[Jobu71]

Hi all.... anyone else had this weird situation... my wifes car...2004 passat 1.9 tdi diesel engine AVB:-
Prior to overheating ( wife run the coolant low) the car always stayed bang on 90º C normal temp.
1. Engine unstable temperature...found some problems..head gasket leak - changed that. . no longer air in the coolant .
2. Have changed thermostat ( twice ), New radiator, coolant sensors ( both.- green one twice ), waterpump ( twice ). Bled coolant system with vacuum
equipment, including the heater hose. with car lifted at the front, & rear.
Result:- car runs, start & drives well. I use an "Icarsoft" diagnostic CR Pro to monitor all functions while driving up & down hills & on flat roads.
Problem:- Temperature varies between 88 - 89º, & long uphill climbs to about max 93º . THis is the result I get from the diagnostic monitoring.
- The temperature guage in the dasboard shoes something else :- during warming up ( from coldstart ) the gauge reaches 90º before the coolant temperature
is at around 60 - 70º . The temp gauge then stays stable at 90º until a hill climb when it then increases to 100-105 on the gauge.
Does anyone experience this on their passat? BTW..when I read off the Coolant temp on my Icarsoft, the engine temp shows 90º, When Iread off the Icarsoft for the dashboard temp- it shows 109º.. Am I doing something wrong here??

 

[Jobu71]

I have just read my last post..a bit confusing?😁 - There are 2 areas of the Icarsoft where I can read the coolant temperature ,- 1 is from the ECU, Coolant temp ( reads 89º-90º. 2.- The dashboard coolant temp which reads 109ºC. Is the dashboard coolant temp a setting for when the secondary coolant fan should switch on?

Secondly..even though the thermostat is working ok, the lower radiator hose is always cool....

 

[Tomvw]

It is normal for the lower radiator hose to be cool, except in extreme heat conditions.

The coolant temp sensor has 2 components, one reports to the gauge and the other reports to the ECM.
The different readings indicates a faulty CTS.

There is only one CTS, the unit in the bottom radiator hose or radiator, is the coolant fan thermal switches.
The gauge shows 90 degrees C for a large range of temps.

 

[Jobu71]

It is normal for the lower radiator hose to be cool, except in extreme heat conditions.

The coolant temp sensor has 2 components, one reports to the gauge and the other reports to the ECM.
The different readings indicates a faulty CTS.

There is only one CTS, the unit in the bottom radiator hose or radiator, is the coolant fan thermal switches.
The gauge shows 90 degrees C for a large range of temps.

Hi & thanks for your help
Hmm.. Sorry if I seem a little confused here...The CTS ( the blue coloured sensor in the bottom radiator hose? Coolant Temperature Switch) which I have recently replaced,
isn't it's primary function to switch on the additional electric fan for additional cooling?- I can always change it again if you mean that is the cause? What is confusing me is that the gauge in the dashboard increases to around 93- max 95º when driving up hills & takes a while to drop down again after on flat roads. DO you mean that because the CTS is showing 109º, will cause the additional cooling fan to not switch on fast enough to hold down the temperature? Sorry my english isn't that great..Really appreciate a reply again if you have time..Thanks once again

 

[Tomvw]

There is only one CTS, it has two resistive elements, one connects to the ECM the other connects to the gauge on the dash.
I don't know its exact location in your engine, but it is near where the coolant exits the head on its way to the top of the radiator,
usually at the back of the head.
Your CTS should be replaced.

The coolant fan temp switch is in the bottom radiator hose, it has two switches (Normally open), one for low speed and the other for high speed.

The coolant fan temp switch and the CTS can be fitted in the opposite positions, but they will not work in the wrong position.
Make sure you have the correct units in the correct places.

 

[Jobu71]

Hi & thanks for your help
Hmm.. Sorry if I seem a little confused here...The CTS ( the blue coloured sensor in the bottom radiator hose? Coolant Temperature Switch) which I have recently replaced,
isn't it's primary function to switch on the additional electric fan for additional cooling?- I can always change it again if you mean that is the cause? What is confusing me is that the gauge in the dashboard increases to around 93- max 95º when driving up hills & takes a while to drop down again after on flat roads. DO you mean that because the CTS is showing 109º, will cause the additional cooling fan to not switch on fast enough to hold down the temperature? Sorry my english isn't that great..Really appreciate a reply again if you have time..Thanks once again

-- A little addition here.. just had the car for a test run..while the temp gauge in the dash is showing approx 93º, the additional electric cooling fan is running... so now what?

 

[Tomvw]

My last post still applies.
Replace the faulty CTS.

Are you aware that the fan should always run while the A/C is running.

 

[Jobu71]

My last post still applies.
Replace the faulty CTS.

Are you aware that the fan should always run while the A/C is running.

Hi again...Thanks once again Tomvw... I'll change it again tomorrow if I can get one & cross my fingers. I will get back to you with the result..Thanks Have a good evening.

 

[Jobu71]

Hi again...Thanks once again Tomvw... I'll change it again tomorrow if I can get one & cross my fingers. I will get back to you with the result..Thanks Have a good evening.

Hi Tomvw.. After re- reading your explanation about the sensors, I see that I misread it. Yes I agree the CTS is at the back of the block, & the blue thermal switch by the bottom rad hose...
I have changed both of them ( the CTS twice ). I have a new CTS & can fit it tmw. - From what you say, the diagnostic readings from the CTS should be the same to both the gauge & ECU?..
- That's what I thought.. I'll let you know.

