91 300d 2.5 - PeachParts Mercedes-Benz Forum

oldiesel · #1 06-03-2007, 08:57 PM

I am going to look at a 91 2.5 300d that has over 200k miles is there anything special that i should be looking for?.Is there anything special about this model? TIA Don

Palangi · #2 06-03-2007, 10:23 PM

Those are generally considered really great cars. The only bad vibes I hear about them is that 200K is usually about when the tranny blows.

pmari · #3 06-03-2007, 11:29 PM

1- The cooling systems are notoriously problematic. If the car hasn't had a recently replaced radiator, watch the temp gauge closely. It should never exceed 100C except in extreme conditions (blazing heat, A/C on, climbing a mountain. The fan clutch can contribute to this too, see below.)
2- The fan clutch is also about worn out after 15 years. If the fan has metal blades, it's the old style clutch, and may need replacement. The new style clutch requires a new plastic fan (from the 606 motors.) Total cost ~$250 for both parts.

3- The serpentine belt tensioner bearings tend to fail and lean at an angle. Look at the tensioner pulleys near the water pump, if they don't look perfectly straight, you likely need a tensioner. ~$100 in parts, not a bad job if you know the trick to R&R'ing the fan clutch. Also the belt shock tends to have it's bushings fail and it causes a rattling noise. Press on the shock body with your fingers with the engine running to see if it quiets down. It will be obvious if it does. ($25 for a new shock from Rusty.)

4- Oil leaks - hopefully you don't have many. Cost and location vary widely. Depending on the severity you may choose to ignore them. The oil level senders tend to seep oil through the body. This is ~$50 and simple to replace at oil change time. Also, the tranny cooler hoses at the front of the engine tend to leak too (I need to replace mine.)

5- The A/C system is expensive to fix. The manifold hose (the main hose assembly) tends to weep oil *through* the barrier, making the outside of the rubber hose wet and oily. Yes, it's actually refrigerant oil! This is the big hose near the ABS pump. If it's oily, you will need to replace it eventually. I just did mine, it's a massive PITA job. The hose is ~$350 new from Rusty or you can have your old one rebuilt for ~$125. Stick with R-12 if the system hasn't already been converted.

6- See if the ELR (idle speed control) is working. There's a black trim plug near the fuse box, with the engine idling pull it out, turn it to a different number (1-7), and push it back in. The idle speed should change. 1 is slowest, 7 is fastest, 20+ RPM per number.

7- The outside temp sensor is often wacky. If it's always WAY off, you can replace the sender ($40?) but even after I did this, it always reads way too high in the summer. It's more accurate in winter. Poor design. If the display is "blacked out" you're hosed, that costs a LOT (several hundred dollars, IIRC... Probably not worth replacing.)

8- The center vent vacuum actuator is often broken (ruptured diaphragm.) Put the A/C on max and see if you get a constant stream of air out the center vents over 10-15 minutes operation. If it EVER stops, the actuator is bad. There's a diverter flap (NOT the recirc flap) that allows air out the center vents, but this flap cycles during normal operation- hence the intermittent airflow. When the center vent flap is open, you can look into the center vent itself with a flashlight and just see the aluminum evaporator down below. If you can't, the door is shut - because the flap isn't open! To replace this $20 part, you must R&R the dash - a 6-10 hour job. NOT fun. I did this on my car last spring. I know 2 other 1987 300D owners who need to do it (my b-i-l and other friend.) :-)

9- Check the sunroof, power windows, locks, seats, etc. Often it's just a switch (cheap) but the sunroof can cost a fortune ($1000+) to repair.

10- Performance - The 1987 300D is NOT slow. Check it with a stopwatch from 0-60. Factory spec is a little over 11 seconds. Less than 13 is probably acceptable if it drives OK otherwise. Much slower than that and you have a problem. Could be as simple as a plugged boost line to the ALDA (free fix), or a turbo ($500-$1000), or an injection pump ($1000-$1500), or both. An engine with bad compression (shot engine) will likely have other symptoms like hard starting, lots of smoke, and high oil consumption.

11 - Smoke should be a minimum, as should oil consumption. Mine uses about a pint per 5000 miles with 226k on the clock and Delvac-1 diesel synthetic.

12- If the trap oxidizer has been removed, great. If it hasn't, you get a new free exhaust from Mercedes, and a free turbo too if it's damaged. Plus, you get an extra 5hp and 1-3mpg.

13- All the usual wear items - brakes, suspension, yadda yadda. The rear torque arms are usually shot. They're $50 for both and take 2 hours to replace.

Marshall Booth (on the subject of 300TD purchase): The OM60x engines used in the W201/124/'86+ 126s are much quieter then the older OM61x engine. Part of that IS the engine and part is the sound encapsulation used in and under the engine compartment (be SURE the one you buy HAS these panels - some misguided mechanics throw them away and they are expensive to replace)! The hydraulic valve lifters CAN make quite a racket if the car has had a steady diet of conventional oil. Changing to synthetic oil WILL considerably reduce and eventually may even eliminate all but an occasional clack/clatter from these "noisemakers" ;-) The '87 300TD is probably my favorite MB ever!

There are LOTS of little things to look at when buying a 13 year old car. Ones that I would look for are: AC system - it must produce good cooling (compressor replacement will usually be well over $1000), the sunroof must work properly in all modes (sunroof repair can be $1000), The tail gate must open, stay up and close flawlessly and the "pull in" motor must engage and pull the gate shut without effort once contact is made, check that the serpentine belt idler pulley (right below the horizontal expanse of fan belt at the front to of the engine) MUST be aligned parallel with the belt - if it's a degree or two cocked, then it MUST be repaired (the costs could be from $100-$1000 depending on what is actually worn or broken), the engine MUST start promptly when dead cold and idle should smooth out within 20-30 seconds! There must be NO evidence of transmission fluid on the grate at the bottom of the bell housing (where the torque convertor lives ;-) as that would be evidence of leaking seals (minimum of $500 to fix) and the transmission should shift very smoothly after the 1st few cold shifts. The power seats should all move effortlessly and all the windows should work at about the same speed. The cruise control should be tested! The radio, antenna and cassette player SHOULD work (though a refurbished radio is available on an exchange basis from Becker for about $130). Wipers (front and rear) should work smoothly. Finally, the car should ride and handle about as well as your 300SD - but just a bit more agile and it should feel more powerful ('cause it is).

Compiled by Joe Knight from bits and pieces written by Dave Meimann and Marshall Booth - mbz.org

The thing to add for a 91 om602 is to do the timing chain and possibly the Vac pump.