Oil consumption woes

[DavidBrough]

I have a 1969 280SL auto which was using rather a lot of oil, about 4 litres per 1,000 miles, I decided to replace the guides and seals. The engine is original and has covered 105,000 miles which I am fairly certain is correct. The work was duly completed and the engineering shop that fitted the guides and ground the valves said that the guides definitely needed replacing. Everything went back together OK with a new timing chain for good measure. A few teething problems were encountered getting the engine to run properly once back together but this was soon sorted and everything runs very smoothly and much better than before. However, it still drinks oil to the same degree as it did before I started. After the first 500 miles I re torqued the head re set the valve clearances and checked that the valve seals were all seated properly. It is quite difficult to see the seals through the springs but I thought if one or more had popped up it would be obvious but to my unpracticed eye all seemed OK with none obviously riding up the valve stem. The car has now covered about 1,000 since the rebuild with no change in oil consumption.

When the head was off I checked the pistons and bores and all looked well with no scoring or obvious lip at the top. The engine does not have any leaks that reach the garage floor so is there any other likely reason for the high oil consumption anyone is aware of or is it more likely that the valve seals are not seated properly and I just can’t see it. I do have a compressor and if necessary will obtain a tool to pressurise the cylinders but don’t want to do that if there may be some other avenue. Does anyone have any ideas as to what is most likely?

[Naj ✝︎]

Sorry, David.
Don't have any answers - interested to know what oil you use?

naj

65 230SL
68 280SL

[DavidBrough]

Hi Naj, Just basic 20/50 for pre 1980 cars from Halfords.

[RBurg]

David:  Let me tell you my story:
1971 28SL 103,000 miles - previous owners? Oil changes freq?
Use quart every 200 - 250 miles.
Values guides were done before I purchased GIGI (280SL) Compression check ok  with oil  and with out. Also did leak down test.We torn into the motor found 3 broken mail and rod bearings (in pecies) nicley polished down to the brass.
My mecchanic stated the due to lack of oil changes with SL's in upper midwest was because they were only drive  3-4 months a year and then put in storage. Oil changes were forgotten about. thus several thousand  miles were put on without a oil change.

The oil comsumpation started all of a sudden on a long drive. When I pulled in to fuel I found no oil on the stick - pour in 2 quart and did not see a mark - poured in 2 more and it still need another quart.
I did a totale rebuilt. Cost with head work $2800.00 pulled and re installed. Good Luck

Ron - Minnesota
71 280SL Tobacco "O GIGI"
97 E420 Silver Mist

[DavidBrough]

Hi Ron, I had rather been hoping that the answer wasn’t a full engine rebuild and had been contemplating having a cylinder leak test in the hope that this may be eliminated and then replacing the valve stem seals again. From your experience that may not tell me anything. What still puzzles me though is where does all the oil go. It must be burnt as it isn’t leaking out anywhere so how does it get into the cylinders if the valve stem seals, rings and bores are OK.

[Naj ✝︎]

David,
Have you checked the oil pressure? If the gage in the car remains pegged when hot, you may have to check with a higher scale gage.
Apparently, high oil pressure can cause oil consumption.
The oil pressure relief valve could be stuck or incorrectly set....
Just a thought...

naj

65 230SL
68 280SL

[DavidBrough]

Thanks Naj. My oil pressure is fairly good, always being on the stop above 1,000 rpm and normally down to 25/30 when hot or 20/25 after a very long hot run. As a result I felt that the crank etc should be fairly sound.

[Ben]

Definitely organise a leakdown test. Anything else is just wasting time IMO !

Good luck !

Regards,
Ben in Ireland.
'64 230SL 4sp.

[A Dalton]

You also may want to check the crankcase vent tube and fittings for possible blockage...............

[Benz Dr.]

Visual inspections are what they are. If you don't know what to look for you won't see it. This engine could have all kinds of bottom end problems yet appear to be OK by just looking at it.
 I can't see or feel a few thousands wear on a cylinder yet the wear is still there. Cylinders usually wear out of round which you also can't see. If you have the proper equipment and know how, then you can make meaningfull meaurements.

In other words, if the top end didn't fix the oil consumption problem, then it's very likely worn piston rings and cylinders, even if they look OK.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[ja17]

Hello David,
Try to find out where the oil is going and you will find the cause.

Oil usage due to bad rings will usually show up on the spark plugs. Oil passing the rings will enter the combustion chamber and be burned causing crusty deposites on the spark plugs eventually fouling them out. Compression may or may not be bad. Oil smoke may be visible at times. Read the spark plugs.

A worn or loose exhaust guide will allow oil to seep into the exhaust ports in the head and then be blown into and burnt in the exhaust system, never entering the combustion chamber. The spark plugs stay clean, but you use oil and may notice various degrees of oil smoke. Compression will usually stay good until extreme wear occures and allows the valve to loose its seal.

