Technical Relationship between coolant temperature sensor and thermostat

[puntonew]

Hi

i am googling to try and find the relationship between a coolant temperature sensor and a thermostat, but cant find an explanation that my mind can quite understand.

(My punto 1.2 8v active 2003 is running with the dashboard temperature needle on zero, by the way, not showing that its heating up at all)

What is the relationship between a coolant temperature sensor and thermostat, how do they interact, affect each other?

Thanks

 

[benny279]

Hi,

Thermostat - Its job is to block the flow of coolant to the radiator until the engine has warmed up. When the engine is cold, no coolant flows through the engine. Once the engine reaches its operating temperature (generally about 200 degrees F, 95 degrees C), the thermostat opens. By letting the engine warm up as quickly as possible, the thermostat reduces engine wear, deposits and emissions.

CTS (Coolant Temperature Sensor) - Aside from regulating the temperature of the engine by turning the cooling fan on and off, the information received from the temperature sensor is also used to determine if the engine needs a richer fuel mixture, to ignore the oxygen sensor rich/lean feedback signal, to open the exhaust gas recirculation or to limit the spark advance during emission.

So they really don't interact much with each other, thermostat pretty much controls coolant flow for the engine and CTS controls the cooling fan and interacts with the ECU (Engine Control Unit) to adjust values as I said above for fuel/air mixture, as an engine relies on multiple sensors scattered all over the engine bay to keep that one engine running sweetly, problem with today cars they getting too advanced in terms of more computer controlled than mechanically controlled!

That's the information I can give you based on those two things, for your issue I suggest testing the CTS by unplugging it and put the ignition on - this will test to see if the ECU see's the sensor unplugged this in turn will activate the cooling fan to turn on because it thinks the car is overheating so the ECU protects the engine from overheating!

Now in a likely case, I'd say you either have a dodgy temp sender sensor or the CTS is fubar'd!

Do you get any heat from the fans after running the car for like 10-15 minutes? Like cold and hot at request?

Ben

 

[puntonew]

Thanks Ben, it makes more sense now

I will check tomorrow for any heat in the radiator, not sure yet. The fan does work though (bonus)!

This info has also just helped me get my head around a thermostat - http://auto.howstuffworks.com/question248.htm

If you ever have the chance to test one, a thermostat is an amazing thing to watch because what they do seems impossible. You can put one in a pot of boiling water on the stove. As it heats up, its valve opens about an inch, apparently by magic! If you'd like to try this yourself, go to a car parts store and buy one for a couple of bucks.
The secret of the thermostat lies in the small cylinder located on the engine-side of the device. This cylinder is filled with a wax that begins to melt at perhaps 180 degrees F (different thermostats open at different temperatures, but 180 F/82 C is a common temperature). A rod connected to the valve presses into this wax. When the wax melts, it expands significantly and pushes the rod out of the cylinder, opening the valve. If you have read How Thermometers Work and done the experiment with the bottle and the straw, you have seen the same process in action. The wax happens to expand a good bit more because it is changing from a solid to a liquid in addition to expanding from the heat.

As i understand it now -

if the radiator emits heat, i likely have a faulty temperature sensor, as the coolant is warm and the thermostat is doing its job correctly of opening as the engine heats.

But if the radiator produces no heat, the thermostat is likely stuck open, not allowing the engine to heat up properly before allowing coolant to flow, thus the coolant is in constant flow?

 

[benny279]

I've worked with loads of themostats on cars not just FIAT's, but I would have to say the MK2's are a bugger for their incorrect readings sometimes, although I put that down to dodgy thermostats:bang: (not rare for that to happen!)

But not entirely the stats fault, sometimes the temperature sender can be at fault here which sends the temperature information to the temp on the speedo, if that sender isn't working you won't get a reading on the speedo.

Firstly, I would try as I suggested unplug the CTS put the ignition on and the cooling fan should come on within a few seconds, if so turn off reconnect.

However, if this doesn't work then there is a possibility the CTS is buggered, but never rule out the thermostat, if the thermostat is buggered only way of testing that is take it off the engine, take it indoors - get a saucepan put water in it drop stat in there and boil the water until you see the stat open if it doesn't open the stat is buggered and needs replacing if it opens but doesnt close then it needs replacing.

