Technical 169 1.2 thermostat 'bypass'?

[koalar]

It's almost always an internal seal problem; every failed Panda thermostat I've seen will pass the boiling water test.

Everything you've posted points to this being down to the thermostat not fully sealing when it closes; the bizarre thing is that you've tried a number of different brands of thermostat with similar results.

If it works normally after the thermostat has been replaced, even for a short while, I can't see what else could be causing the problem. If the coolant is badly contaminated, it's possible the contamination could be stopping the seal from sealing fully.

Some aftermarket thermostats are known to be of poor quality, but usually even those last longer than this.

all correct

definitely a strange one

 

[mjc506]

Hopefully I'll find something, will report back either way. Glad it's not just confused haha

 

[koalar]

not sure on an easy next step

my feeling is its not circulating properly and when going down hill the colder coolant from the matrix is being add quickly dropping the temperature.

or there is trapped air that making the temperature sensor to go dry when going down hill

It is a trivial job to eliminate the thermostat the temperature goes down stop the car and unplug the top hose

what's the level of coolant within the radiator itself. If you undo the bleed screw next to the expantion tank does coolant flow out

 

[mjc506]

No worries, I'll check the electrical connection for anything obvious, do a datalog run, and see what (if anything) shows up

Plenty of coolant in the system, both bleed points (radiator top and the one on the pipe at the rear towards the heater matrix(?) both dribble when opened. No gurgling noises or anything else to suggest there might be an air lock, levels in the expansion bottle stay constant over time.

 

[jrkitching]

Depending on just how great the temperature drop is, and how long it lasts, I'm wondering if there is actually anything wrong with it.

I've no experience with the climate models, but on the 1.2 with manual heater controls, I've seen something similar happening. I always leave the heater on cold until the engine is up to normal temperature on the gauge, and only then turn up the heat - this gives you the fastest engine warmup (but the slowest cabin warmup - brrr!), reducing wear and improving economy.

Now when I first select hot air, you can see a small but sudden drop on the water temperature gauge; not much, but definitely there and also quite repeatable. When you're travelling above about 1400rpm with your foot completely off the pedal, no fuel will be being injected, and no new heat is being added to the coolant, so I'd expect to see a momentary drop in coolant temperature until combustion restarts.

If you have a regular journey that begins with a cold start, try experimenting with various heater control settings and see if you can spot any differences.

Something else you might notice is that if you leave the heater turned right down and start from cold, there's a similar momentary drop in temperature when the thermostat first opens.

This is all rather subtle; the temperature change is not much more than the width of the needle.

 

[mjc506]

Entirely possible! The climate will (from cold, with the cabin temperature set to, say, 20°C) run the fans at minimum (<10%) until coolant temp rises, at which point the fans will ramp up, cabin temp will start to rise, then it modulates the fan speed and mixer flap to maintain cabin temp at the set point.

I need to do a longer run on flatter roads with the heat turned off I think

 

[Popitinpete]

'ning All,

I'm having issues with by 1.2's thermostat - the fairly typical 'not staying at temperature' symptoms (it is meant to get to the middle of the gauge and stay there, right?).

I'm convinced its not just a failed 'stat, as it's on its third in as many months (different manufacturers), and all exhibit the same symptoms and all appear to open and close fine on the stove top. Equally, I'm getting pretty good at bleeding the system, so it's not just an air pocket somewhere

I assume there must be a bypass line of sorts to allow coolant flow without cavitating the pump while the thermostat is shut/cold? Is it possible that this could be blocked, and the resulting coolant pressure is forcing the thermostat off it's seat?

Any better ideas?

I will give you two pence worth on the subject; mine have always done this, even with new stats, never been able to get the needle to stay on the middle, was like it from NEW, when coasting down hills in gear the needle drops to just over a quarter ( no combustion happening, just a high volume of intake air drawn in) then settles between a quarter and half, climbing hills or motorway work get it to just under half, the rad fan kicks in if its been idling with the needle just under half in about 2 to 3 minutes, no matter where the needle is under normal driving the heater is piping hot so I've put it down to that's 'just how they are' in my opinion as long as the heater works OK and it doesn't overheat your fine, you trying 3 brand new stats confirm this, they are a cinch to bleed anyway, they more or less bleed themselves when you put the coolant back in and the heater hose bleed screw undone about 1 turn. Mines been like yours for ten years, as long as your heater works your fine, if your heater is cold you have a problem, hope that helps.

 

[koalar]

right we now have two people with the same symptoms

@Popitinpete is yours climate control or manual

I can only comment on my own cars. All of which stay in the middle

they have manual fans which I only normally run at O, I and II

If I put it on MAX and hot there is a drop of the needle and it very noisy in the car

might be worth switching the climate control off

 

[Pugglt Auld Jock]

Can't resist joining in with this one as I've changed more than a couple of these over the years. I find much the same as jrk describes 4 posts above.

