Technical Thermostat check by diagnostics

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Technical Thermostat check by diagnostics

Chiddleston

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Quick question: Is it possible to tell if thermostat is working properly by having a diagnostics check? I only ask as i feel fobbed of by the garage who say everything is working fine apparently after just a 2 mile test drive and letting it get to temperature in the workshop, checking pipes and a diagnostic check. The gauge is still going up and down like a yoyo when driving, as they were told at the start. Car is a 2012 1.2 Panda Mylife.
 
Diagnostics can only check electrical/electronic signals/readings. The thermostat is purely mechanical, so diagnostics can only see how the temperature is changing, not why.

How far is the temp gauge moving? Is the 'yo-yo' from min to max, or just the width of the needle? On cold days they can move by the needle width, or perhaps a little more, but on warmer days, you'll hardly see any movement.

I'm guessing the current issue is new to you, having seen more normal behaviour before. If you are new to the vehicle, you may be seeing something normal.

Initial opening of the stat is easy to determine, with a hand on the top hose as the engine warms up. Once opened, the top hose will stay hot, so difficult to determine when it opens/closes. The temp at the top hose where it connects to the rad may give a better indication of what is happening.

The garage has given it a 2 mile test, probably driven firmly, as that is what garages mostly do. They struggle to drive as customers do.

You need to document the behaviour. Might be best to get help so a passenger can make notes.
From cold, drive normally until temp reaches normal. Record time/distance and tyrpe of road or traffic conditions.
Continue, and record when the temp drops. Again, time, distance and driving conditions. Outside temp also useful if you know it. Then record as it rises again. Listen for fan operation, record this too.

Most likely problem is thermostat. Simple item, and they do fail in this way. Why not just get it changed, make sure it is a good one, or are you arguing about warranty?
Could be fan cutting in early. Sometimes controlled by a different sensor than the temp gauge, so diagnostics showing live data might be able to compare the two readings. This is possible, but less likely.
 
Thermostats use an expanding wax device to hold them closed against a spring. They always fail open causing the engine to run cold and be difficult to start when hot.

Replace the thermostat. Parts are cheap and labour is no more than an hour. You will also get the coolant replaced which is usually no bad thing.
 
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Thermostats use an expanding wax device to hold them closed against a spring. They always fail open causing the engine to run cold and be difficult to start when hot.

The expanding wax device usually doesn't fail on the Panda. The most commonly reported problem with the old style Panda thermostats with the pre-Euro 5 engine is that an internal rubber seal perishes and lets coolant through when the thermostat is supposed to be fully closed. If you do a classic boiling water test, the thermostat will open and close normally, leading you to the mistaken belief that there's nothing wrong with it.

The OP has a Euro5 version with the temperature sensor built into the thermostat housing (like the 500). The most common failure mode for these is that many of the OEM ones have a plastic hose connection spigot, which breaks down with age, leading to a sudden loss of coolant (and HG failure if you don't get the engine shut down pronto). Some replacement 'stats have a metal spigot; if replacing, try to get one of these if you can. Not quite so cheap just to swap on a hunch, but at least you are replacing both the thermostat and the sensor at the same time.

You will also get the coolant replaced

Not necessarily. It's quicker, easier and less likely to disturb a hose connection to syphon it out, and if you work cleanly, you can just put it back in. If you are just changing the 'stat, you only need to lower it below the level of the thermostat housing.
 
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The expanding wax device usually doesn't fail on the Panda. The most commonly reported problem with the old style Panda thermostats with the pre-Euro 5 engine is that an internal rubber seal perishes and lets coolant through when the thermostat is supposed to be fully closed. If you do a classic boiling water test, the thermostat will open and close normally, leading you to the mistaken belief that there's nothing wrong with it.

The OP has a Euro5 version with the temperature sensor built into the thermostat housing (like the 500). The most common failure mode for these is that many of the OEM ones have a plastic hose connection spigot, which breaks down with age, leading to a sudden loss of coolant (and HG failure if you don't get the engine shut down pronto). Some replacement 'stats have a metal spigot; if replacing, try to get one of these if you can. Not quite so cheap just to swap on a hunch, but at least you are replacing both the thermostat and the sensor at the same time.



Not necessarily. It's quicker, easier and less likely to disturb a hose connection to syphon it out, and if you work cleanly, you can just put it back in. If you are just changing the 'stat, you only need to lower it below the level of the thermostat housing.

correct on both points.


we need to diagnosis the problem


wiring
pump
sensor
airlock
blocked passages
HG
gauge
ECU
Body Computer
Dash electronics
thermostat
battery
heater matrix blocked
probably more

lots of things could be causing a problem


Guessing all the time can get expensive but you can get lucky


I check as much as possible. Before ripping things apart.


Until we have more information from the original poster we are shooting in the dark


for example going High on startup and dropping to normal after a few seconds isn't the same as the temperature is normal when stationary but goes down when either the blower or the car is moving. Or the gauge is jumping up and down ever few second

but all could be described as yo-yo ing around
 
had the car four years years so not under warranty. Problem started about 6 months ago, gauge only moving a few mm down from midway. Almost always while moving, or when heater is switched on. Car doesn't overheat, no steam from exhaust, no mayo in oil or coolant, coolant level seems to be OK, no misfire, engine purrs along good. Last 3 times ive driven it before taking it into garage has been the most noticeable gauge drop, quite quickly dropping about 25% from midway just as it gets back to temperature then a slow climb back up to normal.
 
had the car four years years so not under warranty. Problem started about 6 months ago, gauge only moving a few mm down from midway. Almost always while moving, or when heater is switched on. Car doesn't overheat, no steam from exhaust, no mayo in oil or coolant, coolant level seems to be OK, no misfire, engine purrs along good. Last 3 times ive driven it before taking it into garage has been the most noticeable gauge drop, quite quickly dropping about 25% from midway just as it gets back to temperature then a slow climb back up to normal.

