Difference between leaded and unleaded

[Toffen]

Hi!

I have a Promax 300 and reccommended fuel is 98 RON unleaded (92 posted octane unleaded). Since last year several marinas have decided not to sell this fuel in Norway, and the only fuel I can get is 98RON leaded fuel.

I can get hold of 98RON unleaded at the gas stations, but then I have to use small cans and walk some distance as well.

What is the difference between leaded and unleaded fuel? What does it mean for the engine and performance?

Cheers, Toffen - Norway

[WillyT]

Historically, lead in gas was always a good thing (from a performance point of view, not an environmental point of view). It serves as both a lubricant and serves to slow/extend the combustion process (i.e., it has anti-knock qualities). When lead was first taken out of our gas, many 4-cycle engines had valve failures due to the lack of lubrication and "cushion" provided by the lead. Hardened valves and seats were the only answer. Some outboards at that time, especially certain models of OMCs, were also hard to keep running with just unleaded gas, even at high octain levels. Today's engines are designed to run without lead. Whether today's 2-cycle outboard engines are now so sophisticated that lead will actually hurt them in some way, I do not know. Carbon build-up is a fairly regular problem in outboards. Whether lead makes this better or worse, I do not know. I also don't know if today's fuel injection systems can tolorate lead. Can't get leaded gas here anymore, so never had to face this question. Like I said, lead was always a "good thing," but our current designs MAY not be able to take advantage of it anymore. Unless it "clogs things up" in some way, however, I suspect that it is still superior to unleaded in several ways. Maybe someone else (Jay Smith with his refinery background?) will add to this.

[Markus]

Toffen, you can not get leaded fuel anymore at regular gas stations in Norway. What you can get is fuel with lead substitute to protect the valves of old four cycle engines with soft valve seats. The substitute used is potassium (K). Supposedly, potassium can build up in your exhaust system, which is why so called unleaded fuel is recommended, but I doubt that it is a problem in real life.

[MadMat]

Markus, are you sure.
I'm positive that in Sweden and the UK that the Lead Replacement Petrol, although still classified as 4* petrol contains Sodium to replace the lead, so I'm surprised if norway has potassium. The trouble with sodium is in turbocharged cars the sodium in the exhaust gas erodes away the turbine eventually killing the turbine. Also the levels that are put into LRP DO NOT give as much protection from valve burn and detonation or preignition as the lead did.

As an aside (Try this at your own risk), I have a turboed car that needs the lead and a hight enough octane level. I run normal premium (not super) unleaded with a double dosage of Millers VSP plus. I believe castrol valvemaster is also very good. Neither of these contain the sodium and both contain octane boosters. I have run the car on the race track on a hot day with no detonation or pre-ignition problems. I run double dose because after speaking to the guys at millersoils (http://www.millersoils.co.uk) they recommended that a double dose would give me a higher octane number and more octane=less chance of detonation.

Sorry this has gone a bit off topic, I guess we're still no closer to knowing whether or not leaded or lead replacement fuel will run in a promax but maybe Toffen could consider using fuel additives or even avgas, which in the UK at least still does have real lead in it so I'm told.

This is the car mentioned : http://www.users.totalise.co.uk/~matt.yorke/gallery.htm

Cheers
Matt

[Toffen]

Hi!

I have checked my owners handbook and Merc says that I can use 98RON leaded and unleaded gas. Unleaded is reccommended, but leaded can be used in areas where unleaded is not available.

Question: Will leaded 98RON faul more than 98RON unleaded? Will leaded 98RON give less power than 98RON unleaded, due to slower burning / higher anti knock effect?

Cheers and thanks, Toffen

[Markus]

Toffen, leaded would burn better, but you can not get leaded unless you get an additive that contains tetraoctyl-lead. Klotz sells a product, for example. Between the two kinds of pump gas, there would not be a significant difference, since they contain the same chemicals to increase octane.

MadMat, I am not positive, but in Sweden, the major gas station chains no longer sell gas with lead substitute, so people with old cars have to buy potassium in bottles, and when that change was advertised about a year ago, the story was that there used to be potassium in the gas as well.

If anyone wants to learn more about gas, I have some good links at my links page.