Do Not Sell My Personal Information Jump to content


Gs300 Mk1 - Seriously Poor Mpg


Recommended Posts

I bought a 1993 GS300 recently and I think the fuel economy should be better. I'm getting around 110 miles out of 40lt LPG around town, which equates to about 11mpg! On a run I can get about 165 miles of of a 40lt tank, which is better, but still not good. The car has done 172k miles and admittedly the lpg conversion makes the miles cheaper, but still... :o

I've been perusing this fine forum and I've learned a great deal already, but I still need to clarify a few things.

1. o2 sensors:

Do these affect the lpg consumption as well as petrol?

How many have I got?

Where can I find it/them?

If there are more than one do they all need changing or is there a specific one that will improve mpg?

What's the best place to buy it/them?

I found some US sites selling them pretty cheaply, but some of them refer to "Calif". I presume California have different emission laws to the rest of the Sates, but is this something I need to bear in mind when purchasing?

Are they easy to fit?

2. MAF sensor:

Does this need replacing or just cleaning?

Is it an easy job?

3. Other things:

Are there any other things that I could do to improve things - i.e., other sensors that might be dirty or worn out?

Sorry to bombard you all with so many questions on my first post, but I'm kind of desperate...

Thanks in advance for any light you can shed on this.

Link to comment
Share on other sites


Hi Deke and Welcome.

Must say you have pretty good timing there old bean, as i was just about to post the same question myself today.

I too have an LPG converted GS300 and havnt really driven it much but have pretty much the same problem as you by the looks of it. Last time the red light on the LPG gauge came on i put in £16 of gas which topped it up, but it took around 40litres in. 120 miles later and the damn red light is back on again. I mean it seems to have burned 40litres of gas off like the it was whiskey and the car was a serious alchy! :ohmy:

Was told by the bloke i bought it off that the red light comes on even though the tank has only reached quarter. I dont know if that is true or not but i want to let it run dry so i can get a true figure. However iv been told that letting it run out on gas may let air in and that wont be a good thing, on the other hand if it let it run dry on gas then it should just switch back to petrol.

Damn thing raises more questions than it answers really.

My original theory was the MAf aswell, as my performance has taken a serious hit aswell. Another thing it could be is the spark plugs not taking too well to creating a spark with a fuel that doesnt burn so easily.

I was looking through another thread the other day and there was a link to a site whereby they sold some NGK plugs. Them plugs were claimed to be specifically for cars running on LPG, and that claim was from NKG themselves. And it sort of does make sense aswell, as spark plugs do contribute to MPG.

Link to comment
Share on other sites

I too await the reply with relish. Mine does about 200 miles for every 10 gallons of LPG (about 44 litres) so I am getting roughly 20 MPG, usually just over and mine is a mark1 GS as well. If you are at medway you probably fill at Strood Morrisons like I do. I will be getting my LPG system serviced on 2nd April and will probably be asking all these questions and more while I am there.

I will probably sort out some new leads at the same time as I know they need replacing.

Link to comment
Share on other sites


I too await the reply with relish. Mine does about 200 miles for every 10 gallons of LPG (about 44 litres) so I am getting roughly 20 MPG . . . .

I so envy you for getting that. I SHOULD be getting that, but for some reason im just not.

Just had a thought though Deke, maybe the LPG gauges are not right in our cars. They are not exactly the most accurate things with only 5 lights and if its out even at that then it'l be showing some rough MPG even though you might not have gone through so much fuel.

Link to comment
Share on other sites


Just had a thought though Deke, maybe the LPG gauges are not right in our cars. They are not exactly the most accurate things with only 5 lights and if its out even at that then it'l be showing some rough MPG even though you might not have gone through so much fuel.

I wish it were that simple. I'm talking full to empty. I don't even bother reading the gauge because mine doesn't seem to work.

Link to comment
Share on other sites

Just had a thought though Deke, maybe the LPG gauges are not right in our cars. They are not exactly the most accurate things with only 5 lights and if its out even at that then it'l be showing some rough MPG even though you might not have gone through so much fuel.

I wish it were that simple. I'm talking full to empty. I don't even bother reading the gauge because mine doesn't seem to work.

