance to start looking yesterday evening.
Topped of radiator.
Checked Cooling fan for excess free play, seemed fine.
I started it up in the day light and let it warm while watched and observed
closely. It did not overheat, BUT it had about 50 times too much exhaust,
which gradually tapered down to 10 times too much exhaust.
No external leaks or steam other than exhaust.
Removed oil filler cap while warm & running. I don't usually do this, but I
noticed a vapor / mist and the underside of cap had milky looking sludge.
Pulled plugs - looked white & crusty / scaly thick deposits on electrodes
and insulators.
Tested compression, 1-4 checked: 180 , 189, 190, 185 PSI.. Book says
is should be 171, and max difference should be less than 14 psi.
Went to AutoZone, and borrowed a cooling system pressure tester. Cap pops
off at ~13 PSI. but the adapters in the set did not fit the radiator
neck. bummer.
I would really like to pressure check the cooling system prior to digging
in.

timing chain chewing a hole still seems likely .

Can the timing cover, ....chain tensioners.... be accessed from below by
dropping the oil pan???
The guy at AutoZ suggested it was common to do the job without removing the
head..
In my case the front grill is already off . seams like if radiator I would
have easy access from the front also.

Thanks,
Scott
85 22R 4x4 Hilux


"Roger Brown" <org> wrote in message
newsrg... 
where 
issue 
after 
symptoms? 
a worn timing chain that has eaten into the back of the water pump housing
and caused coolant to leak into the oil. 
while the engine is running, too much might indicate that engine compression
is pressurizing the cooling system and causing it to blow out the radiator
cap and overflow the tank.