[rdr0b11]

At the suggestion of my very knowledgeable mechanic, I'm switching my '92 2.6 over from conventional 10W40 to SAE30 (straight weight) oil (brand is Shell, I assume most straight weight oils are pretty identical).

In addition, I'm adding 1.2 quarts of Lucas Heavy Duty Engine Oil Stabilizer for my next oil change (it's eating a quart of oil every 1000 miles - and there's no dripping leaks)

I do have one question: should I keep adding LubroMoly MOS2 Cold Start additive, or is that partially going to defeat the purpose of switching to a straight weight?

I'll be monitoring oil consumption after this, and I expect it to decrease significantly. I live in sunny Southern California, so cold temperatures will never be a real problem (dropping under 40F here is an extreme rarity), and the extreme heat stress LA traffic puts on this car makes me think this is probably the best way to go.

Has anyone else tried running straight weight in their 2.6? Good, bad experience? I'd love some tips or comments.

 

[1984babybenz]

What makes you and your mechanic think you need to switch oil weight?

Was the car burning oil, running rough, etc..?

 

[rdr0b11]

Yes, I state in the post that the car is using one quart every thousand miles currently.

 

[aardvark]

Step up to 10-40.
If you live in a northern climate do not go straight weight, due to the thickness in the winter.
Also use a good oil brand. Castrol has stopped more than 1 engine I've had from burning oil. I had a S-10 truck going through 1 qt every 300 miles (from a previous owner) . after 3 oil changes w/ Castrol, the oil loss ceased and I drove the vehicle another 200K miles beyond the 75k that was on the clock. Next owner drove it for 2 years that I was aware of.
Just step up a viscosity grade and use good oil.

 

[rdr0b11]

Step up to 10-40.
If you live in a northern climate do not go straight weight, due to the thickness in the winter.
Also use a good oil brand. Castrol has stopped more than 1 engine I've had from burning oil. I had a S-10 truck going through 1 qt every 300 miles (from a previous owner) . after 3 oil changes w/ Castrol, the oil loss ceased and I drove the vehicle another 200K miles beyond the 75k that was on the clock. Next owner drove it for 2 years that I was aware of.
Just step up a viscosity grade and use good oil.

As I said, I currently use 10W40, and as I stated, I live in Southern California. It's probably a good idea to read the post before responding.

 

[Emre-K]

If oil consumption in hot conditions is your main issue, then a conventional 20w-50 makes more sense than a straight 30.

I would run an inexpensive 20w-50 like Brad Penn PG1, Kendall GT-1, or Valvoline VR-1 and maybe mix in 15-20% Lucas HD Oil Stabilzer.

 

[NMBMBZ]

Straight 30W is a heavy viscosity oil, even in Southern Cal during winter months, morning temps can dip into 40's and a 30w may not flow adequately during cold engine startup.

(I use semi-synthetic 10w-30 and it seems to work just fine all year around)

If you have oil consumption issues, try 15w-40 first, it is designed for diesel motors but work just fine for older gas motors, i'd recommend Delo 400LE

 

[aardvark]

Point taken on the reading first. Sorry.
My overall point is a "good oil quality". A good "Detergent" oil quality.

I also have issues with additives. Oil companies spend many millions of dollars doing their chemical research.To throw in an additive messes up the mixes chemistry balance. Assuming their money spent, it is presumptuous to think we can out research the pro's. Some additives of the past have caused more damage than good.
Oil additive companies are after profits. One additive simply cannot be compatible with all oils, since oils are of differing bases.

 

[rdr0b11]

For synthetics, I agree - additives are probably snake oil. For conventional oils, I think they can be a good band-aid for fixable consumption issues, and my mechanic swears by Lucas HD Oil Stabilizer for reducing consumption in older MB engines.

Just put it in the SAE30 and Lucas HD, and took it for a drive for about 30 minutes. Idle oil pressure in gear is hovering around 1.2 bars, whereas previously I would say it was at anywhere from 1.0-1.1 in these temperatures (75F right now). So that's encouraging.

