gocargo

Searching the forum, I read that the 1990-92 300sl models do Not have the dreaded "deteriorating wiring harness". Is this accurate information?

Do all the 104 engines have the head gasket problems around 100,000 miles, even the early r129 300sl?

Thank you..
-Brett

HaraldZ

I have a '90 300SL with 94k miles. Replaced head gasket around 65k, no issues with wiring harness and don't expect any either, those issues started with MY 95 if I recall correctly. Also have oil consumption issue due to sticking piston rings, added a lot of engine cleaners and it has gotten a lot better.
Harald

sl3204me

The wiring harness insulation deterioration has been documented on higer mileage 1993-1995 SL 320,500,and 600 models.I was told it was due to heat in the engine compartment over time.I suspect that earlier MB models will eventually have problems also.Environmental regulations were the culprit.I was told after 1996 the harness manufacturers were changed and the problem was solved.I am one of the unfortunate SL320 owners who experienced the full brunt of wiring harness deterioration and it subsequent electrical problems(instrument cluster malfunction,alternator and voltage regulator replacement,4 harness replacements and repair of some wiring harness underneath the main ECU unit.The MAF meter harness was affected and almost started a fire.Thanks to a very competant MB master electrician he was able to replace the harnesses and repair the few melted wires thus saving me $7000 to replace the harnesses behind the dashboard Yes you heard me correctly $7000.It turns out the harnesses underneath the main computer in the engine compartment are extremely expensive and if they are damaged beyond repair,the the dashboard,seats, everything must come out.So my advice,if you wish to accept it Mr Phelps,is to have any 90-95 SL thoroughly checked out by a MB naster electrical technician and have him look under the main ECU also.Spend the money to have everything fixed correctly.It will not only give you peace of mind but save you thousands in the long run.It is such a shame that Mercedes just doesn't have Honda or Toyota manfacture their harnesses.It would save MB owners thousands of dollars and probably be cheaper for the company.

sl3204me

My 1995 SL320 has 93,000 miles now and MB has told me that head gaslets leaks are common on the 320s.Also MB recommends changing out the timing chain at 100,000 miles.Since I am having no strange noises in the engine,everything is smooth and quiet,and the compression in all 6 cylinders is at or near factory specs along with cooling system pressure checks,I suspect that these 2 items need to be evaluated by your MB technician on a case by case basis.My tech told me he has seen many 3.2L engines go to 150,000 miles before the belt and guides needed replacement.MB is using Mobil 1 oil now in the SL models,so engine lubrication should be excellent and with periodic tuneups,I think head gasket and timing belt problems won't show up until well after 100,000 miles.

j0shua

This is cause for concern. My '92 300SL-24's hitting 95,000 miles. The instrument cluster lights up randomly whenever I indicate left or right, or when the hazards are on. The hard-top release and the entire soft-top mechanism does not respond anymore. The car's ECU failed about a year ago, and that was fixed, but it hasn't felt the same since. There was some work done on the wiring harness previous to this about 5 years ago, there was some repairs to several of the behind-dash wires to rectify some issues, which I can't recall.

Basically the car is loaded with issues, and I'm about to launch a last-ditch effort to fix her up. Other that these issue, the car drives pretty much okay; it just recently had a new radiator installed as there was a leak, and that has sorted out the slight overheating issue. The gearbox was also overhauled a couple of months back.

Thing is, the replacement of the wiring harness will undoubtedly cost a bomb. Repairing it will be cheaper, but how can I prevent further heat damage?

SL320MAN

Does anyone know if the main ECU hard to remove or it this a job for stealership? I am trying replace the wiring harness which has the MAF connection on my 95, sl320.