Hi all. First post here. I joined up because I have a thing going on with a used van I bought and I could use some input. I tried searching threads before I asked but couldn't find any related to my problem.

The van is an 06 express 2500 with the 4.8l v8.

The problem is I lose coolant. I know. Not rocket science. Even for an amateur like me. Find leak. Replace leaky part. Or it's internal and the repairs get spendy.

Thing is, I can't see a leak anywhere. No puddle. No white spots or steaks. So I think internal. But I got no signs there either (that I know of). No milky oil, I remember that from a car I had a million years ago, no white smoke from the tail pipe, no coolant residue on oil cap, no smell in the cabin.

And just for good measure I went to Napa and bought a block tester kit. Which I've used twice. According to directions. Test went as it said it should. Fluid stayed blue. (No hydrocarbons in the coolant).

So I thought to rule out the radiator cap. No joy there. Same loss. (There is that way outside chance that I've replaced a faulty one with a defective one I guess. They only had the cheaper Delco one, not the OEM)

So I'm back to the start I think. What's it do? Well. For a short trip up to the store (5mins) I'll check it the next morning (always way later, at least 8 hours, when it's cold) and no loss. But after like a trip to work (12 miles) I check it when I get off and there is loss. Or like a hwy trip of any distance when it cools all the way I check it and there's loss.

Thing is, there is no constant loss. It's roughly the same amount depleted every time. Whether it's a half hour across town or 3.5 hrs to go fishing. Same volume lost. (Down to the bottom of the neck of the radiator, and a little out of the reservoir.)

I mean if it was seeping into the cylinder or out somewhere else at full pressure would it not stand to reason that the longer I drive the more I lose?

So that leads me to think it's doing something as it cools that causes it to lose that same volume of coolant every time, but only after it's been run for a while and is good and heated up and pressurized.

But that's kind of where I get stuck. My ability to logic my way through it with my somewhat limited car repair experience only gets me so far.

So here I am in a Chevy forum asking if anyone's heard of something like that. And if so can you point me in the right direction? Any help would be appreciated. Thanks.

 

That is some good detective work. How much are you topping it off each time? Sounds like at most half a quart? A small amount like that can be difficult to detect.

I'm not too familiar with the 4.8L, but intake gaskets are weak spot on these vans. You wouldn't see oil if there's no oil galleries adjacent. Consider also that you have aluminum cylinder heads sitting on top of a cast iron block, with different coefficients of heat expansion, and that gasket has to make up the difference. You might want to try a compression test while the engine is cooling off from trip.

Lastly, they sell leak detection kits for not too much money. It's a luminescent dye that you put in, and then leaks glow under UV light.

Don't forget to feel the floor under the front heater core, and rear if you have one of those. If you have a rear unit, then you'll need to check all that plumbing too.

 

Yeah it's not much at all. A couple or three ounces at most at a time. I kind of just had an epiphany after I wrote that long post. More on that at the end.

I have heard of that uv dye. And was kind of thinking that would be my next step. Then possibly move on to the compression test if that has no luck.

Also had considered it may be happening in the heating system. I'm getting no leaks around where I think that is, and no puddles in passenger floor board.

Those are great suggestions and I appreciate your taking the time to help.

More on the thought I just had. I got to thinking, as I do, that this van's radiator has a longer neck than on any other car I've owned. Below the cap is two ports. A tube that connects to another that mounts over by the air intake, (which I've heard is like a return from the engine on those trucks). And above that tube coming from the neck is the one that goes to the reservoir, (and the reservoir also has an exhaust tube of course.) And below lose two ports is still about an inch and a half till the top of the radiator.

So that caused me to go out just now and take a second (80th) look. I only drove it a short time today, and that was ten hours ago so it was cold. And it was at the level that I've been calling full. Most of the way up the neck and to the full cold line on the reservoir. Turns out the level was actually above the bottom port on the neck.

Which leads me to think there is a possibility that I am a big ol dummy. And I was slightly over filling it and when I got up to full pressure/temp the excess was going out the exhaust tube on the reservoir. And quite possibly the bottom of the neck, (top of the actual radiator) is where the coolant is supposed to settle when it's cold.

​​​​​​So, what I did was use a turkey baster to ****** that little bit of over fill from the neck so the level is below the bottom port about an inch or so, where it's been settling. So it's there and the reservoir is up to full cold line.

I'm gonna drive it to work and back tomorrow, checking it after work but not adding more if it's at the same level, and look at it the next morning. If it's at the same level then, then yes I'm a dummy who's been doing it wrong and obsessing, which I can deal with. Or, it's time to go buy uv dye. And then go from there.

Again thanks for the input and I guess letting me logic this out.

If this works I guess this thread can be a heads up to someone like me who's freaking out for possibly no reason, or if it doesn't it'll let people know what else I had to do to track down and fix it if it's an actual problem. I'll check back in with the verdict in a day or two.

Fingers crossed.

 

That's a "burp" tube so air trapped in the engine block can escape.

Your theory is highly plausible.

 

Ah. Ok. Good to know.

And I hope I'm into something. 🤞

 

You might already be doing this but here’s what I do.

leave the radiator cap on and only check your coolant in the overflow tank. I use a piece of tape.

add 2 inches of coolant in the overflow and mark it first thing in the morning before you drive it. Then only check that mark first thing in the

 

that's a good idea. This would give me a marker to be sure.

I checked it two days in a row and I think it's still losing. But without a benchmark like that, I'm guessing.

Currently I am buying a second cap to make absolutely sure it's not that. I already replaced the cap with another cheap one that was exactly the same. They both fit weird and I'm still not 100 percent sure that's not the culprit.

No store around me had the better OEM one. Not even to order. Major chains even. I did find one on Amazon. It comes tomorrow. Then a couple more days of testing. Probably use your method.

I think I may be over thinking this but it's kind of something you have to be sure about. I want to trust my vehicle.

So yeah. New cap. Top off. Mark the reservoir level with tape. And drive it a couple days. See what happens.

Thanks for the idea.

 

Well I blew a head gasket on mine but it was the coolant part of gasket which let it get sucked into cylinder. Put some of your oil in a tablespoon and heat it to see if any moisture starts popping.White exhaust is a sign too. Put head gasket sealer in radiator an it worked for me .
Using a 15 lb cap on radiator now an all I do is keep it's rubber gasket clean

 

Well I blew a head gasket on mine but it was the coolant part of gasket which let it get sucked into cylinder. Put some of your oil in a tablespoon and heat it to see if any moisture starts popping.White exhaust is a sign too. Put head gasket sealer in radiator an it worked for me .
Using a 15 lb cap on radiator now an all I do is keep it's rubber gasket clean

 

Update. So I got a new radiator cap. The OEM one. Topped it off yesterday. This morning same scenario. I definitely needed the better cap so I'm not mad. Should have done that in the first place. The fit is way better.

But. Mystery is still there. So I took the doghouse off and looked around. No seepages that I could see. Then I got the idea to look at that hose that, as I was told earlier in this thread, is for trapped air to leave the engine block. Mounted under the air intake. So I took the air intake filter off to get a look. And the hose connection on the right, one that goes to the radiator, was not quite seated all the way. Was a small gap. But then again it's a small leak. So I carefully loosened the clamp and slid it up on the stem as far up as it would go. (You can see it in the pics. They are not too clear but space was tight and I was using my phone. But you can see what I mean.)

I don't know if that fixed it. It's a wait till tomorrow kind of thing. Since the thing happens during the overnight cool off. But fingers crossed. Again.

There it is.

Different angle. Was trying to get better light. The connection I fixed is on top on this pic. Don't know if that quarter inch was the issue. But maybe....