Technical 169 1.2 thermostat 'bypass'?

[mjc506]

Yup, new stat, stamped 87.5, seal (and seat) in good condition. I'm 99% sure it's not passing. I guess the hole in the casting for the 'stat "piston" might not be deep enough, and so the 'stat is opening sooner than designed? But given the consistent symptoms over a few different thermostats I'm more inclined to think the 'problem' is elsewhere.

Seems like 100ohm additional resistance in series with the thermostat could account for the ECU under-reading by ~15°C at 70°C. And under-reading by 1-2°C at 10°C. If that is the reason, it will read ~95°C at a true 120°C... I hope it's not that!! (I'm sure I'd have noticed other things happening if it was reaching that sort of temperature of course )

Tomorrow's job is to confirm negligible resistance between ECU and coolant sensor (and coolant sensor and ground), confirm the actual opening temp of the 'stat on the stovetop, and see if I can verify the ECU temperature readings somehow...

 

[koalar]

looks the same as a fully functioning car to me, yellow line

 

[mjc506]

So it does! huh, wonder what causes that did then...

 

[koalar]

So it does! huh, wonder what causes that did then...

no idea
its strange how close different cars are
different sensors, capacity of coolant, engine power and so on

your thermostat and sensor look fine to me
I personally think the drop down is something like either blowers or condenser fan and is normal

Strange I never seen it. I am pretty flat in Cheshire. But away from Cheshire I did push my 05 1.2 fairly hard. Been up mountain in reverse as too steep for first and down hills were you felt you were going to slide out of your seat. I can not in all honesty say I watched the temperature gauge all the time. Neither did I have aircon or climate control

 

[09 johno]

Don't forget, the stamped temp on a thermostat is when it is fully open, so it starts to open earlier so around 75 deg C is about right, also this is a point temperature at the thermostat and not where the sensor is located so there will be slight differences.

 

[koalar]

Don't forget, the stamped temp on a thermostat is when it is fully open, so it starts to open earlier so around 75 deg C is about right, also this is a point temperature at the thermostat and not where the sensor is located so there will be slight differences.

not how I see it

the difference between starting to open and full open is only a few degrees Celsius

they dont open instantly.. So if you pop straight into boiling water the don't just pop open. not a problem in a car as they are heat slowly by the car

here's what Fiat says

It is the centrifugal type with vanes, fixed to the crankcase and directly directly by the timing belt.
Mounted on the rear of the cylinder head, its function is to keep the engine at the optimum temperature:

• at a temperature of < 87 ± 2° C the (closed) thermostatic valve directs the coolant directly towards the pump
• at a temperature of > 87 ± 2° C the (open) thermostatic valve directs the coolant towards the radiator.

 

[mjc506]

That's my understanding too. I'll find a saucepan and thermometer, be back shortly haha

Also, the sensor is right next to the 'stat in the fire engine. I can't see why there'd be any significant difference in temperature across that distance (certainly not more than a degree or two)

 

[mjc506]

Yes, confirmed - my two 'spare' thermostats begin to open (and fully close) around 87°C.

Also confirmed that there's no significant resistance between the ECU/ground and the temp sensor on the block. Although 5V appears a little low (but that shouldn't matter, there'll be an analogue reference voltage in the ECU too).

@koalar Where did you get that coolant temperature graph? I can't find anything else online (with different cars) with that similar shaped dip.

I've got some more ds18b20s arriving tomorrow, I'll try strapping these in various places and do another warmup log.

 

[koalar]

Thermostat: how it works, symptoms, problems, testing

What is a thermostat in a car, how it's tested, what are the common problems with the thermostat, thermostat open/closed diagrams

www.samarins.com

 

[Pugglt Auld Jock]

Thermostat: how it works, symptoms, problems, testing

What is a thermostat in a car, how it's tested, what are the common problems with the thermostat, thermostat open/closed diagrams

www.samarins.com

I've come across this Samarins website before and it's got some very interesting stuff to read about on it.

 

[DaveMcT]

Most control systems will created a dip or hump in the referenced signal when there's a step change.
Steam boilers are controlled by water level. When it drops you speed up the feed pump and when it rises you do the opposite. But when you call for more power, the water level rises due to the drop in system pressure and then falls due to higher water usage. Controls have to manage this feature or risk the level dropping too far before the feed pump catches up.
When your central heating opens a radiator valve, the water in the line back to the boiler will get cooler as cold water from your now working rad enters the line. Boiler will ramp up to meet the apparently much higher demand, then throttle back as the warmer return from the new rad comes through. You get a transitory hump in heat demand before it settles to the new higher value.
It's the same with the car thermostat. At the set value, hot water in the engine is released allowing cold water to come in from the radiator. This momentarily drops the engine temperature until the rad has settled into a balanced heat flow. The engine has a high heat capacity so its a small effect but it's there all the same. The temperature gauge drops for a short time then returns to normal.

