1998 Chevy 1500 5.7 liter. Bee having to add about a pint of coolant per week to reservoir for several years but no sign of external coolant leak.

Engine overheated while just idling to warm up heater and overheated with about 1/2 of radiator level down.

NO white exhaust smoke engine running smooth ...but noticed heater not putting out - looked at temperature gauge > peaked on HOT .

I thought it was an intake manifold gasket being it is a 1990-99 Chevy 1500...but mechanic says it is a cylinder head gasket . He wants to do a head job, replace valves (?) , seals, ..and lower intake manifold gasket for $2,000.

I'm not convinced that it is a head gasket due to no white exhaust and engine was running normally - not rough or missing. Just losing coolant into oil...at a pretty rapid rate - about as fast as I could refill radiator it was going down.

Second opinions ?

This is a 82-92 Camaro firebird page. May try a truck forum for better answers.

My guess is the plastic intake gaskets have gone bad which is very common on those vortec motors.

I'm with you. Sounds more like the intake gasket. Compare the spark plugs.
Is the oil level higher than normal and look like a milkshake?

Sure its not leaking all over the ground and you dont know it? lol
BTW:
http://www.pacificp.com/forum/index.php
and
http://www.gmt400.com/

Definitely not leaking externally. Definitely in the oil . Flowing out of cooling ducts into oil about as fast as a coke can be poured into a glass. 2nd opinion pretty much concurs that it is likely the head gasket. I haven't personally checked the plugs myself. First mechanic says will do complete cylinder head job ( new valves, & seals) and replace intakes for $ 2,000. Sounds reasonable. Truck has 128,000 miles. Thank you for your input .

(intake gasket)