A worn or loose intake guide will suck oil into the combustion chambers and will also show up as crusty oil deposites on the spark plug. Compression may1` also stay good until extreme wear. Some oil smoke will be noticable at times.

Severe bottom end problems at 105,000 miles on a 280SL is not normal, however the history of the maintenance can the main factor.

If the mileage is not documented by service records, there is always a good chance the car has more miles on it.

Unfamiliar machine shops make mistakes on cylinder head work. Don't rule out the possibility that a guide may have come loose until you check. I have run in to this many times before.

Follow Arthur's advice and make sure your vent line on the valve cover to the intake is not blocked.

Leakdown tests may not pinpoint the cause, but may narrow down the possibilities.

Some more investigation by yourself should be worthwhile. Dan is right a pair of experienced eyes are a big advantage. We'll try to help you see. Keep us up to date.




Joe Alexander
Blacklick, Ohio

[Cortez-Campos]

High oil pressure can cause oil consumption?? my gage always says 45! in idle and on the highway, isen't that correct??

280 SL 1969 anthracite 172, with red inteior.

[DavidBrough]

Thanks Guys, Thats given me a number of things to check to narrow it down. I have just dropped the car off for a cylinder leak test and will report back when I get the results next week.

[DavidBrough]

Hi guys

Well, the engine doctor has spoken after completing the leak down test and the words are “pistons/rings/cylinders” which would be fine if they were followed by the words “are all OK” and not “trashed” as in my case. So it looks like I’ll have to break out my best crow bar and whip the engine out. I knew I should have sent the wife on that home mechanics course last year. Still, at least it will make changing my shot front sub frame bushes easier!

[ja17]

Hello David,

Sorry to hear the bad news. Keep us up to date. We will help out as much as possible from out here!

Joe Alexander
Blacklick, Ohio

[DavidBrough]

Thanks Joe, I only intend to remove and replace the engine myself, I think the engine rebuild is better left to those with the knowledge and facilities to do it justice. In terms of engine removal, is it better to leave the gearbox in place (auto) or remove the whole lot together? any idea on the weight so I hire the right crane?

[Ricardo]

Hey David
This came up recently and I believe the weight is near to 700 lbs. with tranny. They come out together fairly easily as long as you have at least 8' height as the angle is steep...just be careful when sliding over the front grill area....
good luck

[DavidBrough]

Thanks Ricardo, thats useful.

[ja17]

Hello David,
I also prefere removing both the engine and transmission as a unit. The assembly must be extracted at about a 45 degree angle.  You will also have to use a floor jack to lift the tranmission over the center tie rods during the process.

In my case the head removes easily (about 40 minutes), so I remove it before exracting the engine and transmission.  In this way I can also check the cylinder head for the fault before engine removal. After head removal the engine and tranmission is much easier to remove, since all the mounts and accesories are more accessable.



Joe Alexander
Blacklick, Ohio

[DavidBrough]

Well I’ve got stuck in and the engine is ready to come out as soon as I can arrange the hire of a crane. Everything came off quite easily although I have not been able to remove the speedo cable from the back of the gearbox. I have removed the allen pinch bolt but am not sure how much force can be used, it seem very solidly attached and is quite difficult to get at. I assume this will be easy as I lift the engine out and get more space? However, how would you do this in situ?

[DavidBrough]

Hi Guys, One more question, I have found an engine crane that is quite reasonably priced which I would look to buy and sell on afterwards if it will do the job. It is rated at 2,000kg and will lift 500kg at max jib extension which covers the weight of the engine and trans. However, it will only lift to 2350mm which is about 7'8". Will this be enough?

[Ricardo]

David
That should do it I'm pretty sure...you may have to climb into the engine compartment and lift the tail of the tranny over the grill area, but it's easy to do and  the engine should be fairly well balanced so that there isn't much weight to lift...make sure to put a couple of layers of cardboard etc over the grill/nose area, just in case...
good luck

[DavidBrough]

Hi Guys, Well the cranes arrived and everything is hooked up but I am having a bit of trouble manoeuvring the engine/gearbox over the steering rods and avoiding the throttle linkage on the rear bulkhead at the same time. Is it a case of perseverance or do I have to remove the throttle linkage? This looks tricky as it seems the servo would have to come of and my manual makes no mention of this. All engine ancillaries have already been removed except for the starter motor and the head is still on. I’m sure it would be easier with the head off and I may wait until the weekend and take that off first. Any suggestions would be gratefully received?

[Ricardo]

David
As Joe mentioned, you need to jack up the tail of the tranny to clear the steering linkage, and a floor jack on wheels is the way to go.....you should be able to manouver around the rest, though my experience is with a standard trans. and the auto may present it's own difficulties....I didn't remove the head or any thing other than manifolds and cables etc.
maybe you just need a refreshment break :-)

[DavidBrough]

Thanks Ricardo, I did have a trolley jack under the gearbox but was probably over keen to start when the crane arrived and only had a quick half hearted attempt. I will have a proper go at the weekend now I know it should all maneuver past the throttle linkage.