Thanks JR.  I've just ordered an OBDeleven module and I have a willing co-pilot, so I'll try to get some live temperature data when it arrives.  So far, the car's temperature gauge, once warm, as stayed rock-solid on the 90 mark, in all weathers, long and short runs, with and without aircon.  This is the first time I've towed anything moderately heavy, and the trailer has no frontal area to speak of,  Ambient temperature was 18 degrees, at most, but it was only 13 degrees and raining at the top of Shap on the M6, and it was still overheating.  Oil temperature got as high as 121 degrees, but was mostly around 110-115.

It was just weird, they way it was fine laden, but overheated on the way back in cooler ambient air, and unladen!

Sounds like a sticking water pump impellor sleeve could well be your intermittent cooling issue. There's no way the load on the engine was more with an empty trailer than a full one.

 

I'm not sure what functions you get with OBDeleven but with VCDS you can activate and deactivate the water pump so you may be able to excercie it with the engine running (it uses the water pressure to move the sleeve) and free it off maybe??

The high oil temp has nailed it for me, there is something amiss with the cooling system, towing an unladen trailer with a frontal area less than the CSA of the towing vehicle should give the engine no more load than the same weight of passengers.

 

Your vehicle should never have overheated under those circumstances, I had wondered whether it was a problem with a fauly coolant temp sensor but the abnormally high oil temperature is the key, the oil was actually cooling your coolant!

 

Even without fans it would not have overheated, there seems to be little or no circulation through the radiator. Is the heater working correctly at all temperatures and on both sides of the cabin? It could be the old Silkat teabag bursting.

 

TBH the cooling system is so efficient on these vehicles that your waterpump shroud might be permenantly deployed.

Edited 7 October, 20223 yr by J.R.

Thanks!  And yes, I'd be inclined to agree (although of course, it's a 4-wheeled trailer so there's rolling resistance as well, to consider)!  But... "Silikat teabag"...???!  What's one of those?!

The car has been fine today, by the way (not towing a trailer).  Wife has an 80 mile round-trip in it tomorrow too, so we'll see how it does at higher speeds.

My OBDeleven dongle arrived today, and I had a quick play with it.  I wasn't able to do so for long, but just sat in the car with it plugged-in and the engine idling, it said the coolant was 69 degrees, and the gauge reckoned nearer 80 degrees.

5 hours ago, Avocet said:

just sat in the car with it plugged-in and the engine idling, it said the coolant was 69 degrees, and the gauge reckoned nearer 80 degrees.

Ah the joys  of lying VAG water temperature gauges. The only surprise there is that the gauge wasn't saying 88C.

11 hours ago, Avocet said:

Thanks!  And yes, I'd be inclined to agree (although of course, it's a 4-wheeled trailer so there's rolling resistance as well, to consider)!  But... "Silikat teabag"...???!  What's one of those?!

The car has been fine today, by the way (not towing a trailer).  Wife has an 80 mile round-trip in it tomorrow too, so we'll see how it does at higher speeds.

My OBDeleven dongle arrived today, and I had a quick play with it.  I wasn't able to do so for long, but just sat in the car with it plugged-in and the engine idling, it said the coolant was 69 degrees, and the gauge reckoned nearer 80 degrees.

Thats about right, it has to gradually fudge the indicated reading so that it climbs progressively, by the same token when you start to overheat it does nothing while its within its untruth range but once it exceeds the 105°, 110° or whatever the upper threshold is it wont jump straight to the true temperature which it really should but does it progressively by which time your engine has overheated further and maybe caused more damage.

 

As someone who used to drive all their cars watching the temp guage like a hawk (if you have ever owned a Stag you would understand) i used to be able to see and even predict the minutest fluctuations according to road conditions, speed, wind etc and would immediately know when something was starting to play up well before it caused a problem, I have not been able to do this for 2 decades now since driving VAG vehicles, they really should dispense with the temperature guage and have an overheating warning light.

Update:  The gauge has remained solidly on 90 ever since (but without the trailer).  It's done about 100 miles since then.  Today, I drove it from cold with my willing co-pilot logging OBDeleven coolant temperature against my gauge readings.

Gauge = 55 degrees    Coolant temp 55 degrees
Gauge = 60 degrees    Coolant temp 58

Gauge = 65 degrees    Coolant temp 60

Gauge = 70 degrees    Coolant temp 63

Gauge = 75 degrees    Coolant temp 67

Gauge = 80 degrees    Coolant temp 69

Gauge = 85 degrees    Coolant temp 73

Gauge = 90 degrees    Coolant temp 77

 

And there it remained.  Highest we saw was me thrashing it up a long hill in Sport mode, where the coolant got up to 94 degrees but the gauge was still showing 90.

 

So... forgive my doubting, but it does indeed seem to like to pretend that it's 90 when it isn't!

Next question:  (though something of a thread drift).  When I absolutely mash the throttle pedal into the carpet, the most it will show is 87% accelerator pedal position?!

46 minutes ago, Avocet said:

it does indeed seem to like to pretend that it's 90 when it isn't

I am genuinely not surprised.

Just had my WP replaced so this one must still be working (old one stuck in closed position) engine used to get warm (never had objective data though).

 

Anyway now my 2.0TDI 150PS reaches to 90°c with 3 mins at ~30MPH + 10 mins at 65MPH (ambient temp : 7°c).

 

I hope this helps.

It reaches an indicated 90°c!

 

Avocet, those figures are pretty much exactly what I expected but its nice to have them confirmed.

 

Fudge factor starts at around 55°c guage will read a steady 90°c between a true 77° and 94° which was the limit of your test and unless your engine was overheating with say a stuck waterpump shroud then you would not be able to exceed that anyway.

 

I reckon, and this is only from anecdotal evidence that it would stay on 90°c until the true engine temp reached 105-110°c at which point it would jump up to the true reading, this is why you get reports like yours that when someone slows down or turns on the heater matrix the temp drops rapidly to 90°c, too rapidly for it to have really done so.

 

Give a big thankyou from me to your willing co-pilot and also to yourself!

Edited 11 October, 20223 yr by J.R.