Same here. I only ever fill mine to the brim due to the mileage I do. I must admit that most of my driving is a motorway commute of 100 miles a day on average, and I drive with a feather foot, :) mostly :shifty:

Link to comment
Share on other sites

Same here. I only ever fill mine to the brim due to the mileage I do. I must admit that most of my driving is a motorway commute of 100 miles a day on average, and I drive with a feather foot, :) mostly :shifty:

ah ha . . . . now you didnt say that before :P

I wish it were that simple. I'm talking full to empty. I don't even bother reading the gauge because mine doesn't seem to work.

Deke - if you dont read the gauge then how do you figure its empty?

Do you just run it till it switches back over to petrol or stops? Or is there another way of telling?

Link to comment
Share on other sites

get your diagnostic codes read first.

after that, try the simple things like oil, filter, plugs, leads,

only then look at expensive items like o2 sensors - just had mine replaced, will report back on improvement in fuel consumption

Link to comment
Share on other sites

Yep, just run her 'til she's empty. Mine doesn't switch over automatically, it's a manual switchbox.

Maneesh, thanks for the tip re diagnostics. Is this something only a main dealer can do, or...?

Link to comment
Share on other sites

get your diagnostic codes read first.

after that, try the simple things like oil, filter, plugs, leads,

only then look at expensive items like o2 sensors - just had mine replaced, will report back on improvement in fuel consumption

Unfortunatly plugs and leads aint the cheapest of things on a GS300 but yeah, i see where your coming from. Keep us posted on the O2 sensor.

Oh yeah, how much did it cost you to have it replaced?

Cheers.

Yep, just run her 'til she's empty. Mine doesn't switch over automatically, it's a manual switchbox.

Maneesh, thanks for the tip re diagnostics. Is this something only a main dealer can do, or...?

Diagnostics can be read my main stealers or a half decent garage/auto electrician for half the price of the main stealer. Just take it to a reputable garage in your area, ask if they have the eqiupement to read error codes on your car and if they can then take it from there.

When you "run her til shes empty" does she start coughing and spluttering as a sign of fuel starvation? Or does she just stop? Basically im trying to grasp how you run it till its completely empty as i would like to do this to get an accurate figure of MPG.

Link to comment
Share on other sites

I run it until it starts to lose power, then switch to petrol, but you don't have to run it empty to get an accurate fuel consumption figure. Fill her up then zero the trip counter. Run until you're nearly empty them fill her again and take a mileage reading at the same time.

Mileage divided by litres = mpl (multiply litres by 4.56 if your brain works better in old money).

This will give you a reasonable idea straight away, but for more accuracy do it a few times and take an average.

Link to comment
Share on other sites

mk1 gs will be obd I, so diagnostic codes can be read at home by owner using the paperclip method (have a search for it on these forums, or clublexus) - no need to visit a stealer

plugs and leads can be sourced reasonably priced off ebay or from states.

o2 sensors i got were oem spec (walker brand) but just the sensors, so needed the connector to be spliced on from existing sensor. my dealer charged me 1.5 hours per sensor to take off and fit (so 120 quid labour to change both sensors)

It can take longer if threads get all seized up when taking them out. sometimes need to take the manifold off. lucky for me, mine didn't!

Each sensor worked out at 45 quid, cheaper than the 150 quid a sensor it would cost from the UK!

Link to comment
Share on other sites

I run it until it starts to lose power, then switch to petrol, but you don't have to run it empty to get an accurate fuel consumption figure. Fill her up then zero the trip counter. Run until you're nearly empty them fill her again and take a mileage reading at the same time.

Mileage divided by litres = mpl (multiply litres by 4.56 if your brain works better in old money).

This will give you a reasonable idea straight away, but for more accuracy do it a few times and take an average.

Yeah thats what i was looking at doing and in that manner aswell. But i didnt want it to die out all of a sudden somewhere and then let air into it aswell as that could be a pricey mistake!

But yeah im looking at filling it up and then emptying it as much as i can. That should give me a good idea of how much im getting out of it.

