MPG and running temps linked??

[Kempy 0]

I was wondering if somehow the mpg was linked to how hot the engine is running at?

 

I normally get about 24/25 mpg to and from work( 25 miles round trip mostly motorway), and the motor normally gets up to a good running temp,

 

But I just done a 60 round trip in a the daily all motorway on just touched 22mpg, and the only thing I noticed different was the temps, oil was 80oc and the coolant was about the same which is low compared to normal. Its very cold outside to

 

this is a 16v.. any thoughts?

[boost monkey 0]

That does sound a little low. Have you been playing with the metering head or WUR? Not sure of the 2ltr had that or not.

 

I've had 30+mpg out of my 1.8 16v and we all know it's a shed.

[Kempy 0]

Not touched the metering head. whats WUR? I got a 4 branch and a 3 inch exhaust system. no cat and stuff. I read a thread and they mention brakes binding or bearings, I deffo need to fit new bearings. I do remember getting 30+ mpg in the past. What do you thing might it be on the 2.0l?

[mjcp 0]

I'm getting similar mpg to you, (average over 1700 miles is 26 and change) and that is a good mix of trips/distances etc. I had a 1.8 16v golf many years ago with rocket ship milage and it still did 35+ so I am somewhat disappointed with mid 20's! (could have got a VR and not cost any more!). My Oil temp runs between 105 - 115 most days, depending on outside temp, speed and driving style.

 

I had the same discussion with a mate over the weekend and he seemed to think there was no WUR (warm up regulator) on the 2.0l 16v (at least not in the same way the 1.8 has) as the injection is K-Jet"e", not K-Jet...

 

I too have an after market exhaust (Miltek, with cats) and am wondering if its having a detrimental effect. (On the Golf, a blow from the centre section (standard, but cheap Euro Crap Parts pattern) would sap 3+ mpg off the average)

 

I'm being loaned a VAG com cable/laptop and will let you know if anything relevant pops up.

 

Cheers,

Marc

 

PS... anyone know if a change in exhaust would require a remap?

Edited March 7, 2011 by mjcp

[JMC 0]

I must admit I have been wondering this - whether running temps effect mpg - for my G60 over winter. My MPG has gone down almost 10% since the weather got cold, and I'm wondering whether there is a link. I also have a loose baffle in my exhaust which could be screwing things up. Grrr.

 

If have chnaged the exhaust drastically then it could do with a remap as it'll vary the way in which the engine removes gasses.

[davidwort 0]

Fuel vapourises better when the inlet temp is high, it has to get very hot before air density affects power, so no surprise winter driving uses more fuel, combine that with more wet road days and lower tyre pressures (cold=reduced tyre pressure) then mpg will obviously drop, you can add more use of the HRW and miorrors, demister fan + heat from matrix when engine is still cold.

Main issue is the time it takes to warm up to full operating temp though, Most days for the past 3 or 4 months have been between 0-5 degrees where I am (middle of the country) your oil and water temp is going to be up a lot quicker when starting from 15-20 as it can be in the summer.

Whether you drive an early 16v with it's mechanical warm up regulator, or a VR or 8v with EFI you still get more fuel delivered when the temps are colder.

VW petrol engines of this era were designed to run fairly hot for efficiency, on the warm up or at very low ambient temps fuel isn't entering the engine atomised/vapoursied as well as it could be, so less power from the same amount of fuel. There's a reason there's a warm air pickup pipe from the exhaust manifold into the standard airbox, and a flap to shut off the cold air from around the driver's headlamp, on so many cars this pickup is broken/missing the snorkel has been removed or the whole airbox has been replaced with an aftermarket filter, all these will affect winter fuel consumption.

 

On a dry day with the car fully up to temp I don't see much difference on a stready cruise though from summer to winter (16v, 8v or mk4 1.6), but that first 15 minutes of driving is the killer. especially on the older bigger engines.

 

Oh, and 80 degree oil is way too low for cruising (up-to-temp) on a valver, should be more like 100, that's where optimum engine efficiency is.

Edited March 7, 2011 by davidwort

[Kempy 0]

Why might me oil temp be low? Old oil? I know I got to change the oil and filter asap

[davidwort 0]

Thermostat might not be closing fully.

[Kempy 0]

I will get that changed then, Its a pita from what I remember doing it on the silver valver. Its definitely not getting to optimum temp

 

I have taken the snorkel out, but there is still the warm air hose on the airbox, but its not attached to anything.

 

your using 10w50 oil right?

[mjcp 0]

Just run VAG-Com and found these two (first was "in the memory", 2nd appeared after a memory reset)

 

Looking online, both can/will effect mpg by running the car rich...

 

 

00537 - Lambda (Oxygen Sensor) Regulation

08-10 - Control Limit Surpassed - Intermittent

 

00587 - Mixture Control Adjustment Limit

09-00 - Adaptation Limit Surpassed

By the way... I'm going to be in Newport (S Wales) tommorow... I can bring the cable!

Marc

Edited March 7, 2011 by mjcp

[Kempy 0]

really, What time?

[mjcp 0]

Should be there around 1030-11 then a couple of hours work... so clear around 1 ish... then meeting a mate toward Cardiff (also a VW nut) after 1530...

 

I'll PM my number.

[stretch. 0]

I know I get around 33 - 34 mpg on an 80mpg cruise, oil temp steady 97 degrees, coolant says 70... but I'll beef hooked if I trust that gauge! Early 16v, had it up to 40+ doing a 70mph cruise in warm weather.