Oil pressure issues

[Mario765]

Hello all,

my D24TIC (engine from 1994) has developed some oil-related problems. It just surpassed 520000km (about 320k miles) so I don't know if it has reached the end of it's lifespan or if there is still hope.
Anyways, the problem I'm running into is low oil pressure and high oil consumption.

The oil consumtion has always been higher and is now at about 1,2l/1000km (600 miles), which I think is acceptable in itself, however, the thing smokes like a freshly-lit campfire, even at moderate throttle and especially on cold startup. This is getting embarrassing in parking lots and at work.

And perhaps more worrying is the fact that now, whenever the engine is warm, the oil pressure light comes on at idle and slightly above idle. Depending on engine temperature, it sometimes flashes or stays lit.

You can also hear the valvetrain getting much louder as it used to be when the engine is warm. Certainly not your normal diesel nailing.

What do you guys think? Could the issue be solved with thicker oil? (I'm currently running 10W40 Motul oil) Or is the engine simply too worn? Also, could the turbocharger be the colperate for the blue smoke, or are the piston rings/valve seals more likely to be defective?

I thought I'd ask here before I take any further steps, too see If it may not be worth the effort.

Btw: The engine is always maintained and has brand new glowplugs, overhauled injectors, new timing belt last year and doesn't leak a drop of oil towards the outside.

Thanks and greetings from Germany,
Mario

[ngoma]

The apparent low oil pressure is most concerning. Try fitting a temporary (or permanent!) real oil pressure gauge to give you a better idea of the actual pressure under various conditions. The warning lamp sensor, circuitry, or wiring might be sending erroneous signals.

Oil pump wear is not unheard of, probably the most probable suspect.

Running higher viscosity oil is worth a try, but not a complete solution to the underlying problem. Maybe also try overfilling (1L?).

High oil consumption would have us take a look at the oil control rings first, then maybe valve seals or turbo. How bad is the blowby? Have you checked the compression? Has the engine been overheated (could permanently relax the piston rings)? Has the engine repeatedly been run under high load before reaching operating temperature?

The fact that there are no external leaks would make me want to save this one for sure!

[jpliddy]

hello my 940 has done 296000 miles now been in my ownership for near 23 years
it has been using 1 litre of oil between 5000 mile services since i owned the car
its not been driven too hard by me, but im interested in how long these engines will last before major engine work as the costs may be to high to pay for them as im limited capability on that side i can do a lot of basic maintenance myself,
i have run the car on millers XFE 10 40 semi synthetic oil for 21 years and now been advised to use a 5 40fully synthetic oil millers which i now do, the engine may sound a little bit more noisy when hot i just hope it will last me out but who knows , the car has been a great servant i , i have no problems so far with oil pressure but that may be in the future. there is some very good advice on this web site these people know these engines inside out let us know how you progress!

[Mario765]

Thanks for the replies.

You're right about the oil pressure gauge, I have one on hand and will install it as soon as possible. I will also do a compression test next.

I avoid high load when the engine is cold, but since my place of work ist right next to the Autobahn I have to give it a little more throttle than I'd like to get up to speed. I think the engine should normally be able to handle that, tough.

But since the compression will most likely be less than Ideal, what you are saying is that I'm basically looking at a complete overhaul or at least engine-out of the car work.

I know that will get expensive if done right, so I'm thinking about putting another engine in that I have (D24+T).

But before I do that I'm going to try your overfilling tip and thicker oil, certainly worth it before pulling the engine.

[ngoma]

Compression test is just to get a general indication on the condition of the piston rings, to help pinpoint the cause of the oil consumption. My thinking was if low compression, we can deduce the oil control rings are also weak.

If that 's the case, not sure a complete overhaul is necessary. Might get by with new rings, possible cylinder rehone. Requires oil pan removal so engine out of car makes it more accessible.

The high mileage might be a factor, especially if the engine was run for a significant time on non-synthetic oil.

Does the engine start easily, at all temperatures? Sometimes a clue to poor ring sealing is hard starting when just warm enough to not call for glowplugs yet not hot enough for better ring sealing.

Turbo oil leak could be another factor but I lack experience with this, maybe someone else can share?

What is the blowby (how much smoke puffs out when removing the oil filler cap)?

Originally Posted by Mario765

I avoid high load when the engine is cold, but since my place of work ist right next to the Autobahn I have to give it a little more throttle than I'd like to get up to speed. I think the engine should normally be able to handle that, tough.

