bzman

Just acquired a 91 300d 2.5 turbo today w/235k miles and will be changing oil next week and was told 15w40 would be best...any particular brand?
Also tranny fluid will be replaced as well and again any help or sugesstions would be appreciated. Seems like the tranny is not performing to change gears but will look into matters soon. A little rust in the body but the leather and interior is perfect. One owner car since new just been mostly sitting for past 2 yr's.
Excited to get started working on this wonderful example of a fine 25 yr old car.
Again thanks to you the members for all your expert assistance

marc hanna

Rust will be your worst enemy on the car. Get any rust patches fixed immediately and then commit to regular rust proofing regime. There are some that do a heated oil spray that wicks into all the crevasses.

There are plenty of great oils out there, just stick with a fully synthetic - Amsoil, Mobil 1, Royal Purple, Motul.

Tranny flush definitely a #1 priority. Probably needs a coolant flush to and the glow plugs replaced.

bzman

Yes will be replacing all fluids this week although I was not planning to use synthetic oil b/c of the high mileage...the rust problem is not major but definitely needs to be addressed thanks for the suggestion of the oil bath.

marc hanna

When you do the coolant flush buy some citric acid powder and mix it with a gallon or so of distilled water and let that run in the engine for a half hour so. This will clean all the crap out of there. You can buy the MB brand from the dealer but it might be expensive, otherwise you can buy the food grade in bulk quite cheap from Amazon or other sources. Because it's been sitting for a while, you may want to repeated the flush a couple more times in the first year to get all the scale and other crap out.

Once the rust starts it's hard to stop, so you do have to be diligent.

Enjoy your car!

marc hanna

Regarding the glow plugs, even if they still work, after that age and mileage they run the risk of getting stuck in there or breaking, so in my opinion, it's just best to replace them at regular intervals to save the time and hassle of trying to extract a broken one.

bzman

Glow plugs still working well since car has no problem starting but would hate to have them get broken while in position.

marc hanna

I had a couple burnt out glow plugs on my 87 300D and it started problem free above freezing, but below that it wouldn't. It didn't throw any errors either, so just keep that in mind. If you haven't driven it in the cold yet you just might not be aware of a bad GP.