47-55.1 Coolant leak?

[Livemeyer]

I haven't driven my '51 much since I installed a 327 of unknown origin just after I got the truck in 2016. I bought an aftermarket aluminum radiator that fits the 47-54 models and an aluminum capsule-style overflow container. It has two openings at the bottom, one feeds a long tube that runs to near the top and the other is open to the bottom of the reservoir. In theory, overflow from the radiator cap should run down the overflow hose, into the reservoir, fill, and if it fills to the top, it spills out from the long overflow tube.

Now then, every time I take my truck for a drive, at temperature, even a short 1/2 mile drive, when I get home I notice a puddle of coolant below the radiator and on the ground. There are no detectable leaks from any hoses or from the radiator itself. I thought possibly the radiator cap wasn't sealing well, or was too weak, so I purchased a 16-PSI Mr. Gasket radiator cap that also has a thermostat built in. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Gauge in the truck cab indicates 195F; this cap gauge indicates 200F.

Still, when I took the truck for a quick spin, I came back and coolant had leaked. Thinking it was the overflow reservoir, I removed it. I capped the bottom, poured water into it, waited to see if it leaked. It didn't. I had a bucket under it, it was clamped into the vice and the bucket underneath stayed dry.

I took the truck for another quick drive, no overflow reservoir, and there was a big coolant mess, it had indeed been leaking out from the cap. "Well I'll show you!" I thought, and I put a plug on the overflow nipple at the top of the radiator. Well it's evening now, the truck has had time to cool down. Both the top and bottom hoses had vacuum compressed, so I realized capping the nipple wasn't the answer.

At this point, best I can do is just put the overflow reservoir back on, but I'm still puzzled about the leak. I don't want to keep having to clean up coolant. What am I missing here?

[Livemeyer]

After thinking about this some more, I'm thinking the original cap I bought in 2016 and this new cap aren't sealing correctly. I suppose I should continue my search for a cap that is deeper so there's a bit of pressure on the spring to seal the bottom side to the top of the radiator. Perhaps someone knows what cap works best.

[Jesse Z]

Borrow a pressure tester from your nearest AutoZone. Pressure tester kits usually have an assortment of caps in them, so you can pump up the system and identify the issue.

[flyingdet444]

A friend of mine gave me one of those Mr. Gasket caps because it would not fit his 55 Chevy and thought it would look nice on my 49 5 window,but it would not work on mine and I almost tore the rad. neck off. My suggestion is to hang it on the wall and get a propper cap.

[dsraven]

check the cap to see if it has a gasket on the end, like the spring loaded end,plus another gasket right up under the part you turn. the second one seals the cap against leakage when the spring loaded end releases rad pressure into the overflow. older style rads didn't have that second seal, just the initial spring loaded seal. the second seal or gasket on the newer style should seal against the rad neck at the very outside or top part. when the rad cap blows off the coolant is supposed to go into the overflow tank and the tank should be sized to take the amount. if it is dumping outside then the cap is leqking or the overflow is not big enough or you have another issue. a pressure test would be a given, if you have access,but in the meantime look for the obvious, watwr pump lek hole, intake manifold ends where they meet the heads etc.

[Livemeyer]

Originally Posted by flyingdet444

A friend of mine gave me one of those Mr. Gasket caps because it would not fit his 55 Chevy and thought it would look nice on my 49 5 window,but it would not work on mine and I almost tore the rad. neck off. My suggestion is to hang it on the wall and get a propper cap.

I may tend to agree with you. It's really difficult to put on and take off. And though it's cool to see the engine temp when you're "under the hood," what's it worth if it doesn't keep the coolant in the radiator. You suggestion to hang it on the wall may come to fruition should I not be able to return it. But I think I'll try getting my $35 back first...

