4. From cold, always run your engine up to full temperature on Petrol.
Some LPG installations will not give you this choice, but if you have one that will allow you to select LPG before the engine is up to temp. this can be asking for trouble, especially on damp days or during the winter months (or both).
Be aware that on a cold morning the thermostat placed in the coolant circuit will be closed for much longer. It is unlikely that there will be any circulation of coolant around the heater circuit, and therefore no heat at all going into the vaporiser.
Also remember that your vaporiser relies soley on heat from the engine's coolant system, if you have the heater going full chat to demist the screen as well as running on gas this will greatly increase the time it takes for the engine to get up to full temp.
Overall, it is much better to run up to temp. on Petrol, avoiding any icing problems associated with vapourising liquid gas and only switch over to LPG when the engine is fully up to temp.
Stick to this and avoid a lot of potential problems! (This effect is more fully described in the item 'Will there be any difference in performance after conversion')
If you start up from cold on gas, the vaporiser is not being heated by engine coolant. There is a refrigerating effect as the gas vaporises. It will freeze up and stick, possibly causing weak mixture backfiring or gas leakage. If you run the engine up to temp. on petrol before switching over to gas this cannot occur as the engine coolant will already be hot. Don't be fooled into thinking that the surrounding air is too warm for freezing to occur, outside temperatures do not have to be down to freezing level for this to happen. The vaporiser may freeze at temperatures up to + 25 degrees Centigrade, especially if the air is very damp.
The picture of the frozen vaporiser only shows an extreme case.
A vaporiser may be frozen internally whilst showing no sign of ice on its outer casing.
Even if your vaporiser is only cold or luke warm to the touch it is in danger of freezing within seconds if you continue to run on LPG.
The hand test.....
If your engine splutters or stops whilst on LPG in cold or damp conditions, open the bonnet as soon as possible and feel the vaporiser's body with your hand.
As a general rule, if it isn't so hot that you cannot comfortably hold a hand on it for more than a few seconds, it is not getting hot enough to work properly.
If you cannot do anything about the lack of heat right there and then, switch to petrol and drive to your destination. You can sort out what has caused the lack of heat later.
To investigate the cause, first read Section 7 thoroughly.
There are many more good reasons for cold starting only on Petrol, here are but a few -
Carburetted vehicles -
If you leave the carburettors dry for long periods it is likely that float valves (the things that shut off the petrol supply to the float bowl when it is full) will stick, resulting in petrol overflowing from the carburettor.
Not good when you have to switch over to petrol as a reserve fuel at some point!
Also, seals and gaskets may shrink if left dry for long periods.
Cold petrol starting once a day will help to maintain these items and also stop varnish and gritty deposits building up in the float bowls.
Is there a rule of thumb for suitable changeover temperature, time maybe?
Time on its own is of no use.
Let's say that 4 mins of petrol running produces 1KW of heat. In the Summer that may be more than enough if starting up from +20C because you would only have to maintain that temperature in the vaporiser.
In the winter and starting from - 5C it will not be good enough as you have to raise the temperature of the vaporiser from - 5C to +20C and you are unlikely to do that with 1KW.
Another rule of thumb is required as time alone is demonstrated here to be of no practical use.
Waiting for hot air on the screen is a good plot, it shows there is hot coolant in the heater circuit and therefore the vaporiser.......Only switch when hot demist is available, summer, winter, anytime and you cannot go wrong.
Wouldn't the car's temperature gauge be a good thing to use?
In short, NO!
Temperature gauge information is only valid for the part of the engine its transducer is placed in - In the winter the thermostat could be completely closed with the temperature gauge reading +30C.
This does NOT mean that the heater circuit is also at +30C, nor does it even mean that any coolant circulation is taking place in the heater circuit.
It only means that coolant is up to that temperature around the transducer and that might be tucked deep in the engine galleries.
In this way the temperature gauge is of no real use when assessing changeover temperature.
Stick to the 'warm air on the screen' method and you cannot go wrong.
NOTE that all of the above advice is just as valid for EVERY type of LPG conversion, be it Open Loop, Closed Loop or Multi Point Injection. All of those systems have vaporisers and all of them will freeze if not heated sufficiently.
I think there-in lies your FIRST problem!
V8 has a HUGE amount of low down torque. It makes as much at tick-over as a TDi does at peak, and its easy to 'surf' on the torque, rather than reving the nuts off the thing, in fact its one of the 'joys' of the engine....
BUT!
V8 revs from about 800rpm to nearly 5000
Its geared for something like 120mph at the red-line in top.... wont PULL that gearing as it doesn't have the power to punch a Land rover sized hole through the air at that speed; but that gearing gives about 90mph at something like 4000rpm, which is about 'doable' while giving a 70mph 'cruising' speed at around 3000rpm.
But top is a genuine 'Over-Drive' gear, the output from the gearbox in 5th is turning faster than the input.
