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Print Page - Low oil pressure... what causes it? 450SE

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Garage => Mechanicals => Topic started by: 13B on 08 March 2008, 07:42 PM

Title: Low oil pressure... what causes it? 450SE
Post by: 13B on 08 March 2008, 07:42 PM
Finally have the team car running on all 8-cylinders and got to take it for a but of a drive.  Goes pretty well I must say, gearbox is tight, diff is silent, brakes and steering work well (steering slightly groany but the fluid is low).

Trouble is that oil pressure is reading low...  I'm after some ideas.

Cold start it rises rapidly to 2.5 or 3bar but comes down fairly rapidly.

Fully warmed up and at an idle speed of 750rpm the reading is 0.5bar

Driving normaly fully warmed up it doesn't read past 1.5bar

Since I didn't know if I was doing engine damage I didn't take it on the freeway to test how the car runs at 100-120km/hr (all indications are that it will be happy).

Do you reckon it might be just the OEL guage is buggered?

Here's a video of it (not) in action: http://www.youtube.com/watch?v=Yd7JjuGSpqQ (http://www.youtube.com/watch?v=Yd7JjuGSpqQ)

I.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: carl888 on 08 March 2008, 09:54 PM
Sounds like the gauge Ian, if only because if you had 1.5 bar whilst driving, the engine would have lunched itself by now  ???

Regards,

Carl.


Title: Re: Low oil pressure... what causes it? 450SE
Post by: oscar on 09 March 2008, 12:29 AM
Vroom vroooom geez even without oel pressure that exhaust sounds cool ;D 8)  Wish I had a sub woofer connected to this work computer ;D

That gauge does seem screwey especially the way it jumped up by itself during the idle after it intially pressurised.  Also the way it didn't respond to the RPM.  For piece of mind, take your oil cap off during warm idle, check to see if there's a nice stream of oil coming from the oiler tube on to the cam shaft.

From what I remember of others asking and comparing about oel gauge operation, the needle should move similarly to your 6.9. ie Shoot up to 3 on a cold start and then drop to around 1.5-2 when the oil has warmed and at idle.  The pressure goes right back up to 3 again when the revs move up from idle.

So why is the gauge not working?  I reckon the line's full of sludge.  I don't know but as a guess I reckon a good start apart from checking for leaks is to disconnect the line and flush it.  Perhaps undo it near the gauge, place a container under the end and start the enigne.  Observe the oil coming out.  It dribbled out of mine at idle.  Not a powerful squirt or anything like that but it was free flowing. 

Didn't have a problem with my gauge, I just thought it would be a good idea for fresh oil in there after accidentally discovering one day that oil does come out of that line and onto carpets when the engine is running ::)  So next oil change I purged the line.  No lumps as such but it was black as.  I wonder if thinners or petrol should be squirted into the guage side as well.  I didn't bother with that but perhaps should've.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 09 March 2008, 01:57 AM
Thanks Oscar,

Had a look down the oil filler while the engine was running and the cam is being nicely sprayed with oil.  The engine appears to be overfilled, the level about 1-1.5" higher than the high mark on the dipstick.  The oil appears clean and doesn't smell too fuelly.

Probably best to remove the oil line and give it a good clean out.  Can you tell me where it connects to on the engine?  (I bet its some impossible-to-reach place.)

 From any of your wrecks do you have a Petrol/Temp/Oel guage spare?

Ian.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: torana68 on 09 March 2008, 04:27 AM
rear of the head left side I think, or you could pull the instruments and disconnect the pipe and run some hose over it to a bucket outside? try using much thicker oil if your going to flog it.
Roger
Title: Re: Low oil pressure... what causes it? 450SE
Post by: oscar on 09 March 2008, 04:36 AM
Yeah I'll get a gauge for you tomorrow.

The oil line - what roger says, see pic, right above the engine number.  Surprisingly, not that hard to get to, for a change. ;D  I haven't undone mine as all I did was let the engine pump the oil through.  But I reckon in your case, pumping WD40 or similar through the line would be a good idea.  Also, before you reattach i reckon you might have to let the engine pump oil through again to a) wash out whatever solvent you clean out the line with and b) prime the line so no air is inside it.  Just a guess.