[Livemeyer]

Originally Posted by dsraven

check the cap to see if it has a gasket on the end, like the spring loaded end,plus another gasket right up under the part you turn. the second one seals the cap against leakage when the spring loaded end releases rad pressure into the overflow. older style rads didn't have that second seal, just the initial spring loaded seal. the second seal or gasket on the newer style should seal against the rad neck at the very outside or top part. when the rad cap blows off the coolant is supposed to go into the overflow tank and the tank should be sized to take the amount. if it is dumping outside then the cap is leaking or the overflow is not big enough or you have another issue. a pressure test would be a given, if you have access,but in the meantime look for the obvious, water pump leak hole, intake manifold ends where they meet the heads etc.

Given that the coolant is appearing in the frame crossmember below the radiator, I'm certain there's no leak at the water pump or intake manifold. I'll check the cap for the second seal, though it is a new radiator it's capping. I think perhaps the coolant is somehow filling the overflow tank and then leaking off the top, but that thing holds at least 16 ounces, maybe even twice that. It seems extreme to think pressure is pushing out that much coolant from the engine and radiator. I definitely need to see if one of the auto parts stores can set me up with a pressure test kit. Thanks for the ideas.

[jwhotrod]

The whole idea of a puke tank is to allow the coolant in the radiator when it heats and expands to flow into the puke tank. When the system cools the coolant then flows back into the radiator keeping air out of the radiator, which is an enemy to good cooling. Now when you fill the radiator full, and it heats it could very well put enough coolant into your puke tank to make it "leak" or overflow. Now do not panick, and put more coolant into the system. It is just finding its level, when it achieves a proper level it will stop puking onto your floor. your cap is doing its job, maintaining pressure and letting coolant out into the overflow tank. I hope this helps.
Jim Worrell

[Livemeyer]

Originally Posted by jwhotrod

The whole idea of a puke tank is to allow the coolant in the radiator when it heats and expands to flow into the puke tank. When the system cools the coolant then flows back into the radiator keeping air out of the radiator, which is an enemy to good cooling. Now when you fill the radiator full, and it heats it could very well put enough coolant into your puke tank to make it "leak" or overflow. Now do not panic, and put more coolant into the system. It is just finding its level, when it achieves a proper level it will stop puking onto your floor. your cap is doing its job, maintaining pressure and letting coolant out into the overflow tank. I hope this helps.
Jim Worrell

Jim, the concept is not lost on me, and I have not panicked (I only do that if the engine is overheating). Problem is, it keeps happening, and I haven't been adding any more coolant, and it's a pretty big overflow tank. The one time I took it for a spin sans tank I had coolant everywhere. For a half mile drive I shouldn't have had it puking at all. There should be enough space in the radiator (it's more than a half-inch below the top of the radiator) for the coolant to expand. The tank is there to catch the coolant when it does overheat and the coolant pukes. I wouldn't expect it to do this every time I drive the truck. I spent part of my day today making a new mount for the tank (it was previously on the fender and wasn't level) so tomorrow I plan to do the coolant system leak test.

[mr48chev]

Originally Posted by jwhotrod

The whole idea of a puke tank is to allow the coolant in the radiator when it heats and expands to flow into the puke tank. When the system cools the coolant then flows back into the radiator keeping air out of the radiator, which is an enemy to good cooling. Now when you fill the radiator full, and it heats it could very well put enough coolant into your puke tank to make it "leak" or overflow. Now do not panick, and put more coolant into the system. It is just finding its level, when it achieves a proper level it will stop puking onto your floor. your cap is doing its job, maintaining pressure and letting coolant out into the overflow tank. I hope this helps.
Jim Worrell

He said pretty much word for word what I would havei.

You are still overfilling the radiator if it is a stock type tank on top vertical tube radiator. YOU need a couple of inches at least for expansion in the tank. Empty the puke tank and drop the coolant level in he radiator down to around an inch above the tubes and you should be good. This setup isn't like the later models where the tank starts out filled to a certain level. The puke can will catch the overflow and let it be drawn back into the radiator if you have the right cap but it is not a reservoir that holds a certain level of fluid from the get go.

[flyingdet444]

Mr.48 is correct, the water in the rad. will seek its own level. Not your level.

