rickjordan,

When the car was new, and probably for a decade or more thereafter, it likely ran at about 80 degrees C or just a hair less.

Others on that frequent this site have noted in the manual that it says it is ok to run up to the red zone without damaging the engine. That may be true, but I believe there is some system degradation when the car starts running at 90 or 95 degrees C.

My Diesels have always had the needles seemingly glued about a needle's width below the 80 C mark, regardless of outside temperature and load when all is well. If my cars run hotter than this I take it to mean something is not correct, somewhere, something changed. With the simpler models, the W123 and earlier 240D and even older 220D, this was never more than a bum thermostat, leaking radiator cap or leaking water pump. The newer models have some complications with fan operations and automatic climate controls. I have not had the pleasure of having to dope these out yet on one of my cars, so I am not much help there.

So, I would figure, since the system used to be able to hold you at 60 degrees C, that the part you put in to regulate temperature, the new thermostat, is either faulty or somehow the installation was faulty. These thermostats are a little more complex than the average, as they have two sets of moving parts to control flow bypassing the radiator and flow returning from the radiator. Also, the system is pretty sensitive to venting, and any trapped air can cause problems with the operation of the thermostat.

So, I would try to make sure the system was fully vented. I usually do this by parking on a pretty steep uphill rise (which I have in my yard), with the radiator cap at the high point (right side of car more uphill than left). Then I fill the system, run the car with the heat on full and the radiator cap off until the temps get to their normal maximum temps. I fill with MB antifreeze and distilled water until the system takes no more, then I squeeze all the hoses a few times and do the filling exercise again, until it will take no more fluid.

By the way these thermostats go in one way, and they usually have a little vent hole that is aligned with the high point in the housing. With a bubble of air or steam on one side, thermostat will have a great deal of difficulty responding to the hot side water temperature.

I hope some of this helps, Good Luck, Jim

Car running @95 C = 203 F !!!!!!!!!!!!!
 

Recently changed the thermostat in my TD, which was causing the car to run at a mere 60 C. With the new OEM Behr 80 C thermo., she is now running at about 95 C. I recently figured out what that is in F., 203 degs. That is hot, but apparently not for these engines, because the red line is up at 120+ deg C, which is something like over 220.
Is everyone else running at this temp? Here it is I thought diesels ran cooler than gasoline engines, but I guess I was wrong. My VW Passat with a 1.8 liter turbo runs at a solid 190F.

Thermostats have been known to be bad out of the box, more common now that it used to be.

Should run right at 80C, or 85, depending on application, 95 is too hot.

Check hose condition, fill state (you could be low on coolant if the engine "burped" air after you filled it), and the rad could be crudded up. If you have an aluminum radiator, suspect it as the culprit. You can remove it and have it checked at a radiator shop for flow, or CAREFULLY check to see if it is uniformly warm after running. Cold spots indicate plugging.

Also check that the visco clutch is working -- you should hear the start to roar as the engine gets above 90C, and the aux electric fan must come on at 100C or so.

Peter

I read a message over on the other forum having to do with over heating that I had never heard of before. The "seat" in the T stat housing that the bypass part of the S stat seats against had corrosion, allowing coolant to flow past when it should be flowing through the radiator. I wonder if that is a common problem ? It sure wouldn't, hurt to check it out if your replacing the T stat or before spending the $ for a new radiator.

Also I read someplace that MB started using T stats that ran hotter because of emissions and folks were having better luck with Auto Zone or Pep Boys T stats. Totally to be taken with a "grain of salt", Just thought I would mention it in case anyone had ever heard of such a thing

The same thing happened to me at one night when it was like 0F or something extremely cold.

The water temp would hover at 95C?!@ But if I drive it more the temperature would go back to 80-85C again. It's when I baby the throttle (drive gently) that it goes back to 95C..

it hasn't done it ever since. I'm guessing it's the T-stat.

my gauge usually hovers about covering the top loop of the '8' in the 80 mark ie. horizontal. this is the usual driving mode. on hills or xtra hot outside conditions on the highway it sometimes goes slightly higher. i consider this normal for the car.
i am running a bosch t-stat.

Peter (psfred),

Considering his initial complaint, the car was running at 60 degrees C, it would seem the problem really is a thermostat, or a trapped air, issue. Hardly seems reasonable that after changing the thermostat the car now overheats due to either a viscous clutch issue or a crudded up radiator. If that were the case he would have had the problem before as well, or do I have this picture out of focus?

rickjordan,

A question. Does the car get to this temperature under load or while idling? Do you get any gurgling or other noises when the car is running with the heater on (listen from inside the car near the center dash vents)? How does the interior heater work? If you turn the heat all the way up does the temperature drop?