Link to comment
Share on other sites

mk1 gs will be obd I, so diagnostic codes can be read at home by owner using the paperclip method (have a search for it on these forums, or clublexus) - no need to visit a stealer

Now THAT sounds interesting. I feel a forum search coming on... :)

Link to comment
Share on other sites

mk1 gs will be obd I, so diagnostic codes can be read at home by owner using the paperclip method (have a search for it on these forums, or clublexus) - no need to visit a stealer

Now THAT sounds interesting. I feel a forum search coming on... :)

Im pretty sure its a paperclip between terminals T1 and E1. Then just look at your dash and see how many times the engine management light flashes. Count the flashes, post it here and some one should be able to give you the error code.

I havnt actually opened my terminal up yet so i dont know if there is a diagram underneath the terminal cover to show where T1 and E1 actually are. But if there isnt, then thats what you want to be searching for.

Link to comment
Share on other sites

I run it until it starts to lose power, then switch to petrol, but you don't have to run it empty to get an accurate fuel consumption figure. Fill her up then zero the trip counter. Run until you're nearly empty them fill her again and take a mileage reading at the same time.

Mileage divided by litres = mpl (multiply litres by 4.56 if your brain works better in old money).

This will give you a reasonable idea straight away, but for more accuracy do it a few times and take an average.

Yeah thats what i was looking at doing and in that manner aswell. But i didnt want it to die out all of a sudden somewhere and then let air into it aswell as that could be a pricey mistake!

But yeah im looking at filling it up and then emptying it as much as i can. That should give me a good idea of how much im getting out of it.

I've run mine empty a few times and all that happened was that the engine spluttered a little, lost power, I pressed the switch back to petrol and left the frustrated drivers behind me for dust, as it usually happens just as I am executing an overtaking manoeuvre :blush:

Link to comment
Share on other sites

I've run mine empty a few times and all that happened was that the engine spluttered a little, lost power, I pressed the switch back to petrol and left the frustrated drivers behind me for dust, as it usually happens just as I am executing an overtaking manoeuvre :blush:

Right, time to let it run completely dry then. And i mean to a stage whereby it starts spluttering! :P

Deke/Genius - Just a quick question lads. Do you notice whilst your driving on gas that your petrol is also going down, by a VERY little bit, but down non-the-less. I put in £10 petrol and it seems to have lasted about 125 miles. But i had about £10 worth of petrol and ran it about a 100 miles on gas, only to get there and notice the petrol had nearly gone to empty aswell.

So is it normal for it to be taking a little bit of petrol at the same time to be mixing it with the gas or is that just mine?

Link to comment
Share on other sites

Mine being on LPG aswell im getting around 18mpg 70% local and 30% motorway(44 ltr = 185 miles) and im a feather foot driver too I like to chill out...... and I have a 58-60 ltr tank. on a motorway run i get about 20mpg and +

I have let it run dry, it will just start to lose power where you then switch it over to petrol (mines not automatic either). oh about the red light it does not mean its near finised ( thats what I had 1st thought it was ) infact depending on your tank size you can get 50+ miles more when the red lights comes on.

A trick I use to find out much is left, other that resetting the trip is when the red light is on and when you come to brake you will notice that the green lights come back on again this a a great indication on how much is left in the tank and you can work out how many more miles you can do, if on the other hand you brake and the light remains red then you know your in your last quarter (again depeding on tank size) and should be able to work out how many more miles are left before filling.

When your on gas your petrol should not be effected, unless the air con uses it ( this I dont know and would be good to find out always wondered if on LPG does the Air Con burn the gas or petrol), As far as I know the petrol on mine is used for a few seconds when starting the car up and then switches over.

I last filled it up and have driven it on petrol now and then (5 miles or so every now and then) to keep the engine lubricated ( not had flashlube fitted yet ) other then than it really has not moved and I do about 40miles a day

Link to comment
Share on other sites

I'm not really sure whether mine has been using petrol or not as I tend to click it onto petrol whilst driving to help ensure it is lubed and also if a very swift burst of power is needed. Trouble is I forget and have driven a few miles before I notice :blush: .

Mine does always start on petrol for about 1/2 mile as well though.