Click for a bigger pic.

(http://img139.imageshack.us/img139/6995/oilpressurelinema1.th.jpg) (http://img139.imageshack.us/my.php?image=oilpressurelinema1.jpg)
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 10 March 2008, 12:55 AM
Disconnected the hose at the instrument cluster and ran the engine for a few mins... black drops with no pressure to speak of...

Will disconnect it from the engine soon and try to clean it out.  Maybe the guage is OK...

Hot day today - didn't do much else.  Could something inside the left cylinder bank bleed off the oil pressure so that what is being pushed thru the oil-pressure adaptor is bugger-all?  I guess I need to take off the LH cam cover and look for signs of oil starvation?

Ian.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 15 March 2008, 02:22 AM
Finally got some sensible readings from the OEL gauge after disconnecting it, flushing it out with carb cleaner and compressed air, and re-assembling.

With a hose fitted to the back of the engine into a measuring cup it takes a couple of minutes on fast idle to fill a 500ml vessel.  The restrition in the fitting is very small, maybe 0.5mm to limit pressure coming into the cabin instrument cluster. 

Reconnected the original hose to the engine and observed oil coming out not in a stream but a series of timed drops, maybe 2 per second at fast idle.  This makes sense as you wouldn't want 60+ PSI oil pressure at the oil pressure gauge.

Reconnected the oil pressure guage and started the engine, oil pressure shot straight up to 3bar, and settled down to 1bar with the engine fully warm and sitting in Drive at about 700rpm.  It responds as it should when I step on the accelerator however doesn't respond as quickly as the OEL meter on my 6.9

Maybe someone who owns both a 450 and a 6.9 can tell me whether the oil pressure on the smaller engine is just lazier than that of the big block.

Tomorrow: remove cam covers for a look-see and then a freeway drive at 100-120km/hr

Ian.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 23 March 2008, 03:38 AM
Looking under the car today I noticed the sump is bent - pushed upwards somewhat.

I reckon this will have some impact in the ability of the oil pump to pick up the oil, esp. if the pickup is partly obscured.

What do you think?

I.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: s class on 23 March 2008, 04:00 AM
Where is the dent - at the front?

On my 280SE I once had a heavy landing on a dirt road that smashed up the sump guard about 2 inches, and the sump about one inch.  It smashed up the rubber puck-up bung on the bottom of the oil pump feeder (it is rubber but age and heat had made it hard and brittle)  This bung thing houses a mesh as well.  The base of the rubber has 4 'legs' that normally sit on the oil pan, and oil is drawn in through the spaces between the legs, then through the mesh and into the pump.  I guess if your pan is bashed in, it could have compressed the rubber legs of the pickup and obscured the apertures between them. 
Title: Re: Low oil pressure... what causes it? 450SE
Post by: TJ 450 on 23 March 2008, 06:35 AM
I had a bent sump and a piece of broken timing chain guide ended up wedged it the pickup too, potentially resisting the flow... something to look out for, particularly on an m117. Yes, the castellated rubber insert is very easily rearranged if the sump is bent. 
Tim
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 24 March 2008, 02:29 AM
This is the bent sump.  Due to the angle the photo was taken at it doesn't look bad but I'd say its bent somewhere between a 0.5" and an 1".  I can't see how it was done but maybe some doofus P.O. put a jack under it to lift the car??

Anyway, do you think this would cause a restriction in the oil pickup ability of the oil pump?  Heaven knows what else is damaged in the engine in that case.


(http://ianmav.customer.netspace.net.au/mercedes_b/Sump-small.jpg)

While we're at it, what tool do I need to remove the sump plug thanks...

Ian.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: oscar on 26 March 2008, 12:47 AM
Anyway, do you think this would cause a restriction in the oil pickup ability of the oil pump? 

