synthetics
 

I have an 85 300D with 250,000 mi...everything in great shape. Just rebuilt entire suspension and ready for another 250,000!!

I put 25-30k miles on a year.

I use all synthetics, as follows:

mobil 1 gear lube differential - annual change

amsoil ATF in tranny - annual change with filter

amsoil 15W40 heavy duty synthetic in engine - change oil at 10,000mi, filter every 5,000 (the first time i did this, I sampled oil at draining and had analyzed...everything was good). It is important to use a diesel-formulated oil with low ash, soot inhibitors etc.

valvoline synth DOT 4 brake fluid - bleed annually

redline power steering - every few years

I have done the above for four years (since I bought the car) and I still have no leaks.

I think the best products for the money are Amsoil and Mobil 1. Castrol Syntec is actually a semi-synthetic rip-off...castrol products are good products, but the Syntec is not worth $4+ per quart. Redline products are good, but way too expensive...just as good as Amsoil and Mobil 1.

I settled with Amsoil rather than Mobil 1, as amsoil synthetic is specifically formulated for diesels. Amsoil ATF has better specs than Mobil 1.

Do not hesitate to use synthetic in Auto. Transmission....in these cars, while the engines go 500,000 miles or more, the transmissions generally need work at 250,000-300,000 mi. (from what I have heard). At 250,000 my trans. is excellent, and by using synthetic fluid along with anual fluid and filter change, I hope to avoid tranny work until 500,000mi. Make sure you drain torque converter with each fluid change!!

Also, if anyone wants advice on suspension work...let me know...I did all the work in my driveway, regular tools, shopmade tools, and two special tools (rental ball joint press and spring compressor from IPD/Performance)

MarkM,

How many oil samples did you take before concluding that the oil should be changed every 10k miles? Do you still sample the oil? Are you using the Amsoil filters or oe? I am interested in knowing because I run my car the same mileage per year as you and would definitely like to run syth oil. Please reply.

SW

One Week of Mobil 1 in Differential
 

Got the differential opened up as part of the axle replacement task. This comes after draining and replacing the gear oil about a week before the right axle started failing.

With just a week of use, there is a clean stripe all the way around the differential where the "big gear" (yes, I know it has a name - don't know what it is called) has been slinging oil.

So I'm sure that over the course of a few months the Mobil 1 gear oil would get the whole inside cleaned out just like SWs.

Annual change with this synthetic gear oil sounds like a good idea.

Ken300D

Reply to SW re: synthetics
 

I did not sample oil over time in order to determine the point at which the oil should be changed. My rationale was this: much of the literature pertaining to extended drain intervals with the use of synthetics indicates that drain intervals of 25,000 miles up to 100,000 miles are possible. However, in order to do this special filtration is probably necessary, and I did not want to do that. All I wanted was run synthetics in order to have the lubrication benefits of synthetics, but I wanted it to be cost effective. (At $4.50 a quart, and 8.5 quarts for these beasts, I dont want to throw it away at 3,000 miles!!!). So I calculated what drain interval/filter change regimen for synthetics, at about $4.50 per quart, would cost about the same as 3,000 mile drain intervals/filter changes using conventional oil at about $1.30 per quart, as follows:

8.5 quarts conventional oil @ $1.30 per quart, plus $6 filter, change at 3,000 miles.....cost is $17.05.

Now, for synthetics @$4.50 per quart, with two $6 filters (assuming you change the filter halfway through the drain interval) the cost is the same as above if you drain oil every 8,800 miles. At 10,000 miles, even better.

Mercedes recommends oil changes every 5,000 miles for conventional oil, probably a good bet. I figured I could easily double that drain interval if I still change the filter at 5,000. I did that and tested oil once at 10,000 miles...oil was fine, price is less than conventional oils, so I stuck with that regimen.

I havent sampled again since that time....will probably do once per year.

I use conventional oil filters (Mann, bosch, etc), and I use K&N air filter.

