Temperature Sensor Stuck on "Cold"? - VF SV6 (Series II)

[sam_drury]

Hi Team!

Seeing if I can get some assistance / understanding as to what may be happening.

Recently, my SV6 Wagon has been causing me grief, due to the Temperature Sensor readings on the Dash.

When the Ignition is triggered, all the guages do their dance while turning on.

However, after the "dance", the Temperature Sensor stays on "cold", with a warning popping up saying the "A/C was turned off due to High Temperature".

Initially thought this was due to the Engine Temp Sensor itself (had the check engine light come on) and recently had this replaced. Yet, the problem has come back.

Check engine light is on, temp sensor stays on "Cold" (all the way to the left), Thermo Fans are constantly running at full boar, and AC gets disabled.

After having a read through the forum, it could be one of the following;
- Air stuck in the system
- Radiator Cap fault

Having a look at the Radiator cap, it appears to be fine, no damage to the seal within the cap (from what I can tell).

It could be Air stuck in the system (not 100% certain), as after a couple of days, the Temp Guage reports correctly! Comes back up to a normal operating temperature.



Any ideas brains trust? Happy to provide more info + photos if anyone wants to see more.

 

[NJD-1992]

You'll first need to scan for codes, otherwise it's a wild goose chase.
Well worth getting one of the little Bluetooth code readers from eBay, they come in very handy.

An easy one if you think its air in the system, is to just grab a bottle of coolant, pop some in a funnel at the fill point (Cut open upside down 2L coke bottle works great) and let the engine run for awhile to bleed itself (I also squeeze the coolant inlet and outlet hoses to help it along)

I did experience the thermo fan running at full speed once, but that was due to me disconnecting it, forgetting id done so, then turning ignition on. Car assumed the Thermo Fans were failing so just ran them at full speed until I cleared the code then worked A.OK again

 

[Skylarking]

Get yourself a cheap $20-50 OBD scanner and a free app for your phone, then you can check what DTC the car reports.

Not only can you check for DTC but you can also check live data.

With live data, you can actually see the coolant temperature that the ecu sees. Then you can actually measure the coolant temp using another thermometer (laser thermometer against radiator core?) to verify what the ecu sees is indeed correct.

You can also measure the coolant temp resistance (at a given temp) is within expected range and/or disconnect and jump the coolant temp plug with a known resistor for 70c and see what the ecu/cluster shows/does.

Then if the ecu, cluster, wiring and sensor all look to be behaving reasonably wrt coolant temps, consider the coolant system itself (radiator cap, blockages on the front of the radiator core, air in cooling system, etc, etc).

 

[wetwork65]

My top coolant hose flattened out and the level in the radiator was scarily below the top of the tubes when the engine was cold. The radiator cap seal had changed shape, but looked OK at first. Changing the cap to a genuine one got rid of this issue. Check out some of @Fu Manchu 's submissions for details.
I changed caps on both cars for good measure.
Not saying that is your problem, but changing the cap is an easy and cheap step to take, which should be done after a few years anyway.