Poor economy from a V8 RRC...

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MikeV8SE

MikeV8SE

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Location
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OK, I’ve used the RR quite a bit this weekend and thus have been able to do some proper economy tests – and the results are pretty poor! It is averaging 11mpg – so 55 miles costs £27!! This was a nice constant journey, no towing or idling, just a nice constant 30-50mph all the way to pick up a Discovery for a mate which was a 55 mile round trip. To be fair, even on a tirp with quite a bit of sitting still and some towing the economy seemed to be about the same.


Now, his V8 Disco (same engine!) did the same return journey...and is managing 16mpg! It doesn’t sound a lot, but that’s nearly 50% better than mine with an identical engine (both are auto's too)!!!

So, what can I do to improve the MPG on mine, cos something is not right? Since I’ve owned it I’ve given it a coolant flush, replaced the air filter and given it one dose of Redex as the car had been sat for 4 years previously. Is there anything else I can do? Would another dose of Redex help? Change spark plugs? Clean the MAF? Anything else you can think of?

I’d love to use the car more, but nearly £30 to do 50 miles of gentle driving is ridiculous!!
 
full proper service. My rrc did 18mpg round town, and a nice solid 25mpg when doing a constant 56mph to lock the torque converter.Also the front slitter/spoiler thing costs 3-4 mpg according to the handbook.I took mine off for offroading.
 
The maker's handbook for my '87 3.5efi (auto) lists 26mpg at a steady 56mph & I think that's about right as it will do 22mpg on a journey where most of the driving is at the legal 70mph limit. During the summer it will average 17mpg whilst being used for town & country trips of around 20-30 mile duration but I confess to not checking it in winter! All vehicles will suffer considerable increases in fuel consumption during this weather, even our 2.0litre auto (petrol) Mondeo is down by 17% on local journeys.
 
OK, so when you say a full service - done the air filter and coolant, would need to do an engine oil and filter change, what else? Gearbox oil looks OK - to be honest, the engine oil looks nice and clear too, hence why I haven't done it! Spark plugs? Dizzy looks relatively new to me...

Does the front splitter really make that much difference? I'd be very surprised if it did!!
 
hes right about the temp affecting it.

best thing to do is pull out the plugs and see the colour, its the only way to see how its really running.
 
MikeV8SE said:
OK, so when you say a full service - done the air filter and coolant, would need to do an engine oil and filter change, what else? Gearbox oil looks OK - to be honest, the engine oil looks nice and clear too, hence why I haven't done it! Spark plugs? Dizzy looks relatively new to me...

Does the front splitter really make that much difference? I'd be very surprised if it did!!
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I would be surprised about the splitter too-the rest of the car aint dart shaped, but thats wot its sed in the book.Also the book says change the oil every 6k miles.So i did. If you do the plugs do the ht leads too.Do worry about the dizzy if it looks new.Leave the GB oil alone can be making troubles for yourself there.
 
LPG in an option but not sure I want to spend £1,500-£2k on a £2k car!!

Seems mine is running a bit iffy then - time to have the plugs out. Is this a job I should attempt myself or are they known to seizing/snapping? I know on most cars I wouldn't give it a second thought, but an RRC isn't most cars... ;)
 
goonarmy said:
full proper service. My rrc did 18mpg round town, and a nice solid 25mpg when doing a constant 56mph to lock the torque converter.Also the front slitter/spoiler thing costs 3-4 mpg according to the handbook.I took mine off for offroading.
Click to expand...

Sorry if I'm being dense but when you say 'the front slitter/spoiler thing costs 3-4 mpg ' do you mean it's less efficient with it on as I thought it was meant to give better economy.
 
Mike , you should be ok with the plugs, just watch thet your plug socket/bax spanner walls arent too thick otherwise they can bind against the plug recess in the cylinder head.

The problem is not as acute as on the very early 3.5, the ones in my 72 rrc I can hardley even fit a box spanner in there lol

The only ones I have heard of snapping off were on the later gay38's :p
 
OK, thanks fett!!

One more thing - I think the thermostat is a bit sticky as it takes a while to warm up (although hard to tell in this weather - was -19'C here last night!!) but would that hinder economy too I take it, as the engine takes longer to warm up?
 
maybe a little but just incase you break the housing bolts trying to change it I would leave that untill you are snowless, nothing worse than you landy out of action in the snow, happened to me last year and nearly again this year :doh: lol
 
MikeV8SE said:
OK, I’ve used the RR quite a bit this weekend and thus have been able to do some proper economy tests – and the results are pretty poor! It is averaging 11mpg – so 55 miles costs £27!! This was a nice constant journey, no towing or idling, just a nice constant 30-50mph all the way to pick up a Discovery for a mate which was a 55 mile round trip. To be fair, even on a tirp with quite a bit of sitting still and some towing the economy seemed to be about the same.


Now, his V8 Disco (same engine!) did the same return journey...and is managing 16mpg! It doesn’t sound a lot, but that’s nearly 50% better than mine with an identical engine (both are auto's too)!!!

So, what can I do to improve the MPG on mine, cos something is not right? Since I’ve owned it I’ve given it a coolant flush, replaced the air filter and given it one dose of Redex as the car had been sat for 4 years previously. Is there anything else I can do? Would another dose of Redex help? Change spark plugs? Clean the MAF? Anything else you can think of?

I’d love to use the car more, but nearly £30 to do 50 miles of gentle driving is ridiculous!!
Click to expand...


I suspect economy this time of year gets hit anyway due to running with lights, heating etc etc.

11 on a run averaging 30-50 doesn't seem too much of a shocker if you were running all the goodies as well.
 
Horse_Apple said:
I suspect economy this time of year gets hit anyway due to running with lights, heating etc etc.

11 on a run averaging 30-50 doesn't seem too much of a shocker if you were running all the goodies as well.
Click to expand...

Yeah but you're used to 5mpg anyway! Haha!

I have the heater (Level I or II), headlights and radio on, maybe heated rear screen too? So a few toys, but not EVERYTHING!! Still, will they have that much of an effect? I know aircon can, but that's never used!!
 
MikeV8SE said:
Yeah but you're used to 5mpg anyway! Haha!

I have the heater (Level I or II), headlights and radio on, maybe heated rear screen too? So a few toys, but not EVERYTHING!! Still, will they have that much of an effect? I know aircon can, but that's never used!!
Click to expand...


It would depend on the load on the alternator.

Certainly on mine the massively strong bulbs and the comedy ICE system mean that 5 mpg could be optomistic when commuting in winter ;)

Anyway, ditched the clumsy Overfinch ECU for something more modern and now get 7 mpg round Town ;)
 
In your other article on performance in the snow,you mentioned poor warm up & stuck thermostat. If the stat is stuck open, then in cold weather its like running with the choke on all the time. This will make a big difference to your fuel consumption. An easy test would be to check your mates 3.9 disco and yours and do a cold start and compare the top house and heater matrix hose inlet pipe temperatures during the warm up. use your hand as a temperature gauge or better still use a cheap infra red thermometer.
 
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