Now it's just down to putting on the miles and seeing how much it consumes.

 

[vishvamata]

The suggestion about 15W40 is good. Chevrol Delo or Mobil Delvac. In my 250K diesel, after the typical loading with black soot normal for all diesels, it holds oil level remarkably well and maintains excellent viscosity at operating temperature. Also, on using 15W-40 diesel rated oil -- use it ONLY on older engines, and only use the LE or low emissions type rated API CJ. Otherwise, it can damage newer emission control systems.

20W50 is also an option, as shown on the above graphic. There is no point using synthetic, since its primary objective is longevity between changes. The above graphic (5th bar) shows that 30W is fine for L.A. weather.

Another improvement you can make is to retrofit your coolant fan sensors, so that engine temperature is always below 100 deg. C. That last 20C above 100 pushes the oil viscous capacity, and thins it to the leakage point for the gaps your engine. Think about it, better regulating a lower operating temperature is just like using higher viscosity oil (at the upper end).

 

[sranjesuper]

your very knowledgabble mechanic should have told you to change your valve stem seals as this is the common problem on these engines that burn oil. Mine is also a 2.6 from 1991 and i have about 300,000 on the clock and never changed valve stem seals. It burns quiet a bit of oil i would say 1L every 700km or so. No oil drips as i just had both my timing covers and crank seals resealed. I thought that was the cause of my oil disappearing but now it still is disappearing less but quiet noticable. I read its the valvestem seals not the piston rings on these cars. And you can do them with the head off. Try that instead. Oh and ive tried also using many oils from 5w30 to 10w30 to 10w40 ( what im using now )

to lucas stabilizer (* doesnt do shit on these cars )

conventional vs synthetic, doesnt make a difference. On my car they all burn..

so next thing im doing is my valve stem seals after i get hold of a valvespring compressor.

 

[rdr0b11]

The suggestion about 15W40 is good. Chevrol Delo or Mobil Delvac. In my 250K diesel, after the typical loading with black soot normal for all diesels, it holds oil level remarkably well and maintains excellent viscosity at operating temperature.

20W50 is also an option, as shown on the above graphic. There is no point using synthetic, since its primary objective is longevity between changes. Also as shown on the above graphic (upper limit of 20W30), straight 30W is too thin for L.A. weather.

However, the biggest improvement you can make is to retrofit your coolant fan sensors, so that engine temperature is always below 100 deg. C. That last 20C above 100 pushes the oil viscous capacity, and thins it to the leakage point for the gaps your engine. Think about it, better regulating a lower operating temperature is just like using higher viscosity oil (at the upper end).

Well, I just had the radiator and water pump done, and the fans seem to come on at the appropriate temp. I've not had it spike past 100 once since the radiator was done - so that may help a lot for the foreseeable future.

Straight 30 should be fine in LA temps so long as the engine is adequately cooled, from my understanding? We'll see how it goes until the next change, I may go with the 15w40 during winter and the 20w50 during summer if the consumption doesn't get better.

 

[rdr0b11]

your very knowledgabble mechanic should have told you to change your valve stem seals as this is the common problem on these engines that burn oil. Mine is also a 2.6 from 1991 and i have about 300,000 on the clock and never changed valve stem seals. It burns quiet a bit of oil i would say 1L every 700km or so. No oil drips as i just had both my timing covers and crank seals resealed. I thought that was the cause of my oil disappearing but now it still is disappearing less but quiet noticable. I read its the valvestem seals not the piston rings on these cars. And you can do them with the head off. Try that instead. Oh and ive tried also using many oils from 5w30 to 10w30 to 10w40 ( what im using now )

to lucas stabilizer (* doesnt do shit on these cars )

conventional vs synthetic, doesnt make a difference. On my car they all burn..

so next thing im doing is my valve stem seals after i get hold of a valvespring compressor.

Trust me, he said the valve guides and seals needed to be done eventually, but that this wasn't critical to the continued operation of the vehicle so long as I didn't mind topping off the oil every thousand miles. His suggestion was in regard to reducing, not eliminating consumption.

