Technical Cooling system problem

[Sabbas]

Good morning. I have a Fiat Seicento MPI. After a visit to the mechanic for an oil change, I also replaced the thermostat, the temperature sensor, the coolant expansion tank, and added new coolant in preparation for the summer. Before the changes, when the car reached 87°C, I could see on my OBD scanner that the thermostat would open and the temperature would drop to 82°C. Additionally, the radiator fan would turn on at 97°C and drop the temperature to 92°C.
After the service, I see on the OBD scanner that the thermostat now opens at 92°C and the temperature drops to 88°C. Also, when stationary, the fan kicks in at 98°C, but it runs continuously, and the temperature stays at 95-96°C. I have to turn on the heater to drop the temperature so the fan will stop. My mechanic claims that this is the correct operation for the car. He has already performed a cooling system bleed twice and insists that this is how the car works. What is your opinion? Thank you for your time!

 

[bugsymike]

Good morning. I have a Fiat Seicento MPI. After a visit to the mechanic for an oil change, I also replaced the thermostat, the temperature sensor, the coolant expansion tank, and added new coolant in preparation for the summer. Before the changes, when the car reached 87°C, I could see on my OBD scanner that the thermostat would open and the temperature would drop to 82°C. Additionally, the radiator fan would turn on at 97°C and drop the temperature to 92°C.
After the service, I see on the OBD scanner that the thermostat now opens at 92°C and the temperature drops to 88°C. Also, when stationary, the fan kicks in at 98°C, but it runs continuously, and the temperature stays at 95-96°C. I have to turn on the heater to drop the temperature so the fan will stop. My mechanic claims that this is the correct operation for the car. He has already performed a cooling system bleed twice and insists that this is how the car works. What is your opinion? Thank you for your time!

Assuming yours is in the age band in this book it gives thermostat opening at 89 Degrees Centigrade (column 36 by pen) sometimes different thermostats vary which is why I often check them with a good thermometer in a saucepan of water bringing it to the boil and then watching thermostat open and then close as water temp falls.
Apart from that is there any chance your rad is starting to block in the core tubes making it harder to lose the heat.
Sometimes you can feel if different parts of the rad are cooler than others, or maybe use a laser thermometer if available.
If you feel something is wrong or different to usual don't rely on others, you are the driver and know if something is wrong!

 

[Sabbas]

Thank you very much for your reply and for your help bugsymike.

Assuming yours is in the age band in this book it gives thermostat opening at 89 Degrees Centigrade (column 36 by pen) sometimes different thermostats vary which is why I often check them with a good thermometer in a saucepan of water bringing it to the boil and then watching thermostat open and then close as water temp falls.
Apart from that is there any chance your rad is starting to block in the core tubes making it harder to lose the heat.
Sometimes you can feel if different parts of the rad are cooler than others, or maybe use a laser thermometer if available.
If you feel something is wrong or different to usual don't rely on others, you are the driver and know if something is wrong!

The thermostat had 87 degrees Celsius stamped on its housing. Unfortunately, I did not test it the way you suggested. I replaced the radiator last year, along with the water pump. I believe the issue is likely with either the thermostat or the temperature sensor, as the car was running correctly before those two were replaced. Is there a way to determine which of the two is causing the problem? The car has an issue with its idle speed, and the radiator fan runs constantly without lowering the temperature, which stays stuck at 95–96°C.

 

[bugsymike]

Thank you very much for your reply and for your help bugsymike.


The thermostat had 87 degrees Celsius stamped on its housing. Unfortunately, I did not test it the way you suggested. I replaced the radiator last year, along with the water pump. I believe the issue is likely with either the thermostat or the temperature sensor, as the car was running correctly before those two were replaced. Is there a way to determine which of the two is causing the problem? The car has an issue with its idle speed, and the radiator fan runs constantly without lowering the temperature, which stays stuck at 95–96°C.