I buy Amsoil 15W40 heavy duty diesel mail order in a case of two 2.5 gallon jugs...that is most cost effective.

Regards,

Mark

After reading through this thread, I am very interested in adding synthetic Mobil 1 to my diff. My question is this: I am going to drain and refill the diff. tomorrow (it hasn't been done in probably 3 years) and to add the Mobil 1, do I have to do anything special? Can the Mobil 1 coexist with the residual oil left in the diff.? Do I have to "clean it out" first before I add the synthetic? Is synthetic compatible with regular oil? Thanks so much for the answer

Alex

Do it Alex, synth oil is compatible with the existing oil. No ill effects. My advice would be to drain it after a long drive while the fluid is hot so that most of it drains out easily. The dino juice is dog slow when cold. When you go to the store to but the synth oil, shake the bottle and then shake a bottle of the regular stuff. You'll see what I mean.

Great! I'll do it later today. Looking forward to it.........

Alex

I did it this morning
 

After reading this thread and searching the forum for other information on changing the differential lube, I got up this morning, got my Mobil 1 and changed my diff lube.

I did what everyone recommends- remove the top plug first and then remove the bottom to drain. This is easier than changing the engine oil. Of course, I drove around first to warm up the oil.

My plugs were not that hard to break and they went back in very easy. Drove around some more and checked for leaks.

By the way, my five year old daughter helped. Maybe that's why it took fifteen minutes.

Thanks for this thread. I am having my indy mechanic change the time chain next week. Any suggestions as to service that I should have him perform while he has the engine opened up?

Blair:

Adjust valves, check chain tensioner (which I'm sure he will, anyway), new valve cover gasket if needed. Only the valve cover needs to be removed to change the chain!.

Peter

Thanks psfred
 

I will specifically mention the chain tensioner, the gasket and ask him to adjust the valves.

I am approaching 190,000 miles and figured I would be very cautious and have the timing chain replaced. I do not know when or if the timing chain has ever been replaced. I have read that, sometimes when the chain is replaced, that the engine runs better and there is an improvement in fuel mileage. Whether that is true or not, I don't know. I guess I will find out.

Thanks :)

Blair:

As the timing chain stretches (actually, the rollers and pins wear), the injection and valve timing lag more and more behind the crankshaft. Replacing the chain restores proper valve and IP timing, resulting in better low rpm performance and decreased fuel consumption. However, if the IP timing has been adjusted with the old chain, it will need to be adjusted again, or it will be too fast!

Replacing the chain won't hurt anything but your pocketbook -- have the stretch checked once in while on the new one, replace it again if it gets to 8 degrees.

The only engines with critical chain problems are the single roller 380s and 420s -- they need to have the chain stretch checked every 30,000 miles or sooner, and the 380 needs to be changed over to the double roller chain. Diesels tend to run forever, rairly have chain problems.

Peter

This is an interesting thread!

I changed the diff oil a few months ago (July, I think it was). Put in some synthetic auto oil and added a mix of teflon additives.

I noticed a quieter response but am now left wondering whether I should drain the oil if it does really clean the entirety, and fill it up with Mobil 1?.

Kerry:

Drain it at once and replace with gear oil! Automotive engine oil isn't thick enough to properly lubricate rear end gears, teflon or not -- it gets sqeezed out of the gear contact faces.

There are only a few square millimeters of gear face actually in contact at any given time in the helical cut gears back there -- you are literally pushing the car with your fingertip -- imagine the pressure!


Synthetic gear lub is fine --SAE 90 wt or multiviscosity, but it MUST be gear lub or the rear end will fail.

Peter

Am I getting less rolling resistance with the Mobil 1 in my diff. or is it just in my head?

Alex

please excuse my ignorance-

I'm wondering in the pic, what that chiffon colored "coating" maybe? ...shouldn't the bare inside walls of the diff bell housing appear metallic looking? (vs. coated with a yellow frosting looking gooey substance)

tks-fad