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I have a Maxima that runs hot after about 20-30 minutes of driving.  I have replaced the master air flow, the water pump, the thermostat (faulty?), the radiator and an air sensor or two.  The car runs hot and then comes back down to earth whether I have the AC on or not.  It is very random and does not necessarily happen every day especially if it is 85 degrees or cooler.  If I put the AC on first thing, it seems to help.  Odd.  Any ideas?  Is there another sensor I should look at?  You think the thermostat is faulty?  Faulty water pump?

Thanks!  

i was looking at the wiring diagram for a 98 model...    seems that maximas have used 2  radiator cooling fan for a while... they might even be wires for 2 speeds....

here is the diagram for an 98...

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/07/64/b8/large/0900c152800764b8.gif

there seem to be 3 relays to control the cooling fans...     this is the autozone part number Duralast / Relay 20228

since that is an OBD2 car... do you have a friend with a scan tool?????   you should be able to see the fans cycling on and off with a scan tool.....

can you see both cooling fans come on when the engine comes up to full temp??????

when you turn on the a/c ... can you see the fans come on..

if it possible that the water pump is going bad...   it is also possible that the head gaskets are damaged from prior overheating...      how fast does it built pressure when you first start it...   one to two minutes???   or seconds...    squeeze the upper radiator hose to feel the pressure build up...

you also might want to squeeze the upper radiator hose and make sure the cap is holding pressure...  

unfortunately i don't have a scan tool or know anyone with this here.  i just took it out for a test drive.  at first only one fan came on.  i took it back out and finally the second fan came on and both were going pretty strong.  the car never overheated.  

i checked the cap before leaving and it doesn't appear to be loose.  it isn't low on coolant either.  no leaks that i can see.

the water pump is practically new and so is the radiator.  i had replaced them at two different times when the 3rd mechanic finally figured out that the old water pump was faulty.

one other thing to note...i was having an issue with the check engine light coming on...  then the car shut down on me.  i had a Z car guy replace the master flow and an air flow sensor.  the car ran fine, but the light came on again.  it went through winter coming on and off.  it has not come on in over 3 months now, but i do have this heating up issue that i am trying figure out.

thanks for your help.  

were you able to look at the wiring harness diagram i posted the link to...

both fans look like they should come on at the same time....   not one and then the other...  

the fan relays are controlled by the ecm.....  so if you have a check engine light... the ecm has recorded a possible problem...

code readers start at about 40 bucks... but ... everybody is short of cash... but a scan tool is worth the money...

they start at 80 bucks at some places... you really want one that can display live data...  

here is a link to one that i already have..  it is still a basic unit... and does not read every data stream.. but the emission codes it does...

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=98614

HF used to have a asian car specific scanner... but it sold out..  i don't know if they are going to get more... hopefully...

be sure that when the check engine light comes on.. that the mechanics put down the trouble codes on the work order and invoice...    there are thousands of different codes...   if they don't put the code down... you might end up paying for the same thing to be fixed and fixed again...   and just because it sets a code... does not mean that part is bad...  it means that part is sending its signal to the computer that is out of normal range... so it could be something related to that system...

find the cooling fan relays... put a mark ( numbers) on the tops so you know where they came from.... swap them..  see if the other fan comes on first... that would indicate the relay is bad...   only swap exact relays... and keep track of where they went..  so you don't move troubles to a different circuit...