406oc.co.uk

Hi All,

New to the forum, new to the world of 406s (although used to have a N/A Diesel 405 -what a slug of a motor). I'm having a weird issue with the temp guage....

Seems that from cold-start the needle gradually wanders to around 70-90C, then around 5-10mins of driving the gauge drops to zero for a maybe a second or two before returning back to original temp reading.

I'm not used to "sophisticated" cars...Does the Pug have a short and long cooling circuit?? i.e. a short circuit cooling circuit for cold-starts, this allows the engine to get to temperature quickly; once at 70-90C, thermostatic valve opens the "long" circuit, and that explains the sudden surge of cold fluids past the sender. Coolant mixes and temp then goes back up.

The only thing that argues with this is:
1. The final temperature is back to where the needle was before the drop - I wouldn't expect to see this as hot + cold = tepid.
2. I've noticed this happen whist I had the car driving for 30+ minutes by which time the car was running warm.

The most likely thing is the connection to the temperature sender - corrosion can cause an intermittent signal.

Any pointers RE cooling system complexity would be appreciated.

Squuash

As you suspect, you most likely you have a poor connection on the temperature probe, (but for safety's sake make sure your cooling system is properly filled up / no air locks).
Depending on the age of your car, you may have multiple coolant temperature sensors - early ones had separate sensors for the gauge, fan control and engine ecu info, the post mid-2001 "fully multiplexed" cars have only one, mounted in the thermostat housing.
The cooling system is pretty straightforward, only point to watch, the reservoir tank is not the highest point so bleed screws are fitted on the thermostat housing and one of the heater hoses. Rumour has it parking with the osf wheel on a highish kerb lets you fill up normally without bleeding, I used a sawn-off coke bottle to extend my reservoir last time.

Sounds exactly like my issue.

I agree with Doggy, the culprit is most likely the temperature probe. In some of our cars (pre-mux in particular) there's a separate sensor for the gauge.