2.5 N/A blow-by, smoke - how much is normal

[TheHarv]

OK chaps as posted elsewhere my 2.5 N/A has always been smokey (whiteish) on cold starts, usually stumbles a bit and each miss is accompanied by a distinct puff of (?) unburned fuel:

I have already adjusted the pump timing to spec and had the injectors professionally re-conned and tested and I run RedLine cetane boost and the freshest fuel in town. One warmed up it idles clear.

More recently I noticed quite strong blow-by out of the filler / breather that ends with wispy steam (?) after shutting the engine off:

Tentative diagnosis is headgasket - pressurizing the cooling system / burning coolant, stumbles when cold are due to low compression in one or more cylinders where the gasket is blowing through. Coolant level has certainly dropped but I haven't really been monitoring it.

I have all the bits to do the h/g but just wondering before I dive in whether I'm jumping the gun

- could be normal for these engines (it's a later ex-mil N/A, with the turbo oil return etc, supposedly ABRO re-built in '98)

- could be rings not h/g (I'm seeing some blow-by out of the dipstick tube too)

Would the panel

(a ) leave it and see if it gets any worse

(b ) get a leakdown test and proceed from there

(c ) do it anyway

Bear in mind if I don't do it in the next week or two it will likely be below freezing here right through till April

[pete3000]

The first vid is fairly normal until 2.5NAD's have "warmed up" 10-15mins. The second most definitely isn't you have loads of positive pressure in the valve cover indicating something wrong. I would guess as you say either a head gasket or a ring.

get a compression test done. Someone will be along in a bit who knows more than me, but I can say that is not normal for an ex-mil 2.5d having owned one. I would put money on a head gasket though as the engine does not sound as if it is running irregular on two or three cylinders, can't say for sure though as the sound is not great.

Pete

[Springertastic]

Very interested to see how you get on with this.

Watched your startup video and the smoke in the engine bay.

Myne occationaly puffs from the engine bay but not yet wacthed were from. Its a lumpy startup with a fair bit of white smoke.

Give it a hard rev it runs smooth. Then whilst warming up stutters and puffs when it does this.

Good luck with it anyways ill be watching.

Cheers

[110_USA]

I'm also very interested in this. I have the same questions. Mine is also a Ex-mil.

The start up looks normal, although I usually just have one brief puff of black, occasionally I have what you do.

Have only observed the blow by with the filter removed but I'll disconnect the hose and see if I can't get a video; guessing, I would say you have about 50% more than I.

[jamesmyl110]

Startup up vid is not unusual for 2.5NA, as you say the white puffs are unburnt fuel as when cold the fuel doesnt readily atomise due to the non direct injection design and relatively low compression ratio (for a diesel).

As for the increased crankcase pressure, this would indicate worn rings as you say, I have rebuilt these engines and in my experience a fair bit of crankcase pressure is normal. From the vid I dont think its the head gasket as you would have noticed other symptoms such as loss of coolant or increased pressure in the cooling system, the steam is usually condensation in the crankcase vapourising or oil mist. To be sure I would carry out a compression test and cooling system pressure test, as long as the cylinder pressures are roughly the same I would leave it but if 1 or more are significantly down I would think about doing something. If the cooling system fails a pressure test (10psi for 10-15mins) then its time to look for a fault, possibly the head gasket.

I also have experience of engines rebuilt for ABRO (not by ABRO) and would say it doesnt guarantee a 100% healthy motor!!

[TheHarv]

Thanks I will see if I can get a compression / leakdown test done - at least for the record

I'm sort of treating this engine as a learning tool - got a Mercedes OM617 (5cyl turbo) sitting in the back of the garage that I hope to get in there next year (once I can find a transmission adapter for it...)

If the compression points to general wear like you say I will probably try to nurse it through the winter and have a go at rebuilding it myself once it's out

FWIW I've heard others say the same thing about ABRO rebuilds

[Lars L]

An easy way to check the headgasket is to start the engine with the valve cover off. At least it was on my 200Tdi. A distinct spray of oil emerged from the rearmost pushrod hole and landed everywhere around. Me included.

[TheHarv]

hmm... sounds like a novel way to rustproof the engine bay...

[TheHarv]

UPDATE: (finally warm enough to be wrenching again)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Did a compression test a couple of weeks ago and confirmed two adjacent low cylinders (550 / 410 / 400 / 580 psi)

Based on that I was expecting the headgasket to be blown between the middle cylinders. However I managed to pick up a Milton leakdown tester on the cheap so in the interests of science and not being as brave as Lars I decided to see if they are as useful as they are cracked up to be. After a whole morning buggering around with fittings (the leakdown tester only had a spark plug adapter - the comp tester has glowplug adapters but of course neither the quick releases nor the thread were compatible) - I got set up.

Next problem was finding / keeping TDC. I ended up with the following procedure:

1. out of gear, tester plugged into the glowplug hole but disconnected from the tester, turn crank by hand to where you think the cylinder under test is at TDC (it helps to know the firing order so you can watch the 'next' cylinder's inlet valve)

2. in gear, handbrake on, diff locked

3. connect tester

Nevertheless seemed always to be a little off TDC so the engine turned a few degrees one way or the other when the air was connected, even with the compressor regulator turned down to 50psi. I guess it doesn't matter provided the valves remain fully closed.

Leakage results were 13% - 27% - 28% - 10% at 50psi on the compressor reg and engine (very) cold

Here's where the fun starts. I could hear the air coming out but couldn't find where! No air felt at ANY of the inlet / exhaust ports (neither the cylinder under test nor the adjacent cylinder) and nothing at the dipstick tube either. It sounded like it was coming right out of the top of the valvetrain so I started poking a finger around and listening for a change in tone. It appeared to be from the inlet valve pushrods of the respective bad cylinders. So off with the head and...