When the outside temp here in SE VA gets above say...90 degrees, I notice a small spot of coolant under my '72 Supreme. It's usually on the driver side under the left side of the radiator. I know I don't have any leaks from my radiator, and even on a hot day, she doesn't have any overheating issues...runs a steady 185-190. I do have a crack where the nipple for the overflow hose connects to the filler neck, but that's about it. This only happens when the car has been sitting, not when I'm driving, and again, only when it gets really hot outside.

Could it be expansion and instead of the coolant going into the overflow tank, some of it seeping through that crack and running down?

Like I said, it's not a puddle..just enough to make a spot on my driveway, so should I seal that crack, or do I need to drain some coolant? (My radiator is full up the bottom of the opening for the cap.)

Any info, as always, is appreciated 😀

 

Is your water pump leaking out the weep hole and running down somewhere and then to the floor?

 

I had the radiator in and out probably 5 times on my dads 85 Toronado, every time I took it to the radiator shop they couldn’t find a leak. I finally drove the car there, pumped up the cooling system with my pressure tester, bingo! Leaking at the seam on one of the tanks. The only thing I can figure was tightening the top plate put just enough pressure to open a seam. It wouldn’t leak a bit when it was pressurized in their dunk tank. They soldered the tank, all was good. Maybe you have something similar going on? Or a leak that only shows up when the engine is hot?

 

Nope...no leaks when hot, otherwise I'd be losing coolant which would lead to overheating, which isn't an issue.

 

Nope...no leaky water pump. The spot is directly below the driver side of the car under the radiator. Water pump leak would spot in the middle, plus cause overheating, which I don't have.

 

Not necessarily. Not if it was a slow leak, which is what you're describing. A slow leak is a slow leak no matter where it's coming from. It wouldn't necessarily cause overheating until enough coolant leaked out to cause a problem. Overheating would occur, of course, if the water pump actually failed, but that's a different thing.

 

The drain petcock is usually at the bottom of the driver's side. That could weep slightly easily enough. I've had several that were in awful shape over the years.

 

Put some die in it and run it to get it good and circulated. Then when it leaks again you should be able to see where it is coming from with a UV light.

 

Dave,
You said there's a small crack on the overflow nipple, but that would be on the passenger side of the rad. It's possible that any leaked coolant could migrate to the left side of the rad support and drop to the ground. I'd fix the crack, regardless of what else happens.

As also mentioned, it's possible to have a very small leak at the petcock. That's on the drivers side bottom of the rad. If it's the original one it's possible to have a small failure that is intermittent with temperature. Have you ever had the radiator flushed and pressure tested?

The last thing I could suggest is check your radiator cap to make sure it's the correct one that works with your (OEM??) overflow tank.

 

Hey Allan, I plan on fixing the crack. How would I know if I have the right cap?

Also, as I've already mentioned, I get no leaks whatsoever when I'm driving (even on 90+ days). It's only when it gets really hot outside and it's just sitting in my driveway. That's why I was going with the expansion theory. Should I drain some coolant?

 

The engine and coolant will get a lot hotter while driving on the coldest day of the year than it will sitting in the driveway on the hottest day of the year. If there is coolant outside of the system, you have a leak that should be fixed.

 

I get that, so where is the coolant coming from?

 

I dunno, I am not there to inspect the car. Do as Bill said - put dye in the radiator, then inspect with an ultraviolet light.

My post about temperatures was in reply to your comment about thermal expansion. If there is an issue due to expansion, it will be more evident with the engine at normal operating temps.

 

Gotcha...I'm really not that concerned at this point, I was just tossing my mystery out there for those that are in the know could help me solve it.

 

It's quite easy for anyone reading this post to not understand what you're referring to. Please assign some dimension to a "small spot". A "small spot" is completely relative to nothing at all. Is it the size of a tick, an aspirin tablet, a dime, a penny, a nickel, a quarter, a 50 cent piece, a silver dollar, the tin lid of a tuna fish can, or what?

 

Dave,
The radiator cap for your car should be somewhere around 15 lbs IIRC. You don't need to dump any coolant if you have a radiator overflow container. It's hard to really say what's up with your car, but the thing that sticks out most to me is the petcock. Have you ever drained the pressure release valve on a hot water tank? If you have, you will know that it's darn near impossible to stop it leaking afterwards. The crud on the inner part of the radiator may get into the petcock and prevent it from really sealing properly. When the car is running it generates enough pressure in the cooling system to likely prevent it leaking. When it's cold the valve may shrink enough to close again. Hot 90° ambient temp may be the magic weak spot. Anyway, that's just one theory. I'm really curious to hear what you find.

 

Uh...I guess I should clarify that Norm...thanks for pointing that out. The spot would measure roughly 4-6 inches in diameter, and it's always the same size.

 

I know I've never had the petcock open since I've owned it, and I just noticed it this summer. I'll keep digging...

 

That's a little larger than what I had imagined. When I purchased my '71 CS last year, there was a small amount of coolant seeping from my radiator (drain) petcock. I could see some coolant seeping along the lower rail of the radiator and occasionally onto the garage floor. I tightened the petcock and it did a 'fair' job of abating the issue; yet, there was still a small amount seeping. I didn't want to overtighten the petcock as it is plastic. I placed a bucket under the petcock, removed the petcock, allowed some coolant to flush through the petcock hole, quickly cleaned the petcock with a small wire brush and reinstalled the petcock. It hasn't leaked a drop in the past year. I simply added a 50:50 coolant mixture of the same volume as that which drained into the bucket.

EDIT: And, BTW, the coolant in my radiator (system) is as clean as could be. It was that way when I purchased it. I suspect, before they sold the vehicle, someone flushed the coolant system (there's also a new, or REMAN water pump). This may have dislodged some residual sediment from the system and boogered up the petcock threads enough where the petcock wasn't sealing adequately and a simple flush, clean the petcock was all that was needed.

 

Got it fixed.. sealed the crack on the nipple for the overflow tube and she's good to go😀