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1987 Mercedes 190 E
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Discussion Starter #1
I'm new here and have a question that might have already been asked and answered..but here I go - My husband just bought me an '87 190E and I know it says to use Premium Gasoline Only, But I was wondering if it would really hurt to use regular unleaded? By the way i'm really loving my new benz! It's the first one I have ever owned. Thanks guys for answering my silly question!![:p]
 

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deathrattle - 4/19/2005 4:32 PM

Yo Glo

Not such a silly question,but the issue has been the subject of much debate across several topics.By all means try a few dips in the search field to get an overview.
Basically,the best policy is to follow the instructions in your owners manual(if you have one)for all service matters and only deviate if you are absloutely sure that you will do no harm.
Rather than rely on arbitary terms like 'premium' or 'regular' check the octane requirement for your engine,expressed as RON or MON and ideally avoid filling with a grade lower than specified.
However,the octane rating of any fuel only relates to its resistance to detonation under compression and the conditions inside the engine will be affected by the amount of wear on your engine,the altitude at which you drive and your driving style.Provided you dont hear or experience any pinking or pinging,especially when the engine is under load you can probably get away with using a slightly lower rated fuel,since Benz build in quite a large margin for exceptions when declaring octane requirements. [:)]
But when you say slightly lower I think the US octane is already lower than UK and EU. Isn't your Premium 93 while ours is only 91?

Not me Glo, I say cough up the extra doyuh and get the premium or whatever 91 octane is called where you are. I would hate to have to replace an engine or have major repairs because I was trying to save a few dollars on gas.
 

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1987 Mercedes 190 E
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Discussion Starter #3
Thanks guys for the info. Malibuite I think your right! Why chance it, and yeah our premium here is 91 and our regular is like high 80's. Soon i'll get me some pic's on here of my new ride. I think my husband got me a really good deal on this car so I better take care of it! lol .. It's in fabulous condition, except for a few minor things like a small crack in the windshild.
 

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1989 W201.029/M103 3.0
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Vehicle manufacturers rate octanes as R+M/2, or RON + MON / 2 = fuel octane.

This is because, as Deathrattle related the methods of fuel retailers octane rating vary. RON is a little high and MON is a little low.
Engineer's ratings for actual fuel octane ratings would translate a 95 octane for a 91 MON (premium) unleaded.
A 93 RON (regular) unleaded would translate to an 89 actual fuel octane.
In Australia, premium grades range from 96-98 RON at the pump (about 92-94 actual fuel octane) and is quite a good quality for higher compression ratios and forced induction. Old super-leaded used to rate between 98-102 RON (averaging 96 actual fuel octane at the pump).
I could speculate that US petrol stations prefer the MON ratings as part of the trend from the late 70's towards lower compression engines and tighter emissions, a bit of benevolant marketing psychology getting people away from competing for big numbers (oh yeah, well my 9-billion horsepower SuperTrack Stallionrunner needs 2000 octane just to start without killing its driver). But the truth is I've no idea why they use that rating and the UK/Australia uses RON, and neither use actual fuel octane ratings very often.


Cars which specify premium unleaded are either turbocharged/supercharged or have a static compression ratio of 9:1 or more.
Either of these scenarios requires a minimum of 92 actual fuel octane (a rating of 96 RON or 88 MON) to prevent predetonation at the cylinders as atmospheric temperatures and engine loadings start to rise.
Predetonation cracks pistons, heads and destroys other vital engine components. But it's not quite as bad as all that.
Modern engine management systems (efi), include "knock sensors" which retard ignition timing and richen air-fuel ratios as predetonation begins to occur.

So most newer cars just run gutless with lower octanes. And poor tuning does things like oils up plugs and goes through too much juice (the money you save filling up the tank just gets used by having to pour more through the injectors).

So if it says use premium, use premium. If it says use unleaded but runs better on premium, use premium.
 

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Just to addenda for the real enthusiasts, older engines ping all over the place on lower octanes from 9.5:1 compression onwards. Only k-jetronic Euro-spec Mercs geared for higher quality European 96 RON minimum pump grade unleaded have the 9.5:1 or 10:1 static compression ratios (certain M110 and M117 engines) and even this is offset by camshaft overlaps purely to bring down dynamic compression ratios into the high 8:1 range (these cam overlaps and centrelines actually reduce the performance inherent in the pretty wild Euro grinds themselves).

Later k-jetronic models actually dropped the compression ratios for premium unleaded, perhaps as pump grade qualities became inconsistent throughout Europe.
With the advent of efi, static compression ratios have come back up again on most cars. It's hard to buy even a grannie-mobile that doesn't have a "sporty motor" these days. 1.1 litres and 9.5:1 static compression/multi-point efi for the horsepower equivalent of an old RS2000 hoon-mobile, on a sesame seed bun. Drops a burnout in the first three gears and gets 60mpg...just don't put any passengers in it coz it's got the torque of a lawnmower.

Carburettor'd Merc variants of that era (early unleaded and late leaded fuels) come from factory no higher than 9:1 static compression to prevent predetonation for even premium unleaded at its best.

Post-'76 US spec models have however, 8:1 static compression ratio for the M110 (around 7.5:1 dynamic), and certainly could run on standard grade unleaded. Premium unleaded may not have been universally available in the US at that time as this is typical of vehicles marked "use unleaded fuel only."

The higher compression engines mentioned above, where they do not have knock sensors *will* predetonate using lower octane fuels under loading conditions and they will wear or even collapse well short of the ideal engine life. Something like a 560 Merc will last a matter of countable kilometres.

Leaded engines use super from around 9:1 static compression onwards also. Special low compression engines were made by various manufacturers with static compression ratios of 8.2:1 and thereabouts.
The difference in higher octanes in leaded super were that it could tolerate compression ratios of greater than 11:1 (my old street racer had 11.5:1), and a variety of "performance vehicles" had static compressions in the 10:1 range. A batch of standard grade leaded in something like a 420hp GTHO Ford would get you about 100 metres down the road before a *very* expensive engine rebuild.
 

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1987 Mercedes 190 E
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Discussion Starter #6
[;)] Thanks so much for all the info. I've been taking all of it into consideration. What I have decided to do is: Just stick with what we here in the USA call premium..lol..Thats what it tells me to use and also it's not that much more of a cost. Regular is $2.19 and premium is $2.34 ( for now). I sure wouldn't want to damage anything!! I just found out how much wire's and plugs run..OMG..WOW.. So it's time to baby my new Benz and start dumping some money in her. Again, Thank You All So Much!!
 
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