Overheating and no cabin heat (CUSB)

[Kostas123]

Hi,
I've had my Rapid Spaceback MY2016 (CUSB 1.4TDI) for about a year now.

Sorry for my extremely long description, but I believe it's necessary.

Over the winter I've observed an interesting problem:
Even though the engine seems to have warmed up, for the first ~15-20 minutes I don't get heat, or only a little.
At first the electric heater kicks in if it's cold outside, but I believe it should switch over when the engine is capable of producing heat. Instead the heater switches off, and air output gradually cools down. I haven't done a longer trip for a while but from what I remember it does start producing heat later into the journey.

The fun part, however, only began recently:
A few days ago I made a trip that differs from my usual commute - it started with a 5min drive in a city, 4min hop thru the city bypass (~90 km/h), then ~2 minutes back in the city. Then the engine was stopped for 35 seconds, and I drove away. Then when exiting the tight residential road into a bigger road, I noticed that the acceleration was slightly incorrect for the sound (and revs) the engine was making. When I entered a hill (about 1.5 minutes after starting to drive again) it became really noticeable when I shifted into the fourth at around 47 km/h, and the car started slowing down. I do shift early, and this was a hill, but I knew this shift was possible. I then re-attempted it at higher speed, this time succeeding.
Then I looked at the temperature gauge (I need to switch from digital speed to digital temp so I don't monitor it all the time) and saw something I've never seen before - 119C. This was 13 minutes after the start of the drive, and two minutes after my quick stop. The air from my vents was cold, even if the engine clearly wasn't. I went easy on the car and drove back home using low revs (and no city bypass), and the engine didn't go above 110C after that. There were no warnings from the car, probably because 119C is too low for such warnings. There was coolant in the expansion tank.
I know my temperature in the highway was OK, since I checked it about 2-3min into the bypass (to check if my air still should be cold) and it was showing 90.

This wasn't the first weird thing about the cooling system of my Rapid, however.

The coolant level of the expansion tank was always around the minimum mark since I bought it. However one summer morning after starting the engine the coolant level warning came on. The car was parked on a slight uphill - probably fooling the sensor. After restarting the engine on a level surface the warning went away. I had parked there before without a problem for a few months, so I started fearing a blown head gasket. However there was no exhaust smell in the coolant tank, and no sludge on the oil cap/dipstick, so it remained a mystery. I then ordered some G13.
The weirdest thing though was after I filled it up with G13 up to the maximum level. I waited overnight to fill a cold engine, then I drove forward a few meters to get onto level ground. Filled it up to the maximum, and drove to work. The work I was doing in the summer was deliveries with my Rapid, so I'd put around ~130-150 km on the odometer each day. This was one of such days. After driving for an hour or two I checked the level of the coolant, and I saw it was well above the maximum mark - like 1-2 centimeters above it. Waiting for the engine to cool down didn't make it go back down. It did go back to its previous "sweetspot" of near low, though I don't remember when exactly - maybe around a month? Perhaps less.

The system does hold pressure over a night, as evident by air gushing when unscrewing the cap. Also the service records show the coolant service bulletin being done in 2017. I've read that people had their CUSB engine coolant solenoids fail, but then they do have cabin heat - I don't. So what could it be? The only logical solution currently would be air in the system, but that sounds weird. Could it be something else?

I haven't driven the car since the temperature "incident".

 

Thanks for reading my wall of text.

[Johngerard]

Have a look at the side of the expansion tank and look for "Mit Silikat" written on it, if so, its possible that the bag of silicate has burst inside it and has clogged up the cooling/heating system.  If you put "mit silikat" in the search box above you will see plenty of posts regarding it. Hopefully, this is not your problem but its a good starting point.

Even with no problems, I occasionally slacken off, to  release the pressure, the expansion tank cap (but do not remove it) after a run to release any air that may be present. I always do it immediately on getting a new car as air is very often entrained in the cooling system but I have never had to top up while new, the coolant level may rise (or fall) by 10mm or so in my experience.

Edited 7 April, 2022 by Johngerard

[Kostas123]

11 hours ago, Johngerard said:

Have a look at the side of the expansion tank and look for "Mit Silikat" written on it, if so, its possible that the bag of silicate has burst inside it and has clogged up the cooling/heating system.  If you put "mit silikat" in the search box above you will see plenty of posts regarding it. Hopefully, this is not your problem but its a good starting point.

