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Recurring radiator issue, blown head gasket?

868 Views 31 Replies 13 Participants Last post by  stidley007

I made a prior thread a while back concerning this issue but wanted to make a new one with new insights I've found. The issue is as follows:

The coolant level in my 2007's radiator consistently stays about three inches below the filler neck. It does not decrease below this height, nor will it pull in coolant from the overflow. I have driven it as such for months to confirm this. Upon refilling the level to its proper height to the filler neck, putting on the cap, and starting the engine, coolant will begin to quickly gush out from just beneath the cap after only ten minutes, when the engine temperature reaches the first notch on the temp gauge. I have been through four different radiator caps and none have stopped this behavior.

I have verified that the hose from the neck to the overflow tank is not clogged, and used a ziptie to firmly seal it to the horizontal valve in the filler neck. I can watch it, and it does not leak from the hose. I have rented an Autozone pressure test kit and pressurized the system with the engine off at 16psi. It holds pressure just fine. The mating surface between the cap and gasket is clean, tight, and free of nicks, and the caps are not missing their gasket (see photos).

This troubles me, because I am beginning to suspect there is a greater issue here. I find it hard to believe that coolant is gushing out at the rate it is after the engine barely gets to operating temperature. Part of me wonders if there are exhaust gases somehow escaping into the cooling system, creating excess pressure beyond 16psi that would cause this behavior. But if this is a case of a bad head gasket, shouldn't the engine be burning up coolant over time? It's never run dry or fallen below the same three inches under the filler neck, and I'm not blowing white smoke out the tailpipe either.

Of course I could continue to drive it this way, as most people would. But this small annoyance has been bothering me and I'll be damned if I can't figure out the issue. I've attached a photo of the cap and cap mating surface (AFTER topping off fluid). Any and all insights are welcome. Thanks.

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I’m not sure how to test the thermostat without removing it, but my oil’s been clean and no white smoke.

With the engine cold, cap removed, and not all of the added coolant puked out yet, I can watch the coolant rise up to the very top of the neck in about three minutes. This doesn’t seem normal, especially given the fluid is still cool to the touch.
Are you certain the rad cap is in the "second" notch position, not first?

If pressure gets too high in cooling system, it should dump out to overflow res...
Yes, I’m sure it’s on properly in its “second position” so to say. The fact it pukes out with such ferocity from beneath the cap instead of steadily going to the overflow is what’s leading me to suspect something more foul.
Can I use some silicone grease between the cap and the neck to help seal it? I don’t believe that four different caps are all faulty in a row, each one being a different brand.
I will upload a video and check that neck area and vent on Monday, I’ll be out of town until then. Thanks for all the insight thus far.
Why is there NO HOLE inside that radiator neck, for the excess coolant to go to the hose/reservoir? At least that's what it looks like, a defectively made radiator.
The hole is present, it’s just hard to see in the photo. I’m not sure if the radiator is original or not, the only maintenance history I have on the cooling system is the water pump was replaced at some point around 2017/2018 (previous owner, not sure why or what material impellers).
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Well there you have it:
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I really did not think I’d find anything out of the ordinary with the reservoir, but after a good ten minutes of pulling and straining I got the overflow hose off only to see this.

I couldn’t even poke a paper clip through that gunk, it’s an absolute miracle I had coolant bursting out of the cap instead of a blown hose on the highway. Another trip to the junkyard is in order it seems.

I suspect that before the previous owner replaced the water pump, they used some stop leak to try and remedy a leak in that area, thereby causing this tough gelatinous buildup. At least I learned that lesson the easy way, to not to use stop leak in any of my vehicles.

Thank you all so, so much for the help. I genuinely would not have ever found this out on my own and it’s why I keep coming back to the forum. Much appreciated everyone.
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I did end up removing and drilling it out. Not sure why I opted to get a replacement at first honestly.

It was extremely difficult to get good access to the three bolts, namely the bottom one, but it can technically be done without removing anything other than the battery + tray. Took me about two hours of messing with swivel sockets and small ratchets to get a good angle.

I’m going to get the cooling system flushed out next oil change as the stuff that’s in the system right now has a bunch of dirt and other contaminants in it and I don’t want to have it clog again.
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