While we're at it, what tool do I need to remove the sump plug thanks...

Hi Ian,

My sump used to be a concave shape too after a life on dirt roads and deep ruts.  It was bashed flat again by my mechanic a few years ago without my asking and he said that it would affect the pick up of oil to the pump if I left it like that.  I didn't really take notice of before and after oil gauge response but I'm glad it now looks normal and takes the right capacity.  It looked worse than yours though.

Sump drain plug is a 14mm hex socket like below.  I use this impact type, a bit of overkill but it works.

(http://img151.imageshack.us/img151/8061/03262008267smalljz5.th.jpg) (http://img151.imageshack.us/my.php?image=03262008267smalljz5.jpg)
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 31 March 2008, 05:40 PM
Now that its running on all 8 cylinders and EFI woes seem to have been whipped into a drivable state I've taken the beastie for a decent drive for 25min.

Good points:

Accelerates well
Doesn't overheat
nice idle at 800rpm in drive
1.0bar oel pressure at idle
Revs out
Drives nice manually shifting up and down thru the 3 gears
Long drive burns most of the crap out of the cylinders/exhaust - 1st couple of km were a little smokey

Bad points:

speedo doesn't work
2.5bar oel pressure at 70-80km/h - seems a bit low to me

Got a good used sump and oil pump lined up for later in the week, will give it the best chance of getting decent oil pressure in the engine.

2.5 bar equates to 36PSI at 70-80km hr.  Didn't get up to 100km/hr at any time but assuming 100 brings up 3bar (43.5PSI) does that sound like enough for the engine to survive?  I guess it must be as the PO would have driven it like this before selling it and the engine didn't self-destruct.

On the wankel engines I work on the oil pressure reg limits oil pessure to 71PSI - admittedly thats a long way from 43.5 PSI - but doesn anyone know what the upper regulated pressure limit is on an MB V8 engine?  I've done a search but have come up with no definitive answer.

I.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: koan on 31 March 2008, 07:54 PM

1.0bar oel pressure at idle

2.5bar oel pressure at 70-80km/h - seems a bit low to me

does that sound like enough for the engine to survive?
.

1 bar at hot idle is good - provided idle RPM is not too high. The manual says 0.3 bar is acceptable, it goes onto say minimum 3 bar at 3000 RPM.

The manual mentions a 5 bar relief valve "accessible upon opening of a closing plug in timing housing cover", maybe this valve is stuck open limiting oil pressure, it goes onto say "The pressure relief valve itself cannot disassembled".

As for the engine surviving, I'd say it would but I'd investigate further if the sump doesn't fix it.

koan
 

Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 31 March 2008, 10:38 PM
Thanks Koan ... appreciate your help as always...

Another idea I'm thinking if things don't improve is to attach my Autometer oil pressure 0-100PSI gauge and go for a drive.  Since the dash Oel pressure reads 3bar max, and in all likelihood will read 3bar at 100km/h.  with a full range oil pressure gauge I can rev the thing out under load and see what the actual pressure reached is.

Its highly likely the engine is loose as hell (sure sounds like it) but if in its new higher operating range (3500-6000rpm) it makes enough pressure to protect the engine.  60PSI+ at 6000rpm I would consider acceptable given the age of the engine.

 Will shoot a video shortly showing the improvements in oel pressure and engine smoothness I've made recently.  Sounds and drives like it should now..  suspect the PO misdiagnose the faulty MPS and adjusted every setting for everything know to man to try to compensate for it...

I.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: koan on 01 April 2008, 06:40 AM

If you have a gauge that can be connected up easily to verify the instrument cluster it would be worth doing.

I'm assuming The pressure reading you give are with fresh, clean oil, not diluted black stuff of unknown kms.

koan
Title: Re: Low oil pressure... what causes it? 450SE
Post by: s class on 01 April 2008, 09:26 AM
If I was you, I would still spend an hour and pull off that sump pan.  Well maybe another hour with degreaser first of all before starting removal of the pan.  ;)

It is worth it firstly to panel beat the sump, and second of all to verify that the oil pump pick-up gauze isn't clogged with crap.  I've seen them that way. 
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 12 April 2008, 01:22 AM
2 hrs work and 2 oil changes and I've got the oel pressure not reading pretty much correctly - as good as I reckon its going to be given that its a rattly old engine.... must adjust the tappets when I have a moment...

