[passat-chris]

Hey all. Was a few months ago since I was on here unfortunately. Back in Jan/Feb time the temp gauge was running low raising and lowing from 0-85C then dropping down to 50 then going back up to 85ish constantly. Appeared to be the lower Coolant Temp Sensor. Also the Intercooler had a hole in it and that was replaced.

In the last week half the gauge has started doing something on the other end of the scale. It started to go from the stock 90C and climb to 110,120,125 and drop down to 90/100 and then randomly climb and drop all over the place, a couple of times its gone high enough to flash up the Red STOP sign on the dash.

The coolant level is fine, not leaking, that radiator fan was not going crazy fast like a car overheating or anything either. The Cars efficiency is great still, so I thought as the lower CTS was replaced in Jan/Feb that the other being the same age likely would be the cause. So I picked up one of these and replaced it and it seems to start off a bit better at 90 now and actually gets up the temp faster than it ever used to before the currently issue, so I thought it was solved. But after doing 2 consecutive trips the other day on Saturday it started to rise again, we went out long enough to see if it got the STOP sign to come up but it was hovering more around the 100-120 mark. Red alarm being the 130C.

So only things that come to my low knowledge could be, thermostat/Water pump issue? any other ideas? The radiator fans always turning when the cars engine is running so that's not stopped turning.

I'm a little confused because it doesn't half waiver up and down inconsistently like its a gauge issue because I'd have thought if it was that hot it wouldn't suddenly cool by 10-20C in a few seconds. I don't think the engines burning up because we managed to get back from 100 miles away through country roads and such by alternating the speed we drove at, accelerating or braking up and down hills etc there just seemed to be no pattern at all. Oh yea also, I don't believe the coolant is hot because the expansion/filler tank for the coolant isn't bubbling at all or steaming.

Before I replaced the engine CTS and before this current issue started I'm fairly sure it used to take a while to reach the 90C temp 10-15 minutes I'm 80% sure I remember it taking. With the new CTS in its about 4 minutes to get to 90C.

From reading a few things it seems like the thermostat could be an issue?

Any thoughts would be great to give clues as to how to get this fixed! Thanks!

 

[2002GLXV6]

I do not have much knowledge on the TDI engines, but you have been changing the wrong sensor to solve erratic gauge issues. The Lower sensor controls the fan. The Upper sensor feeds the ECU and the gauge. You may also have a sticky thermostat or failing water pump, but I would start by changing the Upper temp sensor. I assume you have correctly bleed the cooling system of air after changing the lower sensor?

 

[scotts13]

To clarify a bit more, there is no lower coolant temperature sensor. The device at the bottom of the radiator is a thermal fan switch. It doesn't report the temperature anywhere, it just turns the fan on and off. If you indeed installed a CTS at that position, it will cause problem.

Make sure you have the right thing installed at the bottom of the radiator, then go install a CTS where it belongs.

 

[passat-chris]

The garage replaced the lower temp sensor. This fixed the Low temp reading on the temp gauge because they didn't change anything else. that was back in Jan/Feb. I was getting this error code - 17664/P1256 - Ross-Tech Wiki

That problem went away as soon as it was replaced so that lower sensor must give some form of feedback also.

The bottom one was working fine since replacement for 7 months so its unlikely an issue. Also garage fitted genuine replacement part there.

The Engine CTS was replaced a few days ago after starting to get over heat issues. So the upper ones just been replaced so then it goes back to thermostat/water pump.

 

[Tomvw]

scotts13 is correct, If you had read post #15 in your old thread: http://www.passatworld.com/forums/v...2002-1-9-tdi-possible-issues-need-advice.html, you would have sorted this out in January.

If the electric fan runs when the engine is not hot and the A/C is not on; it is almost certain that you have a CTS in
the lower radiator hose, where you should have a fan thermal switch.

You need to get the right parts in the right places, and then diagnose for any remaining issues.