[Quindel3100]

If you still have problems after trying to allow system to find it's own level....I'd consider the possibility of a head gasket issue. Check with engine hot ,remove rad cap and let idle . If you see bubbles in the coolant and the level rises and starts to overflow the rad, then you most likely have a head gasket leak. With the cap on, combustion gets pushed into cooling system and pressurized the cooling cooling system. If the gasket is badly blown you can get air locks in the system causing over heat issues, and coolant leaking into the cylinders,causing hydrolock, and coolant into oil. I know that's not the issue, but presenting the potentially worst case scenario...

[mr48chev]

It might not be a bad idea to get your hands on a radiator pressure tester ( you can do the tool borrow thing at Autozone) and pressure test the system just to make sure there isn't another issue you are fightin.

I still think it is the result of overfilling the radiator and in the process having the puke tank overflow in the process.

[MiraclePieCo]

Originally Posted by Livemeyer

There should be enough space in the radiator (it's more than a half-inch below the top of the radiator) for the coolant to expand.

The best way to pre-set the max amount of coolant in your radiator is with a "Spill-Free Funnel" - a great big funnel that fits in your radiator filler neck. As you warm you engine, the coolant expands and rises into the big funnel. When it's done expanding and burping air, you put a plug into the funnel neck and remove it. Presto, the rad is now at it's optimum hot level.

https://www.youtube.com/watch?v=xYkKW0OyeUc

[Livemeyer]

Interesting, I posted here this afternoon, but it appears that the post didn't go through. Meanwhile, a great number of responses came through, thank you guys.

I did borrow a pressure test kit from a local auto parts store, and both the cap and radiator/cooling system tested good at 17psi. Once finished, I drove the truck about 2 miles (to return the pressure tester) and checked it again when I returned - no leaks. I should note that I was guessing that the level was about 1/2 inch from the top of the radiator based on my recollection, but it was really closer to an inch. When I returned from my 2 mile drive there wasn't even any coolant in the overflow tank.

[dsraven]

ok, now that you have determined you have no internal leak, you still need to get the level in the rad figured out. if it is a top tank rad or a side tank rad it really doesn't matter if it is a closed system. the rad should be full to the neck when the engine is cold. check it when it is cold to see if it is full. at that point there should also be some coolant in the overflow reservoir as well. if the system is a sealed system, with the rad cap that has 2 gaskets, then the rad should stay full, once burped, and the overflow tank is sized accordingly to take any overflow from expanded coolant. the system needs to stay sealed properly. a small leak in the secondary gasket of the rad cap can cause leakage to occur and allow air to get in as the system cools off or pressure to force coolant out past the leak as the system is warming up. this will have an effect on the rad level because the system loses coolant at each cycle of heat up cool down. coolant leaves for the overflow but is replaced with air when the system cools off. check the neck on the rad to ensure the cap seals on both locations. if the rad is full when you take the cap off, cold, and the tank has a bit in it then you are good. if the rad is not full when you take the cap off, cold, then you may have a leak allowing air in, so the system can't draw coolant from the tank as it should. easier to draw air than coolant. also, the overflow tank shouldn't be a mile away or a bunch higher or lower than the rad cap which will affect head pressure on the system and possibly allow a slight vacuum below the rad cap because it can't overcome the head pressure required to draw coolant from the tank if it is too low. also the overflow tank needs to have a vented cap so there is no vacuum in that tank. the location of the rad in relation to the engine can also be a factor if the rad is a bunch higher or lower than the stock location. another thing to check, if an engine swap was done, is to ensure the water pump you are using is turning the correct direction. some pumps were made to turn backwards with a serpentine belt system. sorry if this is restating something someone else has said already, I didn't have time to read the whole post. one other thing is to watch out for the corrugated rad hoses as they cause friction loss from the turbulance in the water flow. a smooth hose will have less friction loss so better flow.
hope you get it figured out and don't overheat first. like said, a bad head gasket or a cracked head could be the culprit or the result if it overheats.

[mr48chev]

Cool beans, just keep tabs on it until you are sure that it maintains that level and you can check it during your regular fluid checks.