Thermal time switch or coolant temperature sensor!

[rickkrockstar]

On my 1981 volvo 245, I'm having a cold start thermal time switch issue, I know how to resolve it, but thats not my question,

My question is that my by brain is telling me a volvo "temperature sensor" works the way same as a cold start "thermal time switch" which cost increasingly more $$$, like $10 and $100 difference,

So could I possiblly exchange one for another, I was wondering if anyone has a reasoning to my madness, thanks

[93Regina]

brain is telling me a Volvo "temperature sensor" works the way same as a cold start "thermal time switch"

Well, find a salvaged temp-sensor, and give it a whirl.

I've got various charts on this topics, but Volvo used at least two different "ECU" temp sensors. These are both "NTC" types, but one grounds to block, and the other one does not.

So, you need to see if "thermal" sensor grounds to block or not...does it?

[lummert]

A thermo time switch is normally closed, but opens depending on the environmental temperature.

[93Regina]

A thermo time switch is normally closed, but opens depending on the environmental temperature.

Oh, like this?

Fuel Injection Thermo Time Temperature Switch 280Z - Datsun 280Z fuel injection sensor. New genuine Nissan OEM engine fuel injection thermo time/Air temp switch for Datsun 280Z & 280ZX 1975-83. Includes washer. Fuel injection control sensor that tells the cold start valve when to operate. The thermo time switch can effect cold starting or possibly cause a leaky cold start injector if it is faulty.

[rickkrockstar]

thanks everyone for your reply's, I tryed a coolant temperature sensor from a 88 Volvo240 and it did the job of the thermal switch, so I you can in some applications use these interchangeable when used with cold start valve, at least from my newest experience,

[93Regina]

1981 Volvo 245

V(V) = I(A) × R(Ω)
volts = amps × ohms

OEM thermal time switch powered start-injector for about 7.5 seconds at -4°F, and then an "open circuit" so start injector would quit.

LH's ECU temp sensors at say 68°F is around 2400 Ω, and at 176°F about 320 Ω, so LH's temp sensors are working in opposite direction ohm wise, and are not an "on/off" switch.

Best way to tackle this issue, is to put a momentary switch inside vehicle, and then touch it to fire up start injector. I did this years ago on a 1981 VW Rabbit Pickup.

Capture.PNG (90.01 KiB) Viewed 4269 times

[jimmy57]

Will not interchange. Very different parts.
TTS has an electric heater and will heat the bimetal spring and open the ground to CSInjector after the right amount of starter time (ambient T at commence of starter operation determines time to heat open so time is variable with temp) to prevent flooding. The TTS also is heated due to location so no ground is available to CSI when not needed.
ECT is a temp variable resistor and is not able to handle current to CSI.
If you want an alternate then get a momentary switch and mount to left of steering column and hold it while starting until it fires off. Only needed when below about 100 F coolant temp. Unplug CSI connector and determine which wire is connected to starter solnoid activate wire. Splice dash switch to the other wire.

[93Regina]

Will not interchange. ... Splice dash switch to the other wire.

IIRC, thermal time switch has 12 volts hot on all the time, so when key is turned on, and it works via ground. So, a grounded momentary switch is what will activate thermal switch.

Unless thermal time switch was rewired so it always had a ground, and then fires up via 12 volt signal (starter's power, and momentary switch).

I used the ground method on momentary switch, so I was in control of start injector.