Starting a car on LPG directly

[Aleks24]

Hi everybody,

How does the starting the car on LPG, every day, (not on fuel) effect the motor? Does it reduce its life period?

I have a system with 3 positions (Fuel, 0, LPG) and I have a carburetor. My LPG installation guy tells me that I can start my car normally on LPG, but is it good to turn sometimes on Fuel, or just to go along driving every day on LPG.


Thanks

 

[patprimmer]

LPG is fuel.

Before unleaded petrol, it was felt that the occasional dose of lead increased engine life, but LPG vs unleaded petrol there is little difference, in fact a dry fuel has a beneficial effect of not washing down the bores on a cold start.

Not using the petrol system will cause degradation of fuel pumps and carburetor diaphragms and seals.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Aleks24]

According to

http://www.go-lpg.co.uk/Do_I.html

it is better to run the car on petrol until warm...

This page makes sense, because of the cooling effect in nozles.

I was wondering though, how often do you think someone should run the car on petrol only for the lubricating effects on diaphragms and seals??

 

[patprimmer]

Ofen enough to keep them full of fuel asnd therefore wet.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

I had a gas only car for many years. It started every time and never gave symptoms of evaporator freezing, but I live in Sydney Australia, not the UK, so it might depend on the climate you will operate in.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[vintageAP]

I would say it would depend more on the type of fuel pump system that is associated with your carburetor and the control system. If you have a mechanical fuel pump (as in an older carbureted vehicle) then your (gasoline) fuel pump would be operating at all times anyway; It would depend on the location of the gasoline fuel shut-off solenoid, and how it is controlled would determine if the carburetor was getting fuel and when.

If you are running only an electric gasoline fuel pump then the same scenario would apply to the wiring/control system.

The main problem with wetting the system is the residue left when a carb is wetted and dries out repeatedly. Modern carb seals and gaskets can be left dry without damage as modern materials are very good (no cork in a quality kit). Think of a newly rebuilt carb sitting on a shelf.

Either you would want to keep it dry or keep it wetted in my opinion, not repeatedly cycle between the two.

 

[rdd48856]

Modern Unleaded fuel still has organomettalic compounds capable of a similar (but weaker than Lead) lubricating effect.

 

[trushie]

Is application gas only? Effects valves as they won't be lubricated. use of oil drip will give lubrication so valves don't dry out. If using duel fuel then shouldn't cause drama's if petrol is used

 

[marcdeluca]

I think that starting the engine on lp and not having the gasoline wash the cylinder walls when cold will more than compensate for any downside of no valve lubricity. I do recommend running the engine periodically on gasoline to keep the gasoline fuel system in good working order. This doesn't seem to be as necessary with FI as carburetion, but still necessary. The valve materials nowadays are good enough that the valves and seats seem to hold up as well on lp as they do on gasoline. I have a Chevy 454 that has high nickel content valve seats and marine valves specifically for lp.

 

[patprimmer]

My gas only car had "unleaded" cylinder heads and had no valve nor valve seat durability problems. It never saw a drop of petrol.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[franzh]

First, valves do NOT "dry out", they are metallic.
Second, any oils dripping into the air and fuel stream in quantities described are so minute as to be fully consumed during combustion. In larger amounts, No would they add to hydrocarbons in the exhaust and will render a catalyst inoperative in short order.

The oil drip system so touted to help with top end lubrication MAY help intake valves, but they have never had any problem, its the exhaust valves. As so properly stated, since the unleaded engines became so prominent in the mid 70's, the rate of valve problems have have decreased to almost nothing.

If ignition timing is not properly tailored for LPG use, increased exhaust valve temperatures could possibly lead to premature failure, but thats not particularly a problem when everything is properly set up.

I have run many vehicles from first fireup on propane with no problem, many of them are in the mid 150,000 mile range, with one in particular approaching 330,000 miles without a valve cover being pulled.

Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[turbocohen]

Ditto Franz. Fuggetabout dripping oil. Keep the oil in the crankcase where it is needed and use modern unleaded engines. I have seen numerous +500,000km oem liquid phase LP engines after teardown and they do not appear to be more prone to valve recession as long as the fuel system does not malfunction.