old oil verses new oil - for an old engine

[Stringer]

can anyone tell me if putting in new oil reduces the actual amount of oil an old engine burns? i.e. does old sooty oil burn more through the rigns or valve stems or less than new oil?

And is a straight SAE 40 better than a multigrade in a hot country, in terms of reducing oil burning in a 1987 300E which shows no signs of burning oil, but is going through a tiny bit?

thanks
M in Beirut

 

[markjay]

I am not sure the engine will burn less oil as such.

Generally speaking using thicker oil on older engines makes sense, but multigrade is always better than single grade.

I would think that for your climate the good old mineral 20W-50 or semi-synth 15W-40 would normally do.

 

[Lxb3]

A 1987 300E is not an old engine in the way that many people think of "old engine". How many miles are on the clock? This is still a very, very well made, high-precision 6-pot. They are very tolerant of different grades of oil, but do use a good brand to minimise wear...
If you're losing some (ie more than, say, 1 litre disappearing per 2,000 miles), check for leaks. It may also be valve stem seals, but in theory you should see blue-ish smoke on startup if that were the case.
According to the owner's manual guide to oil grades, pretty much anything ending 40 or 50 will do! It looks like 20W-50 would be your best option, but if that's hard to get hold of, 10W-40 or 15W-40 will be fine.
Any idea roughly how much it is consuming, per 1000 miles or between changes etc?

 

[grober]

I would use a good semi synthetic 10w40 to MB 229.1 rather than one of the newer totally synthetics e.g. Fuchs TITAN SYN MC 10w-40 High Performance Semi-Synthetic Engine Oil (formerly known as Fuchs Titan XTR) 5 Litres
Most likely cause of oil burning on these engines is worn valve stem seals which harden and crack allowing oil into the combustion chamber. They can be renewed without removing the head.

 

[coupe deville]

Interesting site here - Bob is the Oil Guy
The site is advertising Mobil 1 but has good explanations of viscosity and engine wear at start up with cold oil and the advantages of 0w and 5w instead of 10w, 15w etc. He claims a lot of manufacturer's are coming round to the idea that lower weight oils are better for all engines.

You will need a few hours to wade thru it

 

[Stringer]

is there an easy way of determining whether your valve stems are leaking as opposed to the pots seaping oil through? I can't see any blue smoke on start up, which i read is the normal way of identifying if its the valves.
cheers graham
M

 

[markjay]

The old way of doing this was by carrying-out two consecutive compression tests, and adding a teaspoon of oil into the chambers (through the injector holes) between the the two tests.

If the compression rings are worn, the compression will increase on the second test.

However you will obviously need to be competent enough to remove the injectors, or take the car to a garage.

 

[hotrodder]

It's a petrol engine so you'd pull the spark plugs for a compression or leakdown test. Leakdown test can often be more useful than a compression test since it eliminates variables like battery condition/cranking speed etc but not so useful for valve stem seals though as the valves remain closed

Worn valve guides often show themselves with a puff of smoke on the overrun too, say, coming off the throttle when leaving a motorway
Obviously not probative but as said the M103 is known for valve stem seals (guides too?) and a bomb proof bottom end i.e. odds are if it's not leaking out it'll be the valves

 

[mercperson60]

mercperson60

No expert by any means but always told to use the best oils for long engine life Alan

 

[mercperson60]

not sure if its still available but years ago we always swore by duckhams 20/50 in older engines