Coolant loss mystery - 1967 C10 283

[mr.precision]

My factory stock 1967 shortbed is losing coolant somewhere. It has the original 283 2V motor, which runs well and is in the proper state of tune.
The radiator is a 2 row job, which may not be correct for the truck.
Temp gauge sits in the left portion of the C-H sweep. I have measured with a mechanical and this corresponds to 180 deg F. Even on a hot day in Arizona, it doesn't move higher unless the level goes way down.
Radiator level will drop 2-3" even after a 30 minute drive. There's no evidence of leakage or exhaust contamination.
My thoughts are that the coolant is escaping the overflow vent while driving.
Maybe a four row radiator is the solution. Any thoughts?

[Stocker]

Sounds like the radiator is doing its job since you're not overheating.

Unless a coolant recovery (overflow) tank has been added, it's normal for coolant to be a couple inches or so below full in the radiator. Any more than that will usually puke out when the engine is shut off.

I would add a recovery tank. You can fill the radiator to the top and not lose any coolant. Instead of puking on the ground, it flows into the tank. As the engine cools, it will be drawn back into the radiator.

All you need is a tank and a radiator cap for a sealed system. Run a few feet of plastic hose from the radiator nipple (by the cap) to the tank and you're set.

[1968k20]

One of the best investments that I have made is a cooling system pressure tester. Auto parts stores carry them or online. You take your radiator cap off, install rad pressure tester, pump up to cap pressure and voila!

[Stocker]

Originally Posted by 1968k20

One of the best investments that I have made is a cooling system pressure tester. Auto parts stores carry them or online. You take your radiator cap off, install rad pressure tester, pump up to cap pressure and voila!

That's something I have thought about buying for years, but never got around to it. Thanks for the reminder....

[rockyrivermark]

Follow hose off the radiator cap if it has a hose.
That's likely where your antifreeze is going. Puking on the road while you drive.
Normal for level for be a little low in radiator unless u have an overflow tank which is a good idea as noted here.
If no white smoke out exhaust and no excessive oil level (antifreeze getting in oil) then that's likely what's happening

[geezer#99]

Do the simple easy stuff first.
Put a new rad cap on it.

[mr.precision]

Thanks to all for replies.
Will install an overflow tank and new cap.....see what happens. I believe the 2 row will handle things.... just didn't recognize that thermal expansion of the coolant was that much.
Mike

[Sawlog]

I had this happen to me when I first bought my truck. I would loose a half a gallon on my way to work. 30 miles. I did a psi test and it was good. It ended up being a cracked head, the exhaust was burnig up the water. New heads and no more water loss.

[Sweeet67]

Also check your oil to see if it’s milky. If your leaking into the crank case,(head gasket or crack) it will appear milky.

[lutronjim]

I had a similar situation. Losing coolant but never saw any coolant. I could sometimes smell the antifreeze but never saw any.

Pressure test showed it was loosing pressure but no coolant could be seen. Scared to death it might be cracked heats or block. Ran a compression test and all was fine.

Finally bought dye kit from Summit. Turned out that there was a leak above the coolant level where core met tank - was a crossflow radiator. No fluid would leak until thermostat opened and flow would blow coolant out hole. Of course it was nice and hot and it would evaporate before you could see the coolant.

[jocko]

Just resolved similar issue in a newer truck - some antifreeze smell, no puddles, no overheating, but lost noticeable amount of coolant on a 1 hr drive (in the current TX heat). Newer trucks have the stupid plastic tanks, and I had a hairline crack that expanded when hot and let coolant drain out while driving along, but when I'd stop and get out and check for leaks, zip. Crack wasn't obvious, hard to see until the radiator was out. I realize you don't have plastic tanks, but what I'm getting at is that I think lutronjim is probably hitting the nail on the head. It's worth a close examination of where your core meets the tank - a crack or leak there will give you the combo of symptoms you're seeing.

[frank69]

I've had at least a dozen of there old trucks and they seem to seek their own level happy place which is usually about 3 to 4 inches down in radiator