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Discussion Starter · #1 ·
I've been using Mobil1 15w50 synthetic since my first car(16yrs old,99 camry), no issues until recently.

In my 850 turbo at least once a month I get knocking upon startup, but it doesn't go away until maybe the next day.

I figured it is low oil pressure getting to the head since I barely take it on the highway, just mostly round town 10 mile round trip daily.

The oil level is 3/4 up the dipstick, and is 5 months old.

The same happens on my mom's S430. Knocking upon startup, quiets down after a little while, oil level is ok, 5-6 months old.

I've always used this brand and weight since the first oil change, 3-3.5Kmile intervals, oem oil filters only.

I'm thinking of trying something else for a little while, maybe you guys have inputs on what you use that doesn't cost your turbo car to knock sporadically.
 

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Are you really using 15w50? Jesus that's thick. Your poor oil pump can't move molasses and you fuel economy has got to be in the pits.

You need to switch to 5w30 or 0w30.
 

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Discussion Starter · #3 ·
My fuel economy is 32mpg easy at 70-75mph. Been using this brand/weight in this car since 2010. I'll go the next step lower in thickness next oil change.

If I hear ticking at anytime i'll go to a different brand. What would you recommend. I hear Valvoline Synpower is okay.
 

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Discussion Starter · #4 ·
I'm going to do Mobil1 synthetic 10w30 next oil change on both cars.
 

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Next time you hear the knocking, get a mechanic's stethoscope, or if you don't have one a long screwdriver, and probe around the engine and accessories to see if you can locate the knock. As for the oil, how many miles or kilometres on the odometer? If you're up in the 200K range, try a good high mileage engine oil; I use Quaker State synthetic high mileage oil in my bricks and I'm very satisfied with it.
 

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Alright, let's ask a couple questions and see if you can explain your desire for thick oil.

1) are you driving an extremely high mileage vehicle that was poorly constructed from inferior parts, and therefore suffering from oil control problems with the rings? Or poorly mantained with seeping seals?
2) are you tracking your vehicle and engine oil temperatures are through the roof?
3) do you drive a diesel?

How do we judge oil? We measure its viscosity in low and high temperature applications. Viscosity is resistence to either shear or tensile deformation.

When the oil is placed between the parts of bearing, our goal is provide just enough lubrication that there is no actual metal on metal contact, but also not so much lubrication that the engine must expend additional energy to move oil out of the way. An oil's ability to thin itself out so much that it can provide a micron or two of lubrication without structurally failing is its resistance to shear. When the bearing surfaces squeze it, and it doesn't structurally fail, that's its resistance to tensile deformation.

As you can imagine, single weight oils change behavior depending on the temperature. That's why we use multiweight oils in our cars. You want a thin oil at low temperatures, and you want proportionally thin oil at high temperatures. I use "proportionally thin oil" becauase a 30 weight oil would be too thick to efficiently move and lubricate at 70 degrees, however it is efficient at 200 degrees.

Oil serves many purposes in an engine. Number one is lubrication, number two is heat control, and number three is mechanical (hydraulic lifters and variable valve control come to mind). Thin oil lubricates better, moves faster to remove heat from pistons, and cools quicker.

So, in your application of a turbo inline 5 assuming no actual mechanical issues, you probably have too thick of oil for the oil pump to quickly pump into the lifters, so you get lifter rattle in the morning, until they build sufficient oil volume and pressure, or you have a leaking checkvalve in your filter housing or pump system.

Back in the heyday of American motoring, engines were built with sloppier tolerances, and were not optomized for economy. 10w40 and 20w50 oils were okay. As they tighten tolerances, and started thinking about the energy required to move oil around the engine, they realized lighter oils were more efficient. Then they realized they could get better lubrication by moving more oil and lighter oils were considered better.

I don't know the actual specifications for your mom's S430, but it wouldn't surprise me if it said clearing on the oil cap 5w20. Volvo recommends 5w30 for your car - Try it.

You can use regular oil too, synthetics are more cost effective in longer change intervals. I bet your motor feels more responsive and your mileage goes up, not to mention you'll save 15 bucks an oil change.
 

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Discussion Starter · #7 ·
I'm at 120K, only slight leak is the crank seal(rear main).

The oil cap on the Merc says 5w20 iirc but it now has 240K(got it at 90K). My understanding of the oil cap recommendation is for an engine with under 80-100K miles.

Thanks for the replies so far!
 

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If you have an O'Reilly near you they may have Valvoline 10W30 Full Synthetic High Mileage oil on sale, I would try that considering the leak you have. I bought some today for $4.99 a quart. I believe the normal price is over $9 a quart.
 

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I'm at 120K, only slight leak is the crank seal(rear main).

The oil cap on the Merc says 5w20 iirc but it now has 240K(got it at 90K). My understanding of the oil cap recommendation is for an engine with under 80-100K miles.

Thanks for the replies so far!
Mercedes engines are probably not even worn in yet at 100k. If it needed different oil weights at higher miles, the German engineers would have made a detailed oil weight schedule based up 100 variables and time elapsed. They didn't and they felt so strongly about 5w20, they spent the money to have it put on the cap.

Try following the manufacturers guidance.
 

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Discussion Starter · #10 ·
I'll go down to 10w30 for both cars. Been using 15w50 for years, can't go too thin maybe seeping would occur if I do that.
 

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I used to live in Mobile, AL (which at one time was part of FL) - I lived there over 12 years ago and Mobil 1's formulation has changed since then but I ran 15W50 once in my 1985 740GLE and it actually ran way too cold with that weight and I switched back to 10W30. BTW there are some excellent 5W40 Full Synthetics being made currently, you may want to consider that weight. Given the high miles I wouldn't want to spend too much money on oil - I can usually find Shell Rotella 5W40 for a reasonable price.
 

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Discussion Starter · #14 ·
Just threw in M1 10w30 syn. If any more ticking I will change brand. Thanks all for the help.
 
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