OK i have a lot of problems. First off my fans are not working properly. I have checked all fuses, all relays, all grounds and everything electrical. I ran a jumper accross the relays and they come on and i ran direct power off the abttery. Everything is good there. When i turn the AC on the fan dosnt activate aswell. BUt when i disconnect the temp sensor, the 2 wire plug, the fans come on cause the ECU goes into failsafe mode. I then plugged in sensor from the JDM engine and put a torch to it. WIth a Digital multi meter i measured the ohms in audible. When the ohms went below 300 the auduble hit, the switch closed the circuit and the fans came on. I then proceeded to install that sensor in and started it up but still no fans. I did the same test with the torch and DMM on the sensor i had just pulled and got the same results. Went audible at 300 and closed the switch activating the fans. I then heated the engine up and ran it for about 15 minutes until it reached just below the H and shut her off and back probed the sensor in the intake and it read 1600 ohms. Both sensors worked with a torch to it! What gives?!?!? I went to the parts store today and found out that i have the gauge sensor for the pre 92 sr20de, so i ordered the one for post 92. sr20de. I have the 95 g20 and i'm swapping in the high port sr20de. I don't know what the hell the problem is. I'm ***** replace that gauge and hope it has something to do with it. I mean it ran for 15 minutes and the fans didnt come on. I put a candy thermometer(all i had!) into the radiator fill and it would only get up to 140 degrees. Theres also little if no pressure in the water lines. I can take the cap off without an squirting. I have a 170 degree thermostat aswell. Could the waterpump possibly be bad and not pumping the hot water back to the sensors? I dunno what to do next and i'm running out of ideas. If anyone could give me any other ideas i'd appreciate it cause right now anything is better then nothing. I'm about to put a sledge hammer through the friggen windows!

You said that you changed your Temp guage. Why?

The only way the water pump is not working is if it's seized. You would be able to tell because it wouldn't move at all.

What happens when you run without a thermostat? Any difference?

Make sure you have the 95+ 200sx SE-R sensors. I believe there is a difference because of OBDII.

Fans come on at 203*F. Get an accurate way of checking the Temps.

Check ECU for any possible codes that won't trigger a CEL.

I did a JDM swap and i changed temp sensor gauge because the JDM one is different. I was going to use the old on in the old engine but it was bad aswell(the spade broke off). I will have that by wednsday and hopefully that will give me results.

By the water pump i was thinking maybe the propeller on the back was bad and not pumping water efficiently enough.

How could i run without a thermostat? I never tried, but removing the thermostat from the housing and runing the car without one is something that can be done withou hurting the engine?

The temp gauge i ordered was for 93-2000 se-r's and the same for G20's. I didnt change the temp sending unit for the ECU side because i was told the JDM one would work fine. I even tried the one off the old engine but i got no results as you can see below.

I don't think the water gets to 203 because i can stick my finger in it and its warm but not hot and there is no pressure when i
remove the cap.

I have checked the ecu time and time again and i i get CEL's for unplugged sensors that i unplug purposley, but i will check again.

Thanks for the help, anything else you can suggest?

When you mean guage, do you mean the one in the instrument cluster? I think you mean sender/sensor.

Is your thermostat new? If not, go buy another from NISSAN.

I think your problem lies in a stuck thermostat and the fact that you have the wrong temp sending units (JDM) for the motor. Once you get the new sensors (USDM) and thermostat, you should be ok.

As stated by blackb13, it is certainly worth checking the thermostat. You can check the thermostat by placing in water with a thermometer and heating to check opening against specifications.

Otherwise...

I have had problems like this on a Mitsi' before - lack of circulation so the heat doesn't carry to the sensors and out through the radiator etc.

If the coolant was not kept up to scratch, it is entirely possible that the water pump impellor has corroded away to the point where it won't move the coolant well enough.

Unfortunately this can also mean that things like frost plugs and bypass are corroded and they may spring pinhole leaks as time passes.

When I replaced this pump on the old Mitsi', the impellor was all but not existent. I ended up replacing the radiator, all the frost plugs, the bypass pipe and both turbo coolant pipes due to them springing pinhole leaks from corrosion.

Oh, and ensure the system is bled properly, apparently the DE is sensitive to air pockets in the cooling system.

sounds like your thermostat it sezed shut.
the temprature sender in on the block right?
but the sender for the fans is on the radiator?
so if the stat dosn't open hot water stays hot cold water stays cold and no mix between the two.
to be honest i don't know the locations of the sender units on a sr20. but thats what they are like on my jackaroo and cbr.
and the jackaroo had simular problems.

I mean the gauge sensor. the single spade next to the sensor for the ecu. I had the JDM one in it, then i got a new one which turns out to be for pre 92 engines. I purchased the new one and will ahve it in a few days. I had the JDM thermo in it so i swapped the old one from my old engine in it. The JDM seemed really stiff and the USDM one seemed soft. I may ened up swapping the water pump if i can't figure it out. It's a JDM low mileage engine so i doubt the impellor is corroded away but may broke or not sitting propperly on the back of the pump. I flushed the cooling system last night with super flush and i plan to bleed the cooling system aswell as per the FSM. To pyro_15, the sensor for the gauge and the sensor for the ECU to turn the fans on it right next to one another on a water jacket under the intake manifold. Thanks for the help guys and if anyone else knows any other tricks let me know.