Mercedes-Benz's own technical bulletins apparently say that up to 1 quart of oil consumed every 1500 miles is in the "acceptable range" for the M103 engine. I just want to get it below that mark before now, before I start going having much more costly work done and having the head pulled. If I'm pulling the head, I'm getting valve guides, seals, piston rings, head gasket, and whatever else is recommended done since I'm already paying for that labor. And I'm not ready to do that quite yet, maybe next year.

 

[jzchen]

I switched all our Mercedes to Mobil 1 0W-40 after reading this document:

http://www.startekinfo.com/StarTek/outside/9511/?requestedDocId=9511

('09 C350, '92 190E 2.6, '91 420SEL, and '85 300D Turbo Diesel.)

So far the only one I haven't changed is the 420SEL because we aren't currently using it, and the '09 is factory filled with it...

 

[Bill G]

I switched all our Mercedes to Mobil 1 0W-40 after reading this document:

http://www.startekinfo.com/StarTek/outside/9511/?requestedDocId=9511

('09 C350, '92 190E 2.6, '91 420SEL, and '85 300D Turbo Diesel.)

So far the only one I haven't changed is the 420SEL because we aren't currently using it, and the '09 is factory filled with it...

This is what I'm switching to this w/e:
Mobil 1 SuperSyn European Car Formula 0W-40

I think this oil will produce fewer deposits as well as have good friction properties for an older engine design. I have been running Castrol high mileage for the last 2 years, and I'm not necessarily impressed. We will see if I can tell a difference.

 

[Bill G]

I read its the valvestem seals not the piston rings on these cars..

I have always wondered how the rings wear on these engines. Do you have any sources that can back this up?

 

[Ignatz]

My head gasket let loose this summer putting coolant into the oil. I was using around a quart of oil every 1,500 miles for the last year.
After the head gasket change, I added 1/2 quart in 3,000 miles. I'm at 234,000 now with the original valve seals.
I've also done oil changes with Shell 30 wt I got years back for $.49 a quart. I sent a sample to Blackstone labs and got back great results. Still, 15-40 fleet oil is a better choice to straight 30.
For my car, it was the head gasket that took care of my oil consumption. And my car allways ran good even when it was sucking coolant into the engine.
Because my car never overheated, I just cleaned up the mating surfaces and slapped it together with a new gasket and bolts/washers.
My coolant level has'nt budged since June. The oil consumption improving is just a bonus after changing the gasket.

 

[Bill G]

Ignatz, that's very interesting. Did you do anything to the head at all, like new valve guide seals?

 

[vishvamata]

I respectfully dissent on using 0W-anything on an old engine. The 0W when cold is necessary on newer engines designed to higher tolerance with smaller gaps between moving parts. Thus the recommendation on page 3 of the revised MB fluid recommendations (link posted above), that 0W-40 be used on vehicles 1998 and newer. (Hey, I would love to have a 1998 W201).

Older vehicles are built with larger clearance between moving parts, which then can become even greater with age. Back in the day, milling machines were not nearly as precise as in the past 10 years. In 1984, you were lucky to get +/- 0.04mm tolerance. Now the milling machines are 10x more accurate, and most of them are made in Japan.

The Honda Insight mk1 was the first vehicle to require 0W-20 oil, since the close mechanical tolerances were necessary for maximum fuel efficiency (I once averaged 74MPG over a month, driving over mountains and in city).

I would not want 0W-anything in my old engine.

Also, on using 15W-40 diesel rated oil -- use it ONLY on older engines, and only use the LE or low emissions type rated API CJ. Otherwise, it can damage newer emission control systems.

 

[Ignatz]

Ignatz, that's very interesting. Did you do anything to the head at all, like new valve guide seals?

No, Just carefull and complete job of cleaning the block and head surfaces by hand. No power tools to clean. I didn't even touch the combustion chambers or valve surfaces. I also did not touch the piston tops...... Because I've owned this thing since 97, I can honestly say it still runs like new. Actually, with my MB rebuilt tranny...better than ever. Mine's a 2.3 engine.