Radiator leak?

[east302]

Truck is a 98 Tahoe with 350. I drove it last night for a two minute trip when it was cold--maybe 40 outside--without warming it up. This morning I had a coolant stain on the pavement about 8" in diameter.

It had leaked out of this drain hole at the radiator support--under the drain **** on the driver side.

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The rubber pad under the radiator was wet but there was no obvious leak point. The drain port was dry. I felt around the base of the radiator as best as I could and didn't feel any moisture. The upper hose is dry, the oil cooler lines are dry. I let it run for 20 minutes and it didn't leak.

I did a pressure test on it. It held 16-psi for ten minutes, dropped to 15 and held for another 20. The thermostat housing is barely leaking and a heater hose was leaking...but nothing from the radiator.

Anyone have any thoughts? Could a radiator only leak when it's cold outside? Pressure test was done when it was around 50 outside. It doesn't make sense that the pressure test didn't show anything.




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[RawbDidIt]

Truck is a 98 Tahoe with 350. I drove it last night for a two minute trip when it was cold--maybe 40 outside--without warming it up. This morning I had a coolant stain on the pavement about 8" in diameter.

It had leaked out of this drain hole at the radiator support--under the drain **** on the driver side.

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The rubber pad under the radiator was wet but there was no obvious leak point. The drain port was dry. I felt around the base of the radiator as best as I could and didn't feel any moisture. The upper hose is dry, the oil cooler lines are dry. I let it run for 20 minutes and it didn't leak.

I did a pressure test on it. It held 16-psi for ten minutes, dropped to 15 and held for another 20. The thermostat housing is barely leaking and a heater hose was leaking...but nothing from the radiator.

Anyone have any thoughts? Could a radiator only leak when it's cold outside? Pressure test was done when it was around 50 outside. It doesn't make sense that the pressure test didn't show anything.




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I had a very similar thing happen to my daily driver (2008 Dodge Caliber). It was about 40 degrees out that day as well. Never found the source of the leak, and it never came back. I've since put over 20k miles on it and it's never leaked a drop since. The only thing we could recon was that it was a one off leak from the drain plug. No crack in the plug or in the radiator for me either. I'd keep an eye on it and see if it does it again. Keep an extra container of coolant with you in case it's something more permanent.

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[east302]

Thanks, I'm hoping it was a fluke...not in the mood to swap the radiator out.

I snugged up the drain ****, but it feels like there is more "turn" left in it if I wanted to really crank down on it. I assume that it's just some plastic needle valve (versus a ball valve?) and wonder if it could not be seating.

I cannot think of anything else...short of a small break where the plastic ends on the radiator meet the aluminum part. Seems like that would be obvious, though.


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[c1500deathtrap]

If you really gave er wah when she was cold its possible that a tiny crack or unseated petcock would leak. Cold fluids are more viscous and therefore resist being pumped creating more pressure. Kinda like how your oil pressure is higher when its cold.

 

[RawbDidIt]

Thanks, I'm hoping it was a fluke...not in the mood to swap the radiator out.

I snugged up the drain ****, but it feels like there is more "turn" left in it if I wanted to really crank down on it. I assume that it's just some plastic needle valve (versus a ball valve?) and wonder if it could not be seating.

I cannot think of anything else...short of a small break where the plastic ends on the radiator meet the aluminum part. Seems like that would be obvious, though.


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Usually when the seam between the plastic and aluminium fails, it's pretty evident, I've never seen it fail just a little. You may be right about the drain plug. It might build up enough pressure before it warms up to leak, then as the temperature rises, the valve expands and seals. But you mentioned the puddle was there after you parked the truck, right?

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[east302]

Yes, I noticed the leak this morning. The only time I drove it yesterday was for a couple of minutes last night.

I let it run again tonight. No leaks but will see how it looks in the morning.



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[east302]

Well it was dry this morning...will just have to keep an eye on it.


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[1989GMCSIERRA]

Had a similar issue on a BMW. It dripped coolant but didn’t show up anywhere. Just wetness and a little dribble.
Ended up the radiator had a crack on the upper radiator hose neck. It would only leak when it was at full operating temp and only for a little bit. Since the upper radiator hose was against the radiator neck it had not leaked a tiny bit.
If you have coolant flowing or showing signs of leaking it could be that it only leaks when it’s hot and driven for a long period of time

 

[east302]

Thanks, I'll keep that in mind. The only leak that I'm seeing now is a seep between the thermostat neck and the intake, so will swap the thermostat out this weekend.

It's been dry otherwise...knock on wood.


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[east302]

Well it did it again. Cranked it for the first time of the day and moved it from the driveway to the garage. I come out a few hours later and have a puddle on the ground.

It looks like it's the stupid cap leaking. I guess that's why it passed the pressure test...I never tested the cap.

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Hopefully it's really that simple ($). So for anyone else that runs across a radiator leak from nowhere, don't forget to check the cap.


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