Heating Help

[somedudebob]

Hi, Im hoping someone can assist with my odd heating issue.

i have a 2010 BKP 2.0 tdi passat that the heaters are intermittently blowing mildly warm air when set on high. I have replaced the thermostat, and hosed our the heater matrix. I also noticed on a cold night when on the motorway, the temp needle dropped from mid point, down to just above minimum and then slowly rose back up again, as if the car had just been started from cold.

I have ordered a new heater matrix, and an auxilary coolant pump, as the water pump and belt looks to have been done recently. (Ive only owned the car 5 months and had numerous other problems already)

Ive read that when replacing the matrix that the coolant should be refilled and drained twice, Does anyone know the correct process for this? is it just a case of filling the system and draining again or should the car be run in between?

The air in the car, when set on max, varies between cold and luke warm, warming up slightly more when stationery, and getting to cold when on a motorway run.

What is the aux water pump for?

Any advice gratefully recieved

Bob

[DMitch16]

The BKP engine is a Pumpe Düse with unit injectors. BKP engines have been around since 2005 and I did not think they had auxiliary coolant pumps like the later Common Rail engines?

Perhaps that answers the what is it for question as I believe it should not be needed, nor is fitted on a BKP engine.

If the temperature drops off to minimum from the 90° normal running temp then returns back, it sounds like there may be a wiring or sensor fault. My advice would be to get the car scanned (for faults) with a VAG capable diagnostics tool (VCDS, Autel, Snap On etc.) and look at the temperatures under live engine data. It maybe that one of the coolant temp sensors are faulty (one in the thermostat housing and one in the side pipe from the head below the tandem fuel / vacuum pump) or there is an issue with the associated wiring and / or connectors.

[somedudebob]

Hi. Thanks for the reply.

My mechanic has had it on snap on, and it came up with an issue with the wiring harness for the injectors that was replaced along with the glow plugs. The only other issue was a sunlight photo sensor

No codes for coolant temperature sensor, same with my Bluetooth Carista (I know itÂ’s not as extensive as snap on an vcds but grand for a basic mechanic)

When I put my registration into parts finder it lists the secondary or auxiliary coolant pump as being a valid part, and even if a sensor was faulty, and the temp on the needle was dropping, even if the temp of the coolant was not that doesnÂ’t take account of the fluctuating heat

[somedudebob]

Sorry, just to add. It’s a 2008 and not 2010. And definitely a BKP

I’ve just re ran the scan and the only error is the sunlight photo sensor 2 (which I believe is the one in the dash g134 00709)

I just want to have hot air! Haha

[Crasher]

2008 3C with “numerous problems”... never heard that on before!

This model does not have a heater support pump unless fitted with the optional Webasto additional heater.

In the last few weeks I have started to suspect that G13 antifreeze is causing clogging problems and we have switched to the 2017 onwards factory fill, G12 Evo. Realising the line fill had changed three years ago also set my alarm off and I missed it which annoyed me.

A 3C Matrix cannot be flushed due to its bypass design, even with compressed air and a pressure wash; it’s replacement is a HUGE job.

The gauge dipping down suggests the thermostat you fitted is not working correctly, do you have the details of what it was? The OE number is 03G 121 113.

[somedudebob]

Ok, well that’s a part that can be returned at least then. Odd that it showed up when checking the reg, but no matter. £90 back in my pocket.

I didn’t fit the thermostat. My mechanic did at the same time as the wiring loom for the injectors and glow plugs. I didn’t fancy taking that on myself. But he’s a trustworthy mechanic so I’d be safe to say that he would have fitted a factory replacement.

I should add. I do know that the needle dropped the same way with the old thermostat as well as the new, leading me to believe that the thermostat was not faulty in the first place.

I’ve looked at a couple of videos of people replacing the matrix and think it’s something I’m happy to undertake. Time consuming is ok with me.

I think replacing the matrix, then timing belt and water pump is the only route left to take? Tho I don’t understand the reason for filling and draining coolant twice, or the process for this, when replacing the matrix?

What do you mean by the fill line changed?

Thanks in advance!

[Crasher]

Line fill, factory fill, what they use by default at all the VAG factories.

[somedudebob]

Ok, Thanks for that. I guess its continue on and replace the matrix then, hopefully it is just silted up as many seem to suggest.

Im going to replace the sunlight photo sensor too, although I dont believe that to be causing an issue here?