Diesel Engines

[Lazy-Ferret]

I am on only my second Diesel vehicle in many years of driving (more than I care to remember). My first almost put me off of them for good...

Anyway, reading a few threads on here, and it seems like it is normal to be replacing head gaskets etc on diesel engines.

I realise they have a lot higher compression than a petrol engines, but in all the years of driving petrol cars, I have only ever had one head gasket go, and as nothing else seemed to be wrong and the mileage was fairly low, I considered it as a fault in the gasket, and replaced it with out any other work to the engine, and then went on to do a good many more miles trouble free. Normally though, a damaged head gasket is a symptom, rather than a cause of problems and bad news ensues.

As some of you may have read, our 2.7 Terrano has only done 97K, but looks to be suffering from bad crankcase pressurisation, from either blow by or a leaking head gasket.

If this was a petrol engine I would be thinking about changing the whole lump, but being Diesel I really do expect the lump to last a lot longer than just 97k, so the questions are...

How likely is it that the Head gasket has really gone, and if it has, what sort of other damage might it have done to the engine.

If it is not the Head gasket, would it be worth trying to change just the rings, or is it like petrol engines where if the rings have gone, the bores are worn and will need work as well.

How hard is the lump in one of these to replace, I have done several transverse engines in my younger days, but the last engine I took out was a little SJ, and that was easy. I do not have a work shop, so this would be being done on the front drive.

Any help gratefully received.

 

[solarman216]

Hi, first off a head gasket will not cause crankcase pressurisation, so if that is what you have then the rings or bores and or pistons are goofed, but what makes you say you have cc pressurisation in the first place? does it drink oil? it may be that it was overheated in the past and the rings are stuck in the pistons but if this was the case it will drink oil and be low on performance, Rick

 

[solarman216]

Oh and if you are thinking changing rings, the sump cannot be removed unless you drop the front diff and even then it is not easy as the oil pick up tube is in the way and not easy to remove with the sump in the way, Rick

 

[Lazy-Ferret]

Hi Rick, thanks for the reply, the reason I wondered about the head gasket is if it has blown through to an oil way, either up or down, but as I have not seen it in real life, this was just clutching at straws.

In answer to your question, it is drinking oil like you would not believe, we are using up to 4 litres in 400 miles. It stinks of burnt oil, and the air side of the turbo is always swimming in it, where it runs down from the oil trap / blow by valve into to the flexible air filter hose.

As I say, I have no experience on these or any other diesel engine, so am going on what I read on here plus logic to the best of my ability. I also have only driven this Terrano, so do not have anything to compare it with, to know if it is lacking power etc. It seems Ok though, and towed the caravan with no difficulty, and is happy batting along the motorway at the legal limit plus the odd bit of tolerance when needed.

What is weird is I have never seen the slightest puff of smoke from the exhaust, and there is never any drips on the driveway, just a horrible burnt oil smell as soon as you open the roof or windows. This is the bit I really do not understand, as it used 1/2 a litre the other day in 60 miles, which is a lot of oil, and I would have expected tonnes of smoke.

 

[makeitfit]

Not doubting Ricks words or experience at all but I have read about the Disco diesel engines blowing head gaskets across to the pushrod hole and thus pressurising cc. A long shot I agree :nenau
What about taking a pipe from the oil blow by and putting it into a temp catch tank like a tin can . Blank off the air/turbo intake hole that's left. Then do another drive and see if the oil loss is equated to the oil in the catch tank? It may reduce the burnt oil smell and your cost :lol

 

[solarman216]

If you are burning/using that much oil, a finger up the tail pipe will prove it, dry and black = normal, oily and black = oil going down the exhaust, and yes makeitfit you are correct, blow by into the push rod area is a possibility, I had forgotten that as I have no push rod holes, memory again but this in itself would not increase oil consumption unless it was pressurising enough to blow it out the breather and then he would be seeing it on his drive, it is either being burnt, or leaking on the floor unless it is filling his chassis up, Rick

 

[rayf3262]

but this in itself would not increase oil consumption unless it was pressurising enough to blow it out the breather and then he would be seeing it on his drive, it is either being burnt, or leaking on the floor unless it is filling his chassis up, Rick

If you can't find the expelled oil, then it most of it has been aiding the combustion process!