Hi folks, took delivery a 1994 SL320 on the weekend. 133k km (82k miles). Searched the forum and found similiar problems or solutions but not quite the same so I'll post. The first part of the trip home was a ferry ride and 200 km of highway. No problems, what a car! Temp sitting rock solid at 85-90C. As soon as we got into a city, stop and go driving within 10 minutes the temp gauge is floating between 115 and red line with the 2 electric cooling fans kicking in and out. We stopped, let things cool down, checked coolant level which was fine. Cooling system serviced and tested to -50C by MB in 2005 according to the MB tag wired onto overflow reservoir hose. There was residual pressure at the cap on the tank. I don't know which type of fan clutch is used on this model but even when the engine was indicating hot, I can easily hand spin the main fan (engine off of course). Where should I start looking? I was going to pull the thermostat and run without it and check it in hot water but some are saying a MB shouldn't be run without it. The serpentine belt is in great shape, good tension and the water pump visually looks fine, no leaks or siezing. I'm 3-4 hours from the nearest dealer and a reasonably competent DIY'r, just new to MB. Any advice appreciated.

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1994 SL 320 White

I had a similar problem on my 95 C280 and after flushing system and replacing thermostat I changed this. Problem solved. I'd still check the thermostat. The viscous fan will still spin fairly freely even when hot.

Under the heading of it's cheap and it could be the problem, get a new radiator/expansion tank cap. A bad seal can cause overheating problems. Should be about $5-10.

If it got up to an indicated 115C, and there was no coolant loss then you don't need a new themostat, a new pressure cap, or a new whatever that will likely be suggested. And removing the thermostat to "fix" a cooling problem is just plain stupid, but bubbas do it all the time.

If it has a viscous fan clutch check that it tightens at about 100C. If the electrics engage high speed at 105C, then they and their control circuits and components are okay.

Check the temperature gage connector at the engine sensor and make sure it is clean and making good contact.

If the fans and temp sensor connection are okay get an IR gun and check the temperature of the thermostat housing and upper radiator hose and compare to the gage when it is reading high.

Chances are the "problem" is the temp sender unit, a connection in the circuit, or the gage itself.

In stop and go driving, it is normal for these engines to get to 100-105C. Running the A/C may actually make them run cooler since A/C system demand will energize the electric fans at low speed, which will slow the rate of temperature rise and maybe keep it lower unless it's over 100F outside.

Duke

P.S. To those of you who suggest swapping parts willy nilly without even a thought of diagnostics or discussion of how the cooling system works, you're better off spending your time gaining some system knowledge and learning diagnostics rather than posting "solutions".

Hmmmm,

Kinda harsh eh? A lot of the "willy nilly" parts replacement suggestions you see here are based on people's experiences with the same problem on their own cars. Most of the information I have found on the forums is quite accurate. When 100+ people have had the same problem and a single part was the culprit in 97 of the cases Im going to replace that part regardless of having a correct "diagnosis" or not. Especially when that part has a high failure rate and is cheap.

Thats the whole point of a message board like this to share experiences. Otherwise you have all the information you need with your shop manuals and diagnostic equipment. If you enjoy spending all of your time "diagnosing" by all means do so. Some of us enjoy spending our time driving our cars

duke is a bit crusty sometimes, but there is wisdom in what he says.

rchase, i like your attitude.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.