Hi all,

 

Probably a common question but I've done a bit of search and not found very much.

 

MK3 TSI DSG VRS on 86k, today when leaving early for work the external temp was 3.5 degrees. Had to crank the AC and climate temperature up (25 degrees) to get rid of a misty windscreen. After a few minutes and a steep hill I noticed that the coolant temperature gauge wasn't getting past a third of the way up the gauge, normally it would be almost at 90.

 

Dropped the climate temperature to 17 degrees and the coolant started rising getting to 90. Put the climate back to 25 degrees with AC on full again and the coolant temperature dropped by a quarter. 

 

I've read the main thermostat is part of the waterpump, is that correct? There's no sign of it leaking or coolant level dropping meaning I don't want to go down that rabbit hole of changing it if I can help it - seems some have continued issues after changing. Can I change the thermostat without changing the waterpump? 

 

Also read about faulty temperature senders, could this be the issue?

 

I believe there is also a DSG thermostat, although unlikely could this cause the same symptoms I'm experiencing? Is it a DIY-able job?

 

Thanks for any help,

 

Doug

Edited 1 December, 20223 yr by Dooge

If all this happened within a few minutes of starting from cold then it sounds quite normal to me, the engine would have barely produced enough heat to defrost the screen and but for the sliding sleeve waterpump you would not have been getting any significant heat for 5 miles or so (I dont know if the VRS is a diesel).

 

There is also the fudge factor of the temp guage where it would indicate 90° from 71° upwards, you may have been nudging 70° on the non circulating warm up coolant circuit the taken a big chunk of heat away using the demister set to 25°, that would cause the indicated temperature display to drop much further tha the real temperature drop because of the fiddle factor.

 

If once the vehicle is properly warmed up and the coolant circulating properly (sliding sleeve withdrawn) if you the get indicated temperature variations from using the heater/demister then something is amiss, probably with the DSG thermostat which is a common failure and I believe easy to replace.

How long were you driving for and did it eventually settle? Or did it keep up that behaviour for more than ten minutes? And how was the drive home? 
 

The TSI water pump and thermostat assembly are much one in the same although they come as two parts. They a common failure item. To change is likely going to be a 5-6hr job in a garage. The thermostat housing was just under £400 and the water pump sub £100 last time I got one. If you are going to the hassle of replacing the thermostat housing then the water pump should ideally be changed at the same time since you’ve gone that far. 

Edited 1 December, 20223 yr by alis

It is an easy thing to check. Just turn the car on (and probably drive a bit) and have an eye on the thermostat outlet hose. If it warms up gradually it shows the thermostat is stuck open whereas if it is cold and suddenly gets warm when the gauge temp is close to middle then it works fine. My car has the same issue (gauge temp drop with turning on the heating or when goes downhill) which I think is the thermostat.

 

 

11 hours ago, J.R. said:

If all this happened within a few minutes of starting from cold then it sounds quite normal to me, the engine would have barely produced enough heat to defrost the screen and but for the sliding sleeve waterpump you would not have been getting any significant heat for 5 miles or so (I dont know if the VRS is a diesel).

 

There is also the fudge factor of the temp guage where it would indicate 90° from 71° upwards, you may have been nudging 70° on the non circulating warm up coolant circuit the taken a big chunk of heat away using the demister set to 25°, that would cause the indicated temperature display to drop much further tha the real temperature drop because of the fiddle factor.

 

If once the vehicle is properly warmed up and the coolant circulating properly (sliding sleeve withdrawn) if you the get indicated temperature variations from using the heater/demister then something is amiss, probably with the DSG thermostat which is a common failure and I believe easy to replace.

The VRS is a petrol, for the short journeys I do daily I didnt see much point of going for a diesel. Maybe I was demanding too much of the car. I was thinking that if the car is running is should warm up in a nice linear fashion regardless of the climate control temperature. Normally I drive with the climate control off and just put the heated seat on.

 

I always allow the engine to get out of its cold start and the revs to drop so combined with the driving the engine wouldn't have been on for any more than 4 minutes when I first noticed the coolant gauge not rising. But you are right in that the coolant temperature gauge is damped and inaccurate. I have Torque and an OBD11 dongle so tempted to monitor coolant temperature through that.

 

I've also recently changed my route into work as my standard one is only 4.5 miles long and was basically flat. The new one is closer to 7 with the steep hill to give it a bit of load to deal with. The DSG always keeps the revs so low so I've found it's a car that definitely takes longer to get warmed up in comparison to my old mk6 Golf GTI which was a manual. Not so much coolant but engine oil.

 

Thanks J.R., I will monitor and see if I can investigate. I'm handy to a degree but I don't know how hard these are to bleed so wouldn't want to create an airlock after tackling the DSG thermostat, the coolant systems seem so sensitive with the heater core's.

Edited 2 December, 20223 yr by Dooge

10 hours ago, alis said:

How long were you driving for and did it eventually settle? Or did it keep up that behaviour for more than ten minutes? And how was the drive home? 
 

The TSI water pump and thermostat assembly are much one in the same although they come as two parts. They a common failure item. To change is likely going to be a 5-6hr job in a garage. The thermostat housing was just under £400 and the water pump sub £100 last time I got one. If you are going to the hassle of replacing the thermostat housing then the water pump should ideally be changed at the same time since you’ve gone that far. 

The drive is about 15 minutes and just under 7 miles long. I always let cold start get done and the revs drop before pulling away. I would have been only 3 or 4 minutes into my journey when I noticed the coolant not rising initially and after I thought it hit 90 and dropping maybe 7 or 8 minutes. As I replied to J.R above I only turn them on to demist, normally I just put the heated seat on as I know the journey is short.

 

Good to know, I'm guessing the OEM unit is plastic still? I remember on the mk6 Golf forum they used to talk about metal 'gates' branded waterpumps as an upgrade.

10 hours ago, Vahids said:

It is an easy thing to check. Just turn the car on (and probably drive a bit) and have an eye on the thermostat outlet hose. If it warms up gradually it shows the thermostat is stuck open whereas if it is cold and suddenly gets warm when the gauge temp is close to middle then it works fine. My car has the same issue (gauge temp drop with turning on the heating or when goes downhill) which I think is the thermostat.

 

 

Thanks buddy, I did read your topic but the waterpumps ar different although symptoms the same. I'm going off the gauge which isn't accurate so I'll get my Torque app monitoring it. It's the first time it's done it and I think if I am doing the waterpump I'd do thermostat and DSG thermostat at the same time to be sure, although I'm tempted to do the latter myself as it seems far easier and cheaper option to try first.