Mercedes 126 -V8 -What temp is Overheat?
 

89 560sel. I hear 85C is normal operating temp. Some say OK for temp of 110C. Some say no. I hear Elec. AUX Fan kicks in at 110-115C. I AM CONFUSED. My car runs at 85C. If air temp over 90F- eng. at 90C-95C. If air cond. on above 90F +60mph - guage goes to 110C - turn air conditioning off to avoid an overheat condition. I have seen the damage to an overheated mercedes v-8 where a piston exploded a short while after the overheat - mechanic says the metal properties changed from the overheat. PLEASE - WHAT IS THE HIGHEST TEMP. a 5.6l CAN OPERATE AT WITHOUT ANY WORRY OF DAMAGE TO ENGINE? Is 110C NORMAL on a hot day? What temp. SHOULD NOT be reached to prevent damage? If engine runs hotter-why 85C thermostat? FYI - changed hoses, pressure cap, thermostat, cleaned rad out of car, new water pump & installed new centrifical fan clutch, using genuine Mercedes parts. Temp. still goes to 110C on days over 90F with air cond on, don't know if it goes higher because I turn air off to avoid engine damage. If I short wires from the temp. switch together, the aux fan runs constantly & temp. never goes up over 100C. When the guage reads 110C - the aux fan still does not kick in. Again-- WHAT'S NORMAL??

I cant speak for the 560 but the 420's never get above 90. They are typically at 80-85. In Houston we have very severe heat. And even when idling in stop & go traffic on a 100 degree day, neither ever goes above 90.

Over temp is when the needle is in the red.

Agreed. Last summer was hot here in the midwest and even sitting at long stop lights the 560 never hit 90.

still confused
 

That is what I thought - but reading threads on this site over the summer and into fall- several said thair cars ran at 100-110C and thought it was normal. If it isn't normal - what could cause the temp to go that high - bearing in mind all that I have already done?

while on the subject
 

if the car is not supposed to hit over 90c -why does the aux fan not kick in at90c instead of 110C???

I would suspect the radiator has internal buildup preventing good heat transfer. The fan kicks in at 110 because it is the last effort to stay cool. Its not needed at 90.

Two things cause the fan to run. First is engine temp. Second is the high side pressure in the AC system. If either is too high the fan should run.

I agree I have read several threads stating higher temperatures than what I am use to seeing. So Im not sure I have a good answer for you

Did it always run this hot ? Or is this a recent development.

85-100
 

My 560 typically runs at 85-90 however on a recent hot day while heading up a long steep hill at 60mph the gauge went to 100 and sat there until I had finished climbing when it went down to 90. I always drive with the aircon on as well. Just today I have had a new radiator fitted, with the reinforced necks so it will be interesting to see if this alters my temps at all. If you are really worried about your temps you should get a proper gauge to test with.

Matt.

To Dpetryk: It has always done this since I got the car 3 years ago. So what you are saying is that the aux fan will normally not run??? Is this correct?? Thanks Dave
To Mattman:When we had the rad out of the car, we flushed it and nothing came out - looking inside with a flashlight - it looked clean. When we filled it with hot water (while out of the car) it immediatly got hot on both sides over the entire surfaces so we assume there is no cold spots caused by build up. What kind of guage are you suggesting??
Thanks
Maurice
As an aside - I took to Mercedes Dealership here in Canada and $200 later was told "they all do that" I don't buy it. I have this problem and one other one before I can state that I have restored this car to mint condition. I have already spent over $7000US restoring it- so you can understand why I want it right. Time is not of the essence as I only drive this car in the summer, but I really want to solve this. Any help will be appreciated.
Many Thanks

Do you have the correct pressure cap and if so, is it absolutely tight?

I would experience high temps whenever I fired up the A/C and eventually found out that the system wasn't able to hold sufficient pressure, thus, higher temps. I later found that DUH, the cap wasn't on tight!

Are your radiator hoses collapsed after the engine cools? Again, if the cap isn't on securely, that may be the case.

I've read that the aux fan sensors are designed to kick the fans on at 117C, not 110.

You have an A/C condensor located directly in front of the radiator, so when the A/C is on, the condensor disperses heat with of course, is absorbed by the radiator behind it (hence, higher temps). That is why you have the aux fans, to compensate for the added heat being dispersed by the A/C system. If your aux fan temp sensor is not functioning properly, the fans may not come on at all! Mine is located on top of the coolant pump near the thermostat...

