Engine Coolant Temperature

[AP2000]

How accurate is the "51 Engine Coolant 51 Engine Coolant Temperature (ECT) in deg C(ECT) in deg C" option on the hidden climate control panel?

I've had an issue with the temp gauge on the was sticking very low or fluctuating. The Thermostat and Coolant Temp sensor has now been replaced. Now it takes a long time to get to 90c, 22 mins this morning at 5c outside (once it gets to 90c it stays there now). The fuel economy has been rubbish too, dropping around 7-10mpg overall. The MAF was replaced last month.

The climate control reading does not seem to match up with the temp gauge, the gauge always seems to lag behind.

I am going to try using a laptop with vag-com on the way home, so should the reading for coolant Temperature on there match up with the climate control panel read out? I'm wondering if it picks up the reading from the ECU part of the coolant temp sensor.

The car only seems to blow hot air once the gauge gets towards 90c and not the climate control panel output.

No codes logged on Vag-com when I checked this morning.


Thanks.

 

[MJ]

The dash display is not 100% accurate and most diesels can take a long time to get to temp, is your water pump and cooling fans functioning correctly.

 

[AP2000]

Hi, thanks for the reply.

The fans come on at a low speed when the air-con is on.

I check with vag-com on the way home, the climate control panel was quickest to 90c, then the gauge, then after 17mins vag-com showed 90c coolant temp.

The water pump was changed 1.5 years ago and they replaced it with a plastic impeller one even though I wanted a metal one. I am not loosing any coolant.

 

[S3 AKR]

There's more than one coolant temp sensor too I believe. I don't know where they are though. The other thought I had was that the plastic impellar has broken and the coolant isn't getting around the system very quicky and so giving an inaccurate reading at the temp sensor point.

 

[AP2000]

I hope it's not the water pump, it was changed 1.5 years ago with the timing belt. The timing belt was changed again last month after my turbo blew up.

Would I be getting any other symptoms if it was the pump?

I'm going to check vag-com tomorrow on a proper cold start and check the coolant temp and the fuel consumption measuring blocks.

 

[S3 AKR]

I suppose it depends on the location of the temp sensor being read and the flow direction of the water. If the water flow is slow and the sensor is at the rad, then its going to take longer for the hot water to reach the sensor. It'll get there eventually though. Also - could that be a symptom of a dodgy thermostat ? If that was closed then the water doesn't flow either.

Some one with more mechanical knowledge than me would need to confirm. Thermostat to me would seem most logical, but please don't take my word for it alone.

 

[AP2000]

I hope it's not the thermostat, that and the coolant sensor was changed last week. The gauge never dropped below 90c like it did before but it just takes a while to get to 90c now.

I am having a bad run of faults with the car right now.

 

[AP2000]

Some more info....

One the way to work this morning, 2.5c outside. First to 90c was the climate control panel again then the gauge. However according to vag-com the coolant temp never got to 90c. Hoovered around 77-78 then max to 83c when I got to work. This is a 27 mile journey over 40 mins with no traffic jams, and mainly high speed dual carriageways.

Could it be an issue with the thermostat?

 

[S3 AKR]

I'm sure there is more than one coolant sensor and you might need to know which one you're checking with vag-com. It still sounds to me like the coolant isn't getting around the engine but I am only offering an opinion - I'm not a mechanic!

Does anyone else reading this have any suggestions as to potential cause ?? Are the temps being seen looking anything like "normal" ?

 

[AP2000]

More info again...

On way home 12c outside. Gauge got to 90c after 12 mins, VAG-com was showing the coolant temp as 73c at the time.

After 17 mins vag-com showed coolant temp at 90c. So the thermostat must be fully open then?

Maybe I am just being paranoid and it's the cold morning that is making the car not get warmed up, i.e. actual coolant temp as 90c

Can anyone check in vag-com how long it takes to show 90c on a cold morning?

I have a feeling that vag-com is picking up the reading from the sensor in the coolant temp sender. The gauge and vag-com temps seem to match up to about 73. I believe the gauge is weighted so will show 90c even when below or above 90c

Thanks.

 

[S3 AKR]

Mine takes a good 10-12 mins to get to temp if driving as you should with a cold engine.

 

[AP2000]

Is that 10-12 mins to 90c according to the gauge or vag-com?

Thanks for being the only person to reply!

 

[S3 AKR]

Gauge. Very slow at climbing up the temp scale 1st thing in the mornings but the diesels are heavy iron units and take longer to get the temps up compared to modern petrol engines. I assume that the oil and coolant are both clean ie no caramel in the oil, or oil in the coolant.

 

[AP2000]

Oil and filter was changed last month after the turbo blew up (and engine seized). New coolant from last week. All seems ok and clean. It's going for a full service next week, including oil and air filter again so maybe that could help together with a new fuel filter.

Do you have any way to hook your car up to vag-com in the morning to check the actual coolant temp? Like I noticed today on the way back home, the gauge showed 90c once vag-com displayed it as 73c so I don't believe that anymore as it's just an indication of the temp.

 

[S3 AKR]

I don't use it in the week mate - the Mrs has it (kerbs it, scrapes it, gains little dents and marks on it) during the week as I commute by train. I can prob log temps at the weekend though if you let me know what blocks you're logging.

 

[AP2000]

It's not a problem.. wish I wasn't to lazy to get the train.

I was just looking at 001, but there are other measuring blocks that show coolant temp also. I also looked at 015 for fuel consumption. When warmed up it was 0.6 l/h on idle. When cold I think it was 0.8 l/h

I am beginning to think it's not a fault and it's just weather related. Though mpg is less than expected. It indicated 58 mpg when I got to work when normally it's in low 60s, and once got it to 67mpg.

I will check it again in the morning and see how it reacts.

Thanks again

 

[AP2000]

Right been doing lots of monitoring....

The gauge shows 90c as soon as the actual coolant temp on vag-com is at 73.8c has anyone else noticed that?

In the morning it never gets to 90c on vag-com, this morning it got to around 80c, on the way home at 4pm it gets to 90c after around 17 mins.

Anyone got any ideas if this is normal.. or I have a sticky new thermostat?

 

[S3 AKR]

I think that the MPG is good for a 130bhp engine. 58mpg wouldn't concern me chap. To me it looks like its healthy as you would get issues logged with vag-com for dodgy sensors, and your gauge is reading the same as mine does ie 90.

 

[AP2000]

Yeh normally 58mpg on the trip would be ok, that's probably around 53mpg in reality. However the same exact journey at the same time would have indicated around 65mpg before I had all these issues.

I am just concerned that the actual coolant temp never gets to 90c in the morning after mins long drive. I read somewhere that the optimum temp the engine runs at to get the best mpg is 90c.. which could explain my drop.