disappearing coolant

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Well-known member
Feb 25, 2009
western NC
First post in almost 2 years. I had no idea it had been that long, but... Our '40 Chevy two door sedan, that we've had since I found it in a local junkyard in 1980, has a '62 model 261 six that I installed a few years ago. The engine had 40,000 miles on it when rempved from the school bus and installed in our car. I replaced the head gasket at the time. It still runs great but has started to lose coolant. I cannot see any signs of leakage so I am worried that the head gasket is leaking internally. No steam out the tailpipe though. I am going to remove the sparkplugs and see if any look different. The head gasket I installed was a blue Felpro and all surfaces were thoroughly cleaned and the bolts were torqued correctly.
I was mistaken about the "steam" out the tailpipe. Today was the first cold day, 20 degress colder, that it has been started. Quite a bit out the pipe.
Does your exhaust smell sweet?
Not that I can tell but until today I had been running almost 100 percent water. Today I drained it and put antifreeze in because temps in the teens are forcast for the next few nights.
Did you re-torque after a few heat cycles? plugs should tell the tale...
I might have believed what Felpro says about no retorquing recommende or necessary.
I did a lot of head gaskets back in the day, I have never retorqued the blue coated Felpro head gaskets, and I've never had a problem.

One of the by-products of burning gas is water vapor. Your going to see steam out of the tail pile when the motor first starts, and you will see it for a longer time if the weather outside is cold. The temps of that water vapor inside that pipe are a lot higher then the temps of the surrounding air. You will see steam until the water vapor in the complete exhaust system exceeds the boiling point of water, which is when the exhaust gets fully warmed up, after about 15-30 minutes of running time.

If you have been running 100% water in the cooling system, your exhaust will not have the sweet smell if you have a coolant leak, the sweet smell is antifreeze burning. Its also going to be really hard to find a leak with 100% water as coolant. Antifreeze tends to leave a color trail from leaks, water (unless its rusty) doesn't.

When you get your antifreeze in the motor, be sure to run the motor long enough to mix up the antifreeze you added to all the water in the cooling system. If you just drain the radiator and fill it with the antifreeze and call it good, you can still freeze the water in the motor and break the block. You need to run that motor at least a 1/2 hour to get the antifreeze mixed.

How much coolant are you loosing, and how fast are you loosing it? Does your ride have an overflow bottle? If you have no overflow bottle, are you trying to keep the coolant level up full to the radiator cap? Coolant expands when it gets hot. Without an overflow bottle, if you don't leave enough space for the coolant to expand, it will simply push the extra coolant out of the cap. With a non-overflow system, you need about an inch of expansion room under the radiator cap. The coolant level on the non-overflow systems normally is about 1/2 the distance between the radiator cores and the cap neck.

If you do indeed have a coolant leak, now that you have added antifreeze (for the color), it might be a good idea to have a shop pressure test your cooling system. A lot of leaks only happen when the system is under pressure, or when the motor is running. Your leak could be as simple as a broken hose clamp, or it could be major.
I have used blue Felpro gaskets in the past too, and never retorqued them. The other day, after I drained and flushed the system and installed fresh green antifreeze I let it run long enough to open the thermostat, then drove it a few miles. It has no overflow catch tank, just the stock tube to the bottom of the radiator. I'm running a stock '40 radiator that I found NOS a few years ago and am currently running an original style (no pressure) cap. Although I see not sign of leakage at the cap, I might put on a new low (4-7#) cap when I reassemble it.
I always fill the radiator so that the tubes in the core are just covered, never to the top of the tank. I can borrow a pressure tester and might try that before teardown to see what happens. Just for curiosity.
I had a similiar problem with my daily driver and it has an overflow tank. I pressure checked and did everything I could think of and last but should have been first I replaced the radiator cap. I felt like an idiot. Not to say this is your issue but some times the obvious isn't. Just a thought.

my 63 chevy truck doesn't have a catch tank either. i zip tied a beer can to the support and ran my over flow hose in, found my water leak. weak cap, hope your's is easy.
I added a catch can and my coolant loss disappeared for a long time, then one day I started loosing coolant again. it took a couple of weeks to figure out the catch tank was leaking!

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