To: G-Benz
 

Thanks for input - cap is on properly and is right pressure. Rad hoses do not collapse. You say the aux fan won't kick in until 117C. Now you can understand my confusion. If the fan won't kick in until 117C then does that mean the aux fan will never work unless the engine reaches 117C? Then does that mean that 110C is considered normal in hot weather?? Why I am puzzled is that if the aux fan is designed to take away the extra heat of the air being on - should the engine temp be allowed to go to 117C before the fan is even used?? Won't this damage the engine? -My common sense says that if the engine operating temperature should be 85-90C then the aux fan should be forced to kick on at 95-100C by the temp switch - but the temp switch is 117C. If I short out the temp switch and have the aux fan running as soon as you start the car - I can drive in hot weather with the temp. never going over 100C. As I stated - I put a lot into this car and do not want a Mickey Mouse repair like shorting out the temp switch - even though it works. IF THE CAR WAS MEANT TO OPERATE AT MAX 95-100c THEN I AM MISSING SOMETHING AND APPRECIATE ANY AND ALL SUGGESTIONS. I AM STUBBORN AND HOPEFULLY WITH THE HELP OF ALL HERE IT WILL BE FOUND. THANKS AGAIN FOR YOUR INPUT.

Aux fan temp
 

I believe the aux fan temp is at about 110c, I remember reading in the performance forum about a mod that owners of the 500e's had done to bring the aux fan cut in temp down so that the cars never went over 100c. They seemed to have a similar situation to yours where a few owners seemed to experience hotter temps than others even though they had new radiators, new hoses, new cap etc etc. I assume that these have all been replaced. Certainly replacing the temp sensors might be worth looking at. Also as I mentioned see if you can get hold of a different guage to be sure that your dash mounted guage is displayed the correct temp. Sounds like a well cared for car - you should post some pics somewhere if you can.

Good luck
Matt.

Two more things:

What is your coolant/water concentration? should be 50/50 or 60/40 (or 40/60)...too much water inhibits the boiling (and freezing) point. Too much coolant, and the heat dispersion properties are reduced.

There may be air in the system. Make sure the thermostat does indeed work, and that it is installed so that the bleed hole in at the highest position on the horizontal plane (so that any trapped air can be forced out).

Again the aux fans turn on based on the 117C temp or A/C pressure...so the fans CAN turn on at a lower temp than 117C if the A/C system pressure demands it.

The aux fan sensor is about $30, and is cheap insurance, as we are now watching you throw parts at the problem. I do understand!

My W124 gets 100C temps on really hot Texas summer days (100+F outside), and even 105C when sitting in stop and go traffic under the same conditions. My SL however hits 100C easily during a warm Texas evening. The ML stays at 85C all of the time...go figure. SO I don't know what is "normal" for a 126...

Hi Mattman:
Thanks for your reply. My mechanic is a German engineer who works on and sells Mercedes, Audi BMW and VW as a hobby and has been doing it for many years and really knows his stuff. He has done my timing chain and other stuff flawlessly. When he says the rad is perfect,I believe him as he shows me why he says things - not "just take my word for it". The only thing he was mentioning is that he thought the temp. switch (mounted in the air cond. circuit) was only for freon temp. Is there another temp. switch on block for engine temp that is also in parallel with temp switch for air that would kick in aux fan???
I will look for the mod you mentioned in performance forum. Instead of trying to find new guage like one in dash, I have a laser infrared non-contact IR Thermometer at work which is very accurate. I will have to wait until spring when it warms up up here, but I will check the block temp. with it. Thanks for tweaking my memory!!
When you say this car has been well cared for you are not wrong. 2 years ago we stripped it and removed the interior and front & rear glass and had new metal put in wherever there was any sign of rust. Then stripped the car to bare metal and had it repainted and hand polished to a Factory shine. She looks like from the showroom!!! Even has chromed washer arms on euro headlights. Definately a looker!! Will have a digital camera by spring and will post pictures of her. Thank you very much for your assistance. With everything I have done so far you can appreciate why this problem should be corrected properly.
Maurice

To: tkamiya
 

Second attempt - first one is somewhere in cyerspace - if it shows up - sorry.
What I am saying is : 90F outside, cruising on flat land at 55mph engine temp at 90-95C. Turn on air cond. temp slowly climbs over 5-10 minutes to 110C - turn off air cond. -temp falls to 90-95C.
I should add that if the outside temp is below 80F then my engine temp NEVER rises above 85C.
Changing the temp switch in air cond. is last resort - opens up new can of worms. Must drain and recharge air cond. to change switch. Cannot get r12 anymore up here. Must convert to r134 if system opened. Do not know yet if compressor will have to changed when converting - That's why I want to cover all other bases first.
I should mention that we did not just throw parts into it helter skelter. The fan clutch was slipping a bit -new one helped a little - water pump cannot be checked without removing - when out already - cheaper to change than reinstall old and be safe. Hoses were starting to get soft - that is why changed. Thought thermostat was bad -changed with aftermarket - no improvement - installed Mercedes thermostat - no change.
Just a thought - if the ignition timing was off - could it cause this?
What are chances when engine starts and runs great otherwise?

