Mercedes-Benz Forum banner

1 - 4 of 4 Posts

·
Registered
1979 300CD
Joined
·
1,093 Posts
Discussion Starter #1
Hi,
I’m picking up an old lady 1979 300cd tomorrow and while I’m good with oil and coolant replacement can someone advice what type of differential oil and how much is required for this car.

the car has 48.000km but it has been neglected for too long.

it needs TLC as some say and she is a running project.
 

Attachments

·
Registered
Joined
·
9 Posts
I assume you are running the devil out of the car by now. I use synthetic fluids in my 240d. Synthetics seem to last longer and lubricate over a larger temperature range from what I have read. I would go with synthetic for those cold Canadian winters. (I grew up in northern Minnesota, I know what cold is). I guess you know to remove the fill bolt before the drain bolt just in case something goes wrong. BTW I love your car, I have a massive soft spot for 2 door hardtops. My first 2 cars were a 65 Mustang and a 67 Chevelle. Be safe, Don
 

·
Registered
1985 300CD, 1985.5 Porsche 944, 1969 Triumph TR6, 1998 Land Rover Discovery I, 1992 Volvo 240
Joined
·
1,297 Posts
I like to run diesel specific motor oil as these have a much higher ZDP content than conventional motor oils. My preference is Shell Rotella T4 or T6. The T4 is a 15W-40 conventional motor oil and the T4 a 5W-40 synthetic.

Coolant I only use Zerex G05. I just picked up a 1978 280E and would recommend replacing the radiator hoses as well. And eventually the heater hoses too. They may look ok, but if yours are original like mine appear they are now 41 years old and can fail from the inside. These are relatively inexpensive and I would recommend a brand other than Uro. Original MB hoses aren't inexpensive compared to Uro, but show me an unreinforced Uro hose that will last over 40 years.

In the rear differential I like 75W-90 synthetic and prefer Royal Purple or Amsoil. Remove the fill plug and then the drain plug. Make certain you remove the filler plug first. You don't want to find yourself in a situation with a drained differential and a stripped filler plug that you can't remove. Fill until the gear oil starts to flow out of the fill hole. One bottle (1 liter/quart) will do the job. While your changing the differential fluid take a look at the condition of the boots on the rear axles. If they are torn or cracked this means they need replacing. If dirt gets inside these it will lead to premature wear/failure of the joint.

When doing the fluids don't forget the power steering. I like to use a turkey baster to suck out all the old fluid, add new, run it a while, suck out more fluid, run it a while, etc... I do this several times and then add a new filter. I use any name brand DEX III automatic transmission fluid.

The transmission fluid is easy on these. You will have to determine if you want to drain the fluid in the pan only or the pan and the torque converter. I do the pan and converter, but there are some that say draining the converter is inviting trouble by "disrupting" junk in the converter. I don't subscribe to this theory based on the fact that the converter always has fluid circulating in it anyway. Replacing the pan filter and gasket is easy. Cleanliness is key and very important is not to wipe the valve body with anything. I actually think MG recommends a real leather chamois for this, but you do not want to use a paper towel or ANYTHING that could introduce even the smallest lint particle into your transmission. Just let it drip for as long as necessary. I like to use brake cleaner to clean around the pan before I remove it. I catch the fluid in a clear container and measure EXACTLY how much fluid is drained and replace exactly that same amount.
 

·
Registered
Joined
·
9 Posts
For the power steering fluid I disconnected the return line at the pump and pointed the metal stub up so fluid doesn't run out. Place the return hose in an empty milk jug then suction and fill, run the engine for less than 3 seconds to empty the pump. Refill the pump and repeat. Dirty fluid does not mix with fresh fluid so you can get some mighty clean fluid in the system using 2 quarts of ps fluid. I used synthetic ps fluid there also. Don
 
1 - 4 of 4 Posts
Top