GTD Engine warm-up

[monkeyhanger]

I’ve been monitoring my oil temperatures especially to look for patterns associated with my mpg and DPF regens on my commute.

Despite the ambient temp being a healthy 8-9C all this week, I’ve struggled to crack 42mpg with no active regenning going on.

This morning the car took 9 miles to get up to oil temp (90C +), which is a mile more than usual – it has been doing this all week.

From about 7 miles the oil temp was reading 84C, and seemed reluctant to get any higher – maybe engine generated heat was being diverted to the DPF for a passive regen. One thing that seems really odd to me is that in the next 5 miles (I took the long way to work, 14 miles total) the oil temperature was bouncing all over the place. It could go from 93C to 89C in the space of a few hundred yards (and a change in direction) and then get back up to 93C again just as quickly.

The car really didn’t want to be up to 93/94C for long on today’s journey – it seemed like it was trying hard to maintain 90C.

This is on my first tank of BP regular diesel. The start of the tank was promising – getting 47mpg for the first 50 miles or so and then the car was actively regenning (40/41mpg) for 40 miles and the mpg hasn’t really recovered much since (42/43mpg this week), even though the regenning has stopped (or at least is passive rather than active) for the last 130 miles.

Also, oddly enough, my range calculator seems off for this tank also. Despite the fuel gauge acting as if I am getting 44mpg ave (from full the car is on ½ a tank at 225 miles, as per normal when I am tank averaging 44mpg), the range indicates that I’ll get about 410 miles from this tank but actual usage and the usual gauge readings on this tankful would indicate it will be more like 440-450 miles. My current since fill-up figure is 43.9mpg (current readings being propped up by hitting 47mpg early on).

My gearchange suggestions have been a bit screwy this week too. If I’m sat at 42mph on a 40 road, in 6th then drop to 39, the car wants me in 5th (as expected), so I change down and the car immediately wants another change down 5>4, I do that, then it wants 4>3, I do that (figuring the car is trying to bump up its engine temp to initiate a regen). As soon as I hit 3rd it’s telling me to go 3>4.

Has anyone else seen bounces of 4 or 5C in their oil temp in a short distance within the first ½ hour of their commute? Makes me think that oil circulation may not be the greatest on my car unless the DPF system really is that efficient at sucking engine heat for it’s own purposes, maybe the cooling system is doing more than it should be, or maybe a slightly iffy temp sensor is to blame? I now keep a closer eye on my oil temp than indicated mpg on my commute.

[corgi]

Hi MH,

I've noticed that oil temperature does seem to vary by a few degrees over a journey on my GTD. I have put the effort into studying it that you have, mind 

Last night it just kept going up... and up... and was reading 98C (or more)... when I got home... you guessed it... the fans stayed on!

I noticed this morning (ambient 5C) after 4 miles, oil temperature was 51C, later in the journey (~15 miles it was reading 90C) and hovered between 88-93C for the rest of the journey (~22 miles)...

It doesn't sound like yours is behaving much differently to mine in this regard (oil temp) but in spite of the active regen last night my fuel consumption over 22 miles was 47.8 of A road and town driving...

[monkeyhanger]

Corgi,

It seems as yours and mine are behaving similarly, so I don’t think I have anything to worry about.

I’ve had my engine oil up at a peak of 101C before and it will creep up to 98C a few times a week on a longer journey for a 10 minute spell and then settles down to 93/94C usually.

If I do finish a journey with the oil temp at 97C or more then the fans will be blaring when I park up – interrupted a forced/active regen, no doubt.

If I’d been driving for 22 miles like you, I’m quite confident my mpg would’ve gotten up into the high 40s also, but for 14 miles done, 43mpg was all I could achieve.

This car seems to do a lot more thinking when it comes to regen timing than the last one did. With the Scirocco quicker to get up to temp, it was happy to be running at 94/95C oil temp all the time and I never saw a single forced regen in 28 months of driving it, not sure what great advantages there can to having a preference for the GTD to maintain 90C as the norm as opposed to 95C, apart from the intercooler having to work a little less hard.
I wonder if the GTD is capable of slightly higher mpg than the 170TDI unit, but the way it’s set up makes for less of a chance to have the ideal conditions to do so unless all of your trips are in excess of 20 miles?

[corgi]

If I’d been driving for 22 miles like you, I’m quite confident my mpg would’ve gotten up into the high 40s also, but for 14 miles done, 43mpg was all I could achieve.

So just checked on the return journey.

48.5 for the entire 22 miles. Stationary -> stop/start for the first 3 miles in town(s), then A-road all the way (with the odd sleepy village) to the last half mile which is 30... At 14 miles 44.6 (so within the same ball park as you). Oil temp up to 93C then hovered around 90C for the rest of the journey...

This car seems to do a lot more thinking when it comes to regen timing than the last one did. With the Scirocco quicker to get up to temp, it was happy to be running at 94/95C oil temp all the time and I never saw a single forced regen in 28 months of driving it, not sure what great advantages there can to having a preference for the GTD to maintain 90C as the norm as opposed to 95C, apart from the intercooler having to work a little less hard.

I wonder if the GTD is capable of slightly higher mpg than the 170TDI unit, but the way it’s set up makes for less of a chance to have the ideal conditions to do so unless all of your trips are in excess of 20 miles?

I reckon, whatever it is, it will all be down to making the emissions/performance balance work...