[firebird_1252]

my dad has a 3406b in his t800. anyway, he's getting blow by threw the dipstick. the motor was overhauled 200k ago. runs great, great oil psi no weird sounds or anything. pulls 90k almost daily with no issues what so ever.. hell even great mpg! (well for that thing). anyway, we're cummins people. i know my detroit has blow by just by looking at it the wrong way.. is this a cat thing? if not.. any sugestions?

[Les2]

Mine has blowby also. It mostly comes out the breather tube. Maybe check to make sure it isn't clogged up and check to see if there is antifreeze in the oil if you have a lot of blowby. It could be as simple as the backing plate on the waterpump.

[firebird_1252]

def. dont have anti freeze in the oil. i'll have him check the tube. thanks!

[GMAN]

I own 2 3406E's and have never had a problem with them leaking. Come to think of it one of them is seeping a little around the tube that is underneath the turbo. I have a gasket for it but have not taken time to replace it. I think the 3406E is one of the best engines on the market. It was certainly a good engine for CAT. I have had better service from CAT than any engine that I have owned.

[firebird_1252]

well the only real leak he has is from around the rear main. the splitter ( i think it grinds when going in to high range) is on its way out. so when he does the trans he's getting that fixed. i personally just never seen a cat have blowby

[YerDaddy]

The crankcase breather on the valve cover has steel mesh inside. You could try soaking it in mineral oil and blowing it out to clean it. Check the tubing also. Blow by is normal.

I had mud daubers totally block up my breather tube and the dipstick pushed out and it was spewing oil out the dipstick tube!

[bob h]

Originally Posted by firebird_1252

my dad has a 3406b in his t800. anyway, he's getting blow by threw the dipstick. the motor was overhauled 200k ago. runs great, great oil psi no weird sounds or anything. pulls 90k almost daily with no issues what so ever.. hell even great mpg! (well for that thing). anyway, we're cummins people. i know my detroit has blow by just by looking at it the wrong way.. is this a cat thing? if not.. any sugestions?

Some blow-by is normal, but if you're asking it's probably more than usual. Make certain crankcase breather is not blocked. 'almost' cover the filler opening with your hand, if you feel it puffing against the palm of your hand... that could be enough sign to get it checked. How would Cummins blow-by differ?? Destroyits with blow-by is usually caused by cylinder glazing.