Oil - Type/change frequency or additive at low annual mileage?
 

I drive my w108 4.5 infrequently, last year I drove it less than 500 miles, most of that were 30 mile trips with speeds rarely exceeding 50mph.

For my situation; are annual oil changes really necessary? What kind of oil to use? Would you recommend some sort of oil additive? Thanks in advance.

Some will argue that they are, some will argue that they aren't under some conditions. It depends on how you use the car.

My SL sits a LOT. However, it is driven a few times a year and every time it's taken out, it goes on the highway for a bit to get the engine hot, let the detergents do their thing, and boil off any water or condensation that's collected in the engine oil.

The WORST THING you can do to your car is baby it and let it sit. It NEEDS to be driven and needs to be driven NORMALLY. If you aren't getting the engine hot, driving it around, or taking it on the highway, it's a good idea to change the oil yearly. Moisture and condensation collect in the oil and react with combustion products to form acids which are not good for engine components.

Driving the car and using it normally, even if only a few times a year is enough to drive off moisture, keep the engine lubricated, and allow the detergents to remove varnish and combustion byproducts from the engine.

Having been around MBs since the 60s I would add that running the car hard, that is a full throttle acceleration with some kick downs and hard stops seem to help as well.
Also, in a car used that infrequently you need to also service the rest of the fluids with some regularity including gasoline which now has the added element of ethanol which eats away at fuel systems not designed to tolerate ethanol.
I found ethanol free gas, which makes me feel better about leaving a car sitting.

And just to add that its not a good idea to start the engine and let idle for a while and shut off. This is not like driving the car which burns off moisture and can actually create more condensation in the crankcase than if the engine were not started at all.

Short trips are harder on oil than longer engine up to temp trips. In advanced stages of short runs, the underside of the oil cap will develop a white watery gel. I has one customer that drove normally but parked in a very damp rain forest like garage, The gel was so bad I initially thought they had a leak from coolant to oil until I got the rest of the story.

For what you are doing, synthetic or any sort of additive won't help and will be extra $ for no gain.

What type of fuel system does this car have ? ( Carb, CIS, D jet ) The better the fuel control, the longer oil life.

I would not run the car hard, but I would give it a 10 + mile on the highway drive at 50 to 65 ish after driving around town to get things moving and warmed up. Getting everything up to temp for 20 min + per drive cycle is the key.

You are not wearing out the oil in 500 miles but it will become contaminated with fuel / moisture / acids. I'd change it once a year with filter every other year before planned winter storage if you do that so acids are not eating away at things all winter.

Some might say to change the oil in spring but since the engine is static, there should be minimal to zero oil degradation.

I'd pull and check the spark plugs for fouling once a year or so as an early sign that the car isn't being run to temp long enough.

In my opinion, yearly is good. Oil and filters are cheap.

With older MBs that have MFI or carbs with less precise fuel control the build up of carbon was an issue. You do not have to go crazy but full throttle accelerations to approximately 5,000 rpm in your highway drive is what I was talking about.
I apologize to the thread starter for slightly off topic answer.
Brad

AKA the 'Italian tune-up'.

I just run Mobil 5000 conventional 10/40 in my 4.5. I buy my filters from the dealer. I noticed a little more oil consumption in other M117s when I was using Mobil1 0/40 in them. Could be anecdotal, could be a thing, either way to Mobil5000 is what I use in my 4.5 and my car doesn't burn oil.

I hate when people waste oil, but the flip side of that is oil is a lot cheaper than engines. So I think annual oil changes are probably the way to go.

The 0 / 40 will increase oil consumption over 10 /40 because at low temps is it is thinner. When I ran 10/30 in my old lawn tractor ( with a 12 HP K series Kohler ) and it used more oil / more start up smoke than straight 30 even though they are the same thickness when hot.

And blood old Dino oil is good. I prefer to run the diesel formulas 15w40 in my old benz, bmw and porsches. Delo, Delvac, Rotella or Castrol are my picks.

Me too - any sense in sweating about zinc additives with old cars using these standard dino oils?

I used to run diesel oil in a gas motor however many are not rated for any gas engine use like they used to. Diesels don't have to deal with varnish from gasoline so the formulation is different.

With a diesel, mid time oiled engine parts look shiny new once the sooty oil has dripped off.

Thanks for all your input, very helpful.


So my local auto parts store sells the Shell Rotella T4 15w40 oil. It says on the label it is designed for diesel engines, but this would be safe/preferable to use in my 4.5 gas engine?


Thanks again.

I think the higher zinc content, which can be bad for catalytic converters (which Diesels do not have) is why it says for Diesel engines. At the same time, the ZDDP is good for the cam/rocker setup on these cars, anecdotally (I am unsure if anyone has ACTUAL proof but that may require extensive testing on two identical engines leading to destruction, so there's that). Either way, the Rotella will not harm a gas engine that has no cats, such as your 4.5.