A little more information will help figure out where the problem is. Good luck, Jim

I really didn't think there was a problem per say. I was just commenting on how hot 95C is in farenheight (sp). My problem WAS the car would not get above 60c, regardless of what type of driving. The air from the vents was luke warm, and the radiator was only warm to the touch. So the engine was running too cool. Also, my fuel economy was in the very low 20's. I presented this problem to the "collective" here and everyone said it was the thermostat. I changed it and all my problems went away. The radiator on this car has been replaced, it doesn't look too old. Again, I didn't realize that there may be a new problem. Since redline is just above 120 C, I figure 90-95C is fine. Nothing is leaking, my coolant level is fine. Even when I am driving 75 mph, the temp stays on 95C.

Mine runs at what I assume to be 90-95*, the needle is straight accross to the 9 o'clock position, maybe a little higher and it never moves from there. New T-stat was installed right before I purchased the car. I do still have a wierd "invisible" coolant leak though. Leaves a small, like quarter sized puddle of coolant when it sits for more than a day. No traces of coolant anywhere on the engine, hoses, etc. Its a "magic" leak.... RT

Jim:

Possible, not very likely, unless the outside temp came up at the same time, to where the rad won't cool enough once the engine comes up to temp.

Just commenting that 95C is rather hot, and if fill problems weren't the cause, what else to look at.

And there is such a thing as a bad thermostat in the new box, there have been several reported on this forum!

Peter

OK, now I am confused. Back when I originally posted my problem on another thread, alot of people were saying their cars ran between 85 to 90C and that my 60C was definetly too "cold". Now that my car is running at 90+ C, everyone is saying that is bad, despite the fact that the redline is some 25degs. higher than that. Is the "collective" saying that the thermo. is bad and not opening until 95C? Being it that one can't actually look into these radiators, how do you tell if she is plugged? As I mentioned before, even cruising at 75 mph, for 45 minutes, the temp stays at about 95C. Obviously as it gets warmer out, I will keep an eye on it.

rickjordan,

The point I was making is the car comes from the factory running at about 80 degrees C. This has been the case for all my cars, gas or Diesel. Gas cars will heat up a little in stop and go traffic, especially in the summer and you can hear the various cooling aids come on to keep temps under control - the viscous clutch for the main fan and the auxilliary electric fans. At running speeds, especially highway speeds, even my gas cars run at an even 80 C in all weather.

If your car is running above 80 degrees C, it is not the factory normal temperature and there is a reason. The most common candidates are the thermostat operation being out of specification, or low coolant level.

Now to your question. The manual says all is ok as long as you do not run in the red zone on the temperature gage. So, I guess it is ok to run at 95 degrees C.

I can tolerate a lot of little, non-vital stuff on the car being out of whack, like cracks in the dash or knobs that have developed idiosyncracies that I have learned to live with to turn things on and off. After all I have wrinkles on my face and joints that have developed noises and other idiosyncracies over the years too. But I cannot get used to the temperature gage pointing above horizontal. Drives me nuts because for thirty three years of driving these cars the gage spends 99% of its time horizontal after the car has warmed up. So, 95 degrees C would unnerve me, and I would have to find out why the car decided to run hot. Even if it is not too hot.

Sorry if I am alarming you needlessly. Good luck, and I hope this helps, Jim

I thought factory TS spec was for 87C ?:confused:

Everything I've heard and read says that NORMAL operating temps will vary from ~85-105C with 85C being casual driving on flat roads, etc. and 105C being perfectly normal when chugging up a mountain side.

My car, coincidently, ran for the longest time smack at about 87C (from best I could tell from the gauge) and would maybe get to about 90C in the summer with the A/C, etc.

Just the other day, I looked down while at a stoplight and noticed the gauge sitting at 110C. Long story cut short, I had recently changed out the waterpump and coolant and introduced air in the system that gave me the gurgling heater in the dash noise.

I think that this air pocket worked it's way out yesterday and ended up leaving my system about 1.25 gallons short of coolant. After filling it back up, the temps have come back down.

So...anyway Rick, my opinion on temps are anything from 85C to 105C are *normal* under their given driving conditions. Although, I would have to say that a car running consistently at 95C during normal driving conditions warrants a second look...I'd even go so far as to verify that the temp sender unit isn't lying.