The system's water flow has two "modes". When the thermostat is closed no coolant flows through the top hose, radiator and bottom hose but does flows through the top heater hose, through the heater matrix and back to the engine through the bottom heater hose. Of course this allows coolant to circulate all the time the engine is running so stops the pump impeller stalling and cavitating. In normal running the engine produces more heat than can be cooled by the heater matrix so when the coolant in the engine and heater system gets up to the thermostat's opening temp then the thermostat opens and water can flow through the top hose, radiator and bottom hose so the radiator can disperse the heat. So coolant will always be circulating in the heater system but only through the radiator when necessary.

Like jrk I keep my heater at cold to facilitate as fast a warm up as possible, do it on all my cars - causes many complaints from Mrs J! - and like him I've noticed, especially in cold weather, that you can see the temp gauge needle just dip momentarily when the thermostat opens and allows cold water from the radiator to start circulating - I've seen this on other vehicles, my present "good" car SEAT Ibiza does it. You have to be watching for it though as it's not a big movement and doesn't last long.

There is a long downhill section on one of the routes I can take if I'm going from my older boy's house to my younger boy's house which is descended all the way on a trailing throttle, so there will be a total fuel cut off whilst descending the hill and, as people here have mentioned, Although I'm not watching the temp gauge every time I go down this hill, I have noticed that in winter when I have the heater full on, the temp gauge dipping a little. I guess what's happening is, with no heat being generated in the combustion chambers, that the water temp is falling to such an extent that the thermostat is closing and the heater matrix is actually managing to then further cool the coolant.

My perception is also that there seems to be a wee "dead" part of the gauge around the "normal" (half way) reading where small changes in temp can take place without the needle moving much. Anyone else notice that?

On our earlier engines, where the temp sensor is not screwed into the thermostat housing (I think you can identify which type you have without looking at the thermostat housing - although that's not difficult to do - because, in my experience, if you have a throttle cable the sensor is going to be round the back screwed into where the top heater hose mates to the head. If you have "fly by wire" your thermostat will be screwed into the thermostat housing so when you buy a new thermostat it's a lot more pricey but you get a new sensor with it. I've just gone out to "becky", found her top heater hose where it comes out of the bulkhead and followed it back to the engine. Poked a mirror down the back of the head so I can see the plastic spigot which the pipe fits to and I can see the connector is indeed, as said above, green!

By the way I've got an Original Birth in her that's now less than a year old and seems to be working just fine. I suspect there's actually nothing wrong with your car but just make sure you've got no trapped air (which would usually gurgle through the heater matrix anyway).

We are talking about just a "dip" of the needle here aren't we? If we're talking about the needle going back to the cold resting point then I'd suspect a poor connector or maybe an internal break in the wire which is going open circuit due to movement of the engine on it's mounts when on a trailing throttle.

 

[koalar]

. When you're travelling above about 1400rpm with your foot completely off the pedal, no fuel will be being injected, and no new heat is being added to the coolant, so I'd expect to see a momentary drop in coolant temperature until combustion restarts.
.

correct

I can't say I have ever noticed any decrease in temperature on descents, Then again I am normally concentrating on the road and only glance at the gauges every few minutes


coasting down hill normally requires some throttle to avoid too much engine braking even when the trip computer shows 141 mpg

even parking at the top of the Llanberis pass in the snow and ice the car is toasty warm before the bottom. Although I spend most of the trying to no fall off the road.

 

[Popitinpete]

right we now have two people with the same symptoms

@Popitinpete is yours climate control or manual

I can only comment on my own cars. All of which stay in the middle

they have manual fans which I only normally run at O, I and II

If I put it on MAX and hot there is a drop of the needle and it very noisy in the car

might be worth switching the climate control off

Its manual, non climate. Mine has been like it for ten years since new

 

[Popitinpete]

Yes I can relate to the 'dead' area around the middle, I think it's just a little maybe tad innacurate guage that gets the job done in a roundabout sort of way and let's you know roughly what's happening, they don't alert you to the dreaded rusty front water pipe though I'm lead to beleive.
Funnily enough I was seeing how much I could make the guage move today when I was up hill and down Dale up t'north today.
Came to a really steep long hill today poor thing had to go up in high revs in 3rd gear(much to the annoyance of the milk float behind me)the guage went to just under the middle, traffic lights at top of hill so for a few minutes the needle was bang in the middle, after about a 1/4 of a mile came the long steep descent so I kept it in 4th and engine braked practically all of the way to level again and the guage plummeted, I could actually watch it drop to just over a quarter, normal conditions and it went to its normal 1/3 of its way up.
This got me thinking about the thermal expansion and retraction of the two different metals the head and block are made of and I thought of my poor head gasket trying to cope so I stopped my little experiment.

