9-5 NG Rescue project

[carrera]

Ok, so I realise i can't do a 3 year engineering degree in 30 minutes 

I looked at this https://engineerexcel.com/venturi-meter-and-orifice-meter-difference/ and considering your note above it seems I should look at putting some sort of taper on the underside of the aluminium component to reduce turbulence & effect on flow

With walls of 1.5mm I was also thinking of thinning those out, but then decided I didn't really have the right equipment

On other engines, I am used to there being an excess of capacity, such that the relief valve operates when the engine is cold and revs are moderate. As the oil heats up and becomes less viscous, the relief valve drops out of the equation and low pressure on hot idle is your early warning sign

Indeed, I did an engine once after a long drive at high engine speeds. Somebody pulled out which resulted in a need to drop speed, as soon as the revs came off one of the big ends started to knock & run the bearing. I had to pull over, let it cool down and then drove very modestly to get home

I too hope that the original design does have a bit of a safety factor. Todays engineers are often focussed on value engineering though. Interesting comment on the pickup though 

I think I'll go for it, and see how it goes. After all, removing the sump isn't such a difficult or expensive job 

[sgould]

What you are really looking at is total head loss along the length of the pipe.  A short length of slightly reduced diameter is unlikely to generate a major head loss. 

You could look at the strainer as a lot of small orifices, then allow for a few to get blocked.  The head loss there could be the significant point.  In fact, if you think about it, it may be a slightly blocked strainer that increases the pressure drop in the following length of pipe towards the pump which is the reason the joint that you are replacing sucks air.

The comment you found about not using the Polish part as it reduces the diameter doesn't give any evidence that it actually causes a problem.  It sounds to me like it's been made by someone who doesn't understand fluid flow.

[carrera]

The comment you found about not using the Polish part as it reduces the diameter doesn't give any evidence that it actually causes a problem.  It sounds to me like it's been made by someone who doesn't understand fluid flow.

All the above understood & agreed

On the specific point, I'm sure that person doesn't understand fluid flow. But then there's another post about Frank from MB Motors in Keighley. Seems to have a good reputation, lots of people go to him to have this job done, from a long way away. He won't fit the modified part because at high speed, commented 80-90 mph = ~3000 rpm they do restrict oil flow. Same thread linked earlier, post number 38.

So, does he have the experience to know this, or, given that he will likely end up on the warranty hook if there is a failure, why would he take the risk ?

I don't feel as though I have enough information to attempt any proper calculations & am having a proper argument with myself this morning 

[sgould]

The comment about Frank might be valid, but I’m not sure how he has measured the flow.  Or whether any failures are actually due to the Polish part.

I have never seen the insides of a GM diesel engine, so my suggestions may be wrong.  I’ve only just realised that your picture shows the pick-up pipe lying unfastened in the sump.  Is the seal just a squidgy bit of rubber pushed into the pick-up pipe?  Or is there a spigot on the pick-up that goes into bottom of the engine with the seal around it?

We used to analyse head (pressure) loss in a pipe using diameter and velocity only.  There is a table I have somewhere that converted head loss at step changes in diameter into “effective length of pipe”.  The effective length was measured in pipe diameters.

[sgould]

I’ve had another look at the pictures and it seems that the pick-up is fastened to the engine block with a bolted flange that is very similar to the way a carburettor is fixed.  Why isn’t a flat gasket used instead of an O ring type thing?  Would the best answer be to fit a new standard ring and put a very thin gasket on the flange?  Or just a wipe of Loctite anaerobic sealant?

[carrera]

Maybe this will help

https://www.ebay.co.uk/itm/285603835464?

The pick up pipe, which is a plastic assembly, is bolted to the sump in 3 places, two at the top and below the baffle. Those bolts are just for securing the position of the pipe.

The OE part (black bit) is a push fit onto the oil pump, the serrated bit reduces distortion as it pushed onto the outside of the gallery. The red bit is just for protection

The seal compresses against the flat plate, making an airtight seal, when new.

Then there's this suggestion to coat the  base of the OE seal in RTV to provide both bonding and chemical protection against future deterioration (point 2)

https://insignia-drivers.uk/forum/insignia-ownership-technical-workshop/engine-drive-train-transmission/362123-a20dtr-biturbo-tuning-guide-260ps-517nm-my-experience-with-dyno-print

Now I have the sump stripped the above post makes more sense to me than it did when I read it "cold"

Same as ZD19 / B207 apparently ?

