It's been a month since I bought my daughter an 86 300E for her first car. Since then I have spent a few dollars getting it ready for her but for what I paid, it's still a bargain.

I just discovered today that this car had a new motor installed in it in 1993 by the dealer and has only 59,000 miles on it. No wonder when I put a new timing chain in it last week it looked like new, almost! I replaced the serpentine belt and tensioner also, myself! The other thing I'm having a problem with is the AC. We converted and charged the system but it leaked out overnight. My AC tech said he needed to replace the dryer and expansion valve which he did and had it under vacuum for two days with no leaks(he found the shrader valve was leaking)so he charged the system but he couldn't get the pressures right on the low side so he replaced the expansion valve again today. Same problem! The high side shows 250 lbs(but bounces around a little) and the low side stays at around 70 lbs. It's cooling pretty good, but he says the reed valves are probably shot in the compressor. Does this sound right? Dealing with AC is kinda like witch doctor stuff.

The other problem I have with this car is a knocking noise in the motor. My mercedes tech friend thinks it might be the catalytic converters being loose but I swear it sounds more like a bad lifter only deeper in the motor. We listened with a stethoscope and you can hear it in the rear exhaust manifold. Another shop says he thinks it's a wrist pin or crank bearing. Where should I start? This motor is a 93 with less than 60,000 miles! The top looks brand new!

Any advice appreciated,

I have seen the Cats come loose and knock a bit. I always start on the easy side then work toward the hard stuff.

On the A/C, I have not been able to get a good 134 conversion on a 300E as of yet. The system was not set up for the larger molecules of 134 and the oil gets absorbed by the hoses over time.

I would find the leak, then use 12.

PS, you can check for evap leaks by taking out the blower motor and looking in.