 

[mjc506]

I will give you two pence worth on the subject; mine have always done this, even with new stats, never been able to get the needle to stay on the middle, was like it from NEW, when coasting down hills in gear the needle drops to just over a quarter ( no combustion happening, just a high volume of intake air drawn in) then settles between a quarter and half, climbing hills or motorway work get it to just under half, the rad fan kicks in if its been idling with the needle just under half in about 2 to 3 minutes, no matter where the needle is under normal driving the heater is piping hot so I've put it down to that's 'just how they are' in my opinion as long as the heater works OK and it doesn't overheat your fine, you trying 3 brand new stats confirm this, they are a cinch to bleed anyway, they more or less bleed themselves when you put the coolant back in and the heater hose bleed screw undone about 1 turn. Mines been like yours for ten years, as long as your heater works your fine, if your heater is cold you have a problem, hope that helps.

Ah, this does sound exactly like mine.

My perception is also that there seems to be a wee "dead" part of the gauge around the "normal" (half way) reading where small changes in temp can take place without the needle moving much. Anyone else notice that?

Yes, that's intentional - the temp will always fluctuate a little, and the gauge is really a 'cold/ok/hot' indicator, so the needle moving up and down all the time might worry a driver. I'll try get some numbers for this in a few days.

 

[koalar]

Just done a 100 ish round trip in the passenger seat of an 2010 1.2

heater on hot sometimes knocked down to just over half way, blowers on II all the time

temperature never altered more than the thicknesses of the needle

Although the majority was flat. There was a couple of hills

Even going into the supermarket for 10 minutes only knocked it down an 1/8th and within 100 yards it was back to the centre

 

[Pugglt Auld Jock]

Just done a 100 ish round trip in the passenger seat of an 2010 1.2

heater on hot sometimes knocked down to just over half way, blowers on II all the time

temperature never altered more than the thicknesses of the needle

Although the majority was flat. There was a couple of hills

Even going into the supermarket for 10 minutes only knocked it down an 1/8th and within 100 yards it was back to the centre

Since replacing the thermostat ours heats up quickly, very quickly in fact, and sits rock solid on the "normal" half way mark except for that one hill which is descended with the throttle completely closed with the odd dab on the brake pedal. it's when well down this hill that, on very cold days, the temp gauge needle can be seen to dip slightly but enough you do notice it if you're watching. There's a brief run on the flat through the village at the bottom of the hill and then a steep climb out on the other side. The needle is back to normal before we start the climb. Doesn't worry me in the slightest. I'd never have thought to mention it if this thread had not.

 

[koalar]

I guess, and it only drops by about an 1/8th of full range.

this is a significant drop. more than parking the car. going for a coffee and coming back 15 minutes later.
how long is the hill

I will give you two pence worth on the subject; mine have always done this, even with new stats, never been able to get the needle to stay on the middle, was like it from NEW,

your car temperature should operate just as when its new

when coasting down hills in gear the needle drops to just over a quarter ( no combustion happening, just a high volume of intake air drawn in) then settles between a quarter and half, climbing hills or motorway work get it to just under half, the rad fan kicks in if its been idling with the needle just under half in about 2 to 3 minutes, no matter where the needle is under normal driving the heater is piping hot so I've put it down to that's 'just how they are' in my opinion as long as the heater works OK and it doesn't overheat your fine, you trying 3 brand new stats confirm this, they are a cinch to bleed anyway, they more or less bleed themselves when you put the coolant back in and the heater hose bleed screw undone about 1 turn. Mines been like yours for ten years, as long as your heater works your fine, if your heater is cold you have a problem, hope that helps.

should easily be at 1/2 way climbing hills. Something seems to be slightly out on your car

Since replacing the thermostat ours heats up quickly, very quickly in fact, and sits rock solid on the "normal" half way mark except for that one hill which is descended with the throttle completely closed with the odd dab on the brake pedal. it's when well down this hill that, on very cold days, the temp gauge needle can be seen to dip slightly but enough you do notice it if you're watching. There's a brief run on the flat through the village at the bottom of the hill and then a steep climb out on the other side. The needle is back to normal before we start the climb. Doesn't worry me in the slightest. I'd never have thought to mention it if this thread had not.

Your and mine are the same about the thickness of the needle drop as expected



obviously if anyone has the fans on High and the temperature selector on hot. You will dump a lot of the coolant temperature just as if the coolant was running into the radiator and its fans were on. Its what I do to cool an engine down if I am pushing it beyond its limits in summer.

