Ongoing, intermittent coolant issue

[Jay1983]

Good afternoon everyone. This is my first post and I'm not particularly car-savvy so any help would be appreciated.

I have had my Mk3 Leon 150 FR for a year now and I like everything about the car. I've had some mechanical issues, however, and I'm trying to get to the bottom to what may possibly be related problems;

- The heating in the car takes a good 10-15 minutes to really send out any hot air, even on max fan/high. I had a local garage blow through the system with an air line and it seemed to make some difference, but really it does not appear to be working correctly. I had the car services this week, and the mechanic suggested that the thermostat could be stuck in the open position.

- Intermittent issue with coolant disappearing. I first noticed this on a journey to and from the Midlands to South Wales, with the expansion tank going from virtually full to empty. Randomly I've recorded the tank doing about 300 miles from full to empty and the refill light comes on, other times it is perfectly normal. The mechanic mentioned above could find no leaks from the tank or pipework.

- I have had a 3 EMLs appear since I've had the car. I bought myself a cheap OBD-II to keep a track of what they were. One was an unrelated sensor which I have had replaced and has since not returned. The second was "Coolant Pump Control Circuit High" - I had the coolant temperature sensor replaced and that particular one has not returned. However before and almost immediately since the sensor was replaced I have had an intermittent error code of P190D (with no explanation given other than "Manufacturer Control") appear. After the service I had the mechanic run a diagnostic with VCDS and he was helpful in explaining the various codes and clearing the history of them, but during the drive to work the next day this P190D error light appeared again and will randomly turn on and off. A little bit of internet digging suggests it could be a mechanical issue with the coolant pump itself, others suggest a powertrain issue.

I would say that the coolant reaches temperature (90) correctly and stays at that mark for the driving duration.

I'm a bit concerned that there is a larger issue here that could cause me further problems down the line, so what I'm really asking is if there is a good place to start looking at mechanical fixes, such as the thermostat or coolant pump.

If I don't have the correct sub-forum then my apologies.

 

[BoomerBoom]

My 150FR also takes about 10 minutes to start emitting any hot air, from a cold start and driving normally. If the thermostat was stuck open it would take double that or more.

I would be most concerned about the loss of coolant, which is always a priority.

If it's not obvious where it's going then you'll need to check the less obvious: the heater matrix, water pump, cylinder head etc. The car should never need topping up with coolant, the only exception is after the system has been drained & refilled as air locks move about.

I can't comment on your error, but the dash temperature gauge only gives you an idea - it's a software thing rather than connected directly to a sensor.

 

[Legojon]

As above. Really need to track down where that coolant is going. I'd be looking at waterpump/ cylinder head next. Usually you can see where coolant has been. This is from underneath the car when my head gasket cracked!

 

[Jay1983]

Many thanks for the replies.

I did mention the coolant issue to the mechanic who serviced my car this week, so he has looked around the tank and I would have presumed it obvious from underneath the car if there were coolant stains? I was stood next to him when he had the car on the lift as he had to lift it up again as he had forgotten to re-attach the coolant sensor he detached to get to something during the service. Perhaps not, like I said, I am no expert at all.

I want to have a look at it in daylight. The reason I said to him that it was an intermittent leakage from the tank area is that a couple of months ago when the tank drained I noticed dry and wet coolant from the carriage directly underneath the tank area, and dried it all up with tissue. In fact there was quite a lot, so I know it wasn't over-spill from when I had previously filled up. The cap was definitely on all the way. Since then I have not seen this return, and as it stands now the coolant level is pretty normal. It's a confusing issue but I'll have a good check this weekend.

 

[Legojon]

So is it coming out of the overflow pipe at the back of the tank?

 

[Jay1983]

That is what I can't work out. The first time I noticed it below the tank area I presumed that is what it was, but it hasn't (noticeably) returned. The level is fine at the moment.

What would cause it to come out of the overflow, other than not being filled correctly?

 

[BoomerBoom]

Unfortunately that would usually be gas pressure, either because of overheating or combustion pressure due to a cylinder head crack/leak.

If it happens once, after the system has been over filled, then nothing to worry about. If it repeats then get a mechanic to test the coolant for exhaust traces.