First oil change was to get out the black crap excuse for oil which stank of petrol dilution.  It was replaced with 5 litres of K-Mart's finest $9.99 crapola 25W-50 oil and a bottle of Nulon oil flushing agent.  As per instructions run for 20 min no load and drain and change filter.  The oil that came out, even though only in for 20 min, was black and full of crap.  I guess the nulon worked.

2nd oil change I've decided for the 1st time in my life to use a so called "high milage" oil which is supposed to be helpful with worn rings, worn valve guides and worn valve stem seals.  Pennzoil "High Milage Vehicle" 25W-60 was used and on the 30 min drive which included a bit of low speed traffic and higher speed freeway driving I can report that:

Idle oel pressure when fully warm is not less than 1.0bar
Oel pressure at 3000rpm is indeed 3.0bar or more
Normal driving at 60km/r shows an indicated Oel pressure of 2.5bar
Smoke on overun and prolonged idle due to valve stem seals has diminished
Oel pressure still doesn't fly up to 3.0bar the instant you hit the accelerator, but it is a linear increase at least...

The oil pan wasn't removed yet but it will have to be soon so I can install the sensor for my autometer oil temp gauge, at that point I'll just bash it flat and check the pickup on the oil pump, replace the gauze, etc. 

This thing is looking better all the time!

I.
Title: Re: Low oil pressure... what causes it? 450SE
Post by: oscar on 13 April 2008, 06:55 AM
Re the pan, I meant to post this pic last week before I went away but forgot, it's straight from the manual but it looks though the oil pick up is practically sitting on the pan.  If the pan is as bad as what you say, makes me wonder if the pick up tube is damaged as well.  Anway, it's all working now which is great.  If the oil pick up is the problem, I can't imagine it's going to get worse before you bash the pan flat.  Your still getting adequate pressure so that's good.

(http://img176.imageshack.us/img176/301/imgp4176largedi2.jpg) (http://imageshack.us)
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 13 April 2008, 04:28 PM
Thanks for that.  At least now I know what to expect when I take the sump off. 

Looks like a design which the oil pickup ability could be seriously compromised even if there was a 0.5" dent in the sump in the right place...

If you get to see the number of classic cars that I do (whether holden, ford, mazda, etc.) you know its almost impossible to find one still in daily use that doesn't have a dent in the sump...

Oscar, what are the items the diagram is referring to: A, 1 and 2 ?
Title: Re: Low oil pressure... what causes it? 450SE
Post by: oscar on 13 April 2008, 05:05 PM
"A" is supposed to measure 58.5 mm.  It doesn't list what 1 & 2 are unfortunately.  A lot of images get repeated in the manuals and sometimes a generic photo of a different model might be used to demonstrate a common part and I've found they often come without labels.  I'll have another look for the image later and fill you in if it gives up any more info.

This second shot is all I could find of the oil pick up.  It's on the next page and I dismissed it yesterday thinking it was a m110 until I looked closely just now.  But it is a m116/117 with the upper part of the oil sump removed as well.  Don't think you'll have to remove that much unless you want to dig around but again, no labels in the text for this pic unfortunatley.

(http://img74.imageshack.us/img74/9508/imgp4182largehd2.jpg) (http://imageshack.us)
Title: Re: Low oil pressure... what causes it? 450SE
Post by: 13B on 17 April 2008, 08:49 PM
Thanks Oscar... another question, for anyone who knows.... how does one remove and install the plastic roundy thing on the bottom of the oil pickup?  I was at a wreckers today removing a good used sump, and busted the roundy thing on the oil pickup trying to remove it..

So if anyone knows, please tell - how does it stay in there, and how do you remove it?

I.