 

[passat-chris]

Sorry at that point I was referring to the lower sensor as a CTS. I would expect that the garage replaced the part with the same as was removed. I didn't order a part or do anything personally with that one. The Performance issue was due to the Inter cooler leaking air. What ever was done in Jan/Feb the car has been running perfectly since for just over half a year...

Could the winter months of Jan/Feb have been messing with the thermostat and that actually being the main cause? And now in the Hot months affecting the thermostat at the other end of the spectrum?

The fan behind the radiator just spins around as it always has when I've started the car? I thought they did that then if the engine got too hot the fan sped up to high speed etc?

 

[Tomvw]

The garage replaced the lower temp sensor. This fixed the Low temp reading on the temp gauge because they didn't change anything else. that was back in Jan/Feb. I was getting this error code - 17664/P1256 - Ross-Tech Wiki

That problem went away as soon as it was replaced so that lower sensor must give some form of feedback also.

The bottom one was working fine since replacement for 7 months so its unlikely an issue. Also garage fitted genuine replacement part there.

That part can NOT have any effect on the gauge. If there was any change in the gauge reading, it was just coincidence or they changed something else.

The Engine CTS was replaced a few days ago after starting to get over heat issues. So the upper ones just been replaced so then it goes back to thermostat/water pump.

There is only one Coolant Temp Sensor.

 

[passat-chris]

Sure, maybe coincidence then, but unsure how as it was all over the place for a month or so then it was fine again after.

Ok then the Engine sensor CTS was replaced so unlikly now an issue.

Assume this - "The fan behind the radiator just spins around as it always has when I've started the car? I thought they did that then if the engine got too hot the fan sped up to high speed etc?" - Is correct?

Could this be the primary cause that has given the illusion it was the temp sensor, but really it is the thermostat - "Could the winter months of Jan/Feb have been messing with the thermostat and that actually being the main cause? And now in the Hot months affecting the thermostat at the other end of the spectrum?"

Assume its better to get the Thermostat replaced first? then look at other avenues?

 

[sirwired]

The fan behind the radiator just spins around as it always has when I've started the car? I thought they did that then if the engine got too hot the fan sped up to high speed etc?

The belt driven fan spins at all times. The secondary electrically operated fan is operated with that simple thermal switch in the lower rad hose. (On the 1.8T, I believe it's a two-speed fan that does not run when the engine is cold and the A/C off.) The CTS goes into the ECU and the cluster and is the input for all temp-related functions, like enriching the mix on cold startup, various emissions-related functions, etc.

 

[passat-chris]

Ah the Belt driven fan is what i could see then. Yes that spins all the time fine. Humm, I've not checked the other fan, I guess if that wasn't working right it could not help keeping temperatures down. Yea i keep the AC off so it wouldn't be on unless it was needed. Sure to the CTS, it was in a awkward spot under the far back left side of the engine (UK model) when looking at the engine from the front.

So things to check -
Electric fan works (assume i can test this by putting the AC on and run engine.
Thermostat Replacement - potentially the cause with it reading overly low in winter and overly hot in summer.
Water Pump Replace

Other suggestions??
PS thanks so much for the replies guys really appreciated!

 

[scotts13]

Sorry at that point I was referring to the lower sensor as a CTS. I would expect that the garage replaced the part with the same as was removed.

Assume the dealer replaced the part correctly? That's almost... cute.

 

[fallon]

Ah the Belt driven fan is what i could see then. Yes that spins all the time fine.

The fan might spin but the fan clutch might not be engage fully at operating temp. On mine, I took a rolled up newspaper and applied a little pressure to the outside of the fan ring with the engine idling at operating temp. I found the fan stopped easily while the engine pulley continued to spin. Just something to check. Good luck.

 

[Iowegian]

Thermostats usually fail either open or closed. If stuck open, the engine will take longer than it should to reach operating temp (90) and may not get there at all in cold weather. If stuck closed, the engine will almost certainly overheat in hot weather or high speed operation.

