No matter how much coolant I put in the car it always shows check coolant it overheats all the time wen it over heats the low oil pressure light comes on wat could be the problem

You will have to do a little bit of reading for this one : HowStuffWorks How to Tell If You Have Blown Head Gasket

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limited performance indicates that the ecm put the engine in the low power mode due to a problem encountered with a sensor ( low oil level-pressure, overheat /low coolant level, gear box temperature over heat, loose position sensor/s . Run the fault codes first to determine where the faults are. Check that the cam shaft is turning ( broken timing belt)

I'm sorry your having problems. Specially with your kids in the car. Puts you and them in a dangerous situation. Both of them are obviously wrong. Waters boiling point is 212 degree *F. Pontiac grand am engines are notorious for cracking the cylinder heads. When the cylinder head warms up so does the crack and causes it to expand. This can cause the engine to over heat. The reason it doesn't over heat going down the road is because air flow outside moving the heat away from the engine. I hate to say this but honestly no matter what is wrong with your car. It's normally somewhat costly. But not always. Between what you are spending on towing bills and bad diagnostic. It's costing you more than you would have spent to fix it twice correctly. You need to have the engine and cylinder head pressure tested for leaks. You can check your oil and see if there is any coolant mixed with the oil. If so. Your head gasket is blown and leaking or cylinder head is cracked. The oil will look like black coffee with a lot of creamer in it. Kinda brownish color. Check that first. Also visually check to see if there is any stains on your cylinder head and engine block. These can show you where the coolant is leaking out when it get hot. Your car has a aluminum block and head and it expands and contracts with heat. Hope this helps. But it can literally be so many things. Lets hope for the best though.

Your engine does not overheat because the oil is low. Do you get heat out of the vents? Check the fluid level in the radiator not the reservoir. Due this with the engine cold. If the radiator is low than you have a leak somewhere. Add coolant to the radiator and see if you can see any abvious leaks. You may need to have the cooling system pressure checked in order to find the leak. If the coolant level is full in the radiator than you may have a bad thermostat. If you get heat out the vents than we can assume the coolant level is full and the water pump is working. When the temp gauge is hot feel the upper and lower hoses. If one is hot and one is cold than the t-stat may be the problem. If there is no heat out the vents and the coolant level is full than you may have a bad water pump. Let me know if you have any questions and I'll do my best to answer them. Thank you for using FixYa.com!

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CHECK ENGINE OIL LEVEL SHOULD BE ON THE FULL MARK ON ENGINE DIP STICK. IF OIL LEVEL IS LOW.LOOK FOR OIL LEAKS UNDERNEATH CAR.IF ENGINE NOT LEAKING OIL CHECK OIL PRESSURE SHOULD BE 22 PSI @ 900 RPM IF NOT OIL PUMP FAULTY OR YOU HAVE WORN ENGINE BEARINGS.IF OIL PRESSURE OKAY YOU COULD HAVE FAULTY OIL PRESSURE SENDING UNIT. CHECK COOLING FAN TO SEE IF CAR COOLING FANS RUNNING WHILE ENGINE OVERHEATING.IF NO CHECK COOLING FANS RELAY AND FUSE IF ALL IS GOOD ENGINE COOLANT TEMPERATURE SENSOR FAULTY. IF COOLING FANS RUNNING WHILE ENGINE OVERHEATING.HAVE RADIATOR AND ENGINE FLUSHED OUT. REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP.

if the center 2 cylinders have only 10-15lbs pressure then you need to do a wet compression test to see if it is valves or piston rings that are bad.put about tablespoon of oil into each cylinder and turn over motor and redo the compression test.if the compression goes up you have a ring problem if it doesn`t it is a valve problem.you should check the oil to see if it has a white-caramel look to it as this indicates water in the oil.(head gasket) if the coolant level is low it can be burning coolant,you should have the cooling pressure tested just in case.it could possibly be a cracked head.if it overheats because of the low compression(sometimes happens) the motor is working twice as hard(runs hotter) as the other good cylinders have to work harder to do the same amount of work,

Low oil level can cause an engine to run hot but the pressure must be extremely now for that to cause a rise in operating temperature. Naturally, if the temperature is high on the guage, the engine is already overheating, and there are a multitude of reasons why an engine could overheat, from silly things like low tyre pressures to low coolant levels and water leaks. If you like, come back with some more specific information and lets see if we can put a finger on your problem.

