Hey gang,
Thanks again for your help and feedback when I was working on my fender. It was greatly appreciated. Recently I have run into a new, more significant, problem and I was hoping to know if any of you have experienced a similar problem and if so if you found a good solution.

Here is the deal:
I live in a town about 20 miles from the town I work in, my wife and I commute back and forth the 1983 300d. The town we live in is in a higher elevation than the one we work in, so the ride to work is all downhill and the ride home is uphill at a reasonably significant grade all the way.

Recently, the engine has started overheating (temperature gauge pegs all the way over into the red and you can smell the engine overheating in the cabin) when we come to the first stoplight or stop sign after coming up the hill. Once we can start moving again after the stop the temperature settles back down around the 100 mark, but those temps at a stop are making me very, very nervous.

It does not show this overheating problem after driving around town or while driving up or down the hill to work, only at a stop after the 20 miles uphill at 60 mph on the highway.

I took it to our local Mercedes specialist (who has the patience of a saint and is a miracle worker as far as keeping this car on the road. He has spent a *lot* of hours working with me on my old car and answering questions for me). He replaced the leaking coolant pump, flushed the radiator and did a full fluid change which the car was due for anyway. He also replaced the thermostat and temperature probe.

Unfortunately, this has not resolved the problem. The engine is still overheating after the drive uphill. Our mechanic has said that the next thing to do would be to replace the radiator. He also mentioned that we could try cleaning the system out with a citric acid flush but is concerned that doing so could damage the radiator or heater core. My problem is that I do not think that I can convince the wife to spend the cash it is going to take to replace the radiator right now.

Our mechanic has said that as a stopgap measure to try to keep temps down at a stop we could run the defroster at full blast to blow off some of the hot air.

Does anyone have any suggestions or has anyone run into a similar problem and resolved it in a successful and hopefully not too expensive manner?

Damage to the heater core is completely avoidable; just clamp the feed hose.

Has the fan clutch been checked?

Running the defroster also runs the a/c compressor, which will contribute to the overheating condition. Run the heater only.

How much does your wife think a radiator costs?

First off, I would not continue to drive it if the temp gauge is maxing out. Bad for the engine. Depending on how steep the hill is and how much you are stressing the engine to maintain 60mph, this behavior might not be out of the ordinary. The first thing you need to do is put it in neutral at the stop light and rev the engine to increase the coolant flow through the block and airflow thru the radiator. It's also possible your fan clutch is bad and is not pulling enough air thru the radiator.
I'd also try driving up the hill at a slower speed to see what happens.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Nothing in this world more expensive than not doing required maintenance and abusing a vehicle, which is exactly what you are doing.

Ask your wife if she'd like to buy you a new cylinder head.

Stop driving the car, period, until you identify the problem.

Could be fan, could be rad (assuming your mechanic has done his work properly) rad's are easy, some of the Nissan 4x4 ones fit with some minor hose mods if you can't find a local MB OEM part.

Either way if it is smelling that hot you are guaranteed to be doing irreparable damage to the car...

If you wouldn't mind humoring me in a completely silly question, the mechanic probably did say heater not defroster. Which button on my control panel is the pure heater going to be? The far left one, right?

Well, my wife and I were quoted about $450 for the radiator plus labor.

Heat without a/c is the EC button; fourth from left. And full hot selected on the temp dial.


You can buy a decent aftermarket radiator for around $200. And your radiator is very easy to install.

We just replaced the fan belts last year, so hopefully those haven't gone bad already. While I appreciate the sentiment of trying to sell my wife on the fix now rather than the cylinder head later I doubt it would work. We both have basically pegged this car for end of life considerations at this point, as much as I've loved it for the last 10 years. It seems like we've spent more time with it in the shop or me under it on the weekends the last six months than with it on the road.

It wont be dying a natural death. It's homicide.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Running the heat on max high will help bring down the temps.

I just bought a new Nissens radiator and replaced it myself. Very easy job that you could do yourself. You might could also try cleaning the outside of the fins on the radiator and the condenser. If it's nasty a grimed up, air will not flow through it very well.

__________________
www.myadvoforum.com
http://advopal.com

As counterintuitive as it may seem to you, running the a/c compressor does not contribute to lower engine temperatures. You also apparently do not realize that the temp control is nonfunctional in the defrost mode.

What do you suggest as far as my next steps to diagnose or fix this? How can I tell if it is the radiator vs a fan problem vs something else? I will try out running the heater full blast and revving the engine in neutral at the stop on our way home tonight to keep the temps down in the meantime. As far as not driving it at all, we do need it up and running as our transport to and from work. We can use my wife's car in the interim but there are days when we have to drive separately.

Study up on the component known as the fan clutch. A bad clutch will defeat the best belts available.

You can check the clutch by watching the fan as you shut down a hot engine. If the fan continues to spin after the engine stops, the clutch is not working properly.

when I get home tonight I will check my service records from when the belts were done to see if the fan clutch was done as well. If it wasn't, how much do they run? A quick Google is turning up about $170, does that sound right? How difficult of a replacement is this component?

Any suggestions on how to narrow down the problem to specifically the clutch, radiator or whatever else it may be?

Aftermarket units can be had for less than half that amount.


You have to unclip the fan shroud and remove eight bolts. Four of them are a little bit of a challenge.

Where is the best place to find a guide for the radiator replacement and/or fan clutch? The only manual I currently have is the Chilton generic one and as you can imagine, it isn't very good.