Felicia coolant temp puzzle !!

[eng_ahmad1986]

Greetings to all members

I have a this coolant temperature puzzle that is driving me crazy !!

I'm located in Cairo, Egypt

I own a 1996 Skoda Felicia Combi on carburetor ( 43 KW )

Coolant temperature sensor is the metal one, with one terminal connector.

installed radiator fan switch rating : on at 82 C , off at 68 C

my problem is that the radiator fan kicks in too late , meaning over 90 C , probably 95 at idle , and switches off above between 70 C and 90 C

this condition worsens after driving for a while then stopping , fan kicks in at probably 100 C and off probably at 88 C ( at idle )

there is no thermostat installed

things that have been replaced so far : radiator , coolant pump , fan switch ( same rating as above )

checked head gasket for compression leaks , the mechanic confirmed that the head gasket is OK for there is no pressure build up in coolant hoses . 

my head is going to many thoughts, could it be coolant temp sensor ? could it be temp gauge out of calibration ? could it be any other thing ?

and by the way , if the fan switch is with the above rating , what would be the normal range for the fan to work regarding the temp gauge ? 

this condition is driving me crazy , I don't know what else to do , please help  I really need it urgently

thank you all very much for considering  

[Breezy_Pete]

My theory: CTS is measuring temperature at/near engine coolant outlet? Radiator thermoswitch is acting on coolant that is at/near the bottom of the radiator? So after it has exchanged lots of heat into the passing air, reducing the coolant temperature (the job of the radiator). So a temperature difference would seem to be expected.

[eng_ahmad1986]

Just now, Wino said:

My theory: CTS is measuring temperature at/near engine coolant outlet? Radiator thermoswitch is acting on coolant that is at/near the bottom of the radiator? So after it has exchanged lots of heat into the passing air, reducing the coolant temperature (the job of the radiator). So a temperature difference would seem to be expected.

 

Thank you very much for considering and quick reply , of course I understand that point , but would it be that much difference in temperature ?

that's why I asked what is the normal range for the fan to kick in/out regarding the temp gauge, and according to the fan switch rating mentioned above  

[Breezy_Pete]

Yes, I believe those temperature differences are well within what I would expect.

I can't give any Felicia-specific data, sorry. Try using an infra-red point-and-shoot thermometer aimed at the rad thermoswitch metal parts and see if the temperature there is consistent with the switch rating and fan action?

[eng_ahmad1986]

2 minutes ago, Wino said:

Yes, I believe those temperature differences are well within what I would expect.

I can't give any Felicia-specific data, sorry. Try using an infra-red point-and-shoot thermometer aimed at the rad thermoswitch metal parts and see if the temperature there is consistent with the switch rating and fan action?

 

Thanks again very much for the follow up , unfortunately here in Egypt we don't have access to an infrared thermometer, neither the mechanics use it anyways :( :(

[eng_ahmad1986]

something I'm thinking of : could it be an air pocket behind the fan switch ?

[Breezy_Pete]

With luck someone else reading this (with such equipment available) will be able to do comparison measurements on their (Felicia) car.

 

[KenONeill]

@eng_ahmad1986 - "There is no thermostat" - Well that could explain it. The thermostat does more than just stop water flowing to the radiator when the engine is cold (and that does mean daytime air temperatures in Egypt yes). It also helps regulate the water flow to a hot, say 90C, engine.

[RicardoM]

On 1/18/2018 at 00:33, eng_ahmad1986 said:

something I'm thinking of : could it be an air pocket behind the fan switch ?

Not possible.

[eng_ahmad1986]

17 minutes ago, RicardoM said:

Not possible.

Thank you very much Ricardo for considering, but for an expert in Felicias like you , what do you think it could be ?

and by the way, for the metal temp. sensor, what would be the correct ohm reading per temperature if you have an idea ?

Edited 19 January, 2018 by eng_ahmad1986

[RicardoM]

On 1/18/2018 at 00:08, eng_ahmad1986 said:

checked head gasket for compression leaks , the mechanic confirmed that the head gasket is OK for there is no pressure build up in coolant hoses . 

