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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Mon, Feb-26-2018, 02:28:08 PM   #1
ctres
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Default Coolant Pressure

Can anyone confirm what the correct coolant pressure is in the expansion tank. I'm trying to work out what expansion tank to use in my E30 S54 swap and it looks like the S54 operates at 2 bar (30psi), and a lot of the other common expansion tanks/caps are 1.4 bar (20psi). Are most of the BMW caps compatible? Could I put an E46 M3 cap on an earlier model expansion tank to maintain proper pressure?
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Old Mon, Feb-26-2018, 03:13:32 PM   #2
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Default Re: Coolant Pressure

Iím running a 1.2 cap on my car and Iíve had no issues for a couple years.

https://www.germanautosolutions.com/...12_bar_cap.php
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Old Mon, Feb-26-2018, 03:38:23 PM   #3
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Default Re: Coolant Pressure

I wouldnít go to a lower pressure cap. That will lower the boiling point of your coolant.

As long as you donít exceed the pressure rating of the cooling system, you can go with a higher pressure cap and reduce the risk of boiling your cooling system.


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Old Mon, Feb-26-2018, 11:01:04 PM   #4
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Default Re: Coolant Pressure

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Originally Posted by bigjae1976 View Post
I wouldnít go to a lower pressure cap. That will lower the boiling point of your coolant.

As long as you donít exceed the pressure rating of the cooling system, you can go with a higher pressure cap and reduce the risk of boiling your cooling system.


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This is what I'm getting at. I want to keep coolant pressure at the stock level, not reduce it. FCP seems to indicate that the M3 coolant cap, which is shared with a number of other vehicles is a 2 bar cap. I was wondering if anyone could confirm that, and if not, can anyone confirm that an E46 M3 cap would fit on an E30 expansion tank?
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Old Mon, Feb-26-2018, 11:15:31 PM   #5
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Default Re: Coolant Pressure

Stock is 2.0.
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Old Mon, Feb-26-2018, 11:23:20 PM   #6
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Default Re: Coolant Pressure

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Originally Posted by ctres View Post
This is what I'm getting at. I want to keep coolant pressure at the stock level, not reduce it. FCP seems to indicate that the M3 coolant cap, which is shared with a number of other vehicles is a 2 bar cap. I was wondering if anyone could confirm that, and if not, can anyone confirm that an E46 M3 cap would fit on an E30 expansion tank?
Yes pretty sure it fits. I'm using euro e36 expansion tank and I'm pretty sure it's the same as the late e30 expansion tanks. Also have 2.0 bar cap
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Old Tue, Feb-27-2018, 11:51:50 AM   #7
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Default Re: Coolant Pressure

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Originally Posted by mitch500 View Post
Yes pretty sure it fits. I'm using euro e36 expansion tank and I'm pretty sure it's the same as the late e30 expansion tanks. Also have 2.0 bar cap
Excellent, this is probably the route I'll go then. E46 M3 2.0 bar cap on an e30 or e36 euro reservoir. Thanks for the help guys!
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Old Tue, Feb-27-2018, 02:50:26 PM   #8
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Default Re: Coolant Pressure

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Originally Posted by ctres View Post
Excellent, this is probably the route I'll go then. E46 M3 2.0 bar cap on an e30 or e36 euro reservoir. Thanks for the help guys!

One aftermarket option is a Canton Racing 2L tank with a 36psi cap. Takes some custom work but I think itís a worth upgrade. Only downer is you lose the level sensor or would need to weld on a bung and use an e36 level sender.


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Discussing Coolant Pressure in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)