Help: My 83 300D Turbo diesel has a high crank case pressure (2023 Update)

Craig, you're almost there.

The vacuum pump does vent into the motor, the question is:

Why is the air volume so great?

Because, I believe, your car, not its motor, has a vacuum leak and all that leaked air is being blasted into the crankcase.

A vacuum leak could be a broken vacuum line, brake booster, door lock, climate control duct etc.

Suggest you consider those possibilities.

That sounds more like an oil leak which is VERY characteristic of these engines at about this milage. WIthout looking at it I'd guess the turbo oil return line as it seems to be the first to go and is the messiest.

Yeah well, we all WANT things. The guids on #5 cylinder seem to wear out first for reasons possibly explained by it getting the least oil. Eagle cams claims the oil gally ni the head is too small.

You need to get a (DIESEL!) cmopression test. It's not the same as a gas compression test and not something you can do yourself.

Have them do a leak down test afterword and you'll then know what's going on.

Have you upgraded to the new style breather hose? That helps a bit, it's flat and not round.

While I haven't tied this, I would think the following would be a quick test to rule out the vacuum pump. Disconnect the vacuum line at the pump and block the opening going into the pump. If a vacuum leak somewhere is causing too much air to be drawn in by the pump, this will stop it. Then observe if there is a noticeable diff in gas coming from the crankcase.

Ok, Here is my 2 cents. With as new as I am to MB here it goes. With my 400E and it wiring harness issue I found 2 new reasons for high crankcase pressure not suggested.

1 - Iginition module faulty or plugs or wires maybe even wiring causing the variable timing not to be correct causing MASSIVE blow by while the car still runs smooth as a dream, but leaving puddles on the ground like you poured on all over.

2 - Also after years of hot then cold those poor soft rubber hoses are getting brittle and leaking, when that happens the whole system goes berserk and changes the timing causing the same issue once I figured everything else out.

I h> While I haven't tied this, I would think the following would be a quick

How does an ignition problem cause blowby? If that was possible, std compression testers would be useless.

What hoses? Unless these hodes are connected to the ignition advance, which I doubt in an 83 car, then hoses aren't going to change timing. And since when is timing related to blowby anyway?

Diesels don't have such issues.

As for vacuum leaks, I'm pretty sure those don't exist...

All locks and the HVAC system work excellent. There is no engine oil in any vacuum lines either. I disconnected the main supply line near the fuel filter (where the vacuum line changes from steel to the black plastic). Then I plugged that line on the vacuum pump side. This doesn't seem to help.

Is it possible that a vacuum leak is occuring around the pump itself? Maybe a bad gasket?

I just can't imagine that this engine has that amount of blow-by due to bad rings, but starts/runs so well? It doesn't seem that this engine would run very well with poor compression?

Thanks T.G. Lambach

T.G. Lambach wrote:

Hi Richard,

I checked the turbo oil return line and it is okay... However, the oil is coming from the filter housing. A small hole (I assume it is a drain) in the filter housing allows the oil to drain and drip all over.

I am thinking that I need to disassemble the blow-by oil separator/ vaporizor / breather (or whatever you call it... The part that sends oil back to the crankcase and vapors into the turbo's intake). Then I plan to bond it together with some good sealant. I'm thinking this might stop the oily mess inside the filter housing?

The breather hose is the flat rubber one.

I have done compression tests on CAT diesels and GM diesels by pulling injectors and applying the high pressure valve. (No vacuum pump questions on those since the CAT doesn't need one and the GM had a belt driven one.) The car seems to run too well for compression problems though??

I think it is a deep 27mm socket for MB diesel injectors?? I need to find someone in DFW area to do this for me.

Richard Sext> > >My 83 300D Turbo diesel has a high crank case pressure. There is a lot

it can if 4 cylinders are dead on but #5 is weak. #5 seems to go first because less oil gets back there than the other 4 cyls. It's not uncommon.

The only way to really KNOW if there's a vacuum leak is with a vacuum pump - pull a vacuum and see if it holds - locked, unlocked, climate control various selections to test the duct motors.