How does when verify what the temp sending unit is indicating? When I drive the car again, I'll check the radiator for cold spots. Since she is not running near over temp, I am not too concerned, but as Jim has alluded to, it's worth looking into.

Rick,

The only way I know of to verify the existing sender w/o removing it is to get ahold of one of those laser temp readers and take a temp reading RIGHT WHERE the sender is sitting.

Otherwise, I think you'd just have to replace the sender with a new one (but this doesn't mean the new one is correct either :p )

I think that there's a voltage-temp conversion and you could measure the voltage output from the sender and see if THAT voltage corresponds to the temp your gauge is reading.

Otherwise, dunno :)

...and yes, I agree. Constant 95C temps certainly justify your suspicion.

Chris
'85 300SD

Rick:

Did you get your new thermostat from the dealer?

Seems there was a bad production run of thermostats - and they all went to dealers. :)

I'm serious - I've been following the issue now for over a year.

Get your thermostats from anyplace but the dealer.

Ken300D

Actually I got it through Fastlane. It was the same exact model, temp., etc. that was in the engine.

Another .02
 

It seems that MB diesels built after 1985 run hotter. When I bought my "87 SDL (new), it ran about 88-92C on the open road, (Don't remember the city temps.) Last summer I got a new water pump, t-stat, and much needed fan clutch. Now it runs at 88-92C on the open road (even in 20F weather) and approx 98-103 in city traffic in 100F summer weather. According to published specs, the aux fan doesn't even click on until about 105C ! My 1987 (SDL) manual and my 2000 (ML, gas) manual state - and I quote from the manual: "During severe operating conditions and stop and go traffic, the coolant temperature may rise close to the red marking." The 2000 manual goes on to say don't run the engine in the red marked area. I figure that the temp. gage may be off about +- 5C. Also, in commerical truck diesels, a hot diesel is far more efficient than a cool running one. Of course, what we are all discussing is what is too hot. Now, if you are running 105 - 120 C on the open level road, I'd say that you have a problem. :)

Rick,
If the car runs at the 95C mark and never gets any warmer or boils over I don't see why there is a problem. 200-205*F is not that hot. With a cast-iron engine you don't really have to worry until 245*F/120*C so don't sweat it. You could have several issues here. The T-stat might be slightly out of spec, the gauge/sensor might be slightly out of spec, the radiator may be getting tired. Drive it, keep an eye on the gauge and enjoy your MB. RT

My "Big Benz" runs at the halfway mark between 175 and the red zone in traffic, but if I open the hood, the radiator won't be very warm. I've concluded that either the new t-stat isn't 75C or the temp gauge is a bit off. More likely the later, it's 31 years old.....

Peter

I have heard that "if you can hold the upper radiator hose w/o discomfort its NOT to hot" I have pulled over a couple of times when I thought she was a little hot and used that test.

BTW my gauge needle used to jump around now and then. I changed the temp senors and that fixed that.:D

For what it is worth, I just finished a road trip today in my 81 300D and the temperature sat halfway between the 80 and what think is the 100 mark. So I was running about 90 degrees at 70 miles an hour. I thought that was ok - but now you guys have me worried! I just went out and checked the coolant and it is fine. The only time it ever operated above that point is when my water pump failed and I had to repalce it.

I'll just keep an eye on it as the summer gets here, but I'm inclined to think it is ok.....guess I am just paranoid!:)

Something I found with my 82 240D was that the Temp gauge reads high. It reads about 15C hotter then it should. Checked this with hot water, candy thermometer and a new and the old sending unit. Hooked up sending unit(s) to engine wiring then put sending unit into hot (160F to 200F) water then checked gauge and found gauge to be the problem not engine or radiator. This of course was after I tried everything else I could think of and spending lots of Money. So maybe it would be wise for you to check and make sure your gauge is actually working correctly before replacement of many expensive parts. Learn from our mistakes that’s what its all about.

Bill

If I'm not mistaken, on the 300D turbos, the thermostat doesn't reach its "fully-open" position until_94°C. Mine runs right around 90 to 93 in 85 degree Florida weather under normal driving conditions. I wouldn't get too worried about 95°C.

Rick,
As long as your car can handle pulling decent hills in hot weather don't worry about it. You likely have a bit of air in the system that will probably work it's way out. There are so many places that things like the sending units, gauges, thermostats, etc. can be a little bit off that you can drive yourself nuts trying to get your car to be just like everyone else's. Ultimately, if it's not overheating in hot weather under heavy load you have no problem. Unlike gassers that can get preignition problems if they run a bit on the hot side, diesels actually like it.

