Ian sl500

Hi,
I have bought a 1993 SL500 R129. Great condition and very low mileage and seldom driven over past 10 years. Been replacing the engine mounts, distributor caps, rotor and ball joints. Goes well now but for this issue. The temperature gauge on the dash will rapidly increase to about 40 degrees C and stays there. The engine appears to be over heating. The front fans don't start. Pulse in the top radiator hose to the engine and only slight pulse in the hose below the thermostat so I'm thinking the thermostat needs replacing and am arranging one now.. Not sure what else needed to fix the gauge and front radiator fans from starting. I'm thinking thse two issues are linked.
Does anyone have any ideas. Many thanks
Ian.

sushipaste

How many miles? Do you have any records of cooling work done?

Sounds like maybe you need a new thermostat and a coolant flush, and you should be good to go

Ian sl500

60,000 miles. Thanks. The radiator looks in good condition from the outside. I'll try the thermostat and the flush. Still wondering why the temperature gauge on the dashboard is reading so low.

sushipaste

I believe that’s typical symptom of stuck open thermostat, so replacement with a coolant flush should fix the problem

rideair

Could be the temp sending unit is bad at the engine. I'd suggest changing the thermostat and temp sending unit as a pair since you're already there. Also, if memory is correct, there's a sending unit that's part of the AC system that kicks on the two auxiliary electric fans, but don't old me to that.

Enjoy,

Ian sl500

Thx Rideair
Much appreciated. Ordereing the parts now so hopefully will be able to get onto it on the weekend. Hopefully the COVID things not to bad where you are I'm in Auckland NZ- two lockdowns and clear now but counting....
Regards
Ian

Kebowers47

Unfortunately, your vehicle was assembled during the several years when all the wiring harnesses had defective 'bio-degrading' insulation. The pvc plastic formulation would quickly fail in all the hot areas and crumble to dust. Carefully check each wiring harness i the engine compartment, including the electronic throttles, by carefully slitting the black plastic covering and looking at the individual wires inside. IF the wires are good, they look new. If they have defective insulation, they will be corroded, insulating plastic crumbled, etc. MBZ was able to pay-off someone and avoid having to recall all these cars and replacing the wiring harnesses. Many MBZ cars made with these defective parts 'died early deaths' and were scrapped when the Owners found they had this problem after the standard warranty period ended and Dealers would not warranty replace the defective wiring. People with the V-12 engines faced an over $20,000 bill for the job and many other models also cost more than the car was worth to repair the wiring.

Ian sl500

Thanks. I read about that risk when I was reseaching the car and factored $4K into the price of ownership. I put in a new thermostat. I then used a thermal image camera and found that the car isn't running hot and the fans do cut in at the right temperature. Got the wrong sender unit so still working on that. Fingers crossed.