That is a good sign, it is working, my oil pressure fluctuates like a tachometer, at idle it is low, like 20 lbs, then when I 'm cruising, 35lbs, but it goes up and down when you pump the gas. The pressure gauge is reading the oil pressure at the top of the engine, it will show 45 lbs with only 1 qt of oil in there, it is not an oil level gauge. You might have an oil light buried on the dash somewhere that will light up if the oil gets too low. ,, Now about that coolant leak, it should have nothing to do with the oil pressure. Is it a hose? Radiator? Joint at the top of the engine? Where is it leaking, and what is it doing? Does it over heat? Or did it overheat? Is there oil floating at the top of the radiator? Does it blow steam out the exhaust? Does it have coolant or just water? Check it out. hope this helps.

sounds like the head gasket is no good.pressure is getting into the coolant and overpressurising the resevoir.
if coolant is in the oil,low oil pressure triggered the oil light and check engine trigger results from lost compression.
a compression test will tell you.take a look at the coolant,is there oil in it?

Before you have major repair done on your car because of the "oil pressure light", review the list and see if any of these might be the source.  Some of the things on this list are things you can do yourself, some only done by a mechanic (inexpensively), and others require the aid of a mechanic.
1.  Check to see if you have a leak.  Low oil levels can make the oil sensor light come one.  Check your oil level following the manufacturers recommended procedure or use the information listed here http://autorepair.about.com/od/regularmaintenance/a/checkoil.htm.  If you do not have a low oil level, but still suspect a leak, place a drip pan under the oil plug overnight.  If you have a leak, you'll see signs of it there.  Then take the vehicle to a trustworthy mechanic and let them trace the leak.  It is possible for your engine to only leak when it is hot, so make sure you get the engine nice and warm before you put the car away for the evening and place the drip pan under your vehicle.  Other signs of an oil leak are listed below as well as an "oily" exhaust that leaves it mark on your bumper or "blue smoke" as you drive/idle.
2.  Check the coolant levels. If the coolant is low, the oil will heat up faster and cause a viscosity breakdown.  When the oil viscosity is low (= thin oil), the oil sensor light can come on.  If the coolant is low, add more.  Keep in mind that an engine running hot will heat the engine oil to the point that it thins out and burns off in the cylinders.  If the coolant level is fine, have the coolant (water) pump checked.  If the coolant is not circulating well through the engine, you'll probably have coolant boiling over, too.
3.  If you can afford to do it, change your oil to a higher or lower viscosity.  Refer to your maintenance manual and your trusted mechanic. I say this because, if your oil is thinning out too much because the viscosity is too low, your "check oil" light will come on.  If your engine oil is too thick, you engine will need added internal pressure to get it to circulate.  At lower RPM (just like thin oil), your engine oil light will come one.
4.  Have the oil pressure checked by other than an electronic means.  Your trusted mechanic can place an oil gage between your oil filter and the rest of the engine or on the oil fill cap of the engine.  If you are having an oil pressure problem that is seal-related, that should narrow it down.  If you can't afford to do that, when you get your next oil change, replace: the oil fill cap, PCV valve, and air filter.  All these contribute to the measurement of engine oil pressure by that picky little oil pressure sensor.
5.  Have the oil pressure sensor checked.  You may need some weird add-on to make it behave.  Do a search for the following part and read and you should have a better understanding: "part # 05017800AA a terminal/wire/vent to the oil pressure switch connector".  Never forget that sensor are usually engineered to report a problem well before a catastrophic failure can occur.
6.  If you're driving a high-milege car, make sure you are up to date on all of the engine-specific services.  For some vehicles, it is recommended that the head gaskets are replaced.  If you have internal engine leaks because of it, this will solve most of those issues.  Signs of this include: coolant visible in the crankshaft area (you can see this with the oil cap off), oil fouling your coolant (you can see this in the coolant reservoir), or smokey exhaust.  Expect your trusted mechanic to recommend that you change your spark plugs, timing belt, and cam shaft gasket at the same time.
7.  See if the oil pump needs to be replaced.  A faulty oil pump can contribute to low oil pressure as it fails (but hasn't failed, yet).  
8.  Do all of the above BEFORE you take to recommendation to have your engine replaced.
I have a 1998 Chrysler Cirrus (I know it's not a minivan, but hear me out).  I've been the single owner and have learned more about how engineering oversights or over-cautiousness can send you to the mechanic for just about everything.
Hope this helps!