The CTS measures the coolant temp where it resides in coolant loop. The coolant temperature will not change 10-20 degrees in a matter of seconds. If that is what your CTS is reading, it is probably due to either a bad CTS (they are a common failure) or air in the system (an air pocket at the CTS will cause a sudden temp drop reading).

This "In the last week half the gauge has started doing something on the other end of the scale. It started to go from the stock 90C and climb to 110,120,125 and drop down to 90/100 and then randomly climb and drop all over the place" and this "error code - 17664/P1256 - Ross-Tech Wiki" indicate that there is something wrong with the CTS, its wiring or MUCH less likely, the ECU.

 

[Tomvw]

The only thing the Fan Thermal Switch (front of engine) can do is switch the fan on low or high, depending on the coolant temp leaving the radiator.
It can not affect performance or this code 17664/P1256 - Ross-Tech Wiki
Note: The electric fan can work under certain conditions (such as with the A/C on) with the Fan Thermal Switch completely disconnected/removed.


You had this code in January 17664/P1256 - Ross-Tech Wiki, do you still have it or any other codes ?
This code can only be caused by a faulty CTS (rear of engine) or its wiring/connectors.
The new CTS could be faulty, but more likely you have faulty wiring.


You need to establish that you have the correct parts in the right places and that they are working properly, then start diagnosing.

 

[passat-chris]

Assume the dealer replaced the part correctly? That's almost... cute.

It was actually independent garage not the dealer, but they said they replace with genuine parts. What ever was the lower sensor. However...I'm beginning to wonder now if they actually changed the Engine one.

One thing I noticed when I took out the Engine sensor was that it was Green. Originally these were black I believe so maybe they did change the CTS after all and not the thermal switch lower down.

Thermostats usually fail either open or closed. If stuck open, the engine will take longer than it should to reach operating temp (90) and may not get there at all in cold weather. If stuck closed, the engine will almost certainly overheat in hot weather or high speed operation.

I wondered if this is the symptoms that I'm currently experiencing and the CTS is fine... As its only happened in the last few weeks (hottest time of the year) and then in Jan - Coolest time of the year. So I wondered if these extremes were messing with the thermostat and the thermostat wasn't seized up but sticking/sluggish to respond maybe almost gunked up etc?

The CTS measures the coolant temp where it resides in coolant loop. The coolant temperature will not change 10-20 degrees in a matter of seconds. If that is what your CTS is reading, it is probably due to either a bad CTS (they are a common failure) or air in the system (an air pocket at the CTS will cause a sudden temp drop reading).

I did think that the coolant to change that would be unlikely.

This "In the last week half the gauge has started doing something on the other end of the scale. It started to go from the stock 90C and climb to 110,120,125 and drop down to 90/100 and then randomly climb and drop all over the place" and this "error code - 17664/P1256 - Ross-Tech Wiki" indicate that there is something wrong with the CTS, its wiring or MUCH less likely, the ECU.

Thoughts are now in this order -

Thermostat primarily now.
Air Pocket
Water Pump

The only thing the Fan Thermal Switch (front of engine) can do is switch the fan on low or high, depending on the coolant temp leaving the radiator.
It can not affect performance or this code 17664/P1256 - Ross-Tech Wiki
Note: The electric fan can work under certain conditions (such as with the A/C on) with the Fan Thermal Switch completely disconnected/removed.

Ok then this is discounted as I believe I was referring to this wrong in the previous thread. Also coolant levels aren't boiling/steaming and I don't tend to use the AC - regardless it sounds like it cant affect the current reading issues.

You had this code in January 17664/P1256 - Ross-Tech Wiki, do you still have it or any other codes ?
This code can only be caused by a faulty CTS (rear of engine) or its wiring/connectors.
The new CTS could be faulty, but more likely you have faulty wiring.

There are no codes currently on the car, those two went, I believe they were originally to do with the Inter-cooler issue. Causes were Lost of turbo/Power/Fuel efficiency/power all related. So the N75/Turbo were flagging up also. Once this was replaced all codes went.