It does point towards a sensor issue, however if possible to check with something like a good laser thermometer that you point at near where the sensor is
it may give more information. So a new good quality sensor may be the answer. I can't recall, but I assume you have a separate sensor to trigger the fan than the temp gauge sensor? So both need testing. Presumably and I am guessing, if the two wire connector is unplugged at the radiator the fan should stop, unless a relay somewhere is stuck on.
If you are sure the new radiator is up to the job and you are not losing water through any engine defect, then ideally take the thermostat out and test it, in the old days it was a simple job and in hot weather many just ran their cars with no thermostat, the only disadvantage was they used more fuel if the engine wasn't running at it's correct efficient temperature and also any car interior heater and demister would not work very well in the Winter.
One final word of warning on a recent post on Forum a member took advice from a garage using a laser tester who told him the engine was not overheating, he carried on and blew the engine up! Note this was against my and others advice before the event.

 

[Sabbas]

It does point towards a sensor issue, however if possible to check with something like a good laser thermometer that you point at near where the sensor is
it may give more information. So a new good quality sensor may be the answer. I can't recall, but I assume you have a separate sensor to trigger the fan than the temp gauge sensor? So both need testing. Presumably and I am guessing, if the two wire connector is unplugged at the radiator the fan should stop, unless a relay somewhere is stuck on.
If you are sure the new radiator is up to the job and you are not losing water through any engine defect, then ideally take the thermostat out and test it, in the old days it was a simple job and in hot weather many just ran their cars with no thermostat, the only disadvantage was they used more fuel if the engine wasn't running at it's correct efficient temperature and also any car interior heater and demister would not work very well in the Winter.
One final word of warning on a recent post on Forum a member took advice from a garage using a laser tester who told him the engine was not overheating, he carried on and blew the engine up! Note this was against my and others advice before the event.

Thanks again for your reply. Unfortunately, there is no temperature gauge inside the car; I monitor the temperature via an OBD scanner directly from the port. From what I have observed, there is only one temperature sensor (the green one) which sends the temperature information to the ECU, and it, in turn, commands the radiator fan to start or stop.

 

[bugsymike]

Thanks again for your reply. Unfortunately, there is no temperature gauge inside the car; I monitor the temperature via an OBD scanner directly from the port. From what I have observed, there is only one temperature sensor (the green one) which sends the temperature information to the ECU, and it, in turn, commands the radiator fan to start or stop.

I see , perhaps there is another Forum Member who can give more detail re sensor, sorry.

 

[Mike1alike]

After the service, I see on the OBD scanner that the thermostat now opens at 92°C and the temperature drops to 88°C. Also, when stationary, the fan kicks in at 98°C, but it runs continuously, and the temperature stays at 95-96°C. I have to turn on the heater to drop the temperature so the fan will stop. My mechanic claims that this is the correct operation for the car. He has already performed a cooling system bleed twice and insists that this is how the car works. What is your opinion? Thank you for your time!

That does sound like a thermostat problem. But you say it has 87°C stamped on its housing so that should be ok.
I would guess there is air inside the cooling system after that service and that is causing the problem. Cooling system bleed, may it be performed twice, if performed incorrectly does not get the air out of the system.
I recommend you do the bleed yourself, the right way.
Get the engine warmed, working temp then work carefully as it will be hot. Stop the engine and open the radiator breather screw. Take it off completely and with it off, top up coolant level until it comes out of the breather. Put breather screw back and do the same for heater matrix breather located on the piping. If at the end of doing that coolant level is higher than max line, do extract some out using a little hose or so.

 

[Sabbas]

I see , perhaps there is another Forum Member who can give more detail re sensor, sorry.

Thanks for the help and the information on testing the thermostat.

 

[Sabbas]

That does sound like a thermostat problem. But you say it has 87°C stamped on its housing so that should be ok.
I would guess there is air inside the cooling system after that service and that is causing the problem. Cooling system bleed, may it be performed twice, if performed incorrectly does not get the air out of the system.
I recommend you do the bleed yourself, the right way.
Get the engine warmed, working temp then work carefully as it will be hot. Stop the engine and open the radiator breather screw. Take it off completely and with it off, top up coolant level until it comes out of the breather. Put breather screw back and do the same for heater matrix breather located on the piping. If at the end of doing that coolant level is higher than max line, do extract some out using a little hose or so.