When was the last time you changed the coolant?

 

[puntonew]

When was the last time you changed the coolant?

Will look into the temperature sender sensor also. Didnt realise the dash temp reading was controlled by a sensor other than the CTS, but logically, it has to be.

I havent changed the coolant yet mate, as i only bought the car 2 days ago, but i checked the coolant in the top of the radiator today and it was brown and cloudy.

 

[benny279]

I havent yet mate, as i only bought the car 2 days ago, but i checked the coolant in the top of the radiator today and it was brown and cloudy.

Brown and cloudy!?

It suppose to be either blue or a red/pinky colour...

Blue = 2 years
Red/Pinky = 5 years

I strongly suggest you don't run that car on that current coolant, go to a Motor Factors or EuroCarParts etc pick yourself up red coolant and use distilled water DO NOT use tap water, however you can buy de-ionized water from ASDA for about £5-7 you can use this in your coolant mixture, which is 50% raw coolant and 50% water like distilled or de-ionized.

You MUST buy red or blue coolant that meets the following standards -> Monothylene glycol-based antifreeze (Paraflu 11).

Also, because its brown and cloudy I'd recommend flushing the cooling system out! Before putting fresh coolant in.

Also make sure you buy a new jubilee clip for the coolant tank hose, the bottom one.

It being brown and cloudy sounds like previous owner has left the old coolant in there and never changed it So your issue could be based on the coolant not doing its job probably, so before anything I'd suggest doing what I said above for your cars well-being, and to avoid major problems!!!

 

[puntonew]

Thanks Ben, will do.

I have a water distiller for personal use, and drink nothing but distilled water, so can spare a litre or 2 for the ailing motor.

 

[benny279]

Yeah just use distilled water then you'll only need 50% of distilled water, measure it for 50% doesn't matter if your slightly over by 1-2% this is the correct mixture for over here, but in harsh winters it's a different mixture but we rarely get harsh winters.

So basically all you do is drain that nasty coolant out into a bucket or pan whatever, then dispose of it in the correct way! Don't put it down a toilet or sewage drains.

Then flush it, reason for this if the coolant renewal has been neglected which it has been because of the colour of it being a brown and cloudy sort of muddy water pretty much, which will make the cooling system gradually lose efficiency, as the coolant passages become restricted due to rust, scale deposits and other sediments.

The radiator should also be flushed independently of the engine, to avoid contamination!

You can pick up flushing agents for this purpose, so while you at Motor Factors, Halfords etc make sure you ask for a flushing agent for the cooling system ,and if your unsure of the procedures ask them and should be able to give you a outline guide how to do it.

Once the flushing has been done, drain it out, then put in your own 50/50 coolant mixture, then bleed the cooling system multiple times before running the engine. There is a handy guide on this forum if you take a minute or so to have nose at it, just go to guides and then Punto guides and it should be in there.

Ben

 

[Ziggy122]

If flushing id cheat and use tap water / hose to flush the coolant out and wash the worst out

Then you can use deionised water and a flush agent
Dump
Refill with a 50/50 mix
Most 50/50mix will protect down to -36c which is ample for the uk

Red will last 5 years and on change after 5 ywara from new will probably outlive the car


Ziggy

 

[atom0007]

Thanks Ben, it makes more sense now


if the radiator emits heat, i likely have a faulty temperature sensor, as the coolant is warm and the thermostat is doing its job correctly of opening as the engine heats.

But if the radiator produces no heat, the thermostat is likely stuck open, not allowing the engine to heat up properly before allowing coolant to flow, thus the coolant is in constant flow?

I think you're conflating two different things.

If the radiator emits heat, the cooling loop is working properly. It's a passive system that works exactly the same as a domestic central heating radiator system. It's on or off depending on thermal expansion of wax in the thermostat. This is not controlled in any way by the car.

If the radiator produces no heat, there is no flow to it, so thermostat closed. This happens if the engine is cold (wax not melted) or the engine is hot and the stat is malfunctioning.