Even with no problems, I occasionally slacken off, to  release the pressure, the expansion tank cap (but do not remove it) after a run to release any air that may be present. I always do it immediately on getting a new car as air is very often entrained in the cooling system but I have never had to top up while new, the coolant level may rise (or fall) by 10mm or so in my experience.

 

Thanks for your reply.

My expansion tank does not have "Mit Silikat" written, and is of a different shape then those tanks (mine is more "round"). However I did find a bag of something inside. The coolant didn't let me see what it is, but I did poke my finger to feel it, and the bag is definitely not empty. After four days of not driving, the tank still held pressure, which after escaping made the coolant level rise above the "min" mark. I did notice a few black "dots" floating around, but those aren't uniform or round enough to be silica balls from the bag... Might be regular debris from four years of circulating... (I checked the log and the coolant bulletin was done on 2018, not 2017)

[Kostas123]

Thinking more about it, the bag didn't feel as full as in the pictures of other people. It felt like I could remove it with my fingers, I might just do it... Hopefully won't drop it into the tank itself

[Johngerard]

You can try that, with great care.

My tank (2019 Polo) isn't round and doesn't seem to have that bag, it is part no 200 121 407B.

[Kostas123]

I successfully removed it. Fortunately or unfortunately, the bag stayed completely sealed. Though I'm sure that the way I removed it would have spilled everything left into the tank if it had split open

[Kostas123]

I did more driving and the cabin heat is just intermittent. No idea why, maybe it thinks that there is heat from the main loop and doesn't turn the aux pump? Though I don't know how the fluid would reach the heater core without the aux pump being on..

Anyways, the coolant hoses stay cold and the engine gets hot, but after a bit of driving the coolant starts flowing, bringing the temperature down (though not completely to 90C). Most likely it's the infamous "controllable" coolant pump failure, though I guess the thermostat could also be sticking. Doesn't matter anyways since the car is seven years old with its original toothed belt, might as well do both the pump and the belt at once.

[Johngerard]

Have you a schematic of the cooling circuit with that auxy pump?,  the heater exchanger is normally always in circuit and acts as the only path for the cooling circuit until the thermostat opens, it is then in parallel circuit with the radiator circuit, the cabin heat is controlled by air flow control through the heater matrix. If the cooling pump is acting up with that shroud (and it may well be) then you might expect more cabin heat before the thermostat opens at 86/90C. as all the water is circulating through the heater.

You said in a earlier post that you get a lot of air each time you release the expansion tank cover, you should get little or no pressure normally, especially if you release it before the car idles for long, as the temperature is around 90C

Edited 12 April, 2022 by Johngerard

[Kostas123]

12 hours ago, Johngerard said:

Have you a schematic of the cooling circuit with that auxy pump?,  the heater exchanger is normally always in circuit and acts as the only path for the cooling circuit until the thermostat opens, it is then in parallel circuit with the radiator circuit, the cabin heat is controlled by air flow control through the heater matrix. If the cooling pump is acting up with that shroud (and it may well be) then you might expect more cabin heat before the thermostat opens at 86/90C. as all the water is circulating through the heater.

You said in a earlier post that you get a lot of air each time you release the expansion tank cover, you should get little or no pressure normally, especially if you release it before the car idles for long, as the temperature is around 90C

It seems like the heater core (marked 3) can only get circulation from electric heating pump (marked 4) pulling the coolant thru the heater core and EGR components (6 and 7) into the engine. On one manual 6 is called EGR line servo motor V338, and on other manual it's called high-pressure EGR cooler. Number 7 is called the low-pressure EGR cooler on both manuals. Could the name "servo motor" imply it can restrict the flow within the line on-command?

The air pressure I get is when the engine is cold (usually after a night), I never tried to open it when the system temperature is anywhere near 90C. I wonder if I have additional issues with cooling, hopefully not...

[Johngerard]

That cooling system is beyond me just now, I will try to get something from the VW self-study folders. 

There definitely shouldn't be any pressure with a cold engine, presume its not a vacuum being pulled?.

[Kostas123]

3 hours ago, Johngerard said:

That cooling system is beyond me just now, I will try to get something from the VW self-study folders. 

There definitely shouldn't be any pressure with a cold engine, presume its not a vacuum being pulled?.