Be careful with that. We had a trashed D24T from a person that lived at the bottom of a long steep hill. Approx. 130,000 miles, solid maintenance record from a good shop, etc. but the engine died an early life from all the hard mornings.

[Mario765]

The blowby is above normal in comparison to my 760. When you pull the dipstick oil even splashes out.

I know that driving a cold D24 straight on the highway is far from ideal, but what can you do. I shift as fast as possible and only accelarate to 80km/h so about 2000-2100rpm in overdrive.

It always starts, just a little rough when dead cold. Sounds like its missing on one cylinder for a minute or two.

But the compression test should tell us more. If it's low, for example on cyl. no. 6, which is my guess because of the higher thermal stress, I'm going to swap the engine and set this one aside to live another day.

[ngoma]

It's great to have a spare ready for a hot swap!

[v8volvo]

All good points... I am a little concerned however by what sounds like a sudden change in how the engine is running and the apparently rapid onset of the oil pressure symptoms.

Faulty oil pressure switch is fairly common in these (switch will leak internally and cause misbehavior) but if you are in fact hearing noise from the valvetrain, that would suggest the oil pressure loss is real, and serious. Though agreed of course beneficial to verify with a mechanical gauge.

In addition to what has already been well covered I think you could give a little more attention to the turbo which you mentioned early on. That is one of the few things that I could imagine causing sudden increase in oil use and smoke coupled with a loss of oil pressure, if the turbo bearing and/or seals were failing. I think it is an outside chance since by now a more catastrophic turbo failure would probably have shown itself if there is indeed an issue there, but no reason to dismiss it until you are sure. Easy check would be remove the inlet pipe from the turbo cold side and see how much axial and radial play in the shaft, any signs of mechanical damage, etc. More effort but more information would be to disconnect the exhaust downpipe from the turbo hot side outlet and look for evidence of wet oil, etc.

Otherwise it is hard to think of much that would cause sudden development of your symptoms (at least not in an otherwise well-maintained engine that has not recently been run dry of oil or overheated or suffered some other disaster). Things like worn main and rod bearings happen very gradually over time and anyway are usually very robust in the D24 even to extreme high mileages, again short of some outside factor causing failure. Oil pump wear is something we have seen cases of, but usually that is observed as difficulty building oil pressure after a cold start. Hot idle oil pressure problems are less familiar, though of course possible. Again though, it is just hard to see what would take an engine with 320k miles that may have some wear but is basically in stable condition, in consistent use, and being obviously carefully looked after by you; and suddenly put it on a fast decline.

Thus why a turbo failure could make a little more sense.... Otherwise, maybe some debris passed thru the oil pump and damaged it suddenly? Or oil pump inlet tube loosened up or cracked and it's sucking some air resulting in reduced pressure? But none of those would explain the increased consumption, unless multiple problems were worsening at the same time simply due to age and general wear. I suppose that is not out of the question in an engine that has lived a long life and had unknown care prior to your ownership.

One final idea would be to take a sample of crankcase oil (assuming it has not been too recently changed to show anything) and send it in for laboratory analysis. Not sure if those are readily available in your area but there are several that offer the service by mail here in the US and it is not expensive. If something in the engine is failing or abnormally wearing, the analysis may be able to highlight it. Different types of excessive metal present in the oil can point to specific problem areas, e.g. chrome for piston rings, aluminum for pistons, iron for cylinder walls, tin or lead (iirc?) for bearings, brass (??) for turbo shaft bushing...... excess silicon for a failed air filter letting in dust and tearing up the internals.... excess glycol % pointing to failed oil cooler or headgasket.... etc. Kind of like a blood draw for the engine.

[Mario765]

I don't know if anyone will read this, since it's been a long while, but I thought I'd give an update anyways.

The engine lost all oil pressure on the autobahn with a trailer. Rodnock.

So I changed it out with a known good engine and overhauled the whole drivetrain while I was at it. Completely new front Suspension, full service, different rear axle, different gearbox. Has been running great since two months.

I did a compression test after the fact and it was awful, as i predicted. Below 20 bar on cylinders 5&6, not much more on the others.

I put the broken engine away and will eventually pick up on it, tough i suspect the crank can no longer be used because of the broken rod bearing.

So i unfortunately destroyed another D24 but gave another one new life and the car lives on.

Greetings,
Mario