Change in MPG due to weather??

[Adnic69]

Hey guys.
I normally get about 18ish mpg around town but have noticed that since the drop in temperature I am getting more like 14mpg. I do a 9 mile drive to and from work so the car doesnt really get warm, must be on enrichment all the time on that run.

Anyone else noticed this?

This is on a 1995 4.0ltr Chim

[andy-w]

i think i have a similar problem but mine is due to the thermostat being constantly open...have got a new one on order and going to see if that makes a difference...does your car heat up normally on a long run, just thinking night be worth checking yours...two second job to check and a £12 part if it is broke!!!

[Marki]

There was a thread on this a few weeks back and the general view was that its easier for the car to keep itself cool than to keep itself warm (well sort of)

I have also noticed mpg drop off on the trip to from work since its cooled down

[meeko]

I've noticed that same thing. My 400 used to do 18mpg and now it's around 14mpg. The temp never goes about 65 on a 10 mile run to work. Even if I let it warm up standing still, it will drop down to 65 when moving.

[mongoose]

meeko said:

I've noticed that same thing. My 400 used to do 18mpg and now it's around 14mpg. The temp never goes about 65 on a 10 mile run to work. Even if I let it warm up standing still, it will drop down to 65 when moving.

Your gauge is lying to you due to the temp sensor being chilled by the cold air,perfectly normal,your coolant temp is actually perfectly normal ie 82oC (assuming all else is well).If you cant live with it,Modwise sell an inexpensive kit to overcome this.Theres plenty of threads in the archive if you want to read up more about this.
I dont doubt the ecu will be running cold enrichment for longer at this time of year though,which would explain your increased mpg i guess.In theory your engine will also be sucking in more air as its more dense when colder,so it will put more fuel in to match.dont know if this would be significant enough to notice though?.

>> Edited by mongoose on Thursday 17th November 17:35

[Parrot of doom]

I've always noticed that turbo cars perform well in the cold, I thought due to the colder, more compressed air. Certainly the last diesel I had exhibited that behaviour, much quicker in the cold.

Dunno if the same is true for a NA RV8 though.

[v8 racing]

regardless of outside temperature your engine should still run to what the stat is if its not you probably have a bleed in the stat that lets a bit of water through, buy a new stat without a bleed you dont need them on a tiv

[frankgilbert]

IF THE TEMP GAUGE IS RUNNING COLD THEN THE ECU WILL BE RECEIVING THAT SIGNAL AND WILL THEREFORE BE RUNNING RICH ,HENCE POORER MPG, SOME SORT OF RAD MUFF IS NEEDED I,VE MADE TWO FOR MY 96 CHIM PREFACE LIFT 1 FOR AUTUMN SPRING AND THE OTHER FOR WINTER STILL PERFECTING THE WINTER 1 BUT NOW RUNS OVER 70/80 ALL THE TIME; HAVE FITTED A MANUAL OVERRIDE SWITCH AS A SAFETY MEASURE RETURN OVER 22MPG ALL THE TIME MINED YOU DON,T USE IT TO TRAVEL TO WORK -- WELL DON,T WORK!!!.

[Mad Mitch]

Every car suffers from a drop in MPG when the weather gets cold, some are worse than others. More modern engines are running literaly on fresh air a lot of the time so cold can affect them more than the older lumps. The increase in performance is a real thing due to the colder denser air.... Why use an intercooler if this wasnt the case.??
And dont forget, cars use petrol ticking over. How many of us start it up and let it warm up more now its colder ?? Pretty obvious i know but a lot of us dont take that into consideration when looking at dropping MPG figures.

[mongoose]

frankgilbert said:

IF THE TEMP GAUGE IS RUNNING COLD THEN THE ECU WILL BE RECEIVING THAT SIGNAL AND WILL THEREFORE BE RUNNING RICH ,HENCE POORER MPG,.

The temperature sensor that the ecu uses is a completely different sensor to the one which your gauge on the dash uses.Fortunately the ecu sensor doesn't suffer from 'wind chill' as its mounted on top of the engine,and not at the front.
The modwise kit which makes your gauge read more accurately also uses a sensor which is located on top of the engine and is normally found as a 'spare'being unused,its just there to plug a hole,as the sender was used in this position on previous rv8 applications.Hence the kit overcomes the inaccuracies of the tvr sender position choice, of mounting it behind the distributor.
As i said before,your gauge might show 70oc on the run,but in reality the water temp is around the stat operating temperature.

>> Edited by mongoose on Friday 18th November 08:55

[2 Smokin Barrels]

I've got to say I've never noticed a difference.

At 14 mpg for a 400 I'd say there's a problem.

unless your booting it around town in second!

[mongoose]

meeko said:

I'm sure there is a problem. I was driving to work today and warmed it up to just over 60 before setting off. I covered around 3 miles at <40mph and then several more over 50mph. As soon as I reached 45mph ish the temp dropped off to 50 and the air blower changed from quite warm air to hardly warm. Even if the guage is affected by the wind, the engine is definitely not heating up. I will look into a new thermostat. I just got under 14mpg on the last tank also. I did wellie it a bit more, but from a 400 surely it's bad news. Any ideas of common probs for poor economy or is it a job for a specialist? Cheers

In all fairness it does sound as though your stat may be stuck open if the gauge is reading that low.The heater temp changing to cool definately makes it sound much more likely.My gauge was reading 70 last night on the run,i've seen it get near 60 if its very cold/sustained run,but never down to 50 on any of the three i've owned.Its so easy to pop a stat in,that you may as well change it anyway.