Coolant expansion tank cap cannot be tightened? Screws down, but has no tension

[kamber]

So I went to change my spark plugs today, and to get to them, I had to move my coolant tank forward a bit. When putting it back, I noticed that the cap could spin freely, so naturally I went to tighten it down.

Surprise; it doesn't!

The cap will screw all the way down, but when it gets there it merely just stops without getting tight. The arrows (1 on the cap, 1 on the tank) even line up when the cap is screwed all the way down, however there is no tension/torque keeping the cap in place; it can still freely spin back the other way with the lightest touch. I checked and the threads are not stripped on the cap, nor on the reservoir, which makes me think whatever mechanism is supposed to "click" or put tension on the cap to keep it in place is just flat out missing or broken.

Does anyone know if this issue is as simple as replacing the cap, or is the mechanism responsible for keeping the cap tight a part of the reservoir itself?

Thanks in advanced!

[deansbimmer]

Thought I'd post since nobody else has.

The cap is threaded as is the reservoir. In the cap there is am O-ringed center plug that "floats" within the cap via some tabs that hold it in place. This plug does the actual sealing of the reservoir cavities and pressure release.

The cap will thread all the way down until it is completely threaded on, bottomed out, and can go no tighter, just like a regular nut and bolt. If the cap keeps on spinning with no tension then the only explanation is that the threads are stripped or the cap housing is cracked and allowing expansion/slippage of the threads when tightened.

I would try a new cap first. There is more going on with the cap that the reservoir which is usually pretty robust.

Good luck.

[kamber]

Thanks Dean! I have a new cap on it's way, hopefully that will take care of the issue.

[NeverL8]

Originally Posted by kamber

Thanks Dean! I have a new cap on it's way, hopefully that will take care of the issue.

Did the new cap worked for you? Mine stops at the arrows but it doesn’t feel like it’s sitting right on it, it unscrews easily

[inTgr8r]

that's normal.
The cap doesn't seal, its the plug inside.
if its not leaking, don't worry about it.

[NeverL8]

Originally Posted by inTgr8r

that's normal.
The cap doesn't seal, its the plug inside.
if its not leaking, don't worry about it.

Oh awesome! Thank you! I was little bit concerned because it used more force taking it off

[inTgr8r]

Originally Posted by TheRussski

Oh awesome! Thank you! I was little bit concerned because it used more force taking it off

Yeah, after they've been on a while it gets something on the threads that builds up.
Mine was very difficult to remove the first time I checked fluids.

[NeverL8]

Originally Posted by inTgr8r

Yeah, after they've been on a while it gets something on the threads that builds up.
Mine was very difficult to remove the first time I checked fluids.

Weird system, I turned all the way until it stops and arrows pointing at each other..but it’s soo easy to unscrew it from that moment on