In the thread "lowering coolant temp -Success Story" Tkamiya states"The only problem with the "boil test" is that most MB cars (gas) has 87C thermostat. 87C is a start-to-open temp. It won't fully open until 102C. "
Those familiar with old threads know that many members in the heat of summer say their cars never go over 90C. There is also many members, including myself, who complain that their cars run too hot 100C-110C. Some say the higher temps are normal some say not. Some of us have spent a lot of money trying to get the temp down to no avail.
Now if Tkamiya is right about the thermostat not being fully open until 102C - is THAT temp considered normal?? If the thermostat is rated at 87C shouldn't it be fully open at that temp. On my older NA cars in the past when I bought a 165F thermostat - it was open at 165F. If Mercedes only START to open at 87C - then how in heck can people in hot climates be running at 80-90C???
I AM TOTALLY CONFUSED NOW! Any way we can nail this down once and for all??? I normally use logic to troubleshoot - but something does not make sense here - how can a car run at 80-90C in hot weather when the thermostat only BEGINS to open at 87C???

Over 100C is normal in hot climates. The temp on MB thermostats is the temp at which they start to open. A lot of the time, as thermostat gets old, it starts to open at a lower temp.

If your temp is holding steady at 80C, you need to replace the thermostat. I replaced mine when I changed the coolant, and now it is back in the upper 80s to 100 range. Before I replaced it, the temp was running 82C on the highway.

Think about it, if MB thought that running 100C was not normal, then why did they design it so that a properly functioning thermostat should still be restricting coolant flow into the radiator at 100C? The fan clutch doesn't even start to pull mass air through the radiator until 95C.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

Like most of us, I suspect, I too have labored under this issue of "Is my engine running too hot?" I wish I could really remember what mine was like when I first got it (3 years old, 25 k mi on the clock) but I was not as finnicky or observant then as I am now. The preponderance of the data I've read lately is that just about anything under 110 is OK. Even then, I am not reassured. This winter, it's been mild here, so we have been getting lots of 40 degree F days. On those days, on the interstate, my temp is around 85-90. Seems to me that it SHOULD be 80, like it is when the ambient temp is 35 or below. But then I read that 87 degrees on the coolant gauge is perfectly normal, and that running cooler puts more wear on the engine.

Part of the "problem", if there is one, is that MB uses a linear gauge. Most other manufacturers fudge on gauge readings, probably to prevent owners from complaining and running up needless warranty claims. Every Ford and Toyota and Honda I've owned has had a rock-steady temperature indication once the engine is at operating temperature, every day of the year. THis is an artifact of the electronics used, since I'm pretty sure just about any engine should show some variability in temp depending on season, stop-and-go vs. 75 mph, etc.

MB engineers apparently think we "CAN handle the truth" to paraphrase Jack Nicholson.

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Steve
'93 400E

Thank you all for forging through all of this.

Living in N. California, where the temps can range quite a bit-(Sierras in the winter to the valleys in mid-summer), I too have watched the temp gauges on my diesels (past cars) and with the current ones ('91 300E & '95 E320 Wagon) and wondered what was OK and what was not.

I have driven through Death Valley during a "mild" summer where it was "only" 129 in the old '82 240D. I have also driven through a -15 night in the high peaks. What I have always come back to was what Mercedes recommends.

I have been educated through your comments, research and postings. I was never quite sure where MBZ's temperatures were supposed to be.


Thanks again for this.

Specs for my C280 are all exactly the same as tkamiya posted except for the aux fan control:

Low speed cuts in at 100C and off at 95C coolant temp or
Low speed cuts in at 16 bars and off at 13 bars refrigerant pressure

High speed cuts in at 115C and off at 107C coolant temp or
High speed cuts in at 20 bars and off at 17 bars refrigerant pressure.

So, for my car, they modified the aux fan so that it will run on high speed under high refrigerant pressure. They also added a low speed cut in based on coolant temp, and changed the high speed cut-in so that it does not come on until 115C.

If my car ran 80C on the highway, I would immediately change the thermostat due to the fact that it would have to be broken for this to be possible. My car should not run under 85C, and if it did, I would correct the problem.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

I can say that with my car, when outside temps were 25F and I was going around 70 MPH on the highway, engine temps stayed steady right at 87C.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

I while back I saw an older article (see link below) stating that engine wear increases rapidly at temperatures under 170 F (77 C). What I think is the most damaging to an engine is cold start owing to the pistons expanding faster than the cylinders. I always try to get my engine to temperature a.s.a.p. without revving it over 2500 rpm or so. Also, I believe synthetic oil goes a long way in reducing wear during cold starts. Quite frankly I'm more concerned about hot running engines than cold running ones.

