johnstra

Thought I'd share this because I suspect it's fairly common...

Since I bought my truck last August I've worried off and on if I have a blowby problem. My truck has never left puddles of oil under it and it's never puked oil out of the dipstick tube or CCV, but it's always emitted a steady stream of vapor out the CCV tube (looked almost like steam coming from the spout of a kettle) and overnight it would regularly leave 2 or 3 drops of oil on the ground. Also, I've had a hard to cure oil leak between the gear housing and block.

Now I know why!

Tonight I'll rest easy knowing for sure that I don't have a blowby problem at all. I finally got around to testing my vacuum system and found that it was pulling only 5" of vacuum (manual says it should pull 20"). Didn't take long to find that my main vacuum line from the pump had a good sized hole chafed in it. Patched that and my vacuum went to 20". For those of you that don't know, the vacuum pump vents into the crankcase, so if you have a vacuum leak you will pressurize your crankcase. Symptoms are: apparent blowby, oil leaks.

With the vacuum problem fixed, I climbed under the truck with it idling and checked the CCV tube. Now, instead of the stream, I see only a very faint and very slight wisp of vapor. I'll be very interested to see what happens to my oil leak and whether I continue to drip oil at night - I'll bet both go away.

So if you have any issues at all that look like blowby, check your vacuum lines.

Cheers!
-john

LanceD

thanks!

BTW what kind of tool did you use to check your vacuum with? and where do you get one?

johnstra

I have a vacuum gauge I bought at Sears for $20.
-john

infidel

I use one of these. Cheaper plastic models are also available.
Great for bleeding and changing brake fluid also.
http://www.tooldesk.com/products/pro...il.aspx+id+986

TorqueKing360

That leak between your gear case and block is the tell tale sign that you were KDP'd. I would take the gear cover off and look behind it to make shure thats not the only thing to that got damaged.

johnstra

Nope, my KDP is dead (a.k.a tabbed) - that's the first thing I did to my truck. Over time, the gasket between the block and gear housing can fail. It usually happens underneath the vacuum pump. I actually went to the trouble of pulling the cam and removing the gear housing entirely to replace that gasket only to have it continue to seep just a tiny bit of oil past the brand new gasket. I believe it's because I was prssurizing my crankcase with the vacuum leak. I'm surprised my rear main hasn't failed. Anyway, now that my vacuum leak is fixed, I'm going to keep an eye on the oil leak. If it continues to seep I'm going to replace the gasket again this spring.
-john