Does the coolant temp all come from one sensor?

[dammad]

I've been trying to track down why my '99 996 cab tip runs hot (99-104C according the AC temp hack). Fans run on low speed when the AC is on, but refuse to turn on when the AC is off. Yet, the AC temp hack says the coolant temp is 99C+.

However, the manual says:

"Electric fan, speed 1

(Ground to DME control unit, terminal 35)

Coolant temperature higher than 96.75°C or air conditioning switched on.

Electric fan, speed 2

(Ground to DME control unit, terminal 36)

Coolant temperature > 102°C or air-conditioning fluid pressure switch closed (coolant pressure > 16 bar)."

So what gives? If the AC thinks the coolant is 99C+ and the AC is off shouldn't the fans come on. After all they definitely work with the AC switch depressed?

Could it be that the AC and DME get coolant temperature from different sensors?

[Loren]

I've been trying to track down why my '99 996 cab tip runs hot (99-104C according the AC temp hack). Fans run on low speed when the AC is on, but refuse to turn on when the AC is off. Yet, the AC temp hack says the coolant temp is 99C+.

However, the manual says:

"Electric fan, speed 1

(Ground to DME control unit, terminal 35)

Coolant temperature higher than 96.75°C or air conditioning switched on.

Electric fan, speed 2

(Ground to DME control unit, terminal 36)

Coolant temperature > 102°C or air-conditioning fluid pressure switch closed (coolant pressure > 16 bar)."

So what gives? If the AC thinks the coolant is 99C+ and the AC is off shouldn't the fans come on. After all they definitely work with the AC switch depressed?

Could it be that the AC and DME get coolant temperature from different sensors?

How do you know the AC Hack temperatures are what the DME is seeing?

You need to look at what the DME is seeing with a PST2 or PIWIS.

[dammad]

How do you know the AC Hack temperatures are what the DME is seeing?

You need to look at what the DME is seeing with a PST2 or PIWIS.

Yes, I don't know what the DME is seeing.. May have to take it to the dealer to see.

Just to be clear, I'm trying to work out if there is more than one sensor that the various parts of the car use for 'coolant temperature'.

I've got the wiring diagram from the workshop manual, but can't make head-nor-tail of the various connections from page to page.

[BruceP]

How do you know the AC Hack temperatures are what the DME is seeing?

You need to look at what the DME is seeing with a PST2 or PIWIS.

Yes, I don't know what the DME is seeing.. May have to take it to the dealer to see.

Just to be clear, I'm trying to work out if there is more than one sensor that the various parts of the car use for 'coolant temperature'.

I've got the wiring diagram from the workshop manual, but can't make head-nor-tail of the various connections from page to page.

FWIW, my understanding is that the early cars have one coolant temperature sensor, at the motor. The later ones have a second one somewhere out by the rads, and the OBD averages the two. This is why earlier cars appear to run hotter than later ones do.

This info is a hazy memory, so happy to be corrected if I've got it wrong.

[cbr786]

my car is a 99 C4 cab tip and I am in the UK when I sit in heavy traffic car idle-ing for 15 mins or more my temp haq display reads 104C as well and it sits thier at that reading ???

I know water boils at 100 but antifreeze coolant mix and water should take the boiling point higher right? ....

I know once the traffic eases and i can move a little say do 30 - 40 mph the temp haq goes back to 90c

i was thinking of installing the fan haq via a switch on the dash so the fans can come on when I want them to also being a C4 tip it automatically has the third rad ...