I can't find a temp switch anywhere this is the sensor that has the bullet plug and a ground which I believe was only on the 75-76 280z. I live in FL and it never gets colder than 50 degrees where I live. Can I just plug this hole? Also my other questions is there is a small house coming from the side of the thermostat the wraps around to I believe the manifold. On the l28et I just bought this hole is plugged. What is this hose for? Do I need it or can I plug this also? I live in FL and don't have to worry about emissions and everything. Thanks in advanced.

Do you mean the thermotime switch?

If you disconnect it the cold start valve will not activate in cold conditions and when the coolant temperature is somewhere under 20degC (70degF), cant remember exact temp, but its in the FSM. If its always above 20 degC where you live it should not be a problem.

The two hoses you are talking about go to the vacuum switch for the EGR control circuit. The switch is a thermal valve that opens around 45degC (105degF). Without them you effectivly disable your EGR system.

They also have a second use and that is to warm up the AAV (Advanced Air Valve) in nissan it called the air regulator bypass. It has a bimetal element that operates the throttle bypass valve for fast idle when cold. This vavle will work up to 80degC. The valve is heated two ways or a combination of both to be more precise. The coolant heats the bimetal and the elctrical circuit heats the bimetal. If the water is disconnected the electrical circuit will take much longer to heat it and therfore giving the engine a faster idle until the bimetal element heats up.

Someone has probably disconnected the coolant line to disable the EGR and excepting the possible fast idle for a short time after the engine warms up.

Chas

Ok sorry dont mean to thread jack here, but I have a mystery sensor on my thermostat housing on my 77. If you are looking at the thermo housing from the nose of the car, it would be the sensor on the top right, or if from the drivers side it would be the top one closest to you. The FSM just shows this as a plug, but I have a brass plug with a SINGLE wire coming off of it. The wire has a bullet connector on the other end that is not connected to anything just dangling there. I have searched as many posts and google images and manuals as I can find but I am stumped any ideas?

Its probably something from the PO. He was probably using a second gauge to check the temp or something like that? Normally its plugged.

Looking from the radiator, the top left sensor with a single terminal post is the temp gauge in the car. The other two underneath with the square plug connectors are for the EFI. The brown one (left) is the thermotime switch and the white one (right) is the temp for the EFI fuel mixture control.

Chas

You might have a 76-77 thermostat housing. 76 for sure has four - thermotime switch, coolant temp. sensor (for ECU), coolant temp. indicator (for gauge) and temp. switch for the ignition module (to use the second pickup in the distributor to advance the timing when cold).

The service bullitin on the atlanticz site has a good illustration of the thermostat housing and the sensors positions on different models

http://atlanticz.ca/zclub/techtips/76sb/1976_280z_S30_Service_Bulletin.pdf

Chas

That's probably the best picture of the housing out there, I always forget where it is. Eurodat's probably right, it's just an extra transmitter. Measure the resistance from the bullet connector to ground. If it's a transmitter you'll get a number, if it's switch you'll get zero or infinite.