Last point: the coolant sensor lets the engine know when the coolant temperature is too high. In that case, the radiator fan is switched on for assisted cooling

 

[puntonew]

I think you're conflating two different things.

If the radiator emits heat, the cooling loop is working properly. It's a passive system that works exactly the same as a domestic central heating radiator system. It's on or off depending on thermal expansion of wax in the thermostat. This is not controlled in any way by the car.

If the radiator produces no heat, there is no flow to it, so thermostat closed. This happens if the engine is cold (wax not melted) or the engine is hot and the stat is malfunctioning.

would this also happen if the coolant was already/always in constant flow as the thermostat is stuck open, and so the engine never produces enough heat to heat the circulating coolant?

Last point: the coolant sensor lets the engine know when the coolant temperature is too high. In that case, the radiator fan is switched on for assisted cooling

Does it let the engine, or ECU know this?

Thanks.

 

[atom0007]

With the thermostat open, the hose to the radiator gets hot to touch. So no, it's not possible. I think the coolant set point is about 95 degC, somebody can correct that if I'm wrong. Above that, the fan comes on. 95 is plenty hot enough to feel on the rubber hoses.

It's the same way you can always get hot air from the internal heater when the engine has warmed up.

And yes, I meant ECU. An engine doesn't "know" anything.

 

[puntonew]

Update - sigh of relief!

just drained the coolant from the bottom radiator hose into a clean bowl and it looks fairly fresh - a deep concentrated pinky red colour.
As it settles in the bowl, the liquid in the middle of the bowl has a slightly more orangey brown tint and is slightly cloudy, presumably from rust, and their are some small fragments of rusty metal in their that have settled to the bottom. Around the edges of the bowl the liquid is pinker and not cloudy.

I reconnected the bottom hose and refilled the radiator expansion tank, until fill with tap water, and then drained that after a few minutes.
I did this process 3 times, until the water coming out of the expansion tank, hose/engine, and the top of the radiator was almost clear water colour.
I have left it to drip the last drops of water out.

Does the coolant i removed, from my description above sound fresh enough to re-use, minus the small fragments of rusty metal of course, or should i just start again with fresh??

Thanks.

 

[Ziggy122]

Fill with Fresh coolant my friend mixed with De-ionised water

Halfords its dirt cheap!
If you collect in store - instore price aint bad still

ziggy

 

[atom0007]

fresh, you can't tell how good the rust inhibition is by looking

 

[puntonew]

Thanks guys, fresh coolant it is then!

i have a distiller bought from here, which includes a 3 year guarantee. I mainly drink/consume distilled water, which is pure water. it costs about 10p per litre in electric. i have been consuming 3-4 litres a day for 13 months.

http://mama-penguin.co.uk/#/shop/4558237278/Megahome-943SBS-Water-Distiller/521259

4 litres of tap water takes around 5 hours to distill.

Distilled water is meant to have significant health benefits.

 

[atom0007]

do you have any link to that company?

I would think the relative merit of drinking distilled water versus tap water is insignificant and unverified.....plenty of either better than none of both

 

[fingers99]

Unless you're living in a hard water area tap water will do just fine.

As for drinking, distilled water tastes horrible and -- obviously -- has no health benefits: no animal on the planet actually drinks it, aside from man (who would be better off using the still to make hooch).

 

[atom0007]

Well said!

A cynical person might say that this smells like :spam:

 

[puntonew]

Anyway to conclude the off topic mention of a water distiller, all i know is i prefer pure water free of 99.9% contaminants reading zero parts per million on a TDS meter, than water with chlorine, pesticides, fertilizer, asbestos etc in it. it also tastes better in my opinion.

Apparently distilled/pure water and liquids is the only water that nature produces -
rain, fog, dew, snow, fruit juice, milk, urine.

No i am not a sales rep. And TBH after 13 months, the 5 minute proceedure of filling the distiller every day is getting a bit of a pain, as is pouring the water afterwards. these 4litre distillers are basically portable distillers. a bigger capacity automatic water distiller connected directly to the water supply, maybe 20 litre, would be a lot easier in the long term, but they cost £500+.