Hi everyone, I've a question about the temp sender and gauge . The car I have has had the head gasket changed about 3000 kms ago which included a skim and new head bolts. The car seems to drive ok and I'm getting heat out of the cabin heater. No steam or gurgling or mayo signs. However the temp needle is low and occasionally went to the halfway point and then back to zero over the space of about 30 mins.
Could this be a faulty sensor or thermostat.
Where is the temperature sender on the engine block?
Thanks.

Needle should be glued to the middle. Staying low followed by jump to middle sounds like stat which should/could have been replaced with the hg job. Round these parts there are a lot of poor quality aftermarket stats going around. Don't know where the sensor is on the 16v - on the 8v it's at the right side as you face it. Disconnecting it at idle should bring the fan on.

:yeahthat:

Headgaskets usually go for a reason -- thermostat could be why it went!

Sounds like the thermostat is stuck Open

As a result the engine never warms up, and the hot combustion but over cooling means lots of thermal stresses that aren't wanted

While the cooling system was drained while doing a thermostat job - i'd be looking at testing the sensor too!

Ziggy

Thanks for the steers folks.
Where is the temperature sensor on the 16V engine?
Where do I find the bleed points for the coolant system?

The back one is on one of the heater hoses the front on top of the rad - rhs as you face it probably. There are more ways of bleeding it than grannies have recipes for bread.
The way that works for me is to fill the rad to the top of the filler neck,fill a 500ml drinks bottle with coolant, open the back screw, upend the bottle on the rad and squeeze till the air stops sputtering out the bleeder. Drop the excess with the front one.
Both screws are plastic and the back one in particular is prone to breaking if pushed.

I cooked a head gasket with a stuck-open thermostat, so I would verify the temperature sender unit first, and then whip the thermostat out and do the boiling pan test. I would suspect that the thermostat was the initial cause of your HG failure anyway.

Well this'll teach me to not fiddle with stuff..
I checked the two bleed valves and they were topped up so water was overflowing and then I did them up again.
I also took the battery off for about an hour and also washed the car.
Anyway when I reconnected the battery and started the car up the Engine Management Light was on and the reverse light wasn't working with bulb warning light coming on when in I put the car in reverse.
I then drove for about 6 miles and the EML stayed on the whole way and the temperature gauge was at zero even though the heater in the car was working. Car seemed to drive fine.
What have I done now..

Oh I also removed the spark plugs to check their condition while the battery was off, they seemed fine - NGK DCPR8E

If you have disconnected the temp sensor the EML will light up and stay lit for the next two or three cycles, then go away. It's like the ecu needs telling three times it's reconnected before it believes it.
Sounds like the stat is stuck open. Does the gauge come up if you leave it idle for a while?

Interesting Brendan. I forgot to add that I did disconnect the green temperature sensor plug and then put the ignition on to see if the fan would operate which it did. Thanks for that. Impressed.

I disconnect it at every service just to check that everything still works as it should. Round here the fan rarely comes on and you'd never know if it had seized from lack of use until the day it was needed.

Would this also cause my temp gauge to stop working for a few cycles?
Could this problem I'm having be a temp sensor fault rather than a thermostat?

Kirok said:

Would this also cause my temp gauge to stop working for a few cycles?
Not in my experience. Far more likely the stat is stuck open.
Could this problem I'm having be a temp sensor fault rather than a thermostat?

Click to expand...

I would do a basic check, start from cold. The top hose should stay cool for 5 mins approx and get warm fairly quick as the stat opens. A slow transition from cold to hot suggests stat stuck open. In another 5 mins the bottom hose should be getting hot and say another 5 the fan should come on.The needle should be in the middle after 5 min or so and go slightly above before the fan kicks in. If you then drive the thing and the needle falls below halfway the stat is almost certain stuffed.

Brendan W said:

I would do a basic check, start from cold. The top hose should stay cool for 5 mins approx and get warm fairly quick as the stat opens. A slow transition from cold to hot suggests stat stuck open. In another 5 mins the bottom hose should be getting hot and say another 5 the fan should come on.The needle should be in the middle after 5 min or so and go slightly above before the fan kicks in. If you then drive the thing and the needle falls below halfway the stat is almost certain stuffed.

Click to expand...

bottom hose gets hot first and then the top one

Oh I forgot it's New Zealand.:doh:

That sounds right

Well I've changed the thermostat as you suggested and it seems to be working as it should now. When I removed the old one I took out the thermostat from the housing and noted that the spring in the new one was much stronger. I don't know if this was what was at fault. Anyway works now so many thanks.

Keep an eye on it. Thermostats have a habit of failing just before and just after replacement.
Thanks for coming back.

Well I thought I'd resurrect this thread Brendan as your prophecy has come true.
I was driving the car recently and noticed that the temperature gauge has moving between the quarter and half marks even though the car was already up to temperature. I'd changed the thermostat last year for a QH one but had a new Fiat one ready to use so decided to fit it. When I removed the thermostat there didn't seem to be much water run out of the head and it was pretty brown as well. I had intended to put anti freeze in but forgot...Anyway I fitted the new thermostat and anti freeze and all seemed fine, gauge in the middle after about 5 mins running. Sorted.
Next morning a small pool of green anti freeze under the car. And again the next morning. Nothing just after running the engine but happening over night. Had a look underneath and there's a trace of anti freeze dripping down from the oil filter area. 16V car.
I'm really hoping that I haven't let the car run short of water such that the head gasket has blown again. I didn't notice any water loss since it was just water without any anti freeze so I assumed it was rain water or some such.
The thing that makes me think head gasket is the water loss (about an egg cup full over night) and pretty hard/firm water pipes when the engine is running.
Other than that the car starts and runs fine at the moment, no white smoke. Maybe a very very slight hesitation on a light throttle (but that could be the throttle body needing a clean)
Any things I should be doing to problem solve and fix this? I have my fingers crossed..