Propane and Valves

chevrolet
1500

#1

My truck runs on both gas & propane. At 85K miles it is in getting a valve job. 6 valves & seats are bad.



The guy at the machine shop says he’s recently done 10 of these that run on propane.

I was always told that I should get 3 times the life on this engine because propane burns so much cleaner.



I’ve only burned propane approx. 20% of the time because of the cost and bad mpg.



Was it the propane that burned the valves?

I bought the truck new and maintain regularly.


#2

The propane by itself did not burn the valves…A LEAN fuel mixture is the usual cause of burned valves. Many “dual-fuel” propane conversions are pretty Micky-Mouse, the air-fuel ratio being controlled by crude means…

About all you can do is have an “exhaust gas temperature” gauge installed which will allow you to monitor the fuel mixture the old fashioned way…If your vehicle has an oxygen sensor (what year is it/) this should also give an indication but it MAY not be controlling the propane system…


#3

Retarded timing will burn valves. When switched to propane, how is the spark advance controlled.


#4

What year is this truck and what kind of setup is it? Factory or aftermarket? Do you happen to know any technical details?

Another issue to keep in mind is that with liquid fuels a richer mixture will keep the combustion chamber generally cooler, but this is NOT the case with gaseous fuels-- a rich mixture will cause it to run hotter.


#5

It is a 2000 Chevy Silverado … I don’t know if it has an oxygen sensor?


#6

It almost certainly has O2 sensors – one or more upstream of the catalytic converter(s) and one downstream. I think that’s been a pretty much universal setup since the early 1990s. You’ll need a OBD2 scan tool that allows you to monitor sensors, not one that just checks and clears codes. If you have a laptop computer and use Windows, something like this http://www.obdcom.com/requirements-obd.htm should give you that capability for under $100. But I think that all you’ll really be able to do is see if the fuel mixture handling looks the same on propane as on gasoline.


#7

My guess is the clean burning propane,provides little lubricity or cushioning to the valves(I know this was supposed to have been addressed years ago with the advent of unleaded gas,my other guess would be high EGT)-Kevin


#8

Running on propane or natural gas is nothing new. Bus companies all over the country have been doing it for decades. Same with many of the trucks owned by the gas utilities. Not to mention the conversion kits that have been sold for decades.

It’s NOT the propane that’s causing the problem. Lean mixture is the most likely cause.


#9

I live in Dominican Republic. Lots of people use dual gas/propane cars around here. I myself converted a '94 camry to the dual system and then used it for about a year before selling it. let me chip in.

Caddyman and kcmccune both have points here. this is been observed by many users of these systems around here.

most LPG conversions use a rather crude approach to fuel/air mixture. also, a gaseous fuel will create less deposits on the valves, which turns out to be counterproductive on the valves… go figure.


#10

Again, the valves don’t care about the fuel but they sure don’t like a “lean burn”. The oxygen sensors probably control the gasoline fuel injection but they may not control the add-on propane system…