 

[mjc506]

^^ yes, definitely agreed, the little dip isn't a surprise, but I'm still not convinced that it should happen at ~70°C. In fact, that little wobble would be barely visible on the gauge, and should be entirely hidden in the middle 'dead zone'. If the sensor reading is correct, then that 70°C dip won't be caused by the 'stat, but I'm not sure what else could cause it. Engine load, idle rpm, etc etc have all settled by this point, so there's no sudden changes in heat generation or rejection that I can think of.

 

[koalar]

coolant sensor are generally non linear
the energy entering the system alters as timing and fueling alters with temperature,
the amount of energy that can be transferred into the head and block is altering as they warm up
running in closed or open loop
and so on and on

I would be more surprised if it was a perfect curve.

the fact it closely matches a known Good system, means there's nothing to be gained here

 

[koalar]

I did stick the heater fans on full while the engine was up to temperature

there was a small drop on the gauge. Coasting down hill and it still warmed back up quite quickly

I suspect if I did the same after a long climb and the thermostat was open, the outside temperature was colder and or the radiator fans on the results would have been more dramatic

 

[09 johno]

I connected up my Laptop to my 1.1 yesterday to sort another issue and thought I would look at the coolant temperature as mine also sits below 1/2 when driving. My conclusion is that the results are the same as those shown in the graphs above although my fan cuts in at 97 deg C which is the top of the 1/2 way wide band on the gauge, between 80 and 97 Deg C the needle hardly moves, I think its a meter calibration problem that is the issue.

 

[Popitinpete]

I connected up my Laptop to my 1.1 yesterday to sort another issue and thought I would look at the coolant temperature as mine also sits below 1/2 when driving. My conclusion is that the results are the same as those shown in the graphs above although my fan cuts in at 97 deg C which is the top of the 1/2 way wide band on the gauge, between 80 and 97 Deg C the needle hardly moves, I think its a meter calibration problem that is the issue.

We need a poll of all 1.1 owners guage behavior, I really do suspect its just what they do.

I will start ;

Mine sits just below half under normal use, heats up quickly, never goes past half even when idling on a hot day for half hour, when fan cuts In it's still at half, when descending hills it goes down to just over the quarter but recovers to just under half again.

Its been like this from NEW, have tried a couple of stats but made NO difference.legacy of the last of the dodgy Italian electrics reputation? Poor voltage stabilisation unit on the dash biniacle I reckon because my fuel guage can move dependant on if I'm parked uphill, down hill, leaning left or right or just average calibrations on the binnacle?

Anybody else care to contribute?

 

[irc]

2010 1.1 Active Eco.
Rock solid at half a needle width below Normal mark. Had a new thermostat a few months ago as I had to replace the connected pipe, and didn't see the sense of attaching it to an 11 year old thermostat.
Didn't change the behaviour at all.
Although it never leaves Norfolk, so can't tell you what it does on hills!

 

[koalar]

I connected up my Laptop to my 1.1 yesterday to sort another issue and thought I would look at the coolant temperature as mine also sits below 1/2 when driving. My conclusion is that the results are the same as those shown in the graphs above although my fan cuts in at 97 deg C which is the top of the 1/2 way wide band on the gauge, between 80 and 97 Deg C the needle hardly moves, I think its a meter calibration problem that is the issue.

as expected
no air flowing over the radiator to aid cooling of the coolant bypassing the thermostat. While standing still

put you hand on the top Hose. Should stay cold for a couple of minutes when first switched on. Does it ?

 

[koalar]

2010 1.1 Active Eco.
Rock solid at half a needle width below Normal mark. Had a new thermostat a few months ago as I had to replace the connected pipe, and didn't see the sense of attaching it to an 11 year old thermostat.
Didn't change the behaviour at all.
Although it never leaves Norfolk, so can't tell you what it does on hills!

2010 1.2 Dynamic eco the same

mostly Cheshire not many hills here either

2006 1.1 Active rock solid

2005 12 Dynamic rock solid

old punto rock solid

 

[Popitinpete]

2010 1.1 Active Eco.
Rock solid at half a needle width below Normal mark. Had a new thermostat a few months ago as I had to replace the connected pipe, and didn't see the sense of attaching it to an 11 year old thermostat.
Didn't change the behaviour at all.
Although it never leaves Norfolk, so can't tell you what it does on hills!

See what you mean about the hills lol, what about your fuel gauge? I'm not talking about it swinging about all over the place but if you park so it's tilted to the left/nearside do you find that when you start it up the fuel guage is lower than before you parked? same with facing up hill when parked.
Another little quirk I've found is say for instance you are driving around and you pull up and turn off and get out and the fuel guage was showing BANG ON in the middle for the purpose of this explanation, the next time you get in the needle never registers what it did when you turned it off! It always shows lower than when you turned the bleeding thing off!
With both guages being a little squiffy it may well be a voltage stabiliser problem, they used to be an actual separate item you could 'unplug' from behind the dash binnacle off the printed circuit , I used to sell loads of them back in the day (but I think for Nissan micra, could have been early fiat's too, long time ago), I doubt very much its the same set up on the panda dash now but could the haywire readings be down to another little earthing quirk these cars are so fond of?

Both my 1.1's do this, and my multijet was like this and an aquaintences 1.1 is the same too, can't just be a coincidence?