Technical Looks like i need some advice.. stilo seems to be overheating :-(

[12[X]]

Car behaved really odd yesterday - usual shake was becoming irregular and during acceleration (at low speed only) it felt a bit 'mushy-wobbly' for lack of another word.. The only other time i felt my car behave like this was when it overheated due to water pump failure at 2 years (had to keeping it going long enough to get to the hard holder).

According to the dash - temp is perfect and i've no coolant leeks (though have been losing oil and could not figure out how/where it was going – perhaps it’s just evaporating?) Touching hoses, moving coils about etc. engine was way too hot (coil bolts get hot but not quite hot enough to burn me.. this time they did..) added to that i've had a number of 'coolant temp sensor' loose connection warning this winter (though plug etc was cleaned and these errors never came back)

to the questions then:
1) i know temp sensors are quite reliable - but are they more likelly to fail after overheating?
2) if wrong reading (higher resistance) is coming from the sensor - the car assumes its within normal range while it really is overheating.. plausible?
3) Is it possible to replace temp sensor without draining coolant? (it is immersed right?)
4) My post cat o2 sensor seems to have a stable reading.. but it never changed (EVER) will this cause symptoms similar to a light shake/misfire on occasion?

 

[PNL]

Might be some thing simple like early thermostat failure..

 

[Deckchair5]

Physically the engine thermostat should take care of the engine temp coupled with the radiator and radiator fans when required. But for the fans to come on then they need to be fed the right information from the engine temp sensor.

If it's hot - and you can usually smell it's wrong- then I'd use your cabin heater on full hot and interior fan to provide your own coolant cooling until you're sure it's ok or just not drive it far. A blocked cylinder head waterway might produce your problems of overheating head with no warnings

Temp sensor resistance reduces with increase in temp. Here's a chart


I think follow your instincts as there would need to be two things wrong for the coolant to be overheating AND no warnings. Good time to make some simple electrical tools as I outlined in the Stilo Guides for simulating your engine temp sensor and check everything electrical is working as it should without frying your engine.

Post cat O2 sensor flatlining shouldn't produce any running problems as the precat one does all the work. It should fluctuate between 0.1 and .8v though and so there would be a problem there too

You can buy temp thermocouples for a multimeter quite cheaply if you want to confirm your thoughts of a roasting engine. Handy for taking your own temperature too

 

[Morty Mort]

Is the water circulating while hot? If not, the thermostat might be stuck on closed position - which is rare though.

The newer and more coolant (50/50) you have, the higher the boiling point gets, which is good.

 

[12[X]]

water seems to be circulating ok.. sensor can be removed (but me local didn't have any in stock) think sensor is faulty though (dash temp jumped almost a quarter of the way today - from 50% operating temperature to 90%) although this could be related to a sticking thermostat.. but i've never seen the gauge show an overheat.. so unless i'm lucky enough to have a sticky thermostat & a faulty sensor.. also tried probing resistance on the sensor itself - couldn't get a reading of any kind. Will keep everyone updated (am hoping it is not a head blockage as i’ve no means to fix that.. still if it wasn’t my car it could’ve been mildly entertaining.. probably why my locals mechanics are laughing every time they see me )

 

[Deckchair5]

No reading = open circuit so that would be your problem.
Drinking fuel like no tomorrow too?
Engine only get over hot when you were idling and stationary?
Different ball game if it's overheating when you're at speed

You won't need to drain the cooling system, just wait til it's cold and have the new temp sensor ready to install as soon as you remove the old one

 

[PNL]

water seems to be circulating ok.. sensor can be removed (but me local didn't have any in stock)

Now where did I put that link I have for the sensors..:tempt:

 

[12[X]]

will run to desira tomorrow and get a new sensor It looks like there's more trouble though (possibly caused by overheating) have discovered oil on and around intake manifold

 

[12[X]]

For those that might be interested in this:
Sensor was £13.99 +vat (5 minutes to fit including a smoke break)
Thermostat works just fine, fan kicks in as well.. so no more overheating.. engine is a lot more even (but not as good as it used to be couple of years back) and pulls very very happily (looks like variator is kicking in too.. just put in selenia star). All in all – not too bad.. but damage seems to have been done (although, fingers crossed, it might need time to adjust to new readings both temp and combustion) – in hindsight temp sensor is very cheap and should probably be swapped at 5yr intervals (just in case)

 

[12[X]]

gm thx to pnl and deck the fan was not coming on due to sensor (though it was not off by much) thermostat is in early stages of failing (it's sticking) that's why i see a drop in temp when it kicks in for the first time (coolant in radiator is a lot colder).. as i understand it: a thermostat would start opening slowly as temp is reached (so cold and hot fluids start intermixing brining the whole system to the same temp by the time it opens fully) mine does not do that - it seems to remain locked and then opens fully.. no reading on old sensor is due to my stupidity (sensor needs to be powered.. i'm such a noob )

on the job list remains: a change of coolant (can't find the 3 bleeds on me 1.8 !!! not even with elearn.. and i'm stupid enough to mix up the rigid colant pipe with aircon pipes and bleed that! )

 

[PNL]

Well done..glad you got it sorted..my link was £11.15p + vat for the 1.8 and £7.93 + vat for 1.2 1.6 & Jtd but to late now..

 

[menola]

Hi,
My car is rely warm and temp meter suddenly goes up and the down. Is thermostat problem? No error with software.

/menola

 

[clock34]

hows your headgasket? is it burning/loosing any water from your coolant?

how fast does it increaes/decrease temp? it could be anything from air bubbles hitting the sensor to a earth problem depending on all the above.

 

[menola]

Hi,
I have not lost any coolant fluid. I has been on the same level all the time.

/menola

 

[Stormwatch]

It might be an ECU problem...I hope not. Check similar threads.

 

[menola]

Hi,
I have tested the injector with LEDs and ECU connects every injector to ground. I build a board with LED parallell with injectors. All LEDs light up and are OK. All LEDs light up faster when I gas

No electrical problem according to service.

/menola

 

[menola]

A rubber ring in thermostat. New one mounted
Still slow car.

menola

 

[menola]

Temp still rising suddenly and back.

menola

 

[menola]

Hm, I am thinking that the waterpump i broken. Temp goes up and down rapidly. Have new thermostat and temp sensor.

menola

 

[menola]

Waterpump is changed. Little better but the heat goes up sometime.

/ menola