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Pressure in crankcase 300TDi


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So I have pressure in my 300TDi crankcase, done a pressure test and getting 400-450psi on all the pistons with a warm engine. So changed the head gasket (didn't have the head pressure tested or skimmed though) however there's still pressure in the crank case. This would make me think piston rings but as it's getting pretty even pressure across all the pistons I'm at a loss... any ideas before I send it all away to get sorted?

Cheers

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It's not blowing oil up the dipstick tube but you can feel it with your hand over the oil filler. I cleaned the cyclone a few months ago but will check it again.

I left the cyclone breather pipe disconnected at the air filter end after doing the head gasket and it blew oil up my windscreen. 

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That sounds pretty normal to me, at least the bit about the oil cap.

Without understanding the aerodynamics of the cyclone breather and the passage of air around it it would be hard to make comments on it.

Any engine will have some blow by, it is the nature of the beast, and 4 pistons going up and down at a high rate of knots is going to create a load of turbulence.

I suspect you may be looking at something and worrying unnecessarily.

 

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If I unscrew the filler cap on my 300 tdi with the engine running, it stays in place on the rocker cover "fluttering". If I was to put my hand over the filler I would feel some pulsing or pressure. I would call this normal.

If when you remove the filler it nearly takes your head off and rolls in to the corner of the garage you have a problem.

Are there any other signs such as blue smoke, using a lot of oil ( other than leaks! ) etc.?

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I would say the cap kind of flutters. Sometimes higher than other times, but no flying away. I had the piston rings go on an another engine before and oil was coming out of the dipstick tube but that isn't happening (yet) with this engine. 

It smoked really badly when pulling away but it was more black smoke than blue smoke. And when doing the head I had a slightly bent pushrod so done the belt and replaced the rods but haven't taken it out a drive since so can't really comment. 

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Well it is a diesel, it WILL smoke black when you hoof it. If it goes very well then sounds like someone has been playing with the pump, which will result in even more black smoke. For a diesel (actually and a petrol), black smoke is just unburnt fuel presenting a rich mixture, but it is very normal to have it coming out the tail pipe. Blue is oil, white is either unignited fuel or water vapour from combustion or the cooling system(!)

Why did you change the head gasket? Seems those results aren't exactly terrible to me, though finding specific figures for the 300TDI is proving tricky. What does it test as now?

 

 

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The smoking seemed excessive compared to other 300TDi's that I've driven. Fuel pump is still standard, it's a reconditioned one and I haven't done anything to it (yet...)

Asked a mechanic friend who took a look and said it could be that the gasket has gone between a oil way and exhaust. There were signs of oil leaking in the gasket. I will need to borrow the tester again and will get back to you with figures. 

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So there's every potential I'm being an idiot. But I've taken the cyclone off, started her up and there's some blowing from where the cyclone should be as expected. However when I increase the revs the blowing becomes less? 

Thoughts?

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By way of reference for you 

On my 200 Tdi, when I removed the pipe from the cyclonic separator to the air filter box and routed it into a catch can (seemed like a good idea at the time to reduce air filter Oil contamination) I observed oil expulsion from the the cyclonic separator o ring, from the dip stick tube and through the front crankshaft oil seal. All these leaks stopped once the pipe was replaced.

I think that the Tdi crankcase is positively ventilated via the air box/inlet tract and without this ventilation one can perceive excess crankcase pressure.

Without any of the above symptoms I don't think you are experiencing any pressure above what is normal for the engine.

HTH

Mo

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1 hour ago, soakes94 said:

So there's every potential I'm being an idiot. But I've taken the cyclone off, started her up and there's some blowing from where the cyclone should be as expected. However when I increase the revs the blowing becomes less? 

Thoughts?

What you are feeling is the frequency of the puffing becoming higher, so it is less perceptible, also as engine speed increases, blow-by doesn't necessarily increase.

It sounds to me your engine is in perfect health.

Oh, and other reasons for black smoke when hoofing it, is perished lines, blocked intercooler/hoses and various other things.

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  • 5 years later...

Some pressure is normal along with a light mist. However chuffing and/or a plume is not. Generally it's either a head gasket or rings. A compression check will confirm which piston then I'd pull the head off if the head gasket looks fine then it's probably rings.

Mike

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I believe also on 300s the vacuum pump exhausts into the crankcase ( mad idea in my opinion). So if you have a vacuum leak a lot of air will get pumped through. Quick check would be to take off the hose to the servo at the pump, fit a blank end instead to the pump and see if that altered the crank pressure - don't drive like that as the brakes would be very hard to push. 

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16 minutes ago, cackshifter said:

I believe also on 300s the vacuum pump exhausts into the crankcase ( mad idea in my opinion). So if you have a vacuum leak a lot of air will get pumped through. Quick check would be to take off the hose to the servo at the pump, fit a blank end instead to the pump and see if that altered the crank pressure - don't drive like that as the brakes would be very hard to push. 

All Tdis, and also the diesel 2.5 engines before them (12J, 19J and probably the Sherpa/Taxi 14J, 15J and 16J versions), which all have a rotary vacuum pump driven by the cam shaft where the distributor sits on the 2.25 and 2.5 petrol engines.

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