Thank you very much for your reply. I’m not sure if I can bleed the cooling system properly on my own, as I don’t have much mechanical knowledge. I had tried it in the past with a cold engine; I remember that coolant came out of the radiator hose, but nothing came out of the heater hose. So, I ended up taking it to a garage in my old neighborhood, and they handled it for me.

 

[Mike1alike]

I remember that coolant came out of the radiator hose, but nothing came out of the heater hose.

You just fill in and it will come out eventually. You do need to go over Max line level for it to come out of the hose, but as I said, after it comes out you put the screw back and then can take some coolant out of the system somehow to make it leveled between Min and Max. Few days after you do need to check the level and see how it stands.

 

[Mike1alike]

And it does need to be done on hot engine so thermostat would be open.
I could easily do it on cold engine on mine wich had me questioning how so. Turned out at the time the thermostat internal gasket was damaged, so thermostat wouldn't close completely.

 

[Sabbas]

Thank you very much for your reply. I’m not sure if I can bleed the cooling system properly on my own, as I don’t have much mechanical knowledge. I had tried it in the past with a cold engine; I remember that coolant came out of the radiator hose, but nothing came out of the heater hose. So, I ended up taking it to a garage in my old neighborhood, and they handled it for me.

And it does need to be done on hot engine so thermostat would be open.
I could easily do it on cold engine on mine wich had me questioning how so. Turned out at the time the thermostat internal gasket was damaged, so thermostat wouldn't close completely.

And it does need to be done on hot engine so thermostat would be open.
I could easily do it on cold engine on mine wich had me questioning how so. Turned out at the time the thermostat internal gasket was damaged, so thermostat wouldn't close completely.

Thank you very much for the information. Just to make sure I understand correctly: I should start the engine with all the caps closed, including the coolant reservoir cap, and let the car reach the temperature where the thermostat opens, and then turn it off. Then, I open the radiator cap first until coolant comes out, close it, and then open the cap on the heater core—is that correct? And should I have the cabin heating set to full hot?

 

[bugsymike]

Thank you very much for the information. Just to make sure I understand correctly: I should start the engine with all the caps closed, including the coolant reservoir cap, and let the car reach the temperature where the thermostat opens, and then turn it off. Then, I open the radiator cap first until coolant comes out, close it, and then open the cap on the heater core—is that correct? And should I have the cabin heating set to full hot?

No! Don't open the coolant tank cap with a hot engine unless you want to get badly burnt as it is under roughly 15 pounds of pressure (.98 Bar as it says in my earlier piece at #2 and at nearly the boiling point of water!
What I think mike was meaning was once engine up to normal running temperature the air if any can be bled carefully from the bleeders where he mentioned as the coolant pressure should push the air out. But do be careful only to open the bleeder a little so air comes out and not scalding hot water. This is why you must never open a radiator or coolant expansion tank cap with a hot engine, I saw a lad do it on a Hillman Imp years ago whilst wearing a T shirt , he turned away but was still badly burnt on his back.

 

[Sabbas]

No! Don't open the coolant tank cap with a hot engine unless you want to get badly burnt as it is under roughly 15 pounds of pressure (.98 Bar as it says in my earlier piece at #2 and at nearly the boiling point of water!
What I think mike was meaning was once engine up to normal running temperature the air if any can be bled carefully from the bleeders where he mentioned as the coolant pressure should push the air out. But do be careful only to open the bleeder a little so air comes out and not scalding hot water. This is why you must never open a radiator or coolant expansion tank cap with a hot engine, I saw a lad do it on a Hillman Imp years ago whilst wearing a T shirt , he turned away but was still badly burnt on his back.

