Lpg Study of temperatures

Welshboy

Member
LPG burns hotter than Petrol . This study evaluates the difference on a Nissan 1500cc car. My interpretation of the screenshots below is that while the car would likely run all day at 2800 revs 120km hour the lpg exhaust temperature would be much higher at the same speed. Dropping the lpg speed to 100km hour would produce exhaust gas temperatures similar to petrol at 120km with similar effects on valves maybe.
If interested the full study can be read here https://www.slideshare.net/ucsp/exp...s-of-lpg-on-spark-ignition-engine-performance
 

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Weetank2

Member
Lpg has a higher exhaust gas temp and as a gaseous fuel also lacks lubrication for the valves and seats
You can dose product into the inlet such as flashlube but we have found in our climate tends to wax up in colder temps so needs protection from ambient temps
 

Welshboy

Member
From what I have seen in Thailand the taxis do not use flashlube but they use an additive in the petrol which helps the seating on the valves allegedly.
 

chubbybrown

Member
Italy does really well with LPG as does Poland,With Hardened Valve seats It will never be as bad as Prior to unlead petrol.
I worked for the main National LPG company for years and saw many petrol Engined vehicles using LPG all year with any Problems here in the North of Scotland.
LPG in the Uk tends to be mainly Propane, where as Im not sure if GPL as its called on the continent has Butane mix due to the warmer weather in the summer.
 

Jeff Sutcliffe

A2OC Donor
From what I have seen in Thailand the taxis do not use flashlube but they use an additive in the petrol which helps the seating on the valves allegedly.
I've run a Land Rover Discovery 3.9 V8 with a Romano LPG system for the last 7 years. I can confirm that the LPG exhaust gases are hotter than petrol ones; they melted the welds holding the baffles in my 'lifetime guaranteed' Powerflow stainless exhaust. I believe that the lubrication of valve seats is maintained by most, if not all, LPG systems by their being set up to switch from petrol to LPG only after the water temperature reaches 30 degrees C when starting from cold and, when the engine's warm, still starting on petrol before switching to LPG after a delay, which can be determined by the way that the system is programmed; mine switches over after around 15 seconds.
 

DJ 190

A2OC Donor
I run a Mercedes SLK which I've converted to run on liquid propane injection. I've converted many cars to run on LPG, the first being an Austin 1800 which i did in 1975. Yes, most conversions now start on petrol. I was able to avoid this on my earlier conversions. I think that I can program it out on my latest conversion, too. (I've got the software) Why would I want to do that, you might ask? Well, it does use a significant amount of petrol, so defeating the object of running on LPG. I don't think that, with the mileages that most owners do on LPG, valve recession is going to be a problem. That's just my opinion.

David
 

Weetank2

Member
Starting on petrol is mainly to generate heat in the water system so the vapouriser is at temp before switching over otherwise its lumpy til warm
Pattern of use is the main factor in valve seat problems
Shimmed tappets also a major problem Subarus etc
Our vehicles mainly long motorway trips at 3500rpm with a near identical Merc 111 engine with hydraulic tappets reached limit of travel around 100k consistantly
With modification up to 150k now between cylinder head overhaul
 

Weetank2

Member
Exactly so pattern of use is major factor
The bottom end is still good with 600k+ miles and the internals look new with cleaner burn and less deposits
Basically our trunking vans run at motorway speeds often overnight runs so constant speed on cruise control UK and EU
With a head overhaul or swap after 150k
 

Welshboy

Member
Exactly so pattern of use is major factor
The bottom end is still good with 600k+ miles and the internals look new with cleaner burn and less deposits
Basically our trunking vans run at motorway speeds often overnight runs so constant speed on cruise control UK and EU
With a head overhaul or swap after 150k
Many thanks for the info- very interesting
 

TAABVW

Member
I converted an early 1.8 audi a4 (5 valves per cylinder) at 100K miles. Ran it up to 200K miles with no problems mostly down the motorway. Sold it to my brother who ran it up to 290K miles before burning the valves.
 

Welshboy

Member
I converted an early 1.8 audi a4 (5 valves per cylinder) at 100K miles. Ran it up to 200K miles with no problems mostly down the motorway. Sold it to my brother who ran it up to 290K miles before burning the valves.
Thanks for this -I have an A4 1.8 lpg on 102k so this gives me some hope. I think the auto gearbox will die before the engine
 
I think a lot of the lpg negative waves come from people not understanding ...Toyota r series petrol engines from 1970s onwards have run on lpg In fact as of today those engines run fork lifts water pumps and more all over the world with proven statistics of equivalents to well over 500,000 miles ..
 
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Un4tural

Member
i find it difficult to believe it will make much of a difference on lifespan of an engine, though it might depend on quality/build of an engine. Had an old Passat (1991) when i was a pipsqueek - hand down mum's car (handed down from uncle to mum and then me to a little while) and that thing was a pile of... smelly joy. From memory it was passed down to another friend who did a bit of a refurb to use it on a farm.

it had petrol/gas system installed and with either it would not go over 70mph, no matter what - Top speed unless you're going down hill (less if up hill).

That bloody thing was indestructible - we were on a 30mile trip and it had no coolant at all (it had a leak) motor was boiling hot - poured some water on it and it just flashed off. But it kept running, at its slow pace, clunking along (1.8 i believe it was). economy was terrible(in general) and mostly everything else wasn't great but it kept running.

It is not as popular to run on LPG in UK from what i understand, but in a lot of Europe (and Russia i am guessing) a lot more people run on LPG and have been for decades without much issue - mostly on old german beaters etc. I personally wouldn't worry about it unless car has a picky engine (like the 1.6FSI in A2 case which wants premium fuel).

By no means scientific but I wouldn't expect LPG to make an engine fail by a measurable amount sooner than petrol as long as engine is reasonably reliable/well built/engineered. Hell, new Range Rovers can barely run on fuel they were designed to run on (record for me were 5 broken down ones at side of road with bonnet up, ~100mile round trip to the seaside!)
 

PlasticMac

Member
Im not sure if GPL as its called on the continent has Butane mix due to the warmer weather in the summer.
The ratio of Butane/Propane in mainland Europe (GPL) varies with the seasons. Less Butane in winter. Not just for the vehicles, but also for the storage and distribution systems. Mac.
 

Welshboy

Member
My A4 stopped switching over to lpg so I took it to an Lpg guy in the UK. It was not a system he was familiar with and basically he just shrugged . I took the switch to Thailand and went to an LPG guy there. Again not a system he was familiar with but he dismantled it to the printed circuit then established the micro switch was dead so he replaced the micro switch on the board and charged me a fiver . Works a dream !
 

chubbybrown

Member
The ratio of Butane/Propane in mainland Europe (GPL) varies with the seasons. Less Butane in winter. Not just for the vehicles, but also for the storage and distribution systems. Mac.
as Commercial Butane would freeze around minus 10 and Propane around minus 40
 
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