JohnnyC300

Hi guys,

Bought a 2009 c300 with 52,000 miles almost 3 months ago. First car, waited 'till I could afford the Merc!

Naturally I've been keeping the tank full, of top tier premium 93 only and even gave it 1 bottle of techron concentrate when I got it in October.

I'm noticing a strange pattern, the car seems to perform better (accelerates faster, less bumpy ride) when low on gas. This effect seems to take place when there are around under 75 miles remaining, and gets better when it reaches the "reserve fuel tank" warning on the dash.

Does not matter if I am in sport, comfort, or selecting gear ranges. Seems to perform consistently better in all modes when low.

Has anyone noticed this before, is it even possible? Is there actually a second "reserve fuel reservoir" that is perhaps performing better than my main tank?

I'm hesitant to give it a second bottle of techron because I read here only to do it twice between oil changes and I am not sure when the last time an oil change was performed, about to go for one. Any advice on this phenomena would be appreciated. I am currently hesitant to fill the tank because the ride seems to get more harsh.

Knightmare69

That's probably cuz you're light a tank of gas, that liquid weight does affect performance. Why do you think sometimes race cars don't take a full tank when in the pits.

JohnnyC300

I thought about this, and looked up the weight of a tank of gas and it seems to only be about 100lbs, I don't think this kind of difference could be accounted for by that. Could it be that the techron concentrate (which I had put in when it was near empty as directed) is at the bottom of the tank (even after several refills)? Starting to fear something is broken the car feels like it should near empty.

Glyn M Ruck

This makes no sense other than the weight issue. Fill the tank & check the fuel pressure at the Schrader valve on the front fuel rail that links the injectors. s/b > 3.8 bar or 55 psi.

You could repeat this with the tank close to empty & see if there is a discrepency.

JohnnyC300

I will, thanks Glyn. Also I've read your posts and you seem knowledgeable on oil and additives, what is your opinion on me adding a second bottle of Chevron Techron Concentrate (12oz) without knowing if the cars previous owner ever used it. I am changing the oil as soon as I can and have read before an oil change is the time to use it but am also weary of using more than two per oil change.


Specifically, I've driven about ~1,000 miles / 1,6000km since last using Techron, and don't know if it has ever been used before in the car.

Glyn M Ruck

A second dose of Techron will do no harm at all as long as you don't exceed the treat rate specified on the bottle.

JohnnyC300

The treat rate is two per oil change and as the car's new owner I'm unsure if it has had more than the one bottle I utilized, so I suppose it best I refrain from a second until post-oil change.

Glyn M Ruck

The treat rate is not two per oil change. That is an old wives tale. What I mean is don't exceed the dose rate on the bottle of concentrate per tankful.

Techron in very high doses can become slightly aggressive to some yellow metals. More is not better. At standard treat it is 100% safe. Techron works quickest in stop start frequent heat soak mileage.

Drazil

Chevron has techron already added to their gasoline. If you filled up at Chevron you shouldn't need to treat your tank.

JohnnyC300

No chevron's in NYC but I use only top tier gas companies here (Mobil, BP, Shell) which does have other additives.

Pete7874

........

JohnnyC300

Cool thanks, now to change my oil pretty sure it's long over due but no way for me to check because I don't have a dipstick in the '09.

Glyn M Ruck

There you have it. In all our years of testing Techron I have never seen a case where correctly dosed Techron has shown any reaction with oil additives.

Slight dilution of the crankcase oil is possible but unlikely. Techron is dissolved/dispersed in a light carrier oil.

Techron dosage levels in gasoline are monitored by doing an unwashed gum test. We actually read the level of carrier oil.

My colleagues are just taking a belt & bracers approach.

Pete7874

2009 does have an oil dipstick, but a dipstick is not going to tell you the condition of the oil in any meaningful way.

JohnnyC300

Are you sure? I did a search in the forums and it said no also on youtube videos showing where the oil dipstick is I don't see one in that location on mine.

Pete7874

Are you saying your owner's manual is in fact lying? Page 257...



If there is no dipstick, how do you check the oil level? Is there a readout in the instrument cluster that shows you the oil level?

acr2001

Some model years did not have a dipstick. The tube and a "cap" that looks like a dipstick is still there. In those models, yes it was monitored by the computer and the cluster would tell you how much to add. Mercedes scrapped that stupid idea a while back though.

JohnnyC300

So I was incorrect, even though I had read in the manual that there was a dipstick I did not see mine.

The level is dead middle between the min and max, is their anyway to indicate oil integrity via looking at the oil color? Or if in doubt about how long it's been since i've had an oil change, should I just do it? The dash is saying I'm overdo but I'm unsure if it was reset or not last time oil was changed.

snowmuch

So Half tank would be 50lbs thats a lot. During winter times I put 20lbs of sands in my trunk and it makes day and night difference and I can tell the car slows down and gets horrible mileage. Not to mention 50lbs

JohnnyC300

This is why I keep my car as empty as possible. However I've read various things about it better to keep the tank closer to full than empty, so I'm not going to sacrifice this for a performance gain. Can anyone confirm that filling tank occasionally at least is beneficial?

snowmuch

I only heard that its better to top up fuels in winter to prevent fuel line freezing up(?) or something like that.

JohnnyC300

I read you should never top up. That when the tank is full it's full for a reason.

edit: When you say top up do you mean fill to the top, or after filling and it clicks adding more? Full service in NYC tend to do that and it annoys me.

Glyn M Ruck

Keeping your tank full reduces the chance of moisture condensing out in the tank. Just run the normal cycle from full to close to empty. If you are going to lay the car up for a period then fill the tank.

Topping off the tank when filling is a bad practice. It will usually saturate the carbon canister & the EECS will just dump the excess fuel into the inlet manifold in a controlled fashion via the purge valve.

tonyteetime

Running on near empty is not good as it could overheat your fuel pump and allow dirt or residue from the bottom of your tank into your fuel injection system. In the long run, a clogged up fuel filter will degrade your car performance and you may have to change filter more often. Not worth it.

Glyn M Ruck

It will not allow dirt into your fuel injection system. That's why you have a filter. You will only overheat a fuel pump if you run the system dry. Good practice dictates that you refuel when the light comes on. Then all bases are covered without risk. Dirt in fuel will always ultimately get to the fuel filter. Car fuel tanks suffer severe agitation.