I have a 2 year old SAAB Sport Combi. After driving through heavy rains, we discovered a big puddle of water on the floorboard behind the passenger seat. Mechanic could not find anything wrong with radiator, the undeside, etc. They are getting ready to strip the carpeting, etc. What could be wrong? Seals on windows appear to be ok.

You need to find the conduits for rain - one of them has a leak in it probably from corrosion. Try to locate just where the water is getting in and see if you can use a sealer to stop the water from getting in.

I would remove the glove box and anything else in the way and look for the source when hosing down the car.

your heater core is bad they leak when they go bad youll have to replace its under/behind the dash

I had the exact same problem with my 1995 neon. It was leaking around the tail light. I pulled the tail lights off and put a heavy coat of RTV silicone on the gasket, and 2 years later never happened again

My guess is the window seal.

I agree but just wanting you to understand a little better... If you park under trees with leaves or pine straw that's what it is...It's around your windshield arm openings.. Leaves and pine straw will fall into the holes and clog up small drain hole intended to drain water from when it rains. leaves and pine straw enters the space it clogs up a little rubber drain hose. Water starts to fill up the area and when it gets high enough it will soak through the paper filter and fall on the floor to the passenger side floor board. Take the vent cover off around the windshield wipers.. usually plastic..After you have them off you will see the paper filter down in the area...The water is not draining properly and water is going through that filter and falling onto the passenger side floorboard. Try to get as much Leaves or pine straw out. Then a long skinny screw driver or wire and push it down..It will fall down under your car..You can find the little rubber hose under the car and Push up...But make sure it's clear...Pour some water in there and make sure it's draining before putting back together...also make sure that air filter is ok also...That's where your heater and AC air comes in at...

Floor plug or plugs have fallen out most likely.There Should be some plastic plugs under the floor board outside. Look to visualy check to insure they are still in one piece.

A busted heater core will flood the passenger side floorboard when the heat is turned on.

the windshield could be leaking behind the dash,a good way to check is put the fan of the heater on,hot or cold and get a solution of soapy water and apply to the outer edges of the windshield and look for bubbles.

Engine coolant will feel oily and the windshield will fog up and the car will stink. If it is just water it could be coming from the passenger door weatherstrip at top. The ac drain tube , if stopped up will also leak water in the floorboard.

A/C drain pipe blocked with old leaves and dead flies the outlet is on the passenger side of vehicle lift bonnet and look a lower of firewall for a rubber pipe with a **** in the end and squeeze it and shake it