Lowering radiator cap pressure from mfgrs 15 to 13 psi


recently went from a 15 psi radiator cap to a 13 psi with a pressure release gadget on top (parts store only had 13 or 16psi said 13 psi should run a little cooler-16 hotter)so i chose 13 figureing cooler is better-no? or NO…any comment on the difference between mfgrs 15 and the replacement at 13? thanks for your time


Pressurizing the fluid raises the boiling temperature. Going to a lower pressure capp allows boilover at a lower pressure. Stop at another shop and get the proper cap.

By the way, why did you need to replace the cap? It’s highly unusual for a cap to fail without some “event” such as overheating having caused it.

  • mountainbike


Doesn’t make much difference. The thermostat generally controls the temperature, not the radiator cap. But if your car normally operates at a very high coolant temperature, it is possible the cap may release pressure just shy of this temp. Your vehicle may run at just under its normal temperature but still likely within range. Not a real problem, as I see it.


If this were my car I’d find a cap rated at 15 psi, as the manufacturer specified.


hi mountainbike thanks for the reply–have a small crack at the top of plastic housing that I have been epoxying-posed the question of epoxy yesterday and 4 replys were to replace the radiator.It only leaks when engine is shut off-so I thought if I were to vent the pressure it would buy me time to come up with the $350- $400 to replace. thanks again and yes I should get the right cap


thanks everyone for your time


Call some radiator shops to see if they will do plastic welding. Yes, there are plastic welders.


thanks for that idea…never thought of plastic welding