A brief remark
 

Once I read in a newspaper that operating temperature of 80 degrees is a good one for a petrol engine, 85 is even better, considered perfect. Diesel engines have their operating temp 5 degrees higher than petrol engines- that would make 90 degrees.

With our new 280E the operating temp, indeed, was 85 steady. No matter what the driving conditions were, it had 85 degrees. Now 10 years later the temp rises a few degrees but doesn't exceed 90 degree mark (unles driving in stop-and-go traffic, A/C on etc but that is considered normal).

My 250TD (2.5 Turbo) has its operating temp 85 degrees also when driving in a standard way, though the temp climbs happily to 90-95 in hot summer days, even 100 in stop-and-go traffic. I don't consider this to be a problem, diesels run hotter than petrols, 90 is by all means a perfect operating temperature and variations (95 degrees for example) are a part of running the engine under daily conditions.

Mind that a new petrol engine will run 100 degrees and more when the day is hot and your A/C is on and you hardly move on in traffic. You are only to start worrying when the temp does not go down when your cooling aids kick in or when the temp does not go down when you start moving, allowing more cooling air past the radiator.

Leave it alone Do Not Do What I DId
 

Hey folks,


Ya know I played with the thermostat too much and broke a bolkt off in the housing. ALWAYS USE NEW BOLTS AND ANTI SIEZE.

I wanted it to run cold in the summer and warm in the winter. And while changing out the thermostat *#$&#(*%&@ I broke the bolt off.

That was no fun.

Now I have it at about 90 and if it goes up to 105 I will accept it. I would rather have heat in the winter.

Cleaning the fins on the radiator helped out alot but becareful I broke that too.

Bye

bob c

I've said this so many times I think I'm a broken record: If the gauge temp is above 80C and almost never exceeds 100C, that is NORMAL and don't waste your time or money chasing down a "problem" that doesn't exist.

The thing to look for here is minimum temp of 80C, if it's too low, the problem is most likely a bad t-stat and/or the sender in the head. The senders, when they get old, sometimes read too LOW. A new one is $10, I've replaced them on all my cars as cheap insurance. The other thing is max temp on the gauge under severe conditions - usually the hottest day of summer with A/C on max. Most cars should stay in the 100-105C range here and not get above that. 110C+ may indicate a problem, but regardless the danger zone is 120C+ if your rad cap is ok.

Different engine t-stats (yes, they ARE different for 616, 617, 602, 603, turbo & non-turbo, etc) have different specs. Just because it's rated to BEGIN opening at 80C (like my 603 turbo) does NOT mean the gauge should read 80C! They're usually full open by ~95C, the specs are in your MB service manual - go read it. If your car is running too hot... i.e., 100C+ most of the time, yes there is likely a problem. And yes on the OM61x engines there was a recent discovery by Bruce on the MBZ list that the t-stat housing can corrode and prevent the bypass from sealing off, making the car run hot even with a good rad, t-stat, and fan. Replacement of the housing (~$100) is the proper cure although he did a t-stat modification which also worked.

And of course each car will be different due to a zillion variables. For reference, my W123 with an almost completely new cooling system runs at ~90C year round. Maybe a smidge cooler in winter, but never above 95C in summer, ever. Is 90-95C too hot? NO! IT IS NOT! (deep breath) My one W124 with the new head, and also totally new cooling system, stays parked at 90-95C year round, same deal. I have seen it hit 100C a couple times in 110F ambients or climbing a steep grade, but that's it. Same deal - it's NORMAL. My other 124 has a cracked head/gasket and although most of the time it runs at ~83C, it fluctuates a lot more, popping up to 95-105C at times when it really shouldn't. I don't worry too much because I *know* what the problem is, I just haven't fixed it yet.

In summary: Please don't expect YOUR car to run at 80-85C and freak out if it doesn't. BT, DT, spent the last 5+ years learning this the hard way. Please do change your coolant every 3 years with MB anti-freeze only, make sure the rad cap is good (1.4 bar), and the radiator fins are clean on both sides.

BTW - my post is referring to all MB diesels only, OM61x and OM60x - not gassers.



Regards,

TTT
 

TTT

Re: Car running @95 C = 203 F !!!!!!!!!!!!!
 

rick, the real test would be to bring it to the new england gtg
this saturday:D :D