So this is an interesting one!
91 bird, carb 305/334 (supposedly a 334..doubt it), 3 core hawks radiator, twin fans on dip switches, autometer gauge and sender, fuzzy dice, yada yada.
I'm experiencing magically disappearing coolant!

Fill rad up, system is bled, fill resovoir..over time, it just gets lower. And lower. And lower.
Temps looking great, occasion runs a little warm, it'll get up to 210. Heater works great!
I'm also on straight headers dumping just behind the front pass wheel.

Now, this being said..its not being burned. Zero smoke out the pipes, doesn't smell sweet. At all. Actually burns the hell out of my eyes
Plugs show no signs either.

Oil is bueno, no milky engine blood here.

So that must mean its obviously leaking or dripping, right?
Well, technically yeah. But, that's where the magic starts, and my car is the magician that won't reveal its secrets. I can't find a drip or leak at all, anywhere. I've watched the thing run for half an hour and searched. Not a drop. Nothing from radiator, no small leaks from resovoir, heater core lines are nice and tight. T-stat housing nice and sealed. No leaking in the heater core either..
Rad drain isnt dripping

I've searched the entire system harder than we searched for Saddam Hussein.
Running 50/50ish new coolant as well.
So! Anyone here good at magic?

 

Sounds internal. I wouldn't rule anything out by looking at the plugs and sticking your face in front of the exhaust. I would check the cooling system for hydrocarbons, and pressure test it. Also check the color of the coolant in the radiator, and check the transmission fluid on the stick. I really do hate the heater control valves on these cars. I don't know if it's possible, but I'd check to see if somehow vacuum is sucking coolant out of the system there. Good luck, post up your findings.

 

Sounds like a classic water pump failure.

Usual deal is, the bearing leaks, but only a tiny amount; and it goes into the back of the pulley, which turns it into a mist and slings it all over the front of the motor. Might even all evaporate before it hits the motor and leave little or no trace.

A sign it usually DOES leave however, is a trail down the underside of the lower rad hose. Get up under it and look: if it looks like coolant might have been running down the back/bottom of the hose, you need a WP.

 

Something about my exhaust just doesn't feel like there's coolant. Last motor I had that was dieting on coolant, even in small amounts, the exhaust felt..sticky? Even though I couldn't smell or see it. Coolant is beautiful green, and its a t5 soo.

I haven't updated my profile, this is my fourth bird and I just haven't updated.

Heater control valve?

More background, this was factory tpi, at some point had what looks to be a dirt track "334" dropped in. Don't know cam specs, but I know it has CP domes and 998 heads. I have coolant flowing through heater core continuously, heater on or off.

And about the water pump, that's an interesting idea, I've never heard of or thought of that, but it makes sense. I'll have to check it out. On warmer evenings, it does run about 230ish, which with a 195 stat, 3 core rad and dual fans..shouldn't be getting like that. Doesn't change whether I'm moving or still, one or two fans on, heater on full, or all 3.

Im getting a block tester tomorrow to see if I have a small headgasket leak

 

Coolant dye additive.
The kit at Autozone is $20.00 and comes with the dye and a small "black light" flash light.
Just pore it in and run the car until the system is pressurized for a while. Shut it off and scan the bay for Florissant dye. Best when the sun goes down a bit.


The dye in the kit is specific to the type of antifreeze used so get the right one.

 

I haven't heard of that, but I'll have to get one! Thanks for the tip!

Tested the block, no head gasket leak, so its not internal. Felt a cold spot on my rad, so I pulled it out and back flushed. Yuck. Rust, more rust, and rust with a rust costing. Aluminum rad.. When I got it, this car was overheating, coolant was..disgusting. Looks like it sat for a while. Flushed her out and got good coolant. Only thing not replaced are the heads and block, obviously, but also the water pump. Thinking I have some rust or other crud inside the water pump, she stays around 230 moving or still, even with heater on full and both fans on.

 

i had this issue before. my block ended up being cracked. right behind the pushrod there was a 3in crack allowing slight amount of coolant into the lifter valley. i believe it was evaporating in there because my oil was never milky.

built new motor, retained same water pump and radiator, never had that issue again.

good luck

 

This is the valve I speak of:



It sounds like you don't have one on your car anyway, just since you asked. There are some crappy intake gaskets on the market today, one example is the non metallic fel-pro printoseal line. These gaskets deform over time and allow internal leaks.

Are the 230 degree temps a new thing since you flushed the system?

 

One thing I've done, unhook the hose to the coolant expansion tank. Hook up an air hose and put about 15 psi into the radiator and system. Start looking for leaks. Coolant is going somewhere and might leak worse when cold with pressure on it.

 

Oh, nope. Had one stock, but a previous owner ditched all that, half assedly.
I'm honestly not 100%, I started tracing and discovered I was drawing 1000ohms resistance at the sender when cold, so I corrected that. Now that it was reading properly, I'm staying at 200 unless stationary and both fans off. Usually I just turn the left one on after she's warmed up and I'm good to go. However, it will occasionally spike, as well as heater intermittently stops blowing, even with the blower motor going.
Noticed that the upper half of my rad is cool while the bottom is warm, so I'm suspecting an airlock, since I forgot to bleed the system when I flushed the rad. Gonna try that this weekend and see how it goes, plus a new 180 stat

 

Found the leak! Was a pinhole leak at the bottom front. Not having a condenser means it just blew out inside my bumper, so I never saw it. Well..
Till I put it on a lift and a puddle of coolant fell on my head!