You feel the locks and climate control work well - they're on the small "comfort circuit" that connects to the vacuum pump and can easily be disconnected for a trial. Don't overlook the vacuum reservoir. The fuel flap and trunk lock are part of comfort system.

Then there's the vacuum brake booster - a lot of miles on it.

As to the engine, only a compression test done with known adjusted valves: i.e. You KNOW affirmatively when the valves were last adjusted or the compression test is just wasted energy - a valve could be leaking and you believe it's the piston rings.

But be sure about the vacuum being OK before getting into the engine's compression.

Someone else had this problem about six months ago and found a broken vacuum line was the cause - his may have been the one to the transmission.

Bingo. If you have one of these cars you need a vacuum tester, Look, I'm the chespest person I know (uh, next to my dad) but even I bought one.

Don't get the plastic one, get the metal one, the platic ones won't last long at all. I foudn that out and then had to buy another (metal) one.

Reasons why you need one. For him:

It's a cool tool you need to make sure the the lock dohicky thingies go up and down properly. Good for etsting brake and tranny circuits too.

For her:

This is an expensive precision automobile that may save your life if god forbid we're ever in an accident. It needs cimoplicated and expensive tools to keep it calibrated and in perfect condition to save your life should it need to. This tool is usually close to a thousand dollars if you were to get the proper German ones made and blessed by the Gnomes of Zurich. Bit I got this for under $100.

Ectually most eevry Mercedes has vacuum circuits so you all need one. Unless your neighbor has one

Thanks for your patience on my questions!

I capped the pump itself... That cut out all of the vacuum circuitry on the car; hence any leaks. Still pressure from the crankcase...

I have adjusted valves on these before and I think that is my first step here. It seems possible that a valve that never completely closes could cause a positive crankcase pressure? Valve seals surely are not designed to seal out a diesel's compression, are they?

Maybe I should start by adjusting the valves since I have ruled out vacuum leaks by capping at the source?

Thanks again for your insight.

Craig

T.G. Lambach wrote:

If by "capping the vacuum pump" you also capped the main line to the brake booster and still had a lot of blowby then, its time for the valve adjustment and compression test that will confirm the need for an overhaul. (You see why I stress investigating the vacuum side of this.)

High mileage (worn) engines show symptoms:

1. lube oil use;
2. hard starting;
3. less power.

The valve guides are worn along with everything else but their plastic seals are there to keep the lube oil from getting into the manifolds not the gases into the valve box. Forget them.

An unadjusted valve allows compression to seep into the intake or exhaust manifold so lost compression is the consequence, not blowby.

In my experience 275K +/- 25K is about the useful life of an average maintained diesel so it may be time to assess the car for further investment or just drive it until #2 and #3 arise for it won't suddenly quit, just get worse.

617.950 Specifications:

Normal Compression: 319 - 348 psi Lowest Compression: approximately 218 psi Maximum Variation between cylinders: 44 psi

Thanks Guys... You all have been a great help!

Guess I'm going to adjust valves and have the compression checked to see if car is worth keeping.

Maybe I'll do the same with the 300SDL that I have (minus the adjusting valves part :)

T.G. Lambach wrote:

The deal is these engines are not magic. They are only 5 cylinders, anything over 100K miles will have blow by gases. If Mercedes made a v8 diesel it would last longer. I seriously doubt anything is really wrong with you engine other then the rings and cylinder bores and pistons being worn. Diesel use high compression so when these leak, you get major blow-by gases. An oil additive and or thicker oil may help if your climate is not too cold. I remember my 300d turbo had so much blow-by, it was starting to shut off the fuel fuel pump when I was going up mountain roads - due to high crankcase pressure! The vacuum shut off must be designed to shut off with high crankcase pressure as well as vacuum when key turned off. Subscribe to my Benzproducts channel on youtube. Also, if you have bad blow-by, the engine will start to run hot and overheat in hot weather since so much super hot exhaust is being pumped into crankcase!