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Low Coolant

I have a 1999 GMC Sierra Pickup with a 5.3L-V8, 72,000 miles. I recently saw a drop in my coolant level of one-inch. There is no visable leak, no sign of coolant in my oil (recently changed), or wet carpet inside. I do hear a gurgling sound while driving (like a heater core bubbling) but it is not constant.

Where is my coolant going? Please don’t tell me its through my intake manafold gasket. HELP

Sorry! But the intake manifold gasket would be my first suspect on this vehicle.


A pressure test of the system would be a good idea. You may have a tiny leak that’s only findable when the system is pressurized.

i had the same problem and it turned to be the radiator.
along one vertical side of the radiator you will see a metal line at the top and bottom and these are the transmission lines.

some cars will have a drainage bolt on the transmission and if you do that would be an easy way to check how the fluid looks.

you could check the transmission dipstick and see if the fluid looks creamy. the only other way i would know to check the transmission fluid would be to drop the transmission pan and you would definitely be able to see the consistency of the fluid.

i am only a do-it-yourselfer but if it is a manifold i would think the oil would be affected. so if the oil is okay…

There may be air in the coolant causing the gurgling sound, but I also am leaning towards a leaking intake manifold gasket.

Since you mentioned the words, I take it you know what happens when the coolant mixes with the engine oil?

Keep a close eye on the coolant disappearance. You may find this a bit overdone but I recommend you check the level AND the bottom of the oil filler cap for light brown oil deposit (oil and coolant mix).

Engines always ‘wake up’ in the morning with a moisture (condensation) build up inside which gets burned off as the engine gets up to operating temp. This is normal.

So, check the bottom of the oil cap after you’ve run the vehicle for a little while to get a true visual reading.

Search for external leaks in the meantime. Look under the vehicle every time you approach it for leaking coolant. Some times hoses will leak when hot and some times only when cold (loose hose clamps when cold).

I had the same thing happen with my 2000 Blazer at 45k. I noticed the coolant level dropping slowy after it was changed. I told my mechanic about it when I took it in for an oil change. He noticed a few drops of water in the last of the oil draining from the pan. He would not have noticed it if he hadn’t been looking for it. The mechanic told me to get it fixed ASAP, any coolant in the oil will displace the oil from the crankshaft bearing and make short work of the engine. The dealer verified the problem was a leaking intake manifold gasket.

Ed B.