 

[Tomvw]

The 2 readings from the CTS don't need to be the same, but they should be fairly close.

NOTES:
The coolant fan temp switch only switches the fan on low speed during very high heat conditions.
The coolant fan temp switch only switches the fan on High speed during extreme heat conditions.

The coolant fan is always switched to low speed when the A/C is switched on.
The A/C can also switch the fan to high speed under certain conditions.

When working correctly, the gauge on the dash will show about 90 degrees anywhere within a range between about 70 degrees to 110 degrees.

 

[Jobu71]

The 2 readings from the CTS don't need to be the same, but they should be fairly close.

NOTES:
The coolant fan temp switch only switches the fan on low speed during very high heat conditions.
The coolant fan temp switch only switches the fan on High speed during extreme heat conditions.

The coolant fan is always switched to low speed when the A/C is switched on.
The A/C can also switch the fan to high speed under certain conditions.

When working correctly, the gauge on the dash will show about 90 degrees anywhere within a range between about 70 degrees to 110 degrees.

Hi Tomvw, well I changed the CTS yesterday & took a test run...pretty much the same result- the engine temperature stabilized between 88º - 91º C ( reading ECU cata from the PC diagnostic Icarsoft pro tool ). The dashboard temp gauge after approximately 15 minutes driving increased to show roughly around 93º - 96º, & when reading the Coolant temperature signal to the guage on the diagnostic tool, it showed 112ºC. The engine does not overheat & the car runs fine... It is strange, prior to all the cooling problems & finding there was a head gasket leak, the temperature gauge always stayed bang on 90º.

 

[Tomvw]

It appears that you have a fault in the gauge circuit, maybe a bad connection or failing component.
I wouldn't be too concerned about it, just keep an eye on it and address the situation if it gets much worse.

 

[Jobu71]

Is there anyone out there that has resolved the reason why the 2 signals from the coolant temperature sensor can differ substantially? On my passat AVB engine the ECU signal gives correct temp ( 88 -90º C), but the dashboard gauge signal reads 112ºC! ( on the diagnostic PC. - resulting in the temp gauge in the dashboard showing 95-98ºC.. Car & engine runs fine - doesn't overheat... I've replaced the CTS 3 times... no difference... the 4 wires in the connector seem ok... Anyone?

 

[Tomvw]

One possibility is corrosion in the CTS connector, it has also been known for coolant to wick up the wires to the connectors at the other end.

 

[Jobu71]

Hi Tom... thanks for the reply... Very strange this " error " with the coolant temperature signal to the Temp.gauge.... With my background of electronics, If there was a bad or intermittent connection to the CTS then the gauge would either hop up or down fairly quickly or not work ( The CTS has only 2 thermisters in it - 4 pin -2 + 2 ) .. The error what I am experiencing is that the gauge holds steady at 90º C for a while, then once the engine temp ( real temperature ) is at 90º, then the gauge & signal to the gauge takes off or climbs slightly ( PC diagnostic signal shows 110 -112 º ) -the gauge shows around 95º. - the real engine temperature ( between CTS & ECU ) is 90º & stable. Typical one would think that this is something to do with the pump or thermostat or blockage..the parts concerned
( pump/ thermostat) have been changed twice) radiator changed.. system flushed & checked..
Bleeding of coolant done with vacuum refilling.. ( & bleeding the heater core ) so no air in the system( i hope ). The car drives fine...the ( diagnostic ECU temperature of the engine is stable..you can even see the variation on the diagnostic coolant temp when the thermostat opens... BUT.. I would love to find out what is causing this Dash cluster signal error.. These difficult to find errors can make a man paranoid! 😁

 

[Tomvw]

Hi Tom... thanks for the reply... Very strange this " error " with the coolant temperature signal to the Temp.gauge.... With my background of electronics, If there was a bad or intermittent connection to the CTS then the gauge would either hop up or down fairly quickly or not work ( The CTS has only 2 thermisters in it - 4 pin -2 + 2 ) .. The error what I am experiencing is that the gauge holds steady at 90º C for a while, then once the engine temp ( real temperature ) is at 90º, then the gauge & signal to the gauge takes off or climbs slightly ( PC diagnostic signal shows 110 -112 º ) -the gauge shows around 95º. - the real engine temperature ( between CTS & ECU ) is 90º & stable. Typical one would think that this is something to do with the pump or thermostat or blockage..the parts concerned
( pump/ thermostat) have been changed twice) radiator changed.. system flushed & checked..
Bleeding of coolant done with vacuum refilling.. ( & bleeding the heater core ) so no air in the system( i hope ). The car drives fine...the ( diagnostic ECU temperature of the engine is stable..you can even see the variation on the diagnostic coolant temp when the thermostat opens... BUT.. I would love to find out what is causing this Dash cluster signal error.. These difficult to find errors can make a man paranoid! 😁

"Typical one would think that this is something to do with the pump or thermostat or blockage..the parts concerned
( pump/ thermostat) have been changed twice) radiator changed.. system flushed & checked..
Bleeding of coolant done with vacuum refilling.. ( & bleeding the heater core ) so no air in the system( i hope )."
Your problem is not related to any of these, or any other parts of the cooling system.

This is an electronics issue, check the connectors and wiring from the CTS to the cluster.
As suggested in an earlier post, I suspect there may be corrosion in the wiring, connectors, or cluster.