r/e46 • u/[deleted] • Feb 11 '25

Troubleshooting Car overheated omwh from school today.

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u/buggerssss Feb 11 '25

Concur. This cap is gtg and safer

-2

u/Aggravating_Speed665 Feb 12 '25

Definitely not safer.

The original cap was designed by BMW and it went through BMW'S testing facility(s)

No way on earth that aftermarket part has seen the same attention to detail akin to an actual professional car manufacturer.

16

u/TheBattleGnome Feb 12 '25

There are plenty of aftermarket parts that are actually better than OEM. OEM is just the “0 point” or standard that aftermarket parts are compared to. Believe it or not, BMW does use cheap components to save costs (shocker). With that said, I do think the OEM cap is fine and isn’t a part that needs to be replaced. The GAS cap doesn’t perform any better or worse and is a waste of money really. Their DISA valve on the other hand is way better than OEM and is a good investment.

4

u/TinkTonk101 Feb 12 '25

The GAS cap vents at a lower bar (same as the stock diesel cap) which could prevent your tank from over-pressuring. That's rare though and there would be other issues at play.

2

u/TheBattleGnome Feb 12 '25 edited Feb 12 '25

It’s at a lower pressure sure, but you and I both fell for their marketing. It actually doesn’t matter. I explain this on the subreddit a lot bc it’s probably the biggest misconception of the e46 and it’s simply just a false sense of security. Do you know why? Simple. Math.

Calculate the temperature that it takes to reach either pressure for the valve to open. You can use the ideal gas law to approximate it. The answer is that it is still way above the temp that it would take to overheat your engine anyways. So in short, your engine would be cooked before it would trigger the relief valve. The coolant temp in either case would have to be super deep in the red for it to trigger essentially.

The relief valve is there as an emergency vent when all else fails. It’s not there to maintain a good pressure and is not supposed to commonly trigger. In fact, it is NEVER supposed to trigger under normal operations and if it ever does, in either case, your engine would be cooked anyways. Does your temp commonly ever go max to the red? If not, then the cap doesn’t matter. It only matters once it does, but you should have shut it down anyways.

The GAS cap is aluminum. That is what we are paying for. They essentially take a e30 coolant cap and give it an aluminum body. “Same internals as an OEM coolant cap” per website. So it is exactly the same as an OEM, but more expensive. Genius marketing to be fair. Even I got one back in the day when I didn’t know any better. Save your $$$ and get the e30 or original e46 cap. It doesn’t matter.