Thread: Start on Petrol or LPG?

Originally Posted by Pedro_The_Swift

The gentleman the built my new 4.6 told me to run it on ULP often.
It runs on ULP every time I start it,,
maybe he didnt know that,, but I still wonder why he would say that,,,

I class that as one of the "old mechanics tales". There is a tiny little truth in the assertion that you need to bed in a set of chrome rings on petrol because it weakens the lubrication on the cylinder walls. What kind of deal is that? Either make sure the rings are bedded in properly or fit rings suitable for 100% LPG use. I've rebuilt a few engines in my time and never run a drop of petrol through them for running in purposes. A hard fang up the local mountain and they're all good, for 420,000km in a P76 and in an XF taxi with well over 600,000km.

HI

Mine says to run a 100Ks or so every couple of months, I believe it has something to do with keeping the cat converters happy.

Bedding in the rings is nonsense, LPG certainly produces less wear

Steve

Originally Posted by SteveFarmer

HI

Mine says to run a 100Ks or so every couple of months, I believe it has something to do with keeping the cat converters happy.

Bedding in the rings is nonsense, LPG certainly produces less wear

Steve

Actually it has nothing to do with the cat converters. It has to do with the petrol system as a whole. Old petrol can do damage as it loses its lighter fractions to evaporation and any moisture dissolved with the fuel will accumulate unless you replace the fuel regularly. I don't normally suggest a specific usage distance, other than to make sure you have substantially fresh fuel in the petrol tank within three months at the latest. Either use it up or siphon it out for use in someone else's petrol powered machine. Overly old petrol will be hard to start and possibly very low in octane, apart from damaging injectors. I had a shocker come in last month, the petrol was a year old and pinged like crazy when it had warmed up enough to run on the degraded fuel.

Starting on petrol has a few benefits and one of them is making you keep fresh fuel in the tank, but fuel as in petrol is obviously a liquid and does have upper cylinder and fuel pump and line lubricating properties. Starting and stopping on petrol keeps these components lubricated especially on carby vehicles. LPG in most systems is introduced to the system as a vapour which is dry and will cause seals to dry out over time. I had to rebuild many a carby for this reason. As for emissions, LPG burns cleaner than petrol hence rarely seeing LPG blowing smoke unless the oil is bypassing the piston rings. I have always started and stopped my dual fuel cars this way and have never had to repair any carby or fuel pumps for this reason in my own cars.

screw that noise.

It looks after your fuel rail and injectors by ensureing that there is always fresh fuel in the rail and injectors and that your petrol system works if you need it when you run out of LPG.

ever seen the end result of modern fuels being cooked inside an engines fuel system, remember the gum that used to come in carbies that had these massive holes in them called main jets and idle jets that used to cause problems.

Imagine that with holes that are on average something like 10-20 times smaller than those holes...

addidionally LPG will freeze in the converter causing sporadic running at best and continual stalls until the engine warms up. If you start on petrol usualy after 5-10 minutes theres enough heat to prevent this.


everything else is just an added benefit that keeps the greenies happy.

Originally Posted by Blknight.aus

screw that noise.

It looks after your fuel rail and injectors by ensureing that there is always fresh fuel in the rail and injectors and that your petrol system works if you need it when you run out of LPG.

ever seen the end result of modern fuels being cooked inside an engines fuel system, remember the gum that used to come in carbies that had these massive holes in them called main jets and idle jets that used to cause problems.

Imagine that with holes that are on average something like 10-20 times smaller than those holes...

addidionally LPG will freeze in the converter causing sporadic running at best and continual stalls until the engine warms up. If you start on petrol usualy after 5-10 minutes theres enough heat to prevent this.


everything else is just an added benefit that keeps the greenies happy.

Either there's a whole lot of dodgy gas installers out your way or no-one's there has ever figgered how to operate a gas car. I've been doing gas installs for 30 years and always start on gas in the coldest conditions, drive gently until the temp gauge is off the bottom stop, then give it heaps if appropriate. Petrol cold starts wash oil off the cylinder bores, foul cold running plugs and blacken the oil. I tell people to save their petrol for a warm engine and give it a decent run on the expensive stuff once a week. That's apart from the straight gas cars I've done that go for hundreds of thousands of kays without ever seeing a drop of the stinky liquid.

Originally Posted by Blknight.aus

screw that noise.

It looks after your fuel rail and injectors by ensureing that there is always fresh fuel in the rail and injectors and that your petrol system works if you need it when you run out of LPG.

ever seen the end result of modern fuels being cooked inside an engines fuel system, remember the gum that used to come in carbies that had these massive holes in them called main jets and idle jets that used to cause problems.

Imagine that with holes that are on average something like 10-20 times smaller than those holes...

addidionally LPG will freeze in the converter causing sporadic running at best and continual stalls until the engine warms up. If you start on petrol usualy after 5-10 minutes theres enough heat to prevent this.


everything else is just an added benefit that keeps the greenies happy.

Total bull. The boiling point of Propane , the predominant hydrocarbon in LPG has a boiling point of - 32C, so with an ambient temperature of say 0C there is still 32C of heat going into the system, more than adequate to evaporate sufficient LPG to support combustion.
The freezing point of Propane is - 188C. When you have a converter ( gas heater) freeze up, it is atmospheric moisture freezing, generally indicating that the flow of water through the converter has failed. ie the temperature has fallen below 0C
I have spent most off my professional life working with LPG, and a considerable part of that time inspecting & approving LPG automotive conversions .
If your engine is equipped with an adequate ignition system it will start on straight gas without drama

Originally Posted by bee utey

drive gently until the temp gauge is off the bottom stop,

if you cant start it and nail it from cold (even if you have to set a manual choke) without the engine baulking you....

Originally Posted by Collins

If your engine is equipped with an adequate ignition system it will start on straight gas without drama

I'm going to assume you've heard the name lucas before today right?