Is Blowby the same for a Jetta TDI - PeachParts Mercedes-Benz Forum

arcticathlon · #1 02-05-2006, 10:31 PM

my buddy came over and we changed oil in our cars. i told him to turn his engine on and see how much blowby he had. he was confused and started his car. the oil cap seemed heavier than my 300D cap, and it was almost dancing off the engine block. this is with the plastic cover on the engine, with the cap being lower and in a type of groove. i was very supprised at this and showed him my car. my 85 300D has 173k on it, and the cap would not move when i loosened it.

so my question is this, is blowby a universal phenomenon for diesels? he has been telling me how his jetta has been hard to start and very cranky on cold mornings. this would agree with the blowby test, as he should have lower compression. his 98 jetta has 160k on it.

t walgamuth · #2 02-05-2006, 10:38 PM

blowby test is reliable indicator of motor wear on any internal combustion motor.

tom w

lietuviai · #3 02-06-2006, 12:16 AM

I think it would also depend on how the crankcase is vented. I had a Nissan diesel pick up and all it had was a vent pipe on the side of the engine pointing down, something very similar to what was on pre-1955 gasoline powered cars and trucks (for those of you old enough to remember those). You could take the oil cap off and it had no blow by but you could see it puffing out the pipe a little. That pipe did make one heck of a mess on the suspension components it was draining on though.

ykobayashi · #4 02-06-2006, 02:52 AM

That's right, venting is everything. I used to make blow-by measurement systems (NTK's M100 et al). You could measure the flow through the road draft tube on a diesel by putting a flowmeter inline with it. But if the tube recirculated back into the intake (like on a OM61X) then the flow would be the blowby + the intake vacuum. To complicate matters further, the diameter of the road draft tube/recirculation tube would cause more or less flow restriction...thus making it futile to compare actual liters/min of flow between different crankcase vent setups. In fact, if you used the flow meter with 6' of road draft hose or 2' you'd get different answers because you were changing backpressure. I got a lot of tech support calls on this.

He may have worn rings. But if the car doesn't smoke and makes good power, don't sweat it. The key is to check it against a new 98 jetta...not a MBZ.

I'm not sure about a 98 jetta, but my Rabbit vented to the intake. Tell your pal to check his crankcase ventilation system and PCV (if it has one).

Good luck,
Yoko

arcticathlon · #5 02-06-2006, 08:40 AM

funny how you said smoke, because he smokes a lot. it is blue also. in addition, when we changed his oil, he said it was low on oil and we were only able to get 2 quarts out of it. it takes 4.5 quarts to fill up. this was on a 5k miles interval.

it sounds more and more like a worn out engine to me.

Hatterasguy · #6 02-06-2006, 10:20 AM

Every internal combustion engine has blow by. For diesels it is just death because they need compression to ignite the fuel. A low compression gas engine will run for a very very long time.

I am not sure how to measure it on our cars. I think on the larger diesels they measure crank case pressure. I saw someone do it once on a 6v92TIB but I am not sure of the specs or procedure.

If it runs good ignore it, the only fix is a rebuild.

Hatterasguy · #7 02-06-2006, 02:29 PM

Quote:

Originally Posted by arcticathlon

funny how you said smoke, because he smokes a lot. it is blue also. in addition, when we changed his oil, he said it was low on oil and we were only able to get 2 quarts out of it. it takes 4.5 quarts to fill up. this was on a 5k miles interval.

it sounds more and more like a worn out engine to me.

Does he even bother to check the oil?

You should never let it get that low.

It just sounds like an abused engine, drive it till it won't start or sell it and let the next person deal with it.