Is the radiator system on a 1999 2.4L a closed system? If it isn't...where is the radiator cap? underneath the plastic housing?
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'99 Cavalier Z24 Convertible
Remind me why i keep this car?
The rad cap is on the expansion tank. You don't want to uncork that cap when it's hot - that sucker gushes like a geiser!!
^ Speaks from experience.

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2002 Sunfire -->
- Ractive steering wheel
- ASA 17" EM9 + Nexen N5000 215/45/17 (steelies for winter)
- D-Spec Lowering kit @ 1.4" (issues currently

)
- Rockford P250.1 + MTX MZS1004 + Panasonic CQ-C8313U head unit
- Barely legal tint.
My Jeep Comanche has the same set-up and they call it a closed system. I assume to be considered 'open" you need to have a cap directly on the radiator?
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'99 Cavalier Z24 Convertible
Remind me why i keep this car?
I have't done it myself, but I watched (with horror!) as a buddy of mine opened his just after shutting the car off... car was overheating, he saw the coolant tank was empty and went to add more.... but the fact that the tank itself was empty, didn't mean the rest of the system was... man, did that thing shoot high!! He got burned pretty badly too... not something I recommend... ever opening that cap when it's anything but stone cold.
The track guys call my car a "sealed" system.. so I guess it is a closed system.