Link to comment
Share on other sites

  • 3 months later...
Mine being on LPG aswell im getting around 18mpg 70% local and 30% motorway(44 ltr = 185 miles) and im a feather foot driver too I like to chill out...... and I have a 58-60 ltr tank. on a motorway run i get about 20mpg and +

I have let it run dry, it will just start to lose power where you then switch it over to petrol (mines not automatic either). oh about the red light it does not mean its near finised ( thats what I had 1st thought it was ) infact depending on your tank size you can get 50+ miles more when the red lights comes on.

A trick I use to find out much is left, other that resetting the trip is when the red light is on and when you come to brake you will notice that the green lights come back on again this a a great indication on how much is left in the tank and you can work out how many more miles you can do, if on the other hand you brake and the light remains red then you know your in your last quarter (again depeding on tank size) and should be able to work out how many more miles are left before filling.

When your on gas your petrol should not be effected, unless the air con uses it ( this I dont know and would be good to find out always wondered if on LPG does the Air Con burn the gas or petrol), As far as I know the petrol on mine is used for a few seconds when starting the car up and then switches over.

I last filled it up and have driven it on petrol now and then (5 miles or so every now and then) to keep the engine lubricated ( not had flashlube fitted yet ) other then than it really has not moved and I do about 40miles a day

Aircon doesnt burn gas or petrol, aircon doesnt burn anything, it runs off the timing belt.

Link to comment
Share on other sites

Mine being on LPG aswell im getting around 18mpg 70% local and 30% motorway(44 ltr = 185 miles) and im a feather foot driver too I like to chill out...... and I have a 58-60 ltr tank. on a motorway run i get about 20mpg and +

I have let it run dry, it will just start to lose power where you then switch it over to petrol (mines not automatic either). oh about the red light it does not mean its near finised ( thats what I had 1st thought it was ) infact depending on your tank size you can get 50+ miles more when the red lights comes on.

A trick I use to find out much is left, other that resetting the trip is when the red light is on and when you come to brake you will notice that the green lights come back on again this a a great indication on how much is left in the tank and you can work out how many more miles you can do, if on the other hand you brake and the light remains red then you know your in your last quarter (again depeding on tank size) and should be able to work out how many more miles are left before filling.

When your on gas your petrol should not be effected, unless the air con uses it ( this I dont know and would be good to find out always wondered if on LPG does the Air Con burn the gas or petrol), As far as I know the petrol on mine is used for a few seconds when starting the car up and then switches over.

I last filled it up and have driven it on petrol now and then (5 miles or so every now and then) to keep the engine lubricated ( not had flashlube fitted yet ) other then than it really has not moved and I do about 40miles a day

Aircon doesnt burn gas or petrol, aircon doesnt burn anything, it runs off the timing belt.

Timing belt is run off the engine.the more energy you want from the engine.the more fuel you have to supply.Therefore,the Aircon will effect the fuel consumption.

Link to comment
Share on other sites

Like you I have a Mk1 GS300 and I am amazed that you get such bad fuel consumption, OK if I am 100% around town and booting it heavy up and down hills then, yes it is rubbish MPG but overall I am quite happy with the consumption

There is a lot of confusion about people claiming high MPG and saving a fortune when running on LPG, actually running on LPG gets approximately 25% less miles per litre than running on petrol

The savings aren't in miles per gallon or litre but in fuel cost per mile

LPG at 40 pence per litre that does 18 to the gallon costs 8 pence per mile in LPG

Petrol at 95.9 pence per litre that does 25 to the gallon costs 15 pence per mile in Petrol

in other words LPG is roughly half the price per mile to run than petrol, but you will definately use more LPG than you thought

I think I read on here somewhere that the average costs of a pro LPG conversion on a GS300 is about £2,000 ? so if you work on a cost per mile saving of 7 pence then you have to cover 28,571 miles before you have got back your investment of 2K, only then will you start saving running costs

Also using LPG creates much higher temperatures in exhausts which can cause problems with O2 sensors and other bits and pieces in high tech computer overloaded cars like a Lexus

I did speak to a LPG convertor a whole ago, and he said that where a car like a Lexus registers a weak mixture in the ECU by running LPG it will turn on the petrol injectors as well to bring the mixture back to a normal level, and if the LPG system isn't set up right then for a lot of the time and especially under high speed or high loads you can use almost as much petrol as LPG which sort of defeats the object of the reason to LPG a car

Link to comment
Share on other sites

  • 2 weeks later...
Mine being on LPG aswell im getting around 18mpg 70% local and 30% motorway(44 ltr = 185 miles) and im a feather foot driver too I like to chill out...... and I have a 58-60 ltr tank. on a motorway run i get about 20mpg and +

I have let it run dry, it will just start to lose power where you then switch it over to petrol (mines not automatic either). oh about the red light it does not mean its near finised ( thats what I had 1st thought it was ) infact depending on your tank size you can get 50+ miles more when the red lights comes on.