Wow, very scientific method... not! So this possibility is still on the table.

On 1/18/2018 at 00:08, eng_ahmad1986 said:

could it be coolant temp sensor ?

Yes, it's possible. 

On 1/18/2018 at 00:08, eng_ahmad1986 said:

could it be temp gauge out of calibration ?

Yes, it's possible. Not probable but possible.

On 1/18/2018 at 00:08, eng_ahmad1986 said:

if the fan switch is with the above rating , what would be the normal range for the fan to work regarding the temp gauge ? 

From my experience, you have to add 10°C to the fan switch rating to get the indication on the temperature gauge. For instance, your car needs a 85-80°C fan switch. That means the fan will kick in at 95°C and shut off at 90°C.

38 minutes ago, eng_ahmad1986 said:

by the way, for the metal temp. sensor, what would be the correct ohm reading per temperature if you have an idea ?

Sorry, I don't have the temperature/resistance graph for it.

[Papez]

I can confirm that fan goes off ~10°C higher, than rated temperature. It's caused by sensor being placed on output side of radiator and slow flow of coolant at idle. I have no idea why they choose this system.

 

90° is perfectly OK, it's standart temperature of European version (where fan turns on close to 110°C).

[RicardoM]

4 hours ago, Papez said:

90° is perfectly OK, it's standart temperature of European version (where fan turns on close to 110°C).

I disagree. The fan kicks in at 95°C, maximum 100°C. Never close to 110°C.

[Papez]

Well, thermometer shows little over 90° when driving, so it's not exactly accurate instrument. Maybe it's closer to 100°, I haven't tried to measure it with diagnostics. Also thermoswitch itself have few degrees inaccuracy, co every Felicia will show different value. Important is, that 90°-100° is OK and it won't harm engine.

Edited 20 January, 2018 by Papez

[eng_ahmad1986]

Thank you all very much for considering and this great help, but what really matters : when driving on a highway at high speed for sometime ( may be 120 kmph and over ) and then come to a stop to let the engine idle, why at that instant the fan kicks in more late, and if left idle for sometime the fan kicks in back into the normal range !! is that Ok ? do you all experience this ? thank you all again for considering  

[RicardoM]

2 hours ago, eng_ahmad1986 said:

why at that instant the fan kicks in more late, and if left idle for sometime the fan kicks in back into the normal range !! is that Ok ?

What do you mean "more late"? At what temperature the fan starts/stops?

What do you mean by "normal"? At what temperature the fan starts/stops?

What air temperature is in Egypt when that happens?

@Papez

Can you help with the temperature/resistance graph for the coolant temperature sensor from Felicia MonoMotronic engines?

Edited 21 January, 2018 by RicardoM

[eng_ahmad1986]

1 hour ago, RicardoM said:

What do you mean "more late"? At what temperature the fan starts/stops?

What do you mean by "normal"? At what temperature the fan starts/stops?

What air temperature is in Egypt when that happens?

by more late I mean instead of  kicking in at 92 C it kicks in at 100 C or perhaps a little more, and shuts off at 90C instead of of 80C, but if left idle for a while it gets to the normal range again which is 92-80 .

nowadays the temp. in Egypt is about 15 C to 25 C

 

to clarify this , the fan kicks in and shut off at :

normally at idle : 92 C - 80 C

after driving for a while ( usually highway speed ) , and then come to stop and let it idle : 100 C - 90 C

if left to idle for a while it returns back to 92 C - 80 C

 

all these figures according to the fan switch installed which is : 82 C - 68 C

Edited 21 January, 2018 by eng_ahmad1986

[RicardoM]

To clarify a few things:

• the engine runs best at 90C. I don't understand why are you using a fan switch that keeps the coolant at 80C.
• running without a thermostat is a mistake. See this video
• use a thermostat for tropical climate if it's really hot all year
• the cooling system has to be tight to keep it pressurized
• the coolant reservoir cap opens if the pressure is too high
• using water instead of coolant mixture is a mistake. It reduces the cooling efficiency
• make sure there is no air trapped under the temperature sensor
• keep the coolant level a little above half in the reservoir when the engine is cold

My advice is: follow above rules. Test again the car on highway. 

