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  #1  
Old 05-08-2006, 01:54 PM
W129 SL Fanatic
 
Join Date: Apr 2006
Location: Sunshine Coast, BC, Canada
Posts: 12
SL320 Running too hot!

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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  #2  
Old 05-08-2006, 07:18 PM
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Join Date: Dec 2005
Posts: 16
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.
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  #3  
Old 05-08-2006, 11:36 PM
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Location: Phoenix
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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.
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  #4  
Old 05-09-2006, 01:15 AM
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Location: Southern California
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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".

Last edited by Duke2.6; 05-09-2006 at 01:27 AM.
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  #5  
Old 05-09-2006, 05:56 AM
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Quote:
Originally Posted by Duke2.6

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
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  #6  
Old 05-09-2006, 08:12 AM
t walgamuth's Avatar
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Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 32,114
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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  #7  
Old 05-09-2006, 10:12 AM
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Diagnostics uber alles is as silly as the opposite. Throwing parts at a problem is very often a viable solution - if the part is old, the replacement cheap, easy to replace yourself, and a possible solution. A shop can't really do it - but for a DIYer it's often the way to go, especially if the part costs $5 or $10 or $25, etc. and you plan to keep the car for a while. Do it for a few years, at a cost of no more than a few hundred dollars, and you will have a very strong reliable car. It's the pure extremes that get silly - diagnostics all the time, or throwing parts all the time. There is nothing worse than paying a shop for inconclusive diagnostics and then throwing parts at the problem, which happens more often than you think - as evidenced by threads on this forum. This would be different if diagnostics were an exact science but it isn't - far from it.
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  #8  
Old 05-09-2006, 10:29 AM
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Some of the ill-informed posts I see on this forum are simply amazing.

The diagnostics I suggested for this situation take all of about five minutes.

Duke
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  #9  
Old 05-09-2006, 11:00 AM
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Join Date: Apr 2006
Location: Sunshine Coast, BC, Canada
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Thanks!

Great info folks. When I suggested that I was going to pull the thermostat, I didn't mean to imply that I was looking at a solution. If the engine stayed cool under the same conditions that indicated overheating then that diagnostic would certainly point to the stat. The likelyhood of me getting an IR scanner is pretty slim. I live in the boonies, a boat ride and a couple of hours from the nearest large center. Aren't there some kind of special wax sticks that melt at different temps used in cooling system diagnostics? (Yes, I'm THAT old..) I spent some time with the hood up and my head close to the viscous fan to listen and watch. I could hear the clutch engaging as the engine warmed but it sure seemed feeble, with kind of a metal to metal slipping sound. It didn't seem to move a lot of air but I'm not sure what 'normal' is. The contacts of the sensors on the thermostat housing look like new, but I cleaned them anyway. I'll certainly post as I work through this so we can all share in the solution. Thanks, Lou
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  #10  
Old 05-09-2006, 11:30 PM
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Quote:
Originally Posted by Duke2.6
Some of the ill-informed posts I see on this forum are simply amazing.

The diagnostics I suggested for this situation take all of about five minutes.

Duke
Not everyone here is an expert but at least they are trying to get the information and trying to help someone else. Some information may not be correct but usually a more experienced member will politely indicate this.

Regarding the diagnostics many "newbie" owners don't understand their car's systems and don't have the tools to perform the diagnostic procedures. While its not the "correct" way to service your car it often works for many people at a considerably cheaper price. Technically the correct way to service your Mercedes Benz is to turn it over to the dealership and let the factory trained technician service it and pay the bill when you get the keys back.
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  #11  
Old 05-09-2006, 11:35 PM
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Join Date: Mar 2006
Posts: 783
Quote:
Originally Posted by deanyel
Diagnostics uber alles is as silly as the opposite. Throwing parts at a problem is very often a viable solution - if the part is old, the replacement cheap, easy to replace yourself, and a possible solution. A shop can't really do it - but for a DIYer it's often the way to go, especially if the part costs $5 or $10 or $25, etc. and you plan to keep the car for a while. Do it for a few years, at a cost of no more than a few hundred dollars, and you will have a very strong reliable car. It's the pure extremes that get silly - diagnostics all the time, or throwing parts all the time. There is nothing worse than paying a shop for inconclusive diagnostics and then throwing parts at the problem, which happens more often than you think - as evidenced by threads on this forum. This would be different if diagnostics were an exact science but it isn't - far from it.
Exactly! I get offended when a shop throws parts at a problem because they are supposed to have the knowledge and tools to "correctly" solve the problem. However in the driveway when I have read on the message boards that about 10 people have had the same problem and 8 people's problem was solved by repalcing part X. Its likely that part X will solve my issue and save me some time. Even if the part does not solve the problem the new part is likely not to fail and buy some additional reliability.
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