where there's smoke, there's......what, exactly?

galwaytt · 02-03-2005, 12:58 PM

As you can see from my post count, I'm a newbie, so apologies for asking what may be incredibly obvious to some.......car details as per my sig, below....

mmmm, to smoke or not to smoke, that is the question...............

well, actually it isn't - I mean I know it shouldn't, but neither have I determined any specific over-consumption yet either. Hearing I could go through 1l/1000kms seems oil usage is just the norm with these machines.....

This evening, traffic was appalling. 5mph stuff, idle for periods of minutes at a time. At one point, I noticed in my passenger door mirror (the side the exhaust tip is on, on my car), the curl of smoke. However, a gap opened in the traffic ahead, and I pulled ahead, but keeping an eye on the mirror, the curl had turned into a pawl, then a cloud. I blipped the throttle gently and I could see that certainly a lot of it, if not all (hard to be sure - it was dark), came from the exhaust tip itself. But then it cleared. And didn't do it again. It has done this twice, maybe three times inside the last few months, but it's very hard to determine what the exact trigger is for this, but always involved is lots of idling and traffic.

Time for a confession, I do know there is the slightest amount of mist on the l.h. crankcase, but it's been parked in the same spot for a few months now in the garage, and there isn't a drop on the concrete yet....fingers crossed.

But the cloud I left behind today was embarrassing, to say the least. In fact, the guy behind me stayed well back - he probably thought the car was about to spontaneously combust............

Some questions then: on these engines, could an overfill of the tank cause some of this ? Are these engines, at idle, inclined to 'wet-sump'? I'm presuming here that the oil pump has two functions, and two 'halves' ; 1) to pump fresh oil to the various galleys from the filter and tank, and 2), to scavenge the sump contents back to the tank. Is there a conundrum, at idle where it doesn't scavenge as fast as the galley's drain into the crankcase? BTW, the car has excellent oil pressure.

Or is it all just much simpler, i.e. rings/valve guides? If someone can point me in the direction of a good leak down tester, or how-to on the process, I'm prepared to spend some time on it.

TIA, I'm sure I'll have loads more questions before I know this car inside out.........

Steve87-911 · Steve87-911's Garage

Howdy,
There are bunch of threads on this that you might want to search for. But briefly, yes, if you overfill with oil, then oil can get sucked into the airbox and then into the air intake and can make smoke. And as you may know, cold start smoke puffs are fairly normal but I'd be concerned about smoking when warmed up. Once warmed up, your tolerances should have tightened things up so less chance of oil getting into the boom chamber. As far a long idling goes, someone else might know cuz I avoid any long idling.

asphaltgambler · 02-03-2005, 02:53 PM

It may indicate worn valve guides if your oil level is correct and there is no oil entering the intake from some other source.

galwaytt · 02-04-2005, 12:10 AM

thanks guys, all the more it seems I'll need to reach for Wayne's book on rebuilds................

jdowty3 · jdowty3's Garage

I found that my car started to smoke for an unknown reason after I trailered it up to Michigan. It was mild at first and got worse over the course of a couple weeks. When I got the car up in the air, I found that it was tranny oil from a leaking seal in front of the clutch dropping on to the exhaust crossover pipe.

sammyg2 · 02-04-2005, 07:12 AM

Whoa, don't jump to any conclusions, let's get some more info first:

get your car fully warmed up and on level ground and let it idle for at least a couple minutes, then check the oil level and let us know where it is. Second, get under there and scrub your heat exchangers and exhaust real good to get off and old oil residue, then check em again after you have driven the car for a while and see if any new oil or residue has accumulated.
it might be as simple as too much oil, or a slight leak at a valve cover gasket dripping on the exhaust causing the smoke. Both of those are easier to fix than valve guides (which i don't think are the problem based on the scenario you described).

jpnovak · 02-04-2005, 08:17 AM

Check the simple things first as mentioned above.

btw, Is that trials bike in your avitar? Very cool. I used to do bicycle trials for fun years ago. My shins were never the same.

galwaytt · 02-07-2005, 01:01 AM

Sammyg2 - tks for that. When I changed the oil a two weeks ago, I cleaned up all I could see. I did see a weep on the l.h. crankcase half coming from 'up above' somewhere. It was enough to have dirt stick to the c/case, but not enough to cause a drip - floor is still clean under the car. I've been driving it with Denso plugs for two weeks, and car is much better than when on the Bosch WR4CC.

Checking the oil is infuriating - I think I may have overfilled it originally, but over the 500/600-odd miles since the change, I reckon it's used.........500ml? maybe 800ml? If this is correct, then it's probably a bit much.........

jpnovak - yep, it's a GasGas 250. I'm a beginner of the highest order, and don't get half enough time to do stuff, but this year I promise I will !!!