Engine consumes coolant only when reservoir has fluid

[turtlevette]

I'm a bit puzzled on this one.

Can't find any leaks. I thought the head gasket was about to let go.

Stopped adding antifreeze to reservoir and now that's its dry it no longer consumes antifreeze.

Radiator has been full for a few months now.

 

[Twin_Turbo]

full hot & cold?

 

[turtlevette]

full hot & cold?

Don't have the balls to open it hot. And i'd lose coolant opening hot.

 

[Twin_Turbo]

But it's full cold? When hot the fluid epands, is there no coolant in the tank when hot? It has to go somewhere. How many psi is your cap?

 

[mrvette]

Is the reservoir OEM size or a smaller aftermarket unit??

maybe the expansion fills the res. to overflow, then when cools sucks it dry again...until air comes in, then repeats the process....

:bonkers::flash:

 

[turtlevette]

But it's full cold? When hot the fluid epands, is there no coolant in the tank when hot? It has to go somewhere. How many psi is your cap?

I was just out there and forgot to check the psi of the cap. My understanding is that the fluid does not puke unless it gets hotter than usual. Early cars didn't even have reservoirs.

 

[turtlevette]

Is the reservoir OEM size or a smaller aftermarket unit??

maybe the expansion fills the res. to overflow, then when cools sucks it dry again...until air comes in, then repeats the process....

:bonkers::flash:

no way, It's the stock 75 unit that holds almost a gallon. Over a few months it'll go from full to empty.

I'll have to lay some cardboard under it. Maybe it just has a leak. I don't smell Sierra on the ground.

 

[SmokinBBC]

Rent a pressure tester from AZ. If there's a leak, you'll find it.

 

[Twin_Turbo]

earlier cars had a pressurized expansion tank, it was part of the pressure side with the pressure cap on it. There is an overflow hose on it under the cap. The system is designed so that the fluid expands into the lines and tank, that way the rad is always full exposing maximum fluid level to cooling air.

The cap is a 2 way valve, it can suck in fluid from the external reservoir and pukes it there if the pressure climbs and the fludi expands over the rated pressure of the cap. If you look at the back, the outer rubber seal with the sprung cap is the pressure seal, that's what gives the cap it's rating. Inside it is an (vacuum) pressure valve that lets in fluid if the coolant in the pressurized part of the system contracts (cooling down). Without a reservoir (fed from bottom) you will push out hot coolant and when it contracts you will get a big air pocket in the upper part of the radiator. This is the way old downflow style rads were designed like used on fords and mopars well into the 70s. They only had a pressure cap w overflow hose, when running the rad is all full but check it cold and the fluid is well below the cap. These will spit out a good bit of fluid if you fill the rad on those to the brink when cold

 

[Kid Vette]

Reservoir leaking?

 

[big2bird]

Coolant thieves? Check with KPlot. :rofl:

 

[kwplot34]

Coolant thieves? Check with KPlot. :rofl:

I need all the coolant i can get. for free. Have you checked your coolant level lately Jeff :devil:

 

[turtlevette]

Reservoir leaking?

I don't think so. I ran my hand underneath today and didn't feel any moisture.

Bird/kwplot
I got your coolant right here.

 

[mrvette]

Take some steel wool and burnish the rad cap seal areas, and then replace the cap, making CERTAIN all areas are clean.....

and that the hose from rad to tank is 110% tight....

after that, all I can do is listen....

:flash:

 

[68/70Vette]

full hot & cold?

Don't have the balls to open it hot. And i'd lose coolant opening hot.

I have no problem popping the radiator cap when my engine is at operating temperature...and the coolant doesn't spew. I don't have any water in my engine, just pure ethylene glycol. My 68, my 97 TBird DD, and my wife's 95 Seville all have pure ethylene glycol - the green stuff. The ethylene doesn't boil until 350 degrees F (?) so the coolant system is never pressurized. The first time I took my 68 out for a test drive, I didn't even have band clamps on some of the coolant hoses since the coolant system doesn't pressurize with pure ethylene glycol.

 

[Twin_Turbo]

All fluids expand with temp, it doesn't need to boil to pressurize. In fact, a normal water/coolant mix shouldn't boil @ operating temp. The pressure raises boiling point like in a pressure cooker

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[mrvette]

All fluids expand with temp, it doesn't need to boil to pressurize. In fact, a normal water/coolant mix shouldn't boil @ operating temp. The pressure raises boiling point like in a pressure cooker

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TT, is it the FLUIDS that expand or the metals in the mechanics??

I know water expands when frozen....but when it gets HOT??

:skeptic:

 

[Twin_Turbo]

Water shrinks when cooled but when phase transitions to ice it expands because of the open crystalline structure. As long as there is no pgase transition heating expands, cooling shrinks. When transitioning to steam it expands dramatically but apart from nucleotic boiling there should be no steam. Hotter means more exited molecules requiring more room. At 0 Kelvin the molecules are stationary, 0 K is - 273C. As a result water freezes at 273K and boils at (or beyyer around as it's a boiling trajectory) 373

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[MYBAD79]

As a result water freezes at 273K and boils at (or beyyer around as it's a boiling trajectory) 373

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that's at sea level or 1 bar atmospheric pressure. High in the rockies water boils at a lower temperature.
You'll really see the difference when you're boiling eggs, a 4min egg at sea level is not the same as a 4min egg at 15000' elevation.....

the phase transition to ice and the increase in volume is something you can witness when your beer bottle explodes in your freezer :3rd:

 

[turtlevette]

full hot & cold?

Don't have the balls to open it hot. And i'd lose coolant opening hot.

I have no problem popping the radiator cap when my engine is at operating temperature...and the coolant doesn't spew. I don't have any water in my engine, just pure ethylene glycol. My 68, my 97 TBird DD, and my wife's 95 Seville all have pure ethylene glycol - the green stuff. The ethylene doesn't boil until 350 degrees F (?) so the coolant system is never pressurized. The first time I took my 68 out for a test drive, I didn't even have band clamps on some of the coolant hoses since the coolant system doesn't pressurize with pure ethylene glycol.

As far as i know the only no pressure coolant is the Evans stuff. I'd run it if it was cheap and non toxic. But the other thing that saves you in an overheat situtaion is the liquid to vapor phase transition "latent heat of vaporization" which sucks a lot of heat out of the hot spot in the engine so you probably want something that does transition. Nucleate boiling is the best situation so, pure water is still the best thing if only cooling efficiency is considered. Well maybe liquid sodium would be better but not practical.

I tried using 100 percent antifreeze once and it was a mistake. It did pressurize and the engine overheated once taken on a longer trip 1 hour +. Pure antifreeze has a very poor thermal conductivity. Most all fluids vaporize and have some partial pressure.

Roger on the CF site proposed what i have been thinking. There is a bigger "air" space when the reservoir is empty because it can't fully fill the system. That airspace acts as a bigger cushion so the pressure does not get as high. I have a very small leak somewhere that only leaks through under pressure close to cap rating.