So I have not found a consistent answer to what pressure cap belongs on the coolant reservoir. It seems different sites list either a 18psi one or a 16psi one. The FSM mentions in its testing section for the cooling system to be sure not to exceed 18psi when putting a pumping test device on. Even on the two CRDs I have, one came with an 18# cap another a 16# cap.

So again thought I would ask and see what the consensus here was. (BTW for my purposes won't be doing any heavy towing but will be going up some mountains).

What do folks think?

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2006 KJ CRD

Everywhere I looked except one where they listed the cap pressure, it was 18 psi.
Only NAPA listed a 16 psi cap.

The Mopar part number for the cap is: 04596198

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Supporting Vendor and Moderator of LOST
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I bought a stant cap that i thought was rated to be 2 psi over the stock cap and it kept letting the coolant boil over. Stick with oem if you can.

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2006 CRD - GTB2056 turbo by Dieselguy86, Eco Trans Tune, Lift Pump, Week's, HDS Tstat, Racor Filter, ARP's, OME 790's+Top Plate, JBA 2.5", JBA UCA, Moab's+265/75R16, ARB Bull Bar, 4.10's, TrueTracs

Radiator caps are not precision devices.
It's just a spring and two pieces of rubber.
They function within a psi range. Never exactly what they're rated for.

I've used a 7psi cap on mine. Coolant never boiled.
But I'm at sea level. At a higher altitude you will need a cap rated for a higher pressure.

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U.S. Army Retired