Thread: Blowby

hi have you checked the big breather on right hand side of engine to see thats its clean some of the have a removable top and a mesh thing that gets clogged up if yours is sealed soak it in petrol and hit it with a karcher thats where all the breathing should be coming from if its breathing

Not really sure what to say, I know when I rebuilt my engine I was checking on something whilst the engine was running and I thought my rings were gone, as there was so much crank case pressure that the oil cap would pop out if I wasn't holding onto it. Thats alots of pressure!!
Did a fair bit of testing and found everything normal. It was just the shear fact that every time a piston moved up or down nearly a litre of air was being displaced.
Maybe you CCV breather is blocked?
Did you speedi sleeve your rear main crank surface?
I've seen the rear main seal catch on speedi sleeves and after a while they just start pumping out oil.

Hope its not the rings mate, you'll have to do a compression test.

Good luck

The oil trap is my own design, it's a cyclone type which has no mesh or screen that can block up. But downstream of that it plumbs into the intake just before the turbo, I should replace that hose with a larger one.

The rear crank surface was speedi-sleeved some time ago and it's still good. Well it was when I checked it around 10,000km ago and changed the seal. I should warm the engine up, pull the breather off and see what's actually coming out.

Does anyone know if the oil filler cap will stay put on a healthy 4BD1T?

Not unless it's on tight, mine will blow off if loose

Mine stays put, and I have healthy blowby through the breather. There are a few different type of oil filler caps; my original was a bit on the suspect side, so I ordered a new one from Isuzu. It was quite different, and made out of a more rubbery compound. Maybe order one of these, they push in very securely.

with the wider than normal ring gap,,
could they have all lined up?

Originally Posted by Larns

Not unless it's on tight, mine will blow off if loose

I should clarify that a little.
Mine will stay put every time it's in. But when sat loosely in place it gets blown clean off.

Jeeze I hope the rings couldn't have lined up. They were installed with the gaps 180 deg out and I'm hoping they'd all rotate the same amount in the same direction.
Compression appears fine from a starting point of view. It's just the blowby that has me concerned.

Maybe an additional breather is in order.

Hi mate, Blowby seems to be a normal thing with these motors. What Isuzus dont like is too much idle work.If compression figures are ok and it seems to be going alright dont worry about the blowby.Work it as hard as you can.I havent seen one yet that has little or no blowby.Regards....Bearman