Coolant Question No Radiator Cap

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My wife's Grand Marquis is the first car I have ever worked on with no radiator cap. The overflow tank is pressurized. Does this mean the coolant level in the tank is the same as in the radiator, or does it blow back and forth with pressure? I am used to just popping the cap and looking at the radiator level.
 
Radiator cap is on the coolant bottle. The radiator is completely full on these systems and the level is checked in the bottle.
 
Correct as above plus the fluid goes back and forth with thermal expansion. If you are changing the fluid, check for a drain valve but many cars do not have those either, and you have to pull a hose off at the bottom of the rad. You add the fluid at the expansion tank or if you prefer you can pull off the small hose to the rad and use a funnel. Your choice.
 
I just replaced coolant in my GM. I pulled the lower hose at the radiator to drain. I have heard bad stories about some of the plastic petcocks either breaking or seeping.Fill the bottle to the marks and watch it for a couple days as you will need to top off until all the air is out. It should be filled with G05 coolant.
 
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