So.. easy enough question I hope. 85 Camaro. V6 TPI 2.8L.. I’ve got really erratic tempter rise and falls, all over the place. I’ve burped the system an still nothing. I think my radiator cap isn’t opening and purging into the over-flow tank (That’s what it should do right, when reaching a specific temp?). I haven't seen the levels in it rise or fall an I’ve checked it out with the temps running high and low. I have not overheated yet and theres a new temp sensor in the car.. Question is, how do I know which cap to get? I’m looking at rockauto.com and there are two types. “{Standard Vented Cap (Open or Closed System)” and "{Safety Release Vented Cap (Open or Closed System)" Both rated for 16psi. Which do I go for? An would it hurt if I got a lower psi cap?

Edit: My bad.. should of been under 3rd gen. Regardless.. anyones input?

 

Lets go to third gen shall we...

 

I would look at your thermostat befor changing the cap that is what opens and closes to regulate the temp in the system

 

Leave the radiator cap alone for now (as far as your irratic temp is concerned) and look at the thermostat as suggested. As the coolant gets hotter and hotter, pressure builds inside the cooling system (like a pressure cooker). The cap won't open until internal pressure hits the pressure rating on the cap, then it will spill it into the overflow tank. If the cap is staying closed now, then it's not affecting your temp. But it could be your stat that's acting up. As far as the radiator cap rating, it depends on the condition of your cooling system, the kind of driving you do (city or highway), and your climate. A higher rated cap will put more pressure on the radiator, heater core, and hoses. A lower pressure cap could actually save any one of these from blowing if they are old and weak. You could experiment with a lower cap and keep an eye on your overflow tank. If it still acts normal, you'll be cool![8D]

 

Got'cha, thanks guys. =)

 

What they said. Do the T-stat and if you can get a lower PSI cap. Also make sure you have no leaks letting coolant out and making air gaps.
16 PSI was good for when there were no expansion tanks and they needed to keep the coolant in because what came out went onto the ground and could never make it back inside the system from there. Plus there is less chance of splitting a radiator or hoses

 

Stay away from the "safety release cap" type of cap as I've had one fail after a short period of time with the results you've described. The problem you have is likely what I had where the system is not staying pressurized properly. Just for "grins" put a new 16psi cap on it and fill the radiator and the overflow tank to the "cold" level and then run the engine and see if that solves your problem. It worked for me finally after I tested the thermostat, was stumped, and was told by an Auto Zone parts store guy that the safety caps seem to have this problem of not keeping the system pressurized properly because of premature failure. Hope this works.
Good Luck,
Roy