1989 300te After a few years now of owning this car, I got the glovebox manual. It says engine oil should be 20-50 for my temp range (New York). I have been using 10-30 Mobil One. Should I change? Do synthetic #'s mate with Dino #'s?
My mechanic uses ATF in the steering pump/ rear hydrolic suspension. My Steering pump fluid is low right now...what do I top up with? They suggest an MB product...Any thoughts?
I have to do a brake fluid flush...Can I just use my good ole Castrol brake fluid?
Thanks.

Why would you second guess the owner manual? Use 20W50 if 20w50 is prescribed.
Power steering: There's a thing called "power Steering fluid"....would you use this fluid in your transmission? If the level's low, there is a leak somewhere.
Brake fluid: DOT 4 from a new container.

Second that. I would go with factory recommendations for all fluids.

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Not in this weather!

Quite the wiseguy, huhh Jack. Why does everything have to be sarcastic? I just asked innocent questions. Gotta make sure we never meet.

Use Mobil 1 15W-50, or better yet 0W-40 or 5W-40.

Mobil 1 10W-30 is not approved by Mercedes.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
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Your 1989 M103 engine can use many different oils but make sure you use the right viscosity. I would not put 20W-50 in there in NY. 15W-40 would be the highest viscosity I would put in that car. (Many of these M103's were filled with 15W-40 HDEO from the factory).

Your owner's manual will actually give you a chart showing oils something like 5W-30 and 10W-30 can be used for up to 86 deg F. Many many of these engines have already run to over 200,000 miles without engine troubles using mineral 10W-40 or 15W-40 oils with frequent oil changes. The valve seals and head gasket may fail but the engine in quite bullet proof in the lubrication department.

The 0W-40 and 5W-40 are nice because they can pretty much be used anywhere on the Earth. No need to select anything so it is kind of a intelligently dumb solution.

One thing though. DO NOT use ATF in the self-leveling suspension. It requires a special fluid that is clear in color. There are two types on the market you can use. One is mineral based (Febi) and another is synthetic (Fuchs). Your car calls for the mineral type but synthetic can also be used. You can buy the fluid from the dealer or many online parts places and they are not that cheap, especially at the dealers.

For the power steering (which actually shares the same pump with the self-leveling but two separate reservoirs), you could actually use DEX III ATF in there. It is in MB's Approved Products list. A dedicated power steering fluid works too. I have used the Vavoline semi-synthetic power steering fluid in my 300E's for over 10 years (I change about every 30k miles). Newer models require special power steering fluid and some are synthetic.

A DOT4 brake fluid is certainly OK but DOT4+ is certainly nice. Again, I have used the Valvoline brake fluid in al my cars but I change what is in the reservoir every 6 months or sooner. A couple of years ago, I was curious as how much fluid would diffuse or move from the reservoir to the caliper. I opened a caliper bleeding screw and the fluid coming out was as clear as what was in the reservoir. This car has not had a brake fluid flush for over 8 years but I always changed what was in the reservoir every 10 years. It appears there is far enough diffusion and movement to have the fluid mixed in the system. Remember MB specs these cars by keeping in mind that they need to bring a 130 MPH car to stop. That hardly happens in the USA if you obey the laws. A small bottle of the fluid (for about $2.50) is enough for two cars doing it my way.

All oil temp charts I have seen end at 86F. What are the upper limits of the oils that max out on these charts? What temp should one switch from 10-40 to 20-50? I bought my e420 in Vegas, it came with 20-50 which seems to be to thick for 50 degree mornings in CO.

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Will
94 E420
82 300DT
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69 Thunderbird 429 Thunder Jet
92 Mitsubishi Galant VR-4

synthetic atf is ok to use in both power steering and self levelling suspension.

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michael cole 1980 300SD gone now but not forgotten,87tdt,90 300te 4matic 95 e320 wagon

These temps are air temps and they serve only as a guideline.

Basically, all MB's, or all German cars for that mater, would like an oil that is xW-40 or xW-50 (there are some thick 0W-30 Euro oils out there). These oils can pretty much go anywhere that is hot like in FL. Plus, these oils can also adequately protect the engine when it goes 130 MPH and plus.

If you insist on XW-50, use a synthetic 15W-50 or 5W-50. Do not use mineral 20W-50.

MB's saying that 0W-40 or 5W-40 has to be used. That is for anywhere and also long drain intervals. For that reason, 10W-30 Mobil 1 was not approved in the newer cars because they do not want 10W-30 to be used in the middle-east or hot Florida, for example. One kind has to listen what manufacture has to say but also know why.

However, synthetic 10W-30 is perfectly fine on your engine in your area as long as you observe the drain interval set in your owner’s manual and do not abuse your engine (redline driving). In your area, you need not worry how high of a temp can xW-40 oil can go because it can go well beyond your hottest temp. A mineral, semi-synthetic, or synthetic 10W-40 or the HDEO 15W-40 should also serve you well (probably better). There are literally thousands of these engines that have gone over 200,000 miles that have never used 0W-40 or 5W-40, although these are superior oils.