4th is the normal 'driving' gear, giving a direct 1:1 ratio, with the rest giving variouse 'reduction' ratio's.
In 4th, 90 will come up at around the 5000rpm red-line, and 70 will be about 4000.
Trying to do 30, in 4th, will mean you are making the engine labour right down at around 1,700rpm!
Picture here for you of a V8 power curve, not for the 3.5 I'm afraid so the numbers are all wrong, but the 3.5's trace would be rouchly the same shape, just have smaller numbers, so where this one for the 4.6, peaks at about 200bhp, yours will peak at about 120, so shrink the scale by an apropriete factor, and you wont be far off.
Right; look at the torque trace, and you'll see that its incredibly flat accross the rev range, its making almost 75% of the available force at tick-over as it offers at peak.
THAT is why you can let the motor labour in the taller gears at lower speeds.
BUT, put it on demand, and ask for some hill climbing power, even with your foot to the floor, at that speed, you aren't going to get much more motive force than you would from a Nissan Micra!
To get at some useful power, you have got to get the engine spinning a bit more, and get to where the power is; available power increases 25% between 1500rpm and 2000rpm, by 3000rpm its more than doubled, and if you carry on to the peak at around 4,500rpm, you will have nearly three times what you had available making it labour down near tick-over.
If you look at the torque curve, it has very rounded 'peak' (more a bump, really! but still) at about 3000rpm. That is where the engine is making peak torque, and that is co-incident with getting the best combustion cylinder pressure, so the most 'efficient' point in the rev-range.
I dont have the actual gear ratio's to work out the real numbers, but as a rough reckoner, changing from 4th to 3rd at 36mph, will lift the revs from about 2,000rpm to 2,500rpm, which will find you a bit more useful power.
But, knocking it back to 2nd should get the engine spinning over 3,000rpm a lot closer to that 'optimum' suggested by the torque peak, and making a lot more pottential 'push' available to you on the throttle.
And its STILL a long way from what the engine CAN rev to, if you maxed it out in second, you should be able to do pretty near 50mph, so its not exactly 'thrashing the knackers' off the thing.
Not trying to teach you to suck eggs, but the 110 is a heavy car, with a very low power to weight ratio, and it WILL take a lot more to work it through the gears; than an 'ordinary' car.
Even little micro-compact ecconomy things will have something like two or three times the power to weight ratio, if not more.
{How much power has a Nissan Micra, 50bhp? and weighs what, half a ton?; that's 100bhp per ton. You have two and a half tons, and little more than 120bhp to drag it along, thats barel 50bhp p[er ton)
And your modern eco-car will be that much more tolerant of labouring in the higher gears, not just becouse of the factorially better power to weight ratio, but they dont have the wide-spaced over-drive gear-box the Landy does, to cover the range of loads they have to contend with.
So, I think the first thing here, is that you haven't 'got used' to the Landy yet; it does drive a LOT differently to other cars, and it WILL take a lot more work to drive, and you DO have to paddle the gear-box in them.
That's the first thing.
You said that you are starting it on gas, and thats the way you were told to drive it by the previouse owner!
No! Nu. Nu. Nu Nu Nooooooooooooooooooooooooo!
Well.... sort of..... I forgot your engine is carburated, I'm used to injected engines; however, have a read of the advice from Go-LPG {Its a commercial LPG installers, but their advice page is a 'standard' reference on the topic, becouse its pretty impartial, and very good!}
BUT, this is the important bit
Fact that you aren't using any petrol at all, OK, its a carburated engine and if it is priming the system, it might NOT be set up incredibly badly, but the warm up 'thing' is definitely in there, and if you haven't got the evaporator properly up to temp, that wont be helping anything.
So at this point, I think we're still at the same point.
Read the Go-LPG hints page, as a biriefing on how LPG 'works' and to get an idea of som eof its peculiarities.
You then need to drive the car and get a better 'feel' for it, and you need to drive it on both petrol and gas to see if there is any HUGE difference in the way it behaves.
It will tend to be a bit less 'eager' on gas, and it wont have quite as much 'go' to it.
theres about a 5-10% power 'loss' on LPG, becouse of the fuel, nut also the addition of the mixer putting a restrictor in the intake on petrol, so you get a tad less power on both, but a tad less on LPG than on petrol.
The main difference though, what you 'feel' is on gas, the engine isn't as responsive, as the carburation system isn't as sophisticated, dealing with a 'bulk' fuel, and that can feel like a lot bigger power loss than it really is.
However, warned of that; go play, and tell us how it goes.
Good advice from Teflon.
Only thing I'll add is that from my own experiences check for a worn distributor or a non functioning vacuum advance unit on it.
V8s like their advance and if the diaphragm has split in the vacuum advance unit the ignition won't be advancing enough. You could advance it yourself by loosening the locknut on your distributor and giving it a little twist just to see if it makes an improvement to your performance - but dont overdo it or you'll get a backfire through your inlet system
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