LPG haters - please advise (post 62 & 80)

2779 Views 83 Replies 23 Participants Last post by Dave2302, 2 mo ago

Bohemian TopDown

Discussion Starter · 3 mo ago

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.

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Bohemian TopDown

Discussion Starter · #4 · 3 mo ago

jbanks15 said:
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?

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Bohemian TopDown

Discussion Starter · #7 · 3 mo ago

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.

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Bohemian TopDown

Discussion Starter · #10 · 3 mo ago

Windinmyhair said:
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?

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Bohemian TopDown

Discussion Starter · #20 · 3 mo ago

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...

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Bohemian TopDown

Discussion Starter · #23 · 3 mo ago

Turbo said:
It's not at all unheard of that "something" rattle only at a very specific RPM. Have to do with resonance frequency etc. Something I don't fully understand, but I've seen it proven.

Destroying vine glasses with the voice is probably the most famous example of that..

Also true...
My wife broke some glasses yelling at me when I spilled a drop of oil in the garden, next time will measure the frequency.

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Bohemian TopDown

Discussion Starter · #27 · 3 mo ago

efair said:
@Bohemian TopDown I am just curious: is it easy to find LPG filling stations in your home town? I live in a fairly populous suburban area but the closest LPG filling station is a half-hour drive away.

1 out of 3 gas station has lpg here, very easy to find

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Bohemian TopDown

Discussion Starter · #29 · 3 mo ago

BaD_81 said:
Saying metallic noise, is it from the engine bay or under the car?
Gear Selector has a rubber, that I recently changed disgusting sound, that made me disassemble the cockpit more than once. If you are not sure what is checked, just raise the car on a platform/lift reach for the linkage between gearbox and shifter and make sure you shake it well. That bushing is 2GBP-2.5EUR let's say but the pleasure to replace it....

There is an example for the test, take the FUSE(s) of the lpg out - still the same - no LPG issue.
However inadequate LPG settings will lead to what i860 has covered.
SO, as a different approach, speak with a dyno test garage to check the car underneath (if possible of course) in 2500 rpms.
If they see a drop at 2500 rpms - that is serious.
If not, that would be every spinning component betweeen engine and exhaust - prop_shaft - has bearing, pulleys in the engine bay - bearings... they usually are audible in range, like 2000-2500 not only 2500, but who knows something very small could've keep exactly that frequency.
Can you make a video, like open your glove-box let the phone face up or down and start driving so the video gets that sound.
Someone can recognize it...

Thanks mate, tomorrow I'll make the video and post. Hard to say where it comes from, seems like somewhere between the engine and the cockpit, more to the right side.
When I test it in neutral, it still does the noise, but much less, so it's difficult to find the source.
And of course, when I am with the mechanic it's the quietest car in the world, a Tesla basically. Left the car repair shop, a tractor again.
In the next days I will also go and ask how much it would be to remove the lpg system, just out of curiosity. Again, I am happy with it, but every time you visit a mechanic they treat you like you have the plague. Liquid PlaGue.

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Bohemian TopDown

Discussion Starter · #30 · 3 mo ago

Sneaky Pete said:
As @i860 said lots of stations. In my small town in a 25km radius 63 stations.

Like, for real? Here in CZ I would say one every 10/15km.

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Bohemian TopDown

Discussion Starter · #34 · 3 mo ago

Trying to upload the audio file...

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Bohemian TopDown

Discussion Starter · #36 · 3 mo ago

20230314_134822.m4a

drive.google.com

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Bohemian TopDown

Discussion Starter · #38 · 3 mo ago

Should work now...

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Bohemian TopDown

Discussion Starter · #42 · 3 mo ago

Engine supports are okay, will lift the car and check those metal sheets around the exhaust. Stay tuning.

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Bohemian TopDown

Discussion Starter · #62 · 2 mo ago

So, yes it is the exhaust, mechanic suggested to get a new one, it's 15 yo and never been replaced.
Thanks everyone for the help, this forum is really amazing.
Now I'm thinking about replacing it, with maybe something more sporty

Any tips on European sellers?
Seems like there's not much for such an old car on catalog...

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Bohemian TopDown

Discussion Starter · #63 · 2 mo ago

And about the LPG, so far so good.
It has less power, true, let's say around 10% compared to standard fuel, but I can always press a button and go back to gasoline if I want to have "fun" .
But also let's be honest, the 200k is not that beast of power anyways...

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Bohemian TopDown

Discussion Starter · #64 · 2 mo ago

i860 said:
In my case the car always starts on petrol and when the water reaches 40deg then will swich on lpg.
I set tit up to swich on petronl @4700rmp and swich back on lpg under 2500rmp for the times when i really need to smoke my car.

Exactly the same here

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Bohemian TopDown

Discussion Starter · #80 · 2 mo ago

Rattling noise got fixed today, I can finally listen to black metal without any disturbing noise coming from the engine.

Thanks everyone again.
It was a loose exhaust support, and they fixed it for free. It was a bit hard to find the source because it did it only when the engine was hot.
Brought them two bottles of wine.
And he also recommended to get rid of the LPG asap, again no reason given. So far 4 mechanics out of 4 suggesting to remove it... But at least this one was kind enough to put his hands on the car, without kicking me away like the others did.
I'm very happy with my LPG system, especially when I pay at the gas station: 24 euros for a full tank.
Must say that the tank is pretty small, 300km and it's empty, so yes, to go to Italy I should tank 3 times 🇮🇹
Now let's hope for the good weather to come, it snowed in Prague today, can't wait to open the roof 🤘

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