I just replaced my coolant overflow tank and upon putting on the new cap to it noticed that it was 18psi as my old one was 15psi.Is this reason for concern? Taking a fairly long trip with her tomorrow and don't want to do any damage. Thanks for any advice. PS Tried putting the old cap on but didn't fit.

 

The higher pressure cap will allow the coolant system to reach a higher temperature before it opens the cap into the overflow tank. I would check with the supplier of your new coolant tank and find out from them why they left a higher pressure cap on it when they shipped it to you.

 

From what I have researched, starting with the C6 and on the cap used is 18psi and using this cap on a C5 will not hurt it. I drove the car for over 3 hours yesterday and the temp was fine, around 200 and no leaking. Thanks for getting back to me, it's appreciated.

 

Glad out worked out for you. I think 210°F is the standard operating temp for late model GM vehicles.