[Bohemian TopDown]

So, I took a day off today and went to the best Mercedes mechanic in Prague (judging by the reviews) because of that horrible rattling metallic noise that I have every time the tachometer needle touches the 2500rpm, every gear, both accelerating or slowing down, with or without gear, even revving with the car stopped.

As soon as his dog stopped chewing my leg, he took a look at the engine, saw the lpg system, and said: I'm not touching this car until the LPG is removed. You're destroying the car this way, Mercedes are not intended to be converted. When you install an lgp system in a Mercedes the engine head must be replaced with something compatible with this gas, and here it has not be done.

Now, I bought this car already converted, and given the price of the gas here, I don't mind paying a third. I wouldn't have done it myself, but it was there already, and I must admit it works pretty well.

He didn't say anything about the noise, didn't even want to listen to it, he went on for 20 minutes just cursing the LPG (I left, probably he's still going on).

My concern now is that I'll never be able to have a mechanic, because my car is converted... And yes, I tried the LPG shop, they said no, we only deal with lpg related problems, this noise is not related, go find a mechanic.

Do you really think I should have the system removed? Am I destroying the engine? Is it that bad? I just wanted to get rid of that rattling noise (not the engine supports, got them checked), I'm quite happy with having the option to save some money when I don't need to score the best lap time on qualifying session... But if it's really that bad, I can live without.

 

[jbanks15]

Do you really think I should have the system removed? Am I destroying the engine? Is it that bad?

Yes
Yes
Yes

If MB wanted a LPG version, they would have made 1

 

[efair]

@i860 has some experience with lpg, perhaps he can weigh in.

 

[Bohemian TopDown]

Do you really think I should have the system removed? Am I destroying the engine? Is it that bad?

Yes
Yes
Yes

If MB wanted a LPG version, they would have made 1

Easy jokes aside, can you provide any objective reason?
Nobody produces lpg cars, does that mean that no car should be converted?

 

[jbanks15]

The disadvantages of LPG are

• It causes suffocation, in case of leakage as it heavier than air.
• It is hazardous as it inflammable gas.
• It is consumed more as it has low energy density.
• It does not provide power to the vehicle in mountains or rough terrains.

 

[jbanks15]

Why is LPG being phased out?

A decrease in demand means less revenue for fuel stations and no incentive to continue investing in stocking LPG. It's expected LPG will be phased out entirely in the next couple of years as fuel station owners investing in EV charging points instead.

 

[Bohemian TopDown]

Okay, nothing related to my specific situation.
Also, is petrol lighter than air, and healthy and safe in case of leaking? I am asking if there are some objective reasons, related to my specific engine and car, to remove the system. I am not asking your opinion about LPG, I can google pros and cons.

 

[Windinmyhair]

Loose exhaust baffles or cat breaking down? Have you tried banging the exhaust [where it is accessible] with a rubber mallett?

 

[Alex 3]

So, I took a day off today and went to the best Mercedes mechanic in Prague (judging by the reviews) because of that horrible rattling metallic noise that I have every time the tachometer needle touches the 2500rpm, every gear, both accelerating or slowing down, with or without gear, even revving with the car stopped.

As soon as his dog stopped chewing my leg, he took a look at the engine, saw the lpg system, and said: I'm not touching this car until the LPG is removed. You're destroying the car this way, Mercedes are not intended to be converted. When you install an lgp system in a Mercedes the engine head must be replaced with something compatible with this gas, and here it has not be done.

Now, I bought this car already converted, and given the price of the gas here, I don't mind paying a third. I wouldn't have done it myself, but it was there already, and I must admit it works pretty well.

He didn't say anything about the noise, didn't even want to listen to it, he went on for 20 minutes just cursing the LPG (I left, probably he's still going on).

My concern now is that I'll never be able to have a mechanic, because my car is converted... And yes, I tried the LPG shop, they said no, we only deal with lpg related problems, this noise is not related, go find a mechanic.

Do you really think I should have the system removed? Am I destroying the engine? Is it that bad? I just wanted to get rid of that rattling noise (not the engine supports, got them checked), I'm quite happy with having the option to save some money when I don't need to score the best lap time on qualifying session... But if it's really that bad, I can live without.

Gas is the cheapest thing you put in a car.
It’s false economy IMHO to do this.
i can’t help wonder how much damage has been done so far that will come up down the road.
Get rid of it.

 

[Bohemian TopDown]

Loose exhaust baffles or cat breaking down? Have you tried banging the exhaust [where it is accessible] with a rubber mallett?

Thanks for the hint, what should I look for, when hitting the exhaust?

 

[Windinmyhair]

Probably a 'horrible rattling metallic noise'.........
If anything is loose inside the exhaust you will likely hear rattling.

 

[Windinmyhair]

Could also be loose heat shields or broken exhaust brackets/hangers. Tapping the exhaust might evidence those potential issues too.
Easy test and could rule in or out problems in that area.

 

[efair]

I know the older M111 engines had a pattern rattle due to wear in the camshaft adjuster - the way to check for it is to disconnect the harness from the camshaft adjuster... if the sound stops, you've found the source. I don't know if the same applies for the newer 4-cylinder engines though.

 

[Turbo]

There's several people on here that have done an LPG conversion. I was actually planning on doing one myself at some point..

@i860 @Ad B

 

[efair]

Gas is the cheapest thing you put in a car.

I'm trying to understand this. If you drive a car 20 miles/day, five days/week, 52 weeks/year, that's 52x5x20=5200 miles or ~260 gallons of fuel, at current prices at least $800/year USD. That's much more than you'll spend on oil, tires, brake pads, and all the usual wear items per year.

 

[i860]

I have all my mercedes converted to lpg
slk 200
slk 350
c class 200
c class 280
Not one sigle engine problem.
Lost 8hp at the top end on my slk due to the lpg, mesured on dyno petrol vs lpg
I got it at 62k miles now is 115k and so far so goo
My wife c 280 i go it at 70k now it has 128k and all ok
In your case is a mechanical problem is not due to lpg, find a good mechanic.
I do a compresion test evey year same month and all ok so far.
Intake valves on lpg

People had this think about lpg that is bad, probably from old cars, but new cars have so many sensors if somethign is not ok you get a engine check light so you will blow your car only if you ignor it.
Also my slk 350 has benn remaped since 5 years and so far all ok.

 

[i860]

Do you really think I should have the system removed? Am I destroying the engine? Is it that bad?

Yes
Yes
Yes

If MB wanted a LPG version, they would have made 1

Well, iam disiponted, if you will came on the table with some arguments yes.
Is like me saying a supercharger was not intended for you slk 55...

 

[Turbo]

Is like me saying a supercharger was not intended for you slk 55...

Which is technically correct, the best KIND of correct .

That's why they, MB, created the M113k engine. Stronger parts, to take into account the added compression rate..

But just because something isn't designed for it, doesn't mean it's not a good idea.. Which have been proven .

 

[jbanks15]

He asked the questions
I answered the questions in my opinion
He did not say prove your points until after the fact
No need to chastise one for their opinion

 

[Bohemian TopDown]

You did not answer, you just gave your opinion.
And yes, I asked to prove your points, based apparently on nothing.
But thanks everyone for the hints, my problem is not related to the LPG, at all.
Exhaust checked, didn't hear any strange sound.
It sounds like some loose steel part, shaking... But how is it possible that it shakes exactly at 2500rpm? I mean it stops at 2499 and 2501
Yes, definitely need a good mechanic, very happy with my LPG, disregarding what an antiquated mechanic from the 17th century says...