How do I replace the Water Pump on a 2000 Nissan Maxima? Mine has gone out- I checked the Oil-there's no water in it so I don't think it has messed up the head gaskets. We had it towed to my dad's on a flatbed....tried putting water in and it just ran out the botttom of the engine.

Question edited for clarity.

No to both. The water pump is chain driven and takes water from one side and pumps it out under pressure from the other. The thermostat is fully enclosed in a housing with no access to oil.

Oil in Coolant only comes from a failed head gasket where the oil and water channels are in close proximity and under combustion pressure of hundreds of pounds.

Water pumps are designed to pump water through the engine, radiator, and heating system. Water pumps will not cause oil to enter the cooling system.Oct 4, 2016

Q: Can a bad water pump cause water in the oil - YourMechanic

Water Pump
https://shop.advanceautoparts.com/find/nissan-maxima-water-pump

Thermostat Housing
https://www.google.com/search?q=nissan+maxima.+thermostat+housing

..

Larry, normally engines do not have to be taken out to change timing tensioners, the bumper assy., A/C condenser,radiator,etc is removed to get access. Best if you get yourself a manual.
Check the attached links,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."

DIY Video VQ35DE Timing Chain Tensioner and Water Pump Replacement

NISSAN MAXIMA Timing intro MP4

1995 2001 Nissan Maxima 1 3 Water pump replacement

How to fix timing chain rattle Maxima Forums

If there is water in the oil, it wouldn't last long under the heat/pressure of the engine, so if you are seeing water it must be super fresh. Are you losing coolant? If so, then i'd suspect water pump/water pump gasket if you never had that replaced. It could be head gasket, but you would probably experience a consistent coolant loss with maybe loss of power or misfiring. You can check with a pressure/leak down test for head gasket. Either way, if you are losing coolant I'd check water pump. If you aren't losing coolant than it can't be the water pump or head gasket really letting "water" in.

ok there are two o rings in the water pump one keeps the oil from the timing chain side to come in the water and also keep the water/coolant separate from the oil side the second one keeps from coming out of the engine. i am sure the first o ring i talked about is pinched or damages or is not installed when the water pump was installed.

check your thermostat and possibly your cooling fans and temp sensor for the fans

Make sure there is no debris in front of your radiator or ac condenser

hot engine usually due to clogged radiator or bad thermostat. Take out the thermostat and make sure it is opening fully in boiling water.
Look inside your radiator for signs of clogging. If yes, professionally flush or replace radiator.

The water pump is located behind the timing chain cover. There are two black plates on the front cover. The one near the front of the car has the water pump behind it. The other one has the timing chain tensioner behind it. First you must drain the coolant. Then support engine and remove engine mount. Then remove drive belts. Then remove the two black plates. Push the tensioner in and lock it with a paper clip. Then remove the two bolts holding the tensioner and remove tensioner. Then remove the water pump bolts. Rotate engine crankshaft the take tension off of water pump (about 20 degrees). Then install two bolts into water pump threaded flange (M8). Tighten M8 evenly as water pump will come without damaging it. Check for corrosion. Then replace with new one. Make sure you use new "O" rings. Lubricate with engine oil. Put the original three bolts back in the water pump. Then install timing chain tensioner and black covers. Replace belts and engine mounts. Add coolant and pressure test system.

Have a mechanic check that. If you try yourself, might competely mess up the entire timing.

a lot depends on the location of the water leak.  If you have checked all the hoses, clamps, radiator and cap.  There isn't a lot left. The water pump is on the front of the engine under the timing belt shroud.  This would also be a good time to replace the drive belts, timing belt, any soft hoses and anything else that's iffy.
public library...Chilton or Haynes auto repair manuals or collisionrepairadvice.com
  

No. Only cars with timing BELTS you do that.