It air gushing and fluid moving, might be negative pressure, might be positive pressure - I really don't know.

[Johngerard]

Reading a few topics on the above, it would seem that the auxiliary pump is solely for the cabin heaterand in some cases will restart to circulate water through the block and head if the engine temperature exceeds 107c after shutdown, I read it that it should not affect the main cooling system which is carried out by the (belt driven?) switchable pump and thermostat. I have read in VW Vortex that several users have just by passed the auxiliary pump by connecting the pump inlet & outlet so it acts like the usual system.

You could try this if handy yourself, of course you may have problems with that switchable pump variable shroud as well or elsewhere.

[Kostas123]

1 hour ago, Johngerard said:

Reading a few topics on the above, it would seem that the auxiliary pump is solely for the cabin heaterand in some cases will restart to circulate water through the block and head if the engine temperature exceeds 107c after shutdown, I read it that it should not affect the main cooling system which is carried out by the (belt driven?) switchable pump and thermostat. I have read in VW Vortex that several users have just by passed the auxiliary pump by connecting the pump inlet & outlet so it acts like the usual system.

You could try this if handy yourself, of course you may have problems with that switchable pump variable shroud as well or elsewhere.

I'll try to get the main pump replaced first before I try to tackle any smaller items - maybe the main pump replacement will fix the cabin heat as well. Seems if the aux pump works, the heat should too, so perhaps a simple electric test would tell everything I need to know about it. Though by the fact that heat does exist, the pump works at least to some extent.

 

Thank you very much for helping me!

[Johngerard]

 A link to VW self study SSP 465 will show how the above works but the attached shows a similar system but without a auxiliary pump so replacing the main pump is probably the way to go all right as start.

 

https://studylib.net/doc/18145304/audi-self-study-programme-485---1.2l-tfsi-engine

[Kostas123]

The issue seems to be resolved. I went to a repair shop to get the main belt replaced (since the car is 7 years old anyways), which includes the pump replacement. I haven't tested the heater (since it's summer), but from the few drives I've made with the car, the temperature seems to stay where it should be now. Seems like the diagnosis of the pump was indeed correct!

[Maikel84]

On 25/07/2022 at 12:21, Kostas123 said:

The issue seems to be resolved. I went to a repair shop to get the main belt replaced (since the car is 7 years old anyways), which includes the pump replacement. I haven't tested the heater (since it's summer), but from the few drives I've made with the car, the temperature seems to stay where it should be now. Seems like the diagnosis of the pump was indeed correct!

Did the waterpump solved the problem for overheating and interior heat? I got a Seat ibiza station with the exact same CUSB engine and also the exact same problem sometimes no heat in the cabin but engine is at 90°C and engine heated to 120°C 2 times already and had the thermostat replaced but still have the aame problem.

 

With kind regards

Maikel Poppelaars

[Kostas123]

9 hours ago, Maikel84 said:

Did the waterpump solved the problem for overheating and interior heat? I got a Seat ibiza station with the exact same CUSB engine and also the exact same problem sometimes no heat in the cabin but engine is at 90°C and engine heated to 120°C 2 times already and had the thermostat replaced but still have the aame problem.

 

With kind regards

Maikel Poppelaars

Fixed it for me. Does the engine cool down when cabin heat comes back? Or does yours never come back? Because mine was "sticky", there would be no heat and engine would overheat only in the beginning, but after 10-20 minutes everything would fix itself.

 

Though I do feel like I have air in the system (from incorrect bleeding after pump replacement by the mechanics)

[Maikel84]

If i put on the interior heater when the engine is going above 90°C it jumps quickly back to 90°C in a couple of seconds but when the car is parked for a night especially below 10°C sometimes I even dont get warm air in the cabine or I only get warm air when taking a turn and then drops back to cold air when i drive straight again.

[Kostas123]

Just now, Maikel84 said:

If i put on the interior heater when the engine is going above 90°C it jumps quickly back to 90°C in a couple of seconds but when the car is parked for a night especially below 10°C sometimes I even dont get warm air in the cabine or I only get warm air when taking a turn and then drops back to cold air when i drive straight again.

Weird, no clue if it's related. Below 5C there should be an electric heater that works until the engine gets to ~60C but I don't know if Netherlands cars ship with those.

 

Perhaps you have air in your cooling system? Does the radiator hose get hot, or does it stay cool even when overheating?