Hi folks, can anyone help with 2 queries (I have a ZX 1.9 diesl, 90,000 miles).
(1) what's the value of cleaning out the crankcase breather pipe & how/how often should it be done?
(2) can anyone clear something up for me? I've always understood that if you remove oil filler cap with engine running and can feel 'blow by' gases on the back of your hand, then it seems like worn bores/piston rings are the problem. Well, that's what happens on my ZX diesel, although there are no other signs of worn bores or piston rings - the gases through the oil filler cap are invisible not smokey, the car doesn't burn any oil, and it runs beautifully (touch wood!). I carried out a bit of a straw poll on a number of cars and found the same thing in nearly all of them (e.g. 1.3 mitsubishi colt, immaculately looked after engine, 40,000 miles was blowing furiously through oil filler) with the sole exception of two poorly looked after toyota corollas (no blow by at all). So what's the score? Is some escape gas through the oil filler just an acceptable part of the car's ageing process - or is it time to start worrying?
Thanks all!
crankcase breather / 'blow by' question
Moderator: RichardW
Keeping the breather system clear will help prevent sudden & inexplicable oil burning. Blocked breathers = increased pressure in the crankcase which will create big clouds of blue smoke and as I say, sudden oil consumption.
If the car is inclined towards gunking up the breather, I would suggest making it a once a year job. On petrol engines it can be caused by a faulty thermostat allowing the engine to run too cool for too long particularly cars used on short trips.
As regards the blow by; that's one of life's little mysteries. Again, could be caused by a faulty thermostat. A cold engine has far greater tolerences than a hot one between rings & bore & therefore can start off blowing past a clear pressure which often develops into a vapour as the engine & oil heats up.
Some Industrial stationary engines have a reputation for doing it. I have a slasher that will drench your hand in oil if held about 18 inches above the filler cap whether hot or cold. I complained under warranty as I suspected a sloppy fit & was told "they all do that"[:0]
Now 12 years & thousands of hours later, it's no worse or better than it was. Incidentally, it is also an air cooled motor. Some Ford engines also do the same. The high mileage ones that didn't do it possibly were well carboned up inside & often carbon under the rings forces them into a tighter seal which again is not all that uncommon; they're just as clapped out when you pull them apart.
I would suggest a clean up of your breathing system as well as a new thermostat & I assume you use a good quality oil. If not, don't go changing now; stay with what you've been using as a high detergent oil could wash out carbon deposits & create problems.[;)]
Alan S
If the car is inclined towards gunking up the breather, I would suggest making it a once a year job. On petrol engines it can be caused by a faulty thermostat allowing the engine to run too cool for too long particularly cars used on short trips.
As regards the blow by; that's one of life's little mysteries. Again, could be caused by a faulty thermostat. A cold engine has far greater tolerences than a hot one between rings & bore & therefore can start off blowing past a clear pressure which often develops into a vapour as the engine & oil heats up.
Some Industrial stationary engines have a reputation for doing it. I have a slasher that will drench your hand in oil if held about 18 inches above the filler cap whether hot or cold. I complained under warranty as I suspected a sloppy fit & was told "they all do that"[:0]
Now 12 years & thousands of hours later, it's no worse or better than it was. Incidentally, it is also an air cooled motor. Some Ford engines also do the same. The high mileage ones that didn't do it possibly were well carboned up inside & often carbon under the rings forces them into a tighter seal which again is not all that uncommon; they're just as clapped out when you pull them apart.
I would suggest a clean up of your breathing system as well as a new thermostat & I assume you use a good quality oil. If not, don't go changing now; stay with what you've been using as a high detergent oil could wash out carbon deposits & create problems.[;)]
Alan S
Gosh Alan! Thanks a lot for such a detailed response! It all makes sense now. My daily run is 30 miles each way, 25 of which are dual carriageway (65-75 mph), and 5 of which are in standing traffic that can take 45 minutes or so to get through. I've noticed recently that the engine does seem to be running cooler than it used to - incidentally it takes a good while in standing traffic to raise the temp guage from 80 to 90 c. So, sensor & thermostat have been on my list of things to do. I've only noticed the blow-by since then (although I never looked before). So now it's all starting to make sense!
Thanks for that Alan!
Thanks for that Alan!
The patting feeling on your back of your hand is the engine soil pressure which is good as shows that the engine is in good condition. When you mention the Toyotas that have never been serviced, the reason why you cant feel this is becuase the engine is worn and was not oil pressure.
When engine is knackered you do get a lot of blow by which results in oil caps and dipsticks being blown out. As someone has mentioned all engines get a little blow by and its nothing much to worrk about until the dipstick blows out. But if yours does it dont forget to check to see if your breathers are blocked.
When engine is knackered you do get a lot of blow by which results in oil caps and dipsticks being blown out. As someone has mentioned all engines get a little blow by and its nothing much to worrk about until the dipstick blows out. But if yours does it dont forget to check to see if your breathers are blocked.
Dear aotearoa,
What you are feeling on the back of your hand is not blow-by. Since you have four little pistons busily reciprocating away deep down in your engine, they stir up quite a commotion with the air down there in the crankcase - it's rather like having four small diaphragm pumps wacking away at around 800 times a minute! No wonder there's a bit of air flow when you open up their little environment to the rest of the world!
With blow-by you have only a positive pressure due to combustion gas leakage past the pistons, but you can easily tell that because it stinks of burn gases! Even a new engine will have a small amount of positive pressure, but then thats the reason why you have a breather pipe - it allows the positive pressure to be circulated back into the engine via the intake.
The danger with a blocked breather pipe is mainly if you have mayonaisse forming (hot oil and cold condensation water (usually caused by short journies) this can freeze in winter time and cause a situation where the intrnal pressure increases until something gives - often the oil filler cap - giving the engine a very effective anti-rust treatment (and unfortunately the engine oil starvation) however, itsvery unusual on a diesels!
//NiSk
What you are feeling on the back of your hand is not blow-by. Since you have four little pistons busily reciprocating away deep down in your engine, they stir up quite a commotion with the air down there in the crankcase - it's rather like having four small diaphragm pumps wacking away at around 800 times a minute! No wonder there's a bit of air flow when you open up their little environment to the rest of the world!
With blow-by you have only a positive pressure due to combustion gas leakage past the pistons, but you can easily tell that because it stinks of burn gases! Even a new engine will have a small amount of positive pressure, but then thats the reason why you have a breather pipe - it allows the positive pressure to be circulated back into the engine via the intake.
The danger with a blocked breather pipe is mainly if you have mayonaisse forming (hot oil and cold condensation water (usually caused by short journies) this can freeze in winter time and cause a situation where the intrnal pressure increases until something gives - often the oil filler cap - giving the engine a very effective anti-rust treatment (and unfortunately the engine oil starvation) however, itsvery unusual on a diesels!
//NiSk
Just a word about ZX thermostats. from what I remember the original thermostat fitted was high 80's or 90 celsius. When I went to replace the thermostat in our ZX at the end of last year I was told that the recommended one to fit now was 80 celsius and duly fitted it. The reason I mention it is that this may be the explanation why your car gets to 80 rapidly and takes a long time to get to 90. Incidentally if you do change the thermostat you may have trouble getting the right gasket (O ring) for it. Ours has a thick gasket and a thin one was supplied.