 

[chris3234]

Yes I can relate to the 'dead' area around the middle, I think it's just a little maybe tad innacurate guage that gets the job done in a roundabout sort of way and let's you know roughly what's happening, they don't alert you to the dreaded rusty front water pipe though I'm lead to beleive.
Funnily enough I was seeing how much I could make the guage move today when I was up hill and down Dale up t'north today.
Came to a really steep long hill today poor thing had to go up in high revs in 3rd gear(much to the annoyance of the milk float behind me)the guage went to just under the middle, traffic lights at top of hill so for a few minutes the needle was bang in the middle, after about a 1/4 of a mile came the long steep descent so I kept it in 4th and engine braked practically all of the way to level again and the guage plummeted, I could actually watch it drop to just over a quarter, normal conditions and it went to its normal 1/3 of its way up.
This got me thinking about the thermal expansion and retraction of the two different metals the head and block are made of and I thought of my poor head gasket trying to cope so I stopped my little experiment.

Most modern thermostats are "corrected" for lack of a better word so 90c on the thermostat me be anywhere from 80-100c also backed up by how a overheating car seem to rapidly go from normal position to very hot as it's not a huge temp change needed by that point



This is done to prevent people worrying about small changes in the therm gauge causing them to worry
Also the same reason cars don't tend to have oil pressure gauges now just a low pressure light

Vag group cars apperntly especially bad for the corrected therm gauge

 

[Popitinpete]

this is a significant drop. more than parking the car. going for a coffee and coming back 15 minutes later.
how long is the hill

your car temperature should operate just as when its new

should easily be at 1/2 way climbing hills. Something seems to be slightly out on your car

Your and mine are the same about the thickness of the needle drop as expected



obviously if anyone has the fans on High and the temperature selector on hot. You will dump a lot of the coolant temperature just as if the coolant was running into the radiator and its fans were on. Its what I do to cool an engine down if I am pushing it beyond its limits in summer.

It was like this from new, No nothing wrong, all three of our pandas have done it, yes one from new has always done it and the other was the multi jet.
Its just a thing mine does, as long as the heater gets hot and it dose not overheat its no bother,tis but a quirk.
Obviously ambient temperature has a lot to do with it. In colder weather the needle varies more than on warm days.

 

[Popitinpete]

Most modern thermostats are "corrected" for lack of a better word so 90c on the thermostat me be anywhere from 80-100c also backed up by how a overheating car seem to rapidly go from normal position to very hot as it's not a huge temp change needed by that point



This is done to prevent people worrying about small changes in the therm gauge causing them to worry
Also the same reason cars don't tend to have oil pressure gauges now just a low pressure light

Vag group cars apperntly especially bad for the corrected therm gauge

Yes, I heard a rumour in our workshop once that most guages are magnetically very lightly 'held' in the 'centre' point to avoid the needle dipping and climbing as to not cause alarm. Dipping and climbing on an accurate gauge is just physics doing its thing.
I rebuild classic bikes when the need arises and I was reading an article once where triumph were going to start putting oil pressure guages on their bikes but the chief engineer said something along the lines of " don't do that for Christ's sake you will scare half of our customers off within the first 6 months!" because with a warm engine on the air cooled twin 650cc and 750cc engines the gauge would drop to practically zero oil pressure when idling..even with modern classic oils now its not uncommon for the oil pressure warning light to flicker when hot.
If you think about it the cooling system would have to be managed precisely to keep a needle in the middle of the guage under 'normal' conditions, acceleration, climbing hills, coasting downhill on a closed throttle etc etc, my octavia VRS's needle was just bang in the middle wether travelling through the cairngorms at minus 6 degrees or stuck in traffic at trafalgar Square in a heatwave, I'm pretty sure no stat could keep the needle bang in the middle with no variation whatsoever without a little magnet help or software help, as you say it's to help prevent panic

 

[Pepandaros]

right we now have two people with the same symptoms

@Popitinpete is yours climate control or manual

Three.... Mine is a 1.1 manual non aircon. The needle has never reached the half way marker since I own the car (only a month but driven approx 1000 miles).
From cold the needle goes up and stops just above the quarter marker, when going uphill or stuck in city traffic it goes up but never reaching halfway. Down hill I can see it dropping again but it doesn't go below the quarter marker. I find it strange but it didn't worry me as the engine runs really smooth and I checked the coolant which seems to stay level. When I just got the car I noticed the temperature meter so checked the coolant which was over filled, I took some out to let the level sit just bellow the max marker and it is staying there ever since.
But I'm following this topic with interest...