Where's my coolant going?
 

At a loss to figure out where my coolant is going! All new hoses, radiator is fine, overflow tank is fine, and the car got a new head gasket last year by a local Miata specialist.

The only thing I can think of is a leaky water pump. The car has almost 150K miles and it's never been replaced. (The timing belt was replaced a couple of years ago ... yes I know I should've had the water pump done at the same time .... don't ask. :) )

I also hear some belt squealing, but only when it's cold/rainy, and it always goes away a few seconds after I start the car. Not sure if that's related.

Every time I drive for an hour or so, I lose a half-inch of coolant in the overflow tank once the engine cools down. Need to get this fixed ASAP.

Thoughts?

Always only measure coolant level in the morning when the engine is cold. Its normal for the coolant level to drop after the engine cools off.

That's not what I meant. It drops -- and doesn't come back -- and after a few drives of 45-60 minutes the tank is empty. Clearly it is leaking somewhere. But I already replaced every hose, the radiator is good, and the head is new + installed by a pro. What's left to check other than the pump?

and i take it its not going ur/passengers feet?

Definitely not.

I'm guessing air is still working it's way out of the system.

Could be as well, burp it.

Googled around and saw several suggested methods. Most people say to fill the overflow tank, remove the rad cap, start the cold engine, crank the heat, wait until any bubbles go away in the rad neck, fill it, and re-cap. Sound right to you guys?

Semi-related: maybe I just don't grasp the theory behind the cooling system. After a few long drives, wouldn't an air bubble find its way out, long before I go through multiple whole overflow tanks' worth of coolant?

Nah dont overfill the flow tank since it will just keep leaking out.

Park on an uphill, remove the cap after the engine cools down, and run the engine till the fans start circulating.

When you replaced the coolant hoses, did you use rubber or cheap silicone?

or..... EXPENSIVE silicone???? lol

I was losing fluid through my heater core and never had the floor wet. The coolant was getting blown around in the vents and ending up as a thin film on my windshield and windows. Just a thought

I was having the same issue a few weeks ago. till one day the water pump just started pissing all the coolant out like a race horse.
upon inspection the whole front cover below the water pump was rusty and showing signs it had been slowly leaking for who knows how long.
I'd replace the pump.

Water Pump.

The #1 way to make cold belts squeal is to spill antifreeze on them. If you have air in your system, water will eventually fill in the gaps. That air pocket isn't a bottomless pit. You have coolant coming out of the front of your engine. Put some cardboard on the ground and park on top of it. This will tell you that stuff is indeed coming out of the engine.

Look on the bright side - at least you're going to have a fresh timing belt in place once you're done!!! (Because there's no way in hell that you're going to replace the WP wihtout also replacing the TB)

I replaced my radiator, installed coolant heater for E85 starting in winter...) It took a long time for me to get air out of my system (enough to drive me a bit crazy and wonder what was going on as well). Look for the simplest solution first. If you don't smell coolant, then look at possible air in the system first - then move on to the tougher stuff.

No mention to check the oil for extra fun?

I've had a few different cars with this and everytime it was the head gasket (or in the case of 3800 GM intake manifold gasket) leaking and the engine was using the coolant.

Of course, the GM ran like that for nearly 40k miles never putting any in the oil and running 95% of new until I ditched it.

This is how my heater core failed. Just a small leak that I would never have noticed except I was running a wire under the core and it came out damp.

So .... turns out I was being a big doofus and there were just some loose hose clamps .... fortunately I learned that BEFORE buying parts and doing TB/WP.