My 92 pickup, 22RE, 188k miles has an internal coolant leak.
Oil is clean (no antifreeze) antifreeze is being burned and going out exhaust.
I bought a Snapon cooling system tester on Ebay (very cool tool).
With engine off, pump to 10 PSI, drops very slowly.
With engine running, pump to 10 PSI, drops slowly (just a smidge faster then engine off).
Has the head gasket failed or have there been other failues (in block or head).
Thanks, Jerry

 

More than likely a head gasket. Check the plugs.

 

With the engine off, can you HEAR where it's leaking? You should be able to. Pull ALL the spark plugs & listen while the pressure drops, then turn the engine over & if there's a leak into the system, it will blow it out the offending plug hole.

 

Alternatively you can use a leakdown tester in each cylinder and listen to which one is bubbling into your coolant.