Interesting Blue Smoke - Blow-By?

[bustedbenz]

I've got a curious symptom that I only recently became aware of after switching to a parking lot I never used to use here at school - important to my question is the fact that the parking lot is at the top of a rather long medium-steepness hill.

Rather than riding the brakes all the way down the hill (probably a good four or five tenths of a mile coasting down hill) I usually just use engine braking - downshift into 1 or 2 and coast that way.

When I do a cold start, (cold is defined here as the engine being nominal 50 degrees ambient) and coast down the hill - there is no smoke as long as my foot stays off the accelerator. However, when I'm going down the hill, if I accelerate even slightly - just enough to switch the engine over from "Holding" the speed down to "making power" - I get a puff/cloud of blue smoke out the back which, I understand, is Rotella. If I keep accelerating, after the initial cloud passes the smoke stops. If I go back to coasting/engine braking for a few more seconds, and then accelerate again, I get another cloud of blue smoke.

Here's the interesting part... if I do the same descent after the engine is up to operating temperature and has been driven for a while and gotten good and hot, the symptom completely disappears and I'm back to just little whiffs of diesel smoke once in a while just like normal.

Could this be oil being blown through into a cylinder under the "pressure" of engine braking and then combusting the first time that cylinder starts making power again? It never does it just going stop light to stop light on level ground, the added strain of holding 1st gear going downhill for a prolonged time when cold seems to be the ONLY way to create this symptom. Wondering if maybe it's oil blowing through a ring that gets cold and dry when the car is parked for a week at a time in cold temperatures, and then that ring gets warm and lubricated again and starts to seal more properly.

How much trouble do I have? It seems to run fine... but it's a new symptom. I'm willing to believe the thing is starting to get somewhat worn out, it's got over 200,000 miles on it but we don't know precisely how many. Never been rebuilt or dismantled further down than the valve cover gasket.

[TylerH860]

Does the motor have alot of blowby?

[bustedbenz]

Originally Posted by TylerH860

Does the motor have alot of blowby?

Last time I checked (a month or two ago) there wasn't even enough to make the oil cap shift positions, much less "dance". So no, I'd call it low blowby.

I may be mis-using that term... when I used it in my title, I was envisioning oil "Blowing past" the piston rings into the combustion chamber or something... I don't even know for 100% sure if this is possible, I may have a flawed understanding of engines (to say the least). Or maybe it's one and the same thing...

Anyway, that's what I meant, and the engine does not have significant blow-by pressure at the oil cap.

[rrgrassi]

Cold engines do not burn fuel effeciently. Engine braking just makes the engine rev w/out fueling. It could be burning the oil left on the sides of the cylinders. Going "back to normal" when at operating temp makes sense, as the engine oil is thinner, so the oil wipe ring does a better job.

[TylerH860]

Is engine braking a good idea on old engines like these? Its necessary for truckers, but not for passenger cars.

I’d rather wear out my brake pads quicker than needlesssly making my engine work harder.

[rrgrassi]

I do not see a need for it, unless there is a really steep grade and your car picks up speed with your foot off of the accelerator as you are going down the incline. Trucks not included of course.

[bustedbenz]

Originally Posted by TylerH860

Is engine braking a good idea on old engines like these? Its necessary for truckers, but not for passenger cars.

I’d rather wear out my brake pads quicker than needlesssly making my engine work harder.

In this particular situation (out of the parking lot), I could just ride the brakes... but on the highway going back down the mountain towards home, it's a 2 mile 8% grade... without at least dropping it to 3rd on that one, I can easily see overheating brakes before reaching the bottom. It's enough that they've put truck pull-out sand dune things along the roadside.

I'm not letting the RPMS climb that high... 2nd gear at about 3000 is about where it balances out going down from the lot. If I let it have its own way in D, just down from the lot, the car absolutely speeds up with my feet off the pedals... I'd be doing well over 50 by the bottom, and it's very curvy (with a speed limit of 25 since it's in town)

[winmutt]

Valve stem seals.

[barry123400]

I too was wondering about the valve stem seals. These diesels do not normally suck much oil down them. Your unusual loading might be a contributing factor. If oil consumption is less than 1 quart in 1k I personally would ignore it.

The only other thought I really would have to sit down and think about is. Would this usage oil increase under that senario or lessen if the oil passage on the frontal head area were a little leaky. There is not much gasket material between that passage and number one cylinder.

Again I would have to really roll that around in my mind before I could discount it or confirm it as a possibility. Initially I feel it is not a consideration but.

Over time if this engine exhibits much more smoke and higher oil consumption that is where I would look. Those 603 engines have always had a problem in that area with their head gaskets. A lot of gasket and head redesign was done over the years to try to lessen that problem. Cannot call it a chronic problem exactly but it can be there.

[t walgamuth]

I was thinking its unburned diesel fuel.

I wouldn't worry about it, and I don't believe engine braking is any harm to a motor unless you over rev it and then it does not matter if its high or low mileage.

[barry123400]

Tom's point also deserves real consideration. You never get to burn properly the fuel being fed into the engine under your circumstance. At the bottom of the hill the engine could just be cleaning itself out as it returns to work. I think the smoke should favour black in that situation yet overfuelling produces white smoke sometimes I am led to believe.

If the car operates well in other circumstances as Tom also mentions I would ignore it at present yet keep an eye on it over time. It could well be if we submitted our own diesels to that hill results may be simular.

You could go buy an ebay special and do a comparison drive down the hill and let us know. Most the offerings on ebay are already going downhill. Now at last I understand why many of them get at least 40mpg. If they mentioned the cars emmisions at the bottom of the hills this might be put to rest. Unfortunatly they always leave that part out.

[t walgamuth]

I think the key is its only doing it when cold. If it were oil smoke then I would expect it to do it all the time. Isn't there an enrichment stage when the motor is cold?

Tom W

[oosix]

Hello all,

I'm also having smoke problems and wanted to ask what the definition of Blow-by is. thanks.

[barry123400]

Blowby is the amount of compression by products that get by the rings on the pistons. You can see the effect by removing your oil filer cap with the engine running. There is almost always some present. Should be a little more when the engine warms up.