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ScottyG

What does water temp switch do?

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    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.

    post-5824-14150793526638_thumb.jpeg

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    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.

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    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

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    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.

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    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.

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    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.

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    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.

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    i just got done reading this and i was wondering if any of you know where to get one?
    You'd have to be more specific. One what? A water temperature switch or ???? For what year car? Fuel injected (280Z-ZX) or carbed (240-260Z)? Many things were discussed in this 6 years dead thread.

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    I'm having the same problem as well. The part 22120-N4202 is no longer available anywhere. I've talked to a couple of techs that know these cars well and suggested to plug the switch off.

    The purpose of the switch is to switch between the dual points in the distributor as the car warms up. The 75 and 76 are the only cars that use this switch and was later was discontinued on the 77 and 78 280s. As mentioned in http://www.classiczcars.com/forums/s...ad.php?t=35873, you could change out to a 280zx distributor to resolve the problem. The other option is to purchase the 260z water temperature switch that MSA sells and redo the wired ends to match the 75 and 76 switch. The ends can be easily change out using a male bullet connector and insulator and a ground connector on the other terminal.

    Another suggestion from techs are to use a fan switch, but you need to make sure that the switch will switch over after the car warms up past 100 degrees or less. Not sure on how accurate that would be, and if you could find a switch that would be that low on the temperature to switch, but I guess it's worth a try, plus it's lot less expensive than the MSA part.

    I'm thinking of going with the MSA option and redoing the connections at this point.

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    I'm having the same problem as well. The part 22120-N4202 is no longer available anywhere. I've talked to a couple of techs that know these cars well and suggested to plug the switch off.

    The purpose of the switch is to switch between the dual points in the distributor as the car warms up. The 75 and 76 are the only cars that use this switch and was later was discontinued on the 77 and 78 280s. As mentioned in http://www.classiczcars.com/forums/s...ad.php?t=35873, you could change out to a 280zx distributor to resolve the problem. The other option is to purchase the 260z water temperature switch that MSA sells and redo the wired ends to match the 75 and 76 switch. The ends can be easily change out using a male bullet connector and insulator and a ground connector on the other terminal.

    Another suggestion from techs are to use a fan switch, but you need to make sure that the switch will switch over after the car warms up past 100 degrees or less. Not sure on how accurate that would be, and if you could find a switch that would be that low on the temperature to switch, but I guess it's worth a try, plus it's lot less expensive than the MSA part.

    I'm thinking of going with the MSA option and redoing the connections at this point.

    My switch was bad when I got my car, a 1976 model, and after reading through the manual and figuring out how it worked I realized that with a bad switch, the car just runs a little dirtier when it's cold. The switch advances timing when cold, I believe, to get it to run cleaner. It's only on the non-CA models.

    I could be wrong on the reason to advance the timing when cold, but either way, without the switch, the car just has the timing when it's cold that it would have anyway after it warms up. My car runs fine when cold, without the switch working.

    Once the car warms up, the switch doesn't do anything.

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    The purpose of the switch is to switch between the dual points in the distributor as the car warms up. The 75 and 76 are the only cars that use this switch and was later was discontinued on the 77 and 78 280s.
    The second part of that statement is true, as my 78 didn't have that switch but there were no points on any 280Z, any year as they all had electronic ignition. Read the rest of the explaination in that thread. What is says it that 260Z used a similar switch and it's function was to switch between the points. Edited by sblake01

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    So will the car run fine without.a functioning switch? Asling bthe ground wire broke on mine and I dont know if its safe yo drive without. Sorry to revive old thread

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    Sarcasm or I can really drive it? And if I do what would be different about how it performs?

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    Yes, you can really drive it.

    In conjunction with the alternator relay (IIRC), it forms a simple logic circuit that controls the fuel pump on start up.

    Originally designed to stop flooding the carbie's on a hot start.

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    Mine is a 76 efi 280 i dont have carbs? Im reffering to the temp switch. Its only on the 75 76 model...

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