83 300D running warm
 

'83 turbo, with 143,900 miles. In May, '05 due to the same problem, running warm, mostly around 100, I had the radiator rodded and cleaned, new thermostat, and seals. Ran great, never over 90 until 2 weeks ago. Now, same problem again and I replaced the fan clutch, as it was spinning too freely. Now, once again, the temp rises to 100 and will not drop below on its own, so, I shut the AC off and turn on the heat. It does this regardless of speed, and not consistantly. It goes days between "episodes".

I am back to square one, what should I do next?

Thanks in advance,

Keith

Mine also does that in episodes, most of the time it runs at around 85C with the needle pointing straight across, but othertimes, (especially at 70+ on the freeway) it rises to between 100 and 105ish, then stays up there till the next time I drive the car. It has never overheated though, even at max throttle up very long (miles) hills. I bought a new higher pressure aux coolant tank cap, the 1.4 bar version, maybe that will keep the temps more normal, my cap is in pretty icky condition, so who knows. Higher pressure= cooling system more effective....it should be here in a couple days, I'll report my findings once I have been running it for a while...the previous cap is only a 1.2bar when its brand new, and as the spring weakens it can release pressure when its not supposed to, which causes temps to go up.

your
 

water pump may be going south. did you check the weep hole on it?

tom w

pawoSD -

I'm gonna try that as well and am looking forward to hearing from you with your results.


T Walgamuth -

I edited my original post and inadvertantly deleted the water pump issue before I origianlly posted, my apologies. At any rate, no water at the weep holes nor is there ANY coolant loss. But I will keep a watchful eye on it.

Thanks to you both.

Keith

There is quite a bit of discussion in the archives about the 617 running a bit warm in the summer months. Many folks with perfect cooling systems can maintain temperatures that are close to 90°C. even when it's 95°F. outside.

But, others will observe the temperature climb close to 100°C. under these conditions. My SD is in this category.

Please understand that there will never be any damage done to your engine if you run it at 100-105°C. all the time. That red zone on the gauge is above 120°C. That's the point where you should turn on the defroster and slow the vehicle down. You won't hurt the head or the block at any temperature below 120°C.

This presumes, of course, that the cooling system is filled with coolant and that it is holding pressure.

There are several members who have done the same thing as you have done and replaced all the components of the system other than the radiator. But, in the end, it's the radiator that is usually the culprit. As they get older, they simply can't dissipate the heat as well as they could when new. This is especially true if the old coolant has not been changed on a proper schedule.

So, rest assured that you won't have any problems with the vehicle if you operate it with the temperature gauge at 105°C. If it goes above this value on a regular basis, consider replacing the radiator.

One other thing to consider, and often overlooked, is that if you use a coolant mixture of more than 55% antifreeze it can cause your engine to run hotter than normal.

Antifreeze DOES NOT dissipate heat very well. Check your coolant mixture.

Here is a Quote from Mercedes"

"Concentration
50% anti-freeze/corrosion inhibitor offers protection against freezing down to approx. -37°C. A higher concentration is only practical when the ambient temperatures are lower.
A 55% concentration of anti-freeze/corrosion inhibitor offers protection against freezing down to approx. -45°C.
More than 55% concentration of anti-freeze/corrosion inhibitor reduces the protection against freezing and has a negative effect on the heat transfer."

Phil

i always heard
 

that 5050 mix on antifreeze is optimal for cooling.

tom w

Brian,

I appreciate your response as it addressed my main concern, engine damage. Now I can rest easier.

Ordered a new expansion tank cap, but since the problem is only occasional, I'm just gonna let it ride for now.

Thanks to everyone elses' input as well.

Keith

I believe 50/50 is optimal overall, considering boiling point, corrosion protection, low surface tension, pH, etc. However, from a pure heat transfer point of view, pure water has higher heat transfer coefficients than a mixture. That's why race cars use straight water and some people run 60(water)/40(antifreeze) if they don't need good freeze protection. If you keep adding antifreeze and you get too far above 50/50 it will start to reduce cooling.

I changed out my lower radiator hose today, it was still in realy good shape, don't know how old it was....at least 4 years. I put in my new one with the block heater spliced into it, works great, leak free, I have yet to test the heater though, I'll try it soon and see how warm it keeps the engine. My coolant I drained out was sediment free, still perfect from a year ago, so I poured most if it back in and then added some more of my 50/50 mix to make up for what was spilled in the process of draining, ran it, temps are perfect now, with the new pressure cap on, holds 83C now no matter how I drive (thats 2C lower than before) I've yet to try it out on the freeway, but I'm hoping it will be good or stay lower than before at least....it generally went as high as 110C on the freeway.

The old cap was in definately worse shape than the new one, the spring tension is far different between them, I can barely press the new one with my thumb, the old one was rather easy to compress....

I agree.

There is no magic to 50/50. In fact, the best mixture is the one that will just barely prevent freezing. There is no benefit to prevent freezing down to -34°F. if your climate never gets that low. A 60/40 mix or a 75/25 mix will do just fine.

The lower the concentration of antifreeze, the better the cooling. Antifreeze has about 78% (approx.) of the heat transfer properties of water.

I have to add new coolant to the SD soon. I might just go with 60/40. We never get below 0°F.