[Breezy_Pete]

When you are on the highway travelling fast, the engine produces a lot more heat than when idling. But the radiator also has fast airflow through it, so coolant at higher temperature can enter it, yet still not trigger the fan thermoswitch because the heat from the coolant has been transferred into passing air, lowering the coolant temperature by the time it reaches the thermoswitch.

 

When you come off the highway, that airflow suddenly reduces dramatically, so the coolant loses less heat/temperature during its passage through the radiator. Now the fan switch operates.

 

At steady/sustained idle, there is no airflow at all through the radiator, unless the fan comes on, so there is little temperature difference between the coolant entering it and leaving it, so the temperatures 'seen' by the radiator thermoswitch and coolant temperature sensor will be much closer. Now the fan must produce airflow as required to maintain equilibrium.

 

I think what you are seeing is normal.

[RicardoM]

5 hours ago, Wino said:

I think what you are seeing is normal.

I have never observed on my car the behavior described by our friend from Egypt. It's hot in my country all year long.

 

What you described in your post makes sense though.

[eng_ahmad1986]

Tomorrow I'm going to the mechanic , I will tell him to disassemble the cylinder head and visually inspect the head gasket for leaks and replace if necessary, I will install a thermostat and a matching fan switch, and let you know how will it go  

 

but I have a question : what would be the correct thermostat rating and the matching fan switch rating, knowing that my Felicia is the hot climate version as mentioned by Skoda ? its not the part numbers that I want, but the correct ratings, because auto parts sellers here in Egypt deal more with ratings rather than part numbers !!    

 

just to remind you my dear friends, my Felicia is the carbureted 43 KW version, and the thermostat housing is the metal one  

 

thank you very much for all this help , I really appreciate your help, caring, and considering  

 

and I apologize if my English is not that good, my native language is Arabic  

Edited 21 January, 2018 by eng_ahmad1986

[RicardoM]

35 minutes ago, eng_ahmad1986 said:

I will tell him to disassemble the cylinder head and visually inspect the head gasket for leaks and replace if necessary,

Hold on, that is not necessary the first option. Not to mention it is labour intensive. It's not like changing the oil sump gasket. The cylinder head and block must be tested for flatness/warping and pitting then rectified/skimmed and so on.

 

Thermostat: I recommend Wahler 3032.80.

[eng_ahmad1986]

44 minutes ago, RicardoM said:

Hold on, that is not necessary the first option. Not to mention it is labour intensive. It's not like changing the oil sump gasket. The cylinder head and block must be tested for flatness/warping and pitting then rectified/skimmed and so on.

 

Thermostat: I recommend Wahler 3032.80.

 

thank you very much for the quick reply, then how can we test the head gasket for compression leaks into coolant without disassembling ? some mechanics suggests :

 

while the engine is cold, fill the expansion tank up to the neck, disconnect the ignition coil plug, and have a friend crank the engine while you observe the coolant for bubbles or coolant spillover.

 

now is that a good method that could rule out the head gasket failure even it is a minor leak ?

 

and for the mentioned thermostat I see it has a rating of 80 C , so what would be the matching fan switch rating ?

 

I really wish to thank you in person for all this help and consideration  

[RicardoM]

4 hours ago, eng_ahmad1986 said:

then how can we test the head gasket for compression leaks into coolant without disassembling ?

This is the recommended DIY method in case you don't find the tool to buy

 

4 hours ago, eng_ahmad1986 said:

and for the mentioned thermostat I see it has a rating of 80 C , so what would be the matching fan switch rating ?

85-75C or close.

[eng_ahmad1986]

hey guys, it turned out that the engine block is rusted and is leaking coolant into cylinders and leaking compression into coolant, now I proceeded with engine replacement with a used one , now I have a different question , now the new engine ( which is a complete engine - cylinder head and short block altogether ) is a 136B engine, while the old one was a 135 engine on carburetor as you know, but I'm going to install the carburetor on the new engine, now what is the rated power output of that engine originally ,and how will this be affected by installing the carb rather than the mono-motronic ?