2017 diesel 2.0 150 4x4 DSG. Set out today, towing my big trailer that weighs about half a ton empty. After about 50 miles, stopped to pick up a bout a ton of firewood. Towed the trailer with the wood in it, for another 100 miles - no problem at all, but there was a strong headwind and the car was working hard. At 60 on the motorway, the slightest incline would cause it to drop down into 6th. Averaged 30 to the gallon, heading South Southwest. Dropped the wood off, so the trailer was empty again, and headed for home.

 

Within about 10 miles, the temperature gauge was creeping over 90. On the uphill bits it got to about 105 degrees so I slowed down to about 50 and the temperature dropped again. And so it was, most of the way home. Any uphill bit (even with the wind behind me and the trailer empty), the gauge would start reading over 90. Going up Shap, it briefly touched about 112 degrees. However, the engine wasn't working as hard. It stayed in 7th gear and the average fuel consumption went up to 37 to the gallon.

 

However, for the last 40 miles, heading West, it was fine again. This is the first time I've towed any significant load with it. The car does NOT have "towbar prep", and it's an aftermarket towbar. The wind today, was quite strong, and South Westerly. What I THINK is happening, is that with the wind on the nose, even though the engine was working harder, there was enough getting through the radiator to cool it. On the way home, with the wind largely behind us (except the last 40 miles), there wasn't. Does that sound plausible? If so, does anyone know what the necessary cooling system mods for "towbar prep" are, please?

I would not expect any overheating in the circumstances you describe whatever direction the wind was in, not even in the height of summer, I think you have a problem somewhere, possibly the cooling fans not working but at motorway speeds they should not be needed, more likely a sticking water pump impellor shroud.

 

This is what i just wrote on your other thread:

 

I have towed large frontage storage trailers loaded with probably double that for 500 mile trips and the temperature guage has never risen, oil temperature has reached 115°c perhaps more a few times though.

 

I should add that many of these journeys were at the height of this summer where we had temperatures over 40°c and my fuel economy was down to 24mpg to give you some idea of the load on the engine and the ambient temperature, the guage never rose from the 90°c mark, my vehicle does not have towing preparation and has also been remapped from a standard 108hp to an alleged 184hp without any cooling system mods, I just have a £100 Ebay towbar and current sensing relay both fitted by myself.

Edited 6 October, 20223 yr by J.R.

Thanks, as you say, cooling fans shouldn't have been part of the equation on the motorway.  In fact, slowing down to a stop, and letting the engine idle, would bring the temperature down very quickly.  As luck would have it, the car is due for a cam belt, so I'll probably ask them to throw another water pump at it anyway.  I was of two minds whether to do so or not, but I think this has convinced me!

Just really odd that on the way down, the ambient temperature was higher (18 degrees) and the trailer was laden, but on the way back it was unladen and the ambient temperature was lower, yet that's when it overheated, and it stopped immediately I turned West and headed into the wind.

So maybe the second thermostat regulator as discussed in the other overheating or coolant temperature fluctuating threads. 

 

As to Towbar prep and the changes that involved as far as the Coolant system, they will have designed and engineered that because they thought it was necessary.

Thanks, yes.  I'm just trying to understand what those changes are.  If it's just a case of opening out the slots in the radiator grille, then I have a file and a holesaw...😉

What I'm really struggling with, is why it was fine, laden and only overheated when it was unladen!  Yes, the engineers will have worked out that a bit more cooling was necessary, but they'd have done this, based on a worst case, situation towing 2 tons, in the middle of Summer in the South of France, up a mountain, I imagine, rather than half a ton up Shap in Autumn!

I think the most likely explanations so far are:

1.  Water pump shroud starting to fail

2. A windy day with the wind behind us on the way back, so much less airflow through the radiator. 

The latter would explain why the problem went away when I turned West and although not directly into the wind, at least some of it was on the nose.