Sorry, I didn't mean to write 'radiator cap'; I meant the radiator bleed valve. One last question: if the bleeding is done while the car is running and by opening the bleed valves slightly, doesn't that remove all the air?

 

[Mike1alike]

Thank you very much for the information. Just to make sure I understand correctly: I should start the engine with all the caps closed, including the coolant reservoir cap, and let the car reach the temperature where the thermostat opens, and then turn it off. Then, I open the radiator cap first until coolant comes out, close it, and then open the cap on the heater core—is that correct? And should I have the cabin heating set to full hot?

Almost so.
Yes, start the engine with all caps close and have it reach the temp and open thermostat. Then stop the engine and first thing open the coolant filler cap, radiator cap or expansion tank cap, depending what you have. Yes, coolant is hot inside and there might be pressure but it can be safety open. Just with care. I opened the radiator cap many times just after engine running and not once coolant came out of it. Only time it would come out would be when radiator fan's thermic fuse was broken so fan wouldn't run on 1st speed, only on 2nd, that making temperature and pressure inside cooling system higher than normal.
So... you open the filler cap careful. Not at once. As you take it off, you will hear the pressure being released so that's it, no coolant would come off. Just a hiss. So carefully make sure you can take the cap off. Like let it loose, listen for the hiss and watch if any coolant comes out. Then let it loose more and take it out completely if no coolant comes out.
Then open the breathers caps, radiator's first, heater's second and with them opened fill in with coolant until it comes out on the breather's holes and then put the cap back after it does.
It's totally safe and more practical, more efficient and safer than doing it on the engine running when it's harder to get all the air out and is easier to have the breathers caps pushed out and hot coolant gushing out there.

 

[bugsymike]

Sorry, I didn't mean to write 'radiator cap'; I meant the radiator bleed valve. One last question: if the bleeding is done while the car is running and by opening the bleed valves slightly, doesn't that remove all the air?

Hopefully.
Do what you want, but personally on all the cars I have bled the air out of the cooling system I have done it using the pressure in the coolant system to push the air out of the bleeders. this is why I only open the bleeders a small amount so the air hisses out and you shut it off safely before the hot water/coolant comes out.
I have also done the same with a cold engine but using a garage coolant pressure tester to build up pressure in the system as this helps bleed the air out.
This is the sort of coolant pressure tester I use.

 

[Sabbas]

Almost so.
Yes, start the engine with all caps close and have it reach the temp and open thermostat. Then stop the engine and first thing open the coolant filler cap, radiator cap or expansion tank cap, depending what you have. Yes, coolant is hot inside and there might be pressure but it can be safety open. Just with care. I opened the radiator cap many times just after engine running and not once coolant came out of it. Only time it would come out would be when radiator fan's thermic fuse was broken so fan wouldn't run on 1st speed, only on 2nd, that making temperature and pressure inside cooling system higher than normal.
So... you open the filler cap careful. Not at once. As you take it off, you will hear the pressure being released so that's it, no coolant would come off. Just a hiss. So carefully make sure you can take the cap off. Like let it loose, listen for the hiss and watch if any coolant comes out. Then let it loose more and take it out completely if no coolant comes out.
Then open the breathers caps, radiator's first, heater's second and with them opened fill in with coolant until it comes out on the breather's holes and then put the cap back after it does.
It's totally safe and more practical, more efficient and safer than doing it on the engine running when it's harder to get all the air out and is easier to have the breathers caps pushed out and hot coolant gushing out there.

Thank you very much for the explanation again, but I still don’t feel confident doing this,I’m afraid I might make the situation worse, so I’m going to visit the garage again.

 

[Sabbas]

Hopefully.
Do what you want, but personally on all the cars I have bled the air out of the cooling system I have done it using the pressure in the coolant system to push the air out of the bleeders. this is why I only open the bleeders a small amount so the air hisses out and you shut it off safely before the hot water/coolant comes out.
I have also done the same with a cold engine but using a garage coolant pressure tester to build up pressure in the system as this helps bleed the air out.
This is the sort of coolant pressure tester I use.

