Can anyone tell me what the purpose of the "water temp switch" does? The water temp switch that threads into the thrmostat housing.

See picture attached of switch, it is the switch on the top right in the pic.

What year and model car do you have? those parts aren't on my 240 or 260Z.

I've never seen anything like that on either of my 70 or 71 Zeds.

-Brandon

There are several switches/sensors on the thermostat housing of fuel injected cars (75-78 280Z's). The temp switch and thermotime switch signal the fuel injection computer for various things and tell it what the engine temperature is so that the computer knows how to control the FI. Do you want to know exactly what the temp switch does, or just this info in general? I could look it up in my '78 manual if you need to know exactly what it does.

These probes are also on Flat Top carbureted 260's

There are actually 2 on FT 260's.

One is the actual temp probe for the temp gauge, the other is for the electric pump cut off. This was a simple logic device that would cut [switch] off the electric fuel pump when the coolent was over a certain temperature and the motor RPM was below 600 [from memory].

HIH

There are three temp sensors for coolant.

One is for the temp gauge.

The thermotime and coolant temp switch work to signal the ECU to either richen or lean out the mixture by changing the lenght of time the pulse is to the injectors.

They also control the cold start valve ( or injector) in the front of the manifold that is in all actuality the same as a choke to richen the mixture on a cold start.

Originally posted by 2ManyZs

cold start valve ( or injector) in the front of the manifold that is in all actuality the same as a choke to richen the mixture on a cold start.

The first part is more accurate. The cold start valve is more like an injector, which ADDS fuel. A choke blocks the air going into the carb/intake. Both have the same effect- richening the mixture.

The proof is, the problem with some cold-start valves staying open after the engine starts and gets warm, so the mixture is always too rich. It has been said that the cause of that is a faulty thermotime switch( a temp sensor), which doesn't close off the cold-start valve.

Go to: http://www.72hours.net/~zcar/

You can download a pdf version of the factory technicians

troubleshooting manual.

This is a must read for anyone who has fuel injected 280Z's!

Thanks for the link, hadn't seen that one before!

The car in question is a 76' 280z

I have four sensers/switches on my thermostat housing . 1 is a thermotime switch. One is a temperature sensor. one is the water temperature switch. and I am not sure what the third is.

I downloaded the EFI theory and trouble shooting file yesterday and I have been going through it step by step to find the gremlin in my system but no luck yet. The file does not say exactly what the temp switch does exactly.

Please see my other post if you think you can lend a hand http://www.classiczcars.com/forums/showthread.php?s=&threadid=11361

Thanks everyone for your help.

On an Aus delivered 77 260 carbied car the water temp switch is actually part of the fuel system.

Under the drivers seat there are two relays, water temp relay and alternator relay.

These two relays are connected in series and activate the fuel bypass solenoid, next to elec fuel pump.

The water temp relay cuts off current to the bypass solenoid when the coolant temp is below 35 deg C it gets the reading from the temp switch.

The alternator relay cuts off current to the bypass solenoid when engine speed is above 400 rpm.

Because these relays are connected in series with the bypass solenoid, the solenoid will only operate when the engine is operating above 35 deg C and running below 400 rpm.

I would think it does a similar job on the 280 but i'm not 100% sure.

i just got done reading this and i was wondering if any of you know where to get one?