90 240SX Elec Fan / Temp Sensor(s) ?

[pgtrr]

I've got a 90 240SX with a KA24E S13. It's a very original 140kmi 1 owner car w/ no mods. The mediocre wiring diag I have doesn't include colors so I'm looking for some add'l help here.

Recently I've been chasing out a water leak where it was boiling & dumping water after shutting off and it now has a new set of hoses, clamps, tstat and cap. Seems to be OK so far (knock on wood) but that's not what I'm posting about...

Even while idling with the AC on max in near triple digit ambient temps and an increasingly lower that optimal radiator water level the temp gauge NEVER inched above halfway which surprised me. But when I'd shut it off the water would be boiling in the radiator and overflowing through the tank (thus bringing the rad level down). Also the auxiliary elec fan on the radiator never once kicks on. I don't know that it ever has. So I'm starting to wonder about the gauge, temp sending units and what not and want to make a few add'l checks before closing the books on this project.

Questions:

Q: Where is the temp sensor located on the engine that controls the DASH temp gauge?

Q: Does it ALSO control the aux ELEC fan?

Q: If not, WHICH ONE does and where is IT located? (I found one odd sensor spliced into the bottom rad hose near the rad)

Q: What are the 'CONDITIONS' that trigger turning on the aux elec fan on the radiator?

Thanks

[pmkls2]

First, your car keeps overheating probably due to air trapped in the cooling system. The temp sensor will not properly register temp if it is not submerged in cooland, thus your normal reading. Both temp sensors are located on the front of the intake and there is also a bleed screw located next to them for helping burp air out of the system. The sensor for the gauge has just 1 wire coming out of it and the one for the computer has 2. The aux fan is controlled by the a/c switch and run through that sensor you found in the lower rad hose. The sensor in the hose is a thermal switcfh designed to not allow the aux fan to operate until the car has reached operating temp. It seems to be common for that sensor to go bad and not let the fan kick on. I simply bypassed the sensor and wired the fan to run anytime the compressor is running. Anytime you fil the cooling system you will need to burp all of the air out of it or you will continue to overheat the car. The easiest way to bleed air from the system is jack up the front end or park on a steep incline with the front end pointing up. With the car running turn on the heater and open the cap and keep adding coolant and squeezing the upper hose until you gat all the air out. HTH

[benemorius]

What he said, plus:

The sensor for the gauge is the single-wire one. The two-wire one is for the ECU. Are you using pure water or a 50/50 mix with antifreeze or what?

[pgtrr]

Thanks everyone! Very helpfull info. I really like the idea of hardwiring the aux fan to run w/ the compressor.

FYI the car was not and is not overheating per se - just had a pesky leak that has been fixed by new hoses/clamps.

thanks again

[pmkls2]

well glad to hear you fixed the leak and just remember anytime you have to add coolant you need to burp the system to prevent overheating problems due to air bubbles. also the reason for the thermal switch inline with the aux fan is to allow the engine to reach operatng temp if it hasnt reached operating temp yet. I really havent had any problems with hardwiring it though and i have dual electric fans that also run along with the aux fan anytime the compressor is running

[GU240sx]

I'm having the same problem. Just bought my 240 and found out the thermal switch had been deleted so the aux fan is not connected at all. How did you hardwire the aux fan to run w/ the compressor? (I'm not too keen on running it all the way thru the firewall to connect to the fan switch.) And I'll def burp the system next time I need coolant. Thanks.