Great equipment! I wish I had one—and the knowledge, of course—to be able to repair my own car. The way the mechanic bled the system at the shop was: he opened the reservoir cap, poured in the coolant, disconnected the first bleed valve until liquid came out, and closed it. Then, he opened the heater bleed valve and blew into the coolant reservoir with his mouth to force the liquid out of the heater core. Is that the right way to do it?"

 

[Mike1alike]

The way the mechanic bled the system at the shop was: he opened the reservoir cap, poured in the coolant, disconnected the first bleed valve until liquid came out, and closed it. Then, he opened the heater bleed valve and blew into the coolant reservoir with his mouth to force the liquid out of the heater core. Is that the right way to do it?"

For that to work, he should have keep blowing into the reservoir all the time until he put the heater breather cap back. Which I suspect he didn’t. Otherwise, as soon as he stopped blowing the coolant, coolant dropped back down into the system under heater breather and air got back in there again.
And doing it on cold engine, with thermostat close is impossible to get all the air out. There's always air trapped inside thermostat that doesn't get out.
So, most certainly, mechanic did the bleeding wrong.

I still don’t feel confident doing this,I’m afraid I might make the situation worse, so I’m going to visit the garage again.

I don't think you would make it worse, but you can’t do it if you don't feel confident to do it.
You can bleed it using system pressure, might be easier. That needs to be done with care too, because of high temp and risk of having the breather cap pushed out. But if you open them only a little that won't happen. Just takes a little more time. And it's better to verify that again after you first do it.
So having the coolant heated up, stop the engine. And loosen up the breathers caps, same order, radiator first. When coolant comes out with cap loosen very small amount will come out and it's best to let it for some seconds, to have all air there taken out. Then tighten the cap and move to heater's cap. There should be enough pressure still in the system to get all air out there too. If not, drive a little then start with heater's cap. Doing this 3 times, driving, releasing air out, will have the system bled. When it is, coolant comes out immediately when you open the breather cap after engine ran.

 

[bugsymike]

Great equipment! I wish I had one—and the knowledge, of course—to be able to repair my own car. The way the mechanic bled the system at the shop was: he opened the reservoir cap, poured in the coolant, disconnected the first bleed valve until liquid came out, and closed it. Then, he opened the heater bleed valve and blew into the coolant reservoir with his mouth to force the liquid out of the heater core. Is that the right way to do it?"

Not the way I would do it it, but probably works to a certain extent. If he had my equipment he could do it more professionally.
Alternatively as I said , with engine warm it is under pressure already as long as the pressure cap is screwed down so when you open the bleed screws then the air will come out.
Another very important thing to consider is why you have a pressurised cooling system in the first place. It allows the engine to run at a slightly higher temperature where it is more efficient whilst still keeping a safety reserve.
Note, it is not the high temperature which damages an engine, it is when that water/coolant boils and becomes a gas, at which point any localised hot spots can rapidly exceed the normal boiling point of water, it is why pressure cookers work.
Remember for every lb of pressure above the water in a pressurised cooling system it means the water boils at 1.5 degrees Centigrade higher than the normal boiling point of water at sea level of 100 Degrees Centigrade, so a 10lb rad cap will allow the water to reach 115 Degrees Centigrade before boiling and causing damage, so with your coolant system the rad. cap which is almost 1.Bar pressure it means that the water could be 122.5 Degrees Centigrade without causing damage. However once you open that rad cap the water will instantly boil causing damage, you mentioned a temp reading of just roughly 98 Degrees Centigrade from your OBD scanner so if that is correct it would mean the water /coolant if you opened the pressure cap would be just about to turn to a gas! So not a good idea to remove the rad cap on a hot engine.
Many times in the past I have seen a motorist drive in to the forecourt with a hot engine release the rad cap and the next thing a jet of steam and water shoot out as he jump away dropping the rad cap, what often then happens is the idiot grabs the watering can and puts cold water into his hot engine with a very good chance of cracking the aluminium cylinder head.