LPG Consequence

Submitted: Tuesday, Feb 21, 2012 at 20:57
ThreadID: 92027 Views:2128 Replies:6 FollowUps:3
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I have an NM Pajero that has done 175000km. I put it on gas about 3 years ago - injected, the dearer option - by LPGAS1 in Lilydale.

Last weekend I was driving and I heard a large explosion and then a flapping-type noise - very strange. The car had never missed a beat and has never missed a service.

Had to arrange a tow-truck and, to cut a very long story short, I had blown a sparkplug out of the head.

My mechanic said he hadn't seen this sort of thing very often - less than a handful of times - but in every case, the car was on gas. I'm unsure about keeping the car now, have lost a bit of confidence. My mechanic suggested only running it on petrol.

Has anyone heard of anything similar and what do you think about the longevity of the motor now?
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Reply By: Michael ( Moss Vale NSW) - Tuesday, Feb 21, 2012 at 21:17

Tuesday, Feb 21, 2012 at 21:17
Did it blow the whole plug out or just the middle? Is the thread in the head damaged?? I would have thought that being a gas and not as volitile, it would be easier on the engine. It doesnt sound logical to me.. Michael
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AnswerID: 478368

Follow Up By: garytee - Tuesday, Feb 21, 2012 at 21:23

Tuesday, Feb 21, 2012 at 21:23
Mechanic said that gas is very harsh on engines designed for petrol.
LPG burns at a higher temp than unleaded.
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FollowupID: 753860

Follow Up By: dazren - Tuesday, Feb 21, 2012 at 23:01

Tuesday, Feb 21, 2012 at 23:01
Never, Never, heard of that before, would not take the word of One mechanic that blames it on Lpg ??? lots of Paj's out there on Gas that have done heaps more K's than yours with no problems, I have driven Duel fuel cars for well over 2 million Klm's over 20 years, and never happened to me ?? Thousands of Taxis out there that have been doing many Millions of Klm's since the 1970's and have not heard of that problem from them either ??/
I would put it down to ''one of those things'' ??? and put in another plug, and away you go, you have a good tug there with a Pajero, But All vehicles will have something go wrong sometime. dazren
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FollowupID: 753867

Follow Up By: garrycol - Wednesday, Feb 22, 2012 at 00:51

Wednesday, Feb 22, 2012 at 00:51
LPG does burn hotter than petrol but has less oompf than petrol - LPG was not the cause of your issue.
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FollowupID: 753871

Reply By: Whirlwinder - Tuesday, Feb 21, 2012 at 21:44

Tuesday, Feb 21, 2012 at 21:44
Garytee,
I have a 2.7 Hilux Workmate and it blew a plug with thread clean out of the head and it is petrol. The thread repair guy said it happens a bit and repaired it no trouble. I asked if I should do all 4 at the time but he talked me out of it. If you are in Sydney I can give you his name. He is at Warriewood and called "The Threadman". 0414237354
Ian
AnswerID: 478372

Reply By: hazo - Tuesday, Feb 21, 2012 at 22:59

Tuesday, Feb 21, 2012 at 22:59
Firstly I'm not fond of gas conversions full stop. But I would think it more likely an over zealous service person who has overtightened the spark plugs in an ally head, and pulled the thread.

When ally heads first came out in the uk many years ago it was a very common experience. I used to own a service station in a former life.
Helicoil (thread replacement system) made a fortune out of it.
AnswerID: 478375

Reply By: Dust-Devil - Wednesday, Feb 22, 2012 at 00:42

Wednesday, Feb 22, 2012 at 00:42
Gary

In 1981 I purchased a Brand New Datsun Series I Bluebird StnWgn. It had a 200B engine in it that was in reality a bored out Datsun 1600 engine. That was their ideaand extent of engine development in those days.

Anyway I put it on LPG gas in 1986 and it never ever ran on petrol again. As a matter of fact I removed the fuel pump and all the petrol lines in the engine bay.

I played around with the Head a tad and raised the compression from 9:1 to 13:1 which made it fly like it had a rocket up it's behind. The down side was cracked heads - clean across the middle which was later found to be a design fault in the block.

Point is - in 360,000Kms on LPG and at the outrageous compression ratio's I played with, that engine never ever blew a spark plug out by stripping the thread etc.

The spark plug threads were always coated with 'never seize' on install and torqued up to the correct settings.

I believe your problem is as stated above - over torquing/tightening of the spark plugs themselves.

Remedy: Repair the damaged head thread with a Heli-coil or similar product and all will be okay. Use a never seize type product from now on and ensure the sparkplugs are torqued to the correct setting.

It you don't have a tension/torque wrench, then screw the spark plugs in by hand until they seat on the heat expansion ring, and then turn approx half a turn.

NOTE: Check them after a 100Km or so and if necessary tighten a fraction more.

Even better - get hold of a torque wrench and do it correctly.

DD
AnswerID: 478384

Reply By: Member - Royce- Wednesday, Feb 22, 2012 at 18:41

Wednesday, Feb 22, 2012 at 18:41
Your mechanic just hasn't happened to see enough of this to decide on LPG vs petrol. It happens. Dodgy thread for whatever reason.

New thread and plug and you're away. No probs.
AnswerID: 478433

Reply By: The Bantam - Thursday, Feb 23, 2012 at 10:53

Thursday, Feb 23, 2012 at 10:53
There are some issues with gas in engines designed for petrol, due to the dry nature of gas and its higher burning temperature.
In particular,cylinder bore abrasion and valve seat recession.

But as long as the appropriate measures are taken...an oil suitable for gas and suitable valve seats AND the engine is correctly tuned.

There is plenty of evidence to sugest that motors run longer and cleaner on gas.

cheers
AnswerID: 478466

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