http://www.gi.alaska.edu/ScienceForum/ASF7/747.html

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Reno

'93 300E 4Matic
'98 Nissan Altima
'00 Yamaha Road Star Silverado

GREAT DISCUSSION!! - So those of us who are at 100 -110 should (pardon the pun) chill out. It is normal. So if we can accept that up to 110 is normal (depending on outside temp - & air cond on) I have only one other question before my queasy stomach relaxes. When someone says their Mercedes overheated and the engine was damaged --- what temperature did it hit to do the damage??? As a side note- my car(88 560sel) is in storage for another 2 months. As soon as I get it out - I have an infra-red non-contact laser guided temperature reader - I am going to check the temperature on the motor, rad and hoses and compare them to the guage in the dash. Maybe those whose gauges read 80-90C normal are off or maybe ours at 100-110C are off - when I find out I will post results.
I think I speak for a lot of us when I say all we trying to do is ensure we don't unintentionally damage our prized cars by running them too hot.

Hi Moedip,

For one thing, the higher the temperature the faster the oil degrades and loses its lubricity. One has to be more conscientious about oil changes and fluid level checks (engine coolant and oil) with hot running engines. Also, heat damage being cumulative, check for operating temperature creep over time as this is a sure sign that something is going wrong. As you said, temperature gauges are not very reliable in absolute terms but they can tell you, in relative terms, if your maximum operating temperature is creeping up.

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Reno

'93 300E 4Matic
'98 Nissan Altima
'00 Yamaha Road Star Silverado

Makes sense to me. My 560,if outside temp is about 88F or lower with air cond on never goes above 100C - 90C max with air off. However- I drive down to Indiana to visit my sister every summmer and the temps there are usually 95-100F. Under these conditions cruising down the highway at 70MPH my max temp is 100-105F if I put the air on it starts climbing over about 3-5 minutes to 110 at which point I turn the air off, sweat, and continue till it drops again. In my worries about overheating, I have had the rad flushed and tested (it is 100%), new hoses, thermostat (twice), new water pump, new viscous fan, new rad reservoir cap. All changd with absolutely no difference with the temps. All I have left to try are the temp sensors. But if you are saying that if I let the engine go past 110C to maybe 115C - there would be no engine damage and I might be surprised to see the aux fan kicking in. At 110c now it does not kick in. I hot wired the aux fan so it is on full time and under the worst outside temp conditions with air on the engine will not climb over 100C. That is why I worried about 110C. Thank you very much for your input -- I am feeling more comfortable about higher engine temps.

To: Tkamiya
I sent you my email - please forward the article -I'd really appreciate it. Unfortunately you are wrong where I live. I live on the cold Canadian Prairies where we can get up to -45F tempertures, so my antifreeze has to be set for -50F protection as I have unheated storage. My daughter's car had a slipping alternator belt the other day - by the time she drove home with her lights on(45 minutes) it was too late. At -35F the battery froze. New battery time.
There are 2 temp. sensors I believe - 1 on air cond pressure and one for coolant ( I think) - since car is in storage till spring -that was my next step)to look up in cd manual and change.Are you referring to the coolant sensor when you say it can drift? Changing the air cond. one scares me as up here it is illegal to use R-12 as of Jan 1 this year. To change the air cond sensor means to convert to R-134, maybe change compressor to proper type - yadda - yadda -yadda - In other words - I really don't want to change it unless it is absolutely necessary as my air cond works great!

To :Tkamiya
Thank you for your help. Please don't forget to email me the article.
Many Thanks
Maurice

send to: mdepiero@mb.sympatico.ca

To Tkamiya:
I got the article - Thank you very very very much. The work I could have saved plus the money!!!! Unbelievable - IT REALLY IS NORMAL to hit 115C!!! May I quote from the article " if the outside air temperature is in the 90's and you have the air conditioning on full blast with 5 people in the car - you can expect to see 110C on the guage" NORMAL NORMAL NORMAL. Please contact the Moderator of Tech Help and see if you can upload the one meg file to a thread - I guarantee you there are many Mercedes owners out there who are just as paranoid as I was. I think it would be a great service to make this article available to ALL members who request it. I now firmly believe after reading that article that anyone who has a Benz that is running at 80-90C when the outside temp is 100F - has a faulty guage or sensor. Oh Man - the hours I wasted - Phil should stock up on Red Line Water Wetter and try to get Mercedes Antifreeze - Never thought of the Ph factor!! Sorry for rambling - I am so relieved!!! If the Jpeg files are too large to post - let me know and I have text recognition software that can convert the images to text . If there is too much text I can post the three pages individually. I can do it early next week. Have a Great Week end!
Maurice

Jimf has done extensive research on this Perhaps his website might help.

http://pages.prodigy.net/jforgione/MB_S500.html

Kuan