signum 2.0t coolant loss and faulty temp gauge

**catbic** · 24th July 2011, 08:32

hi - not sure if this is in the right part of the forum - but i have a longwinded problem with my signum. about 2 months ago the coolant warning light came on and the car overheated almost into the red. i took it to local vauxhall dealer who did a pressure test and said prob the head gasket and poss cracked cylinder head and would cost a fortune. so i limped it down to my local garage who took it all apart and said that it was only a gasket on the water pump which he replaced. all was well for about a week of local driving when the coolant warning came on again. this time local garage stripped it and said there was loads of crud in the block which had blocked a pipe - which he flushed out. it was now able to run long distance but the temp gauge stayed at nil for ages before climbing to midway and hovering between 80 - 90 never staying still. it still loses coolant - at high pressure it will leak slightly when i switch it off - i can cope with that by topping up once a week or so but the temp gauge worries me. drove 22 miles yest before it moved from zero. there is no water leaking from exhaust and local garage is adamant it isnt head gasket. any ideas?

cheers cathy

**Jezzy** · 24th July 2011, 09:44

Firstly, you mentioned that you're losing coolant - do you know where from, or just from the fact that you need to top it up frequently?

Secondly, the erratic temperature reading is more likely to be a faulty thermostat rather than a problem with the gauge (or temperature sensor). The thermostat may stuck in the open position, thus keeping the water too cool.

**catbic** · 24th July 2011, 10:08

hi - i dont know where the coolant is lost but it drips out slowly on the ground when the car is hot. Yes i suspect there is a valve stuck open somewhere allowing the car to stay too cool. if it is stuck open would that explain it taking ages to register any reading on the gauge and then dropping to really cool again as i drive along the motorway? is it a big (read expensive) job to replace the thermostat?

**soulman** · 24th July 2011, 10:38

thermostat not a big job ...
coolant loss.hmmm you say the car drips when you are stationary ,sometimes this is actually water from the Aircon system .
catch the water and check to see if it is actually coolant.

**Jezzy** · 24th July 2011, 10:53

Originally Posted by catbic

...Yes i suspect there is a valve stuck open somewhere allowing the car to stay too cool. if it is stuck open would that explain it taking ages to register any reading on the gauge and then dropping to really cool again as i drive along the motorway? is it a big (read expensive) job to replace the thermostat?

Those are the classic symptoms of a faulty thermostat, especially that the temperature drops too far when you drive at motorway speeds.

It's not the easiest thermostat to change, but nowhere near the hardest either.

The coolant needs to be drained from the system, then the vaccum pump needs to be removed - after the electrical module attached to it has been removed as well.

The the thermostat housing needs to be unbolted, the old thermostat is then swapped for a new one, then GM anerobic sealant (part number 90542114) needs to be applied around the edges of the thermostat housing, before the top housing is bolted back on.

The vacuum pump goes back on - after fitting a new rubber seal, then the electronic module. Then the system is refilled with coolant and the air bled out.

If you don't know where the coolant is leaking out of, then the cheapest cause to fix is to replace the coolant bottle's cap, as that may be leaking under pressure. If that doesn't sort it, you should replace the coolant bottle itself, but it's much easier to do that when the thermostat is being replaced, as the coolant will have been drained anyway.

**catbic** · 24th July 2011, 17:32

if the thermostat is faulty eg jammed on open, does it matter to drive the car when it is always running cold.

**Jezzy** · 24th July 2011, 17:37

I don't know what long term damage it can do, but short-term it will adversely affect performance and fuel economy.

**catbic** · 25th July 2011, 08:55

thanks jezzy - i noticed from hopping round the forum that you replaced your signum thermostat last july. how long did it take you. just wondering whether to get hubby to do (with his limited spare time) or pay the local garage.

Does anyone know what kind of cost it would be reasonable for a local garage to charge - never know if my guy is charging me a fair price but wary of going somewhere totally unknown.

**Jezzy** · 25th July 2011, 09:42

It's not a difficult job for someone used to doing basic car-diy, and therefore has a few spanners etc. It took me longer than it should have, as I wasted a good half hour (maybe more) looking for a non-existent 2nd drain plug that the Haynes manual said should be opened (I'm 99% certain it doesn't exist); but that was because no one on here had done it before, so there was no advice to follow. If you want, I can write a more detailed guide, including part numbers for the Vauxhall-specific items.