Hi, I'm new to this forum but I have been following for a while so now finally I'm stumped. I have a 2000 blazer with 150k on it. When I first bought it the thing was a junker now it runs like a champ. The only issue now is the coolant reservoir is losing coolant and me nor my brother inlaw (certified GM mechanic) can spot a leak. My coolant temp gauge is usually sparattic and it will go anywhere from normal temp all the way to about 230 and back down and repeat hotter at idle and cools down when moving but not all the time does this happen,sometimes it cools down when idling and heats when moving. Its pissing me off.

Anyhow here's what has been replaced recently
Fuel Injectors
Plugs & wires
Distributor cap & rotor
Thermostat
Intake manifold & gasket
Fuel pump
Alternator
AC clutch
Reservoir when I bought it a year ago
Radiator hoses

On a side note I don't believe there is a heater core heater does not work. Also head gasket has been ruled out already checked for it as far as we know.

Please help

PS I live in a
AZ

 

Leaking OEM lower intake manifold gaskets are a very well known problem on the 1996 through 2005 4.3L engine. Rule of thumb is, if they're not leaking now, they will be shortly. They can leak at any of the corners where they are supposed to seal the passages between the cylinder heads and the lower intake manifold. They can leak internally, externally, or both. The OEM design is inferior, and they need to be replaced with Felpro MS98002T gasket set. If clean up, prep work, tightening sequence and torque specs are used, they will not leak. Provided you chase the threads on the intake bolts, and in the cylinder heads, and then apply thread sealer, there is no need to replace the bolts. A cooling system pressure test will locate external leaks. Coolant in the oil is usually detected by a chocolate milkshake substance on the underside of the oil fill cap, and or rocker arm covers.

 

There is no coolant in the oil I haven't done a pressure test yet I'm going to replace radiator cap just in case it was last replaced about 6 months ago

 

#1 factory gauges are about as accurate as a weather man getting the Forecast right the first time

#2 if it has the heater hoses running to the fire wall I would guess it has a heater core

#3 check your fan clutch, engine off grab it, should spin with a little resistance and no wobble or play - upon a cold start and during acceleration it should have a kind of a jet engine or whooshing sound

#4 radiator shrouds in good shape, radiator core in good shape inside and out, any gunk built up in the fins causing air blockages or internal fluid blockages VIA mineral or sludge build up

 

Missing lower fan shroud, would a coolant temp sensor cause antifreeze loss in the reservoir maybe even a water pump?? The temp will go to like 230 and shoot all the way back down to operating temp within like 3 seconds

 

Also heater doesn't work

 

The fan should rotate with very noticeable resistance when the clutch is cold, and when the engine is overheating. At normal operating temperature, it should rotate with slight resistance. It should never spin freely, or wobble, if it does, it's junk


Good call on the fan shroud! Definitely will cause an overheating issue. Same with the shield that covers the oil filter.


Coolant temp sensor and water pump will cause coolant level to drop in the reservoir only if they're leaking, and you'd see that


Remove the two heater hoses at the core, connect them together and see if the coolant level continues to drop.