A trick I use to find out much is left, other that resetting the trip is when the red light is on and when you come to brake you will notice that the green lights come back on again this a a great indication on how much is left in the tank and you can work out how many more miles you can do, if on the other hand you brake and the light remains red then you know your in your last quarter (again depeding on tank size) and should be able to work out how many more miles are left before filling.

When your on gas your petrol should not be effected, unless the air con uses it ( this I dont know and would be good to find out always wondered if on LPG does the Air Con burn the gas or petrol), As far as I know the petrol on mine is used for a few seconds when starting the car up and then switches over.

I last filled it up and have driven it on petrol now and then (5 miles or so every now and then) to keep the engine lubricated ( not had flashlube fitted yet ) other then than it really has not moved and I do about 40miles a day

Aircon doesnt burn gas or petrol, aircon doesnt burn anything, it runs off the timing belt.

Timing belt is run off the engine.the more energy you want from the engine.the more fuel you have to supply.Therefore,the Aircon will effect the fuel consumption.

Agreed of course, but if the engine is running on lpg, the air con can't be burning petrol, as I said the air con doesn't "burn" either, but it does put a load on the engine therefore if running on lpg, using air con will use more lpg.

Link to comment
Share on other sites

Like you I have a Mk1 GS300 and I am amazed that you get such bad fuel consumption, OK if I am 100% around town and booting it heavy up and down hills then, yes it is rubbish MPG but overall I am quite happy with the consumption

There is a lot of confusion about people claiming high MPG and saving a fortune when running on LPG, actually running on LPG gets approximately 25% less miles per litre than running on petrol

The savings aren't in miles per gallon or litre but in fuel cost per mile

LPG at 40 pence per litre that does 18 to the gallon costs 8 pence per mile in LPG

Petrol at 95.9 pence per litre that does 25 to the gallon costs 15 pence per mile in Petrol

in other words LPG is roughly half the price per mile to run than petrol, but you will definately use more LPG than you thought

I think I read on here somewhere that the average costs of a pro LPG conversion on a GS300 is about £2,000 ? so if you work on a cost per mile saving of 7 pence then you have to cover 28,571 miles before you have got back your investment of 2K, only then will you start saving running costs

Also using LPG creates much higher temperatures in exhausts which can cause problems with O2 sensors and other bits and pieces in high tech computer overloaded cars like a Lexus

I did speak to a LPG convertor a whole ago, and he said that where a car like a Lexus registers a weak mixture in the ECU by running LPG it will turn on the petrol injectors as well to bring the mixture back to a normal level, and if the LPG system isn't set up right then for a lot of the time and especially under high speed or high loads you can use almost as much petrol as LPG which sort of defeats the object of the reason to LPG a car

Yes you'll lose about 25% fuel economy, but its worth it. I bought my GS with lpg fitted (it didnt increase the value of the car either!) so I don't need to do any miles to recoup any outlay, so essentially when I convert my pence per mile into petrol costs, I equate to around 45 mpg over the last 12 months. Not bad, although it was better when the differntial in price was sometimes 3 times!! Considering I would have had to buy petrol to do the same miles without the LPG, it represents a major saving for me.

Interesting about the fuel use, for the last 20,000 miles odd of LPG I've used in the GS, I've put two tankfuls of petrol in it. Mine clicks over to lpg soon after start up and runs on the stuff all day. High miles too, and many long fast motorway trips. I guess I'm just lucky, and was also as lucky with my Range Rover which only ran on LPG, although the V8 engine finally gave up the ghost after 210,000 miles.

The only problem I experience on lpg is lack of range. doing a 200 mile commute most days i need to fill up nearly every day.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...




Forums


News


Membership