# What PSI radiator cap for a "68"



## Layzdude (Jun 14, 2015)

As the title says, what PSI cap should I use.

I have not been having any overheating issues, but the last couple of times I took the car out on 90+ days I noticed that after I shut it off I get fluid out of the overflow. About a cup or 2. I currently have a 7 PSI cap and was thinking of going with a 15 PSI. Will going to a higher PSI cap cause me overheating issues? Radiator was not overfilled. Planing on flushing the system. Thanks for the help.

One more thing, I currently do not have an over flow tank. Were they factory or added after. She is a driver so I don't care so much about originality.

John


----------



## geeteeohguy (Feb 2, 2008)

You should be running at least a 15psi cap. 16-18 is even better. 7psi is not correct for these cars.


----------



## Goat Roper (Oct 28, 2014)

^^this^^
Also the '67 didn't come with a puke bottle, not sure on the '68 but if you overfill it then it will puke some out.
Not a big deal unless so much comes out that the coils on top inside the radiator are exposed then you have a thermostat or pump issue.
These cars came with a 190 degree thermostat, lots of opinions on what you should use but I stuck with the factory specs.


----------



## Layzdude (Jun 14, 2015)

Thanks for the info. Stopped by the local auto parts store and got a 16 psi. Not sure why the PO had a 7 PSI?


----------



## PontiacJim (Dec 29, 2012)

Pontiac Service Manual for '68 says 15 lbs on the radiator cap, 190 degree T-stat, and the fill level should be 3" below filler neck.

The 15 lb cap raises the boiling point of the anti-freeze to 258 degrees before the pressure releases out the cap.

Personal opinion - I like a 160 degree T-stat for summer use. Not so good if you use your car in winter cold as it opens too soon and you won't build good heat for your heater/defroster. The 180 is my choice if I use a higher temp T-stat, but that is splitting hairs compared to a 190, just always found 180 a more common rating at the parts stores.


----------



## geeteeohguy (Feb 2, 2008)

Been running 160 'stats in all my GTO's out here in CA for almost 40 years and will continue to do so. If I lived in colder climes, I would maybe go 180. But never a 190. Cooler is better, and you have to remember: When the '68 Pontiac Service Manual was printed, the 100 octane fuel recommended for the same car was available, and 25 cents per gallon. Times change, and _we _must change to be sucessful. So, cooler is better.....


----------



## Rukee (Feb 8, 2007)

Increasing the pressure also increases the boiling point of the AF/water.


----------



## Layzdude (Jun 14, 2015)

Not sure what T stat is in their now. On the list of things to investigate. Thanks for all the advice.

John


----------

