mechrisme

My brother bought a 98 12 Valve 5 speed dually awhile back for a 1000 bucks. It had around 119,000 miles on it and he basically bought it without it running. The truck sat for over 3 years it looked like its been through alot living on a ranch and you can tell its seen its bump gate from the missing dually fender. Basically he replaced everybody panel so its looking pretty good but it did have some pressure out of the crankcase and blow by tube but the pressure out of the oil filler neck went away with driving but there is still pressure out of the blow by tube. It doesn't use any oil but I thought it would use oil if it had blow by and how does an engine with such low miles have blow by. I read somewhere online that the vacuum pump leaking into the motor could cause blow by but I'm not sure. Does anyone have any advice? He got an 12 valve engine out of a 95 Ford F800 to swap in it.

cj360trider

ALL engines have some measure of blowby. if its not using oil then i wudnt worry about it. you dont see this on fords much because its a closed system. if its not puddling under the blowby tube you dont really have anything to worry about. i have 224k on mine it forms a drip from time to time but its still too small amount of blowby to concern myself with. honestly he probly doesnt need to swap the motor. keep the maintenance up and dont use cheap oil you shud be jus fine

torquefan

I've seen a couple that vented enough out the road draft tube that there was oil dripping off the back bumper. If it isn't making the bottom if the truck all oily it doesn't sound like as much of a worry.
In addition to the vacuum pump, in some cases the turbo can cause it too

infidel

If you're not using more than 2 qts of oil between changes don't worry about the blowby.

mechrisme

He fixed the vacuum pump leak but now the plate on the side of the engine is leaking. The vacuum pump and valve cover gasket only really leaked over 60 mph. He said the blowby tube started to drip some but I guess its not dripping bad.

IanM

How much would be too much blow by? I've seen a puddle about the size of 4 quarters laying side by side after driving it for 20 mins and letting it idle for 10mins....

cj360trider

still wudnt worry about it

infidel

It's pretty amazing how what looks like a lot of blowby and a few drips is a lot less oil than it appears.
I have a three cylinder diesel generator whose blowby continuously looks like a smoke stack when it's running.
Even though it only holds three quarts of oil the level is barely down on the dipstick at every 100 hour oil change.

I use 12 quarts of oil on my Ram's oil changes. At every 10k mile oil change the level drops about a quart. Sort of nice not having to add oil between changes. I'm sure the oil loss is coming out the blowby and consider it completely normal.
When oil starts dripping from your tailpipe then you can start worrying.

We're actually pretty lucky that our blowby vents to the atmosphere, it hasn't been allowed on gassers for at least 40 years and on diesels for about seven. That's why new to diesel owners often have questions about excess blowby, they're used to the crankcase venting back into the intake via the PCV valve. Instead of the oil painting the bottom of the vehicle it gets burned in combustion. Doing this on a turbocharged engine requires a pump and makes an oily mess.

cj360trider

or you cud be like ford and put the pcv in front of the turbo so it soaks the turbo and makes it look like your turbo is leaking oil

jstouth

Do you have access to a leak down tester? This can tell you alot about your rings etc. Another option is to have an oil analysis done at your next oil change. It will give you a pretty good idea what parts are wearing and at what rate. My 24 valve has nearly 400000 miles on it and blows oil all over itself but really doesn't lose level. Once you cut down the major leaks the blow by won't seem so bad.