Mystery Coolant Leak or Spill? - SOLVED

[TheBigCheezeBall]

2017 Tahoe LT 5.3 2WD - 92,000 miles, single owner, garage kept.

Ok, I am a bit perplexed and just want to see if I am missing something here.

Today I changed the oil and did a coolant drain / refill on our Tahoe. While I was refilling it, I noticed a large puddle of coolant under the vehicle that wasn't there 5 minutes before. I thought maybe the petock wasn't closed all the way, but when I looked under the vehicle, the leak appeared to be coming from the wheel well cover, and was soaking through, right under the reservoir tank. I looked around up top again, thinking I must have spilled some while filling it, but I could not see any trace of coolant up top around the tank or on the side of the tank. The only thing I could find was a little coolant under the tank. Given this, I assume I had cracked the tank while opening it (it was a bit hard to open). I tried to jostle it a bit more, but nothing seemed to cause the leak to start up again. I was a bit confused, as why would it stop leaking after it was filled? I decided to finish the fill, close it up and take it for a short drive to confirm that it was indeed leaking. After I got home, I cleaned up the mess in the garage, pull it back in and the coolant level is still full, and not a drop has leaked out from what I can tell.

Obviously you can't tell me if I spilled it without detection, but you could confirm that I am not crazy and there isn't a away for a massive coolant leak to manifest while filling, only to stop once filled and never appear even while pressurized right? I am about to take this vehicle on a 800 mile road trip, so I want to be sure I get this right.

My exact procedure was as follows:

1. Jack the passenger front up, remove the wheel and wheel well cover.
2. Hook a small 1/2 tube up to the radiator and loosen the petcock.
3. Remove the coolant cap.
4. Once about 6 Qt of coolant drained, remove the tube and tighten the petcock.
5. Install the wheel well cover and wheel.
6. Lower the Vehicle.
7. Add a gallon of coolant.
8. Notice the puddle of coolant on the floor and try to figure out where it came from, give up, clean it up.
9. Fill the coolant to full.
10. Drive Vehicle until fully warmed and find no more leaks.

Thanks for any help or insight any of you can provide.

 

[Joseph Garcia]

You got me on this one.

When you were trying (with some resistance) to get the cover off the reservoir, did you notice any pressure release? If yes, that pressure release could have spilled over some existing coolant that you did not notice was happening at the time.

 

[TheBigCheezeBall]

You got me on this one.

When you were trying (with some resistance) to get the cover off the reservoir, did you notice any pressure release? If yes, that pressure release could have spilled over some existing coolant that you did not notice was happening at the time.

I don't think there was any pressure, it definitely wasn't hot, and I don't remember a hiss at all.

I checked it again today after my wife drove it, and while the tank had dropped slightly, no leaking on the garage floor at all. I think the slight drop in the tank level is fairly expected after a drain though as the air all purges. I will keep an eye on it this week and if it doesn't drop again I am going to chalk it up to a spill that I didn't notice.

 

[TheBigCheezeBall]

Solved!! I figured it out. So no more leaks and coolant level remains stable. Well I had ordered a new reservoir just incase which I received today. I looked it over and noticed a strange hole in the bottom. Turns out there is a vent built into the top of the lid. The cap is a 2 stage cap, where I guess under certain pressure will raise enough to vent gas or fluid out of the hole near the top. When I was pouring in, I was not using a funnel and I can see where coolant would be sloshing around and down the vent path. Next time I will use a funnel. I confirmed the existing tank has the same vent hole.

 

[Joseph Garcia]

Yes, the reservoir and cap have an integrated dual purpose.

I'm glad to read that your issue is resolved. Please add the word "FIXED" or "SOLVED" to your thread's title, to let others who are experiencing a similar issue know that this thread has an identified solution.