My Poor Car

[marchanna]

Are these engines designed for 91 octane? You should always use the octane rating that your engine is defined for - i.e. compression and timing. With a lower octane than specified, obviously there is the risk of preignition, but there's usually no risk with going with a higher octane, except for a little power loss - there's more potential energy in lower octane fuel.It seems there are a lot of oil pressure issues with these engines, maybe it's worthwhile using an oil such as Motul 300v.

[adelaide J]

Just an update, I have 10,000 kms on this rebuilt engine and all is fine. Just put the snow tires on and she is ready for another winter. I always used 91 octane in the smart and still have no replys from MB as why my car had a valve problem

[marchanna]

It's good to hear that all is well now. It would be nice though to figure out the cause to prevent this from happening again. In my experience MB has been pretty useless in this respect - I think they've become lazy or unknowledgeable and have devolved to "parts replacers."

[jzchen]

A few years ago I started switching the Mercedes in the household to Mobil 1 0W-40 per the approved fluids list I had found on startekinfo. I can't help but wonder if oil/oil pressure could be part of the issue. I am new to smarts, ours just turned 1 this last October. I wonder what oil the older smarts have been using?

Anyways, I did find that there is a similar oil warranty in Canada, (as I noticed this is primarily a Canadian forum,) here:

http://www.mobil.ca/Canada-English-LCW/Fil...on-warranty.pdf

Here in the US the warranty is quite similar if you are using Mobil 1 oils. If you did find out that the failure is oil caused while using Mobil 1 you could possibly use the warranty stated here:

http://www.mobiloil.com/USA-English/MotorO...1_Warranty.aspx

to get Mobil to cover the labor portion that you had to pay....

[Huronlad]

I stand to be corrected but typically motor oil has nothing to do with exhaust valve failure.

[marchanna]

Exhaust valves tend to run very hot, which can lead to failure. Motor oil (in addition to lubrication) provides a function of heat redistribution (or heat equalization) throughout the engine (whereas coolant takes that heat away). Therefore the failure directly or indirectly of the oil to perform this task can cause a concentration of heat in one section of the motor resulting in heat associated failure. Further to this, poor oil circulation can result in friction (and subsequent heat) causing wear and heat associated failures.Heat associated failures can be in the form of disproportionate thermal expansion rates between components and metallurgical property changes (such as hardening, reduced shear and tensile strength, and brittleness to name a few).This could also be a design flaw in the engine.

[jzchen]

I stand to be corrected but typically motor oil has nothing to do with exhaust valve failure.

I'm not a mechanic. I consider myself a car enthusiast. I did read something about cylinder wall wear, (I just reread posts to check.) That has me a little suspicious about the oi/oil pressure. But I may be putting my foot in my mouth....I honestly don't know too much about exhaust valve failures and their causes....

[GoFaster]

I've worked on my share of motorcycle engines, not car engines, but it's the same idea.Valve trouble nomally starts when, for some reason, the valve does not seal. If the valve doesn't seal adequately, then hot combustion gases start blowing past, which accelerates seat erosion and adds more heat load to the valve, until eventually the situation goes catastrophic.Why would the valve not seal ... Normal gradual wear of the valve and valve seat to the point where the valve reaches zero valve clearance. Then some period of hot-running operation (raises the exhaust valve temp) and you have leakage. Modern engines built with good valve and seat materials shouldn't have much valve seat recession. (Granted, we are talking about Mitsubishi here - not one of my favorite engine manufacturers.)The other, more likely cause is carbon buildup. And why would that happen ... Too many short trips, lousy fuel quality, never getting the engine fully warmed up, bad injector spray pattern, or oil leakage past the valve stem seals and valve guides. A little bit of oil past the valve seals is actually a good thing; nothing else lubricates the valve guides. But too much ... and you get carbon buildup.Running too lean or with slow/delayed combustion can overheat exhaust valves, too, but modern engine controls are designed to hold the air/fuel ratio in a tight range ... unless you start getting a weak cylinder due to a partially clogged injector or some such thing. The engine controls will average out the air fuel ratio and in this case, you would have two rich cylinders offsetting one lean cylinder.So, what to do? Well, I'll tell you what I do.Use good quality fuel. In this area, that's either Shell V-Power or PetroCanada Ultra 94. This engine wants high octane. Don't let it be retarding the ignition timing to compensate for you having put the cheap stuff in.Don't do short trips - or if you do short trips, offset at least every couple of short trips with a good long run.Use the proper motor oil. When I got my car (at 89,000 km) it was using a little bit of oil, but who knows what the previous owner put in, and I doubt if the Mazda dealer that I bought the car from used the right stuff. I will also confess to using a small amount (less than half the amount the bottle suggests ...) of that Bardahl No-Smoke stuff. But now, oil consumption seems to have dropped to next to nil.And ... use some sort of lubrication additive in the gasoline, be it Marvel Mystery Oil or Lucas (which I used until the bottle ran out) or the cheapest option, TCW3 two-stroke oil (which is what I have switched to). Every once in a while (perhaps at the time of oil change) give it a shot of injector cleaner instead.I have another engine (motorcycle) which is notorious for eating intake valves. I've been using a dash of two-stroke oil in the gasoline religiously. Since doing that, never had an issue, never even had to change a valve-clearance shim, engine maintains good compression.If you go the two-stroke oil route, make sure it is TCW3 ashless ... you don't need a clogged catalyst. Internet searching indicates the proper amount is somewhere near 1 part in 500 to the fuel, so you will not be making a smoke-screen.On the bike engines, you have to make sure the valve clearances are correct, or else. But the newer engines are good at holding stable valve clearances.The Mitsubishi engines use shim-type clearance setting, just like most motorcycle engines. And they are supposed to be checked at 100,000 km. Too bad the easiest way to check them seems to involve dropping the engine ... I have not had mine checked ...

[smart142]

I stand to be corrected but typically motor oil has nothing to do with exhaust valve failure.

But poor lubrication of a hydraulic lifter could cause a premature failure resulting in exhaust valve failure.

[GoFaster]

Aye, but the Mitsubishi 3B21 doesn't have hydraulic lash adjusters. It's shim-and-bucket, like a motorcycle engine.Wrong viscosity oil can get past the rings and valve stem seals and lead to carbon buildup, and *that* can hang a valve open.