D1 Fan clutches

1of40

Well-known member
Oct 23, 2017
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Question for the experienced crowd. My factory stock reservoir cap says 9lb psi, whereas a new cap I recently purchased says 15lb psi. Which one would you run?

Note this is a NAS defender with the small metal res tank cap, that the D1 plastic tank/cap combo.
 

p m

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Apr 19, 2004
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Interesting point.
I found here that "Using a pressurized radiator cap can raise the system pressure and thus the coolant boiling point. A typical 1 Bar (14.5psi) pressure cap theoretically raises the boiling point of 50-50 coolant to 253°F."
You really don't want to be near 253°F.
 

1of40

Well-known member
Oct 23, 2017
120
19
Va
Interesting point.
I found here that "Using a pressurized radiator cap can raise the system pressure and thus the coolant boiling point. A typical 1 Bar (14.5psi) pressure cap theoretically raises the boiling point of 50-50 coolant to 253°F."
You really don't want to be near 253°F.
That’s my thinking as well. 15psi, assuming it doesn’t cause any other leaks should in theory help keep the temps down more so than 9psi.
 

p m

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Staff member
Apr 19, 2004
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www.3rj.org
That’s my thinking as well. 15psi, assuming it doesn’t cause any other leaks should in theory help keep the temps down more so than 9psi.
Sorry if I wasn't clear.
That's exactly against my thinking. A 15-psi cap will not keep the temps down any more than a 9-psi cap, but it would allow the engine running hotter without losing coolant - until the heater core blows up.
 
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