Typical of a Thermostat that isnt controlling flow properly :eek:

A replacement thermostat will cost around the same as a diagnostic

By the way..

Is your temp.gauge a needle.. or series of 'blocks'?
 
Make sure there enough coolant

Make sure there’s no air at the heater pipe bleed screw

Start the car from cold

Put your hand on the pipe top front right if standing in front of the car going to the radiator


Does this stay cold for at least 2 minutes.
 
Typical of a Thermostat that isnt controlling flow properly :eek:

A replacement thermostat will cost around the same as a diagnostic

By the way..

Is your temp.gauge a needle.. or series of 'blocks'?

Had the same issue recently on our 2011 my life. New stat fitted and its fine again. New stat with metal spigot has built in seal and was simple to fit once the battery and tray were removed. Touch wood its really running well now. Catch can is still catching a lot of water but all the sensors and the manifold are clean and dry.
 
if the gauge is only dropping below normal

would point to the thermostat letting coolant bypass and into the radiator when it should be fully closed.


this is what we are testing for in the test above


its fairy Common for the internal rubber seal to fail letting coolant leak into the radiator, causing it to over cool.

If this is the case. It will never overheat. But will be slower to get to temperature, heaters not as hot as normal, and the gauge drops when you have had the heaters off and then put them on full or when driving at over 50 but rises when driving slower
 
Just get the thermostat replaced and ask the garage to replace the coolant. Total cost will be parts plus an hour's labour.

You "Can" do the job without dropping the coolant but most garages will take the opportunity to replace the old stuff. Less come-back for them and more chargeable work for them.
 
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These symptoms are so typical of a "tired" thermostat that, if it were me, I'd just be fitting a new thermostat. The My Life used the 69hp VVT engine I think? so the thermostat is going to be the more expensive one which includes the temp sensor: https://www.shop4parts.co.uk/?name=store&op=Product&ProdID=18857

As has been said, some come with a plastic heater hose spigot but this one from S4p seems to have a metal spigot. I'd be giving them a ring to check that all three of the makes they offer have the metal pipe before making up my mind which one to buy and I would steer clear of the ones with a plastic spigot. Also, unless it's been changed very recently, for all the cost involved, I'd just be filling up with new coolant. Some people seem to experience problems with bleeding out when refilling so if you're not confident it could be worth getting a garage to do the whole job for you rather than risk damage to the head gasket because you start driving about with a lot of air trapped in the system.
 
Typical of a Thermostat that isnt controlling flow properly :eek:

Is your temp.gauge a needle.. or series of 'blocks'?

Needle


Make sure there enough coolant

Make sure there’s no air at the heater pipe bleed screw

Start the car from cold

Put your hand on the pipe top front right if standing in front of the car going to the radiator


Does this stay cold for at least 2 minutes.

Bled it at heater bleed screw, no air in it. After 2-3 minutes heater pipe is very warm, pipe from radiator to Stat felt luke warm

As has been said, some come with a plastic heater hose spigot but this one from S4p seems to have a metal spigot. I'd be giving them a ring to check that all three of the makes they offer have the metal pipe before making up my mind which one to buy and I would steer clear of the ones with a plastic spigot. Also, unless it's been changed very recently, for all the cost involved, I'd just be filling up with new coolant. Some people seem to experience problems with bleeding out when refilling so if you're not confident it could be worth getting a garage to do the whole job for you rather than risk damage to the head gasket because you start driving about with a lot of air trapped in the system.

Ive done coolant changes before, just not on Fiats still hate getting underneath to undo hoses
 
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the radiator top Hose should stay stone cold for the First few minutes.

You have the answer right there

Any garage should be able to sort this even if you took it in with a warm engine.

After asking you the symptoms. They should have asked you to come back in a couple of hours. And tried the car from cold
 
Ive done coolant changes before, just not on Fiats still hate getting underneath to undo hoses

Removing the bottom hose (or the so-called quick release connector) is a pig of a job; there have been numerous posts from folks who've had problems with broken parts/leaks after doing this. Fortunately on the 1.2 Panda/500 models with the expansion tank at the side of the radiator, there's no need; you'll get just as much coolant out by vacuuming/syphoning it out - the bottom of the tank is the lowest point on the system.

I did once remove the bottom hose as a check after doing this, absolutely nothing came out.

You'll save yourself a potential headache by just leaving the lower bottom hose connection alone.

Fortunately the one on the thermostat housing is easily accessible and straightforward; easiest way without special tools is to snip off the OEM clip and replace with a jubilee clip afterwards.
 
Complete agreement with far more experienced members - did this job last month and syphoning makes coolant change very simple. Variable temperature now disappeared with thermostat change, this is despite the top hose check being inconclusive.
 
Variable temperature now disappeared with thermostat change, this is despite the top hose check being inconclusive.

On the versions without the built in temperature sensor, those with DIY skills would probably do well just to change it if trouble is suspected - the whole job can be done for less than £10.

Conversely, if you have the version with the sensor, take it to a garage and have them change it; you're likely to be looking at a minimum of £100+VAT; more than ten times that cost - so in that case, you want to be reasonably sure about the diagnosis before getting the work done.
 
Got new thermostat with all metal piping same shape as old except sensor has green connector. Old one has brown, whats the difference between these?
 
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