This should be a quick question,
Crankcase pressure, how much should there be and where is the vent so I can un block it? I'm sure theres way too much at the moment.

There's a small rubber tube goes from the rocker box to the inlet manifold, if I take off the tube and put my finger on the end of the pipe coming off the rocker box, pressure builds up quickly, and eventually stops the engine?

Is there another vent hidden somewhere? The pressure is bad, as it will run on the oil from this vent tube if you let it once its hot.

If its not the vent where should I look next? new rings? check compression?

Thanks for your help and if any one knows of an online engine drawing that would really help, until I get a book.

Cheers

Yes, that's the vent. If it runs on oil from that vent, I'd check the compression. However, depending on what year your vehicle is, you may have a vacuum pump with a failed diaphragm that is feeding oil into the intake. Is there a hose from the top of the vacuum pump over either to the air filter or the intake? If so, check to make sure it does not have oil in it.

Putting your finger over the vent and having the engine shut off is normal on these engines. It's putting pressure on the shut off diaphragm. If you search on the topic you will find lots of old threads on how many seconds a good versus bad engine will run once that hose is plugged. I think it's a poor test and not a wise thing to do because it puts pressure on all the seals in the engine and and engine that runs a long time with the hose plugged may not be in good shape, but may just have a leaking seal.

For other viewers, the 307d has the 616 engine.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thanks Kerry,

thats answered a few bits.....compression seems good as it starts and runs well.

So the excess pressure needs to be sorted or investigated..thats the next job then!!

I've been trying to understand why that maneuver (plugging the vent) does what it does. Your explanation is the first that has gotten through the brick between my ears. It's creating a pressure differential just as applying vacuum to the shutoff valve does. (Why didn't I think of that???)

Hmmm...this also gives people with vacuum problems another shut-off option, should the red STOP lever also malfunction.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

So is this the only vent? I was hoping for a blocked vent to be causing the crank case/rocker box pressure, but if this is it then its more serious like rings I guess?

And Kerry, I'll look for a vacum pipe once it stops raining

Can someone please tell me there is another vent?

I must get a book on the engine.

It's done well so far as it came from North of Stockholm and has driven to South West England with two horses.

Thanks, seems like a good forum.

No there is no other vent.

But don't despair, a lot of blowby does not hurt the servicability of these engines all that much. They will run for years that way. If they start decently and idle smoothly don't worry about it. If they are using some oil, just keep an eye on it and don't ever run it low.

I wouldn't go into one unless it was getting unreliable or just using so much oil that it inhibits its natural usefulness.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Well it starts on the button even after 6 months in a field, doesn't use oil and idles smooth so it seems like I just have to sort out the vacuum system for leaks, and maybe clear oil ways to stop a build up of oil in the rocker box, which could be causing the running on.

cheers all.