[carrera]

I'm not with the car, so can't take pictures, but the listing for the Polish seller has good pictures, numbers 2 & 8 are perhaps the best

[sgould]

Yes, "gluing" in the sealing ring would make sense.

A couple of further thoughts...

Is the problem of air ingress into suction pickup pipe allowing it to drain down and empty?  Or is it that the air through the seal is allowing air ingress for the pump to suck air? 


If it's air entering to allow the pipe to drain down, it would only drain down to the level of the oil in the sumo, so maybe not much in practice. But is it this that's allowing the air in?  Could it be a poorly seating pressure relief valve?  This could allow the system to drain down and empty the pump itself, which would be more serious.  In addition, could the same thing happen if there is a non-return valve in the oil filter?  On the old cars there was a cheap "paper" flap to stop the oil filter emptying.

If the air through the seal allows the pump to suck air, why would it not continue and leave the oil "unsucked up".

Maybe the hardening of the seal has been blamed in the past in error?

[carrera]

From the earlier link https://www.alderleyautos.co.uk/blog/a20dth-engine/

The seal at the bottom where the oil pickup is starts to harden and then lets the oil drain back into the sump causing oil starvation and in the end, a goosed engine.

The seal goes hard, air is then sucked in which then causes oil starvation.

The first noticeable thing you’ll see is an “Oil Pressure Low – Stop Engine” error message every morning or when the car has been sat.

My way of thinking about this is that the tube, from the oil pump, which is above the sump just like on an OG, is effectively like a straw which was put vertically in water, with a finger over the end before the straw is withdrawn from the glass. The water stays in the straw due to air pressure on the bottom of the straw and a seal at the top. Remove the finger, air pressure is operating at both ends of the open column and so gravity takes over.

One the A20DTH engines etc, the oil pump is the finger and the poor seal allows the oil in the pick up tube to drain away, but very slowly as the warning light only starts to come on when cars have been left for 24 hours.

It has been suggested that as well as age, failed DPF regens allow diesel to enter the sump and the diesel attacks the seal in a way that engine oil does not and causes it to become hard

The lower sealing ring on the old one is definitely less flexible than the new one

Does that make sense ?

I am now with the engine... and have all options available. £17.50 from Vauxhall dealer, £43 from ex Saab dealer, £10 delivered from Neos. You can see just how much the lower part of the seal is deflected upon fitting. The red bit is the special tool for fitting, placed just above the feed tube

[sgould]

Looking at the options side by side, it does look as if the metal one is a bit thicker than it needs to be, but the idea is sound.

I think I would go for the new seal, bought from a reputable source, and add some sealant to fix it.  As long as the sealant doesn't degrade it.  If it does harden and let in air, it looks as if the air can only get in between the flange faces.  If so, and the sealing ring seals radially, and not by crushing, some sealant on the flange faces would work as the seal won't be relying on an absolute face to face touching.

[carrera]

I'm having a coffee break

That's the same conclusion I arrived at. Ironically, the GM genuine part from a Vauxhall main dealer was also made in Poland. The seal does operate by radial deflection. 

I'm on my second sump fitting. The hard to access screw that secures the air separator connection went walkies when I was trying to fit it. It took me a while, but I finally figured out it had gone down the PCV hole into the sump    So remove, clean flange, replace making sure the two smaller Torx at the gearbox end don't fall out into the void in the bellhousing. There's a definite technique to making this job easy, Frank from MB Motors probably just whistles at the cars coming in by now.

From here-on in, it's just basic mechanical reassembly. Best remember to put some oil in

Thanks 

[sgould]

Good luck!

[carrera]

We have a runner !

My plan was to crank the engine a couple of turns to prime the pump, before going for a start.... but with push button start you don't really have that option.

Anyway, she started, the oil pressure red warning light didn't seem to appear and the important "Low Oil Pressure" dash warning didn't come on either, so I think that's that job done.

No leaks from the sump that I can see either. Ultimate test will be when I start her up again at the end of the week

[sgould]

That's great!

[TomPaine]

Excellent - been following this with interest (and hope).