You need to establish that you have the correct parts in the right places and that they are working properly, then start diagnosing.

I've checked the invoice it was a G62 - 059-919-501A that was replaced by the garage so that explains why the sensor removed the other day was green. SO the sensor can be pretty much ruled out as they are both pretty much new. Ignore any past references to the lower Temp sensor for the Fan.

 

[Tomvw]

You had this code in January 17664/P1256 - Ross-Tech Wiki, do you still have it or any other codes ?
This code can only be caused by a faulty CTS (rear of engine) or its wiring/connectors.
The new CTS could be faulty, but more likely you have faulty wiring.

There are no codes currently on the car, those two went, I believe they were originally to do with the Inter-cooler issue. Causes were Lost of turbo/Power/Fuel efficiency/power all related. So the N75/Turbo were flagging up also. Once this was replaced all codes went.

The one code 17664/P1256 (Not codes) that I referred to, was as I stated caused by a fault in the CTS circuit.
I like to spend some time trying to help people, but if you just want to incorrectly dispute everything I say, I am not interested.

 

[passat-chris]

I really appreciate your help, and I believe it was an issue or so with that part in Jan

As I mentioned I believe now that the sensor was replaced in Jan, and now its just been replaced a second time, so not sure it's going to be a problem now as there are currently no codes showing up?

I'm not disputing anything? What I'm saying there is that that code on the other thread was fixed when the CTS was replaced in Jan, and changing the sensor again hasn't helped i believe. So unless there is an airlock somehow, then surly it is likley to be something else?

 

[Iowegian]

The code is a wiring fault for the CTS. Just because the sensor itself is OK doesn't mean the entire circuit (sensor, wiring, whatever electronic parts process the raw sensor output and drive the gauge needle, etc) are OK. Sudden jumps in the displayed temp are most likely a fault somewhere in that chain since it is impossible for the coolant temperature to change that fast. Air bubbles are a wild card and could cause weird sensor output but I would check the electrical items first.

 

[passat-chris]

Sorry for the delay. I was away for a couple of weeks. Now have returned to the issue.

Ok, tried 2 CTS now. Both are fine and new. I dont think this issue is a sensor.

After taking the car for a drive around and trying different things some patterns started to form.

Ok when the engines at the normal temps (warmed up)

Up to 40mph temps hold around 90-95C
At 50mph temps go to 100
At 60mpg 110-115

Tried a hard acceleration from 30-60mph and it peaked at 120C then stabilised after a few mins to 115C

Slowed back down then to 35mph and temps dropped to 110C

Going to 70mph it was at 120C
Then as slowed back down to 50mph the temps dropped down agian to 112-115C

When slowing the car back down to 30mph the temps hovered between 90C-100C but generally 90-93C

Averages were 112-115 at 50mph
115-120 at 60mph
got to 125C at 70mph (on a 10s 70mph burst)

So the pattern is to do with engine speed now.

Does this then mean that the Thermostat could be sluggish/sticking or not opening fully? Thus not allowing the coolant to flow around the full radiator system fully. So the loop within the engine that is used at start up to get to temperature is sticking on that so then the engine temps rise? but some is going to the Rad?

Or would this indicate another issue? My gut feeling is that its a combination of the engine loop/radiator loop is being used and the thermostat is sticking half open as the engine temps rise and fall in-line with the speed?

If anyone has any more thoughts on this it would be massively appreciated.

Thanks a ton!
Chris

 

[gigi123]

The engine "produces" more heat when you drive faster and accelerate. It seems that your cooling system can't keep up with the cooling. It's possible that ur thermostat doesn't open enough. It's possible your radiator is partially clogged. It's possible that your water pump is not circulating the coolant properly.
Assuming you have the correct CTS in all the positions.
How are the fans behaving? The electric one in particular? Running at all? If yes, slow or fast?