fonetico

Before I do something irrational, I'd like an expert opinion.
I'm haemorrhaging coolant and have tried the usual tests but still can't find where it's leaking.
I've just noticed the heating seems to be either full on or off and only warm anywhere in between. So I assume it's the disc valve as I've had one fail in the past, but it didn't leak.
I read they're prone to failure but is it normal for them to leak?
I'm not entirely convinced the heater's malfunctioning and I don't want to replace the valve unnecessarily.

Mrmerlin

if the HCV is older than 7 years swap in a new part along with the short hose,
this is the common failure point for the cooling system.

NOTE make sure your HVAC vacuum system is leak free replace any worn rubber junctions or diaphragms.
Inspect the temp sensor connection in the fender well probably best to cut the connector out and solder the wires together.


Next would be the hoses at the water bridge, if these are original then replace all of them.

Next look at the top side of the radiator where the crimps are,
the black tank will crack at the flange where the crimps are at the top,
then you will see a white crusty deposit going down the tank.

Worst case examine the head gasket edges see if you find white crusty deposits this means the HGs are leaking

fonetico

Thanks Stan, that should keep me busy.
Just as a matter of interest, the car's suffering from high idle. Could this vacuum system in any way related to the idle control?

Chris Lockhart

Stan, pardon my ignorance, but why solder the wires together? Thanks in advance.

Mrmerlin

removing the outside temp connector will reduce the tendency for them to corrode where they are connected.

the factory connectors are fair ,
and the wire to connector pins is poor,
and next to impossible to detect corrosion.

This recommendation is for continued operation .

dr bob

Chris --

Note that Stan isn't proposing that the temp senor be removed from the loop, only that the connector there is so sensitive and subject to corrosion that the connector could be bypassed.

Maybe more than you want to absorb:
The temp control in the car has an electrical loop that passes through the inside and outside sensors and the slider. The little setting motor has a servo in it that moves based on the difference between the cabin and slider, with the sensors having opposite thermal coefficient. The difference is an error number that it strives to maintain at zero. The servo motor moves based on that delta, making a contact that opens the heater valve. The outside temp is also compared with the slider setting to help decide whether the outside temp air will help or hurt the effort to heat or cool the cabin, within some allowable error. Bottom line on all of this is that any "extra" resistance caused by corrosion in a connector will throw off the balance between the sensors in the loop. A small amount can be compensated by the driver as he/she moves the slider around to keep the cabin comfortable, without regard for the numbers stenciled on the controller face plate. As the primary loop drifts though, the action of the recirc flap drifts too. And when the slider correction approaches the end of available travel, you actuate one of the little micro-switches that essentially override the readings and force the servo to full-hot or full-cold. On the servo, it appears that anything that isn't pretty much full-cold (~25%) is the same as full-hot as far as the heater valve is concerned.

Mrmerlin

Thanks Dr Bob thats was a great description and reason why I made the suggestion