Wierd coolant temp sensor/gauge behaviour

[ThisPhil]

Im figuring out a european 88 narrow body and stumbled upon a wierd coolant gauge behaviour.

Right below the thermostat housing on the intake manifold are 2 temp sensors:

• 1 acutal sensor with a T shaped connector
• 1 temp switch with just a ground connection

 

Here is what I dont understand:

The coolant temp gauge needle only moves if the temp switch is closed. If the switch is closed, the temp gauge needle instantly jumps as high as it goes. Even if the engine is stone cold and I short the switch to ground, the same behaviour occours. 

Im pretty certain that the T shaped connector is for the coolant temp but Im beginning to doubt that. I will install an aftermarket temerature gauge just to be on the save side because I know that too much heat has some pretty bad effects ion these engines.

Can someone explain whats going on?

 

[admin_JAinsworth]

[kev]

I'm confused what is meant by a 'T' shaped connector.   Although, the image posted above should help.

Item 3 is the CTS for the main ECU.   It is a variable resistance thermostat.

Item 1 is the temperature gauge in the cluster.   It is variable resistance based on temperature.   On 87 and earlier cars, this is a single pronged connector.   87 and earlier cars have another thermostat on the heater core piping under the dash to control the operation of cabin heating.   88/89 cars removed that inside thermostat and simply use the same thermostat on the intake, #1, for this purpose....thus these years have two prongs on this sensor.     I will say that my knowledge is limited to only to the North American market.   EU market cars may be different.   

Item 4 is for the air conditioning only and it is an on-off thermostat switch.  If the temp reaches a certain level, it shuts off the air conditioning

Item 2 is a thermostat that is used for the fuel vapor system....this is an on/off type of switch as well.   It simply keeps the purge valve closed until the engine is warmed up such that it isn't allowing fuel tank vapor from entering the intake system and increasing emissions under engine warm-up conditions.   It's important to note that this is all that it does.  If you pull both vacuum lines to this thermostat and plug them, the purge valve still shuts at idle and opens off idle based on the vacuum/boost before and after the throttle plate.   

 

[techboy]

I think by "T" shape he is referring to #3, the CTS. The prongs are arranged in a "T".

You most likely need to replace sensor #1. That's you gauge sender to the cluster.  If a new sensor does it fix it, trace the wiring and make sure there's not an issue with the physical wire.

[ThisPhil]

Thanks for the replies and yeah, with the T shaped connector I ment the prongs on the CTS.

I really only have 2 instead of 4 items (there are so many small differences to american models which makes research really frustrating sometimes). My guess is that the singe prong connector on my intake is equal to item #1 in the image admin_JAinsworth posted. I think I lead myself on a false path by thinking that the CTS is connected to the temperature gauge in the dash.

I already replaced sensor #1. I will however compare its resitance to the old one in some hot water.

[kev]

Oh wow, yes definitely a different intake than the North American spec cars.  But, yes, the two prong one is the CTS for the ECU.  The single prong connector runs the gauge in your dash.   I've had bad luck with aftermarket sensors.   Although haven't experienced exactly what you are describing.   My issues were in calibration.  The aftermarket sensor displayed either real low or real high on the stock gauge when at normal operating temperature.   Actually, I never found an aftermarket sensor that I ended up keeping in the car....I've always ended up tossing in an original one.