Don't know if this helps - but Hey!! I have noticed in pictures of Mercedes for sale on Ebay that there is no Hood insulation on cars in Florida. My insulation is foam and 1" thick - could this be holding the extra heat in?? All those in Texas and elsewhere who are getting normal 85C-90C temps - do you have insulation pad under hood? Those whose temps are like mine - do you have insulation pad?? Maybeeeee????

First thing I would say is that the numbers on the readout are frequently not accurate. Perhaps the infrared thermometer will tell. If that is the case then you will know how far it is off. These problems can be real frustrating. I had an Isuzu Trooper that would overheat. Replaced everything except the radiator and still overheated (had to even replace cracked head) tried a flush product and no improvement. I ran a gallon of vinegar in the coolant for about 100 miles and then flushed it about 100 times (or so it seamed) till there was no odor of vinegar. Never overheated after that. Do not know if it would damage a MB cooling system. So follow the normal disclaimer, I cannot be held responsible... bla bla.

did you put vinegar with water or vinegar in antifreeze??? Any one think of any damage to mercedes system doing this??? Won't the acetic acid etch the aluminum parts in moter and water pump??

I don't think I would be running something as acidic as that through my car. A new radiator is only about $220us, if it hasn't been replaced then it is well worth doing.

Matt.

I have seen a suggestion that if the engine was running lean that it would add extra heat load to the cooling system. Its possible if the mechanical mixture control was set lean and the oxygen sensor or Lambda control system was not working.

Its conceivable, but not too probable in my opinion.

To answer another question, I have my hood pad and I live in Texas and I have no overheating or over temperature symptoms described in this thread.

I used about 3/4 gallon of vinegar and filled the rest with H2O. Kind of like you would use for cleaning out a coffee maker or even weaker. I left it in for about 100 miles or 2 days. I flushed it out very well. I think you could have drank the final flush water. I used a garden hose hooked up to one of the hoses and disconnected each of the other hoses including the inlet and outlet of the heater core.

Please note this was a last ditch effort. This is why I gave disclamers.

To Continue
 

To summarize:
1) outside temp below 90F - air cond on or off - eng. temp NEVER goes over 95-100C.
2) outside temp over 90F - engine NEVER goes over 100c if air cond NOT turned on.
3) outside temp over 90F air cond. on - eng temp climbs to 110C at which point I turn it off and it returns to 100C or below.

Question : my mechanic said that for the temp switch in air cond circuit to kick in -FREON temp has to be over 117C - which can and usually will occur in real hot weather. It does NOT relate to the Engine temp. Question is: is there another temp switch in antifreeze circuit that should kick the aux fan in when engine temp hits 95C or over????
After talking to my mechanic this weekend he is down to two possibilities:
1) temp switch in antifreeze circuit (if there is one)
2) car runs so good - misreading temp gauge in dash.
As stated earlier, I have an IR non-contact thermometer that I will try this summer once heat returns up here in Canada and will post results. Only other question my mechanic has is: is the aux fan a one or two speed??
Thanks for your patience guys!!

forgot to mention in above post
 

For got to mention:
If I Hot wire the aux fan so it is on ALL the time - engine temp NEVER gets above 100C regardless of outside temp or if air cond. on or off - That is why I am down to the questions above.
Thanks Again

I think u have you internal headblown gasket

To clarify the fan issue: I referenced the '86 schematic I have, and the '91 car I have. I assume all are pretty similar.

- The electric fans have two speeds - low and High.
- Low speed ONLY comes on when the AC high-side reaches a certain pressure. It is not tied to coolant temp.
In warm weather with AC on, low fan speed will run most of the time during stop/go driving. The mechanical fan just cannot keep the AC condensor cool enough.
- High speed will come on when the coolant temp reaches 115, and turn back off when it cools to 105.
- If the AC is off, the low speed will never come on, so in stop/go driving, when the mechanical fan cannot keep the temp down sufficiently, the temp will rise to 115 before the electrical fan comes on.
- The mechanical fan has little or no impact above 40 MPH - the air forced through the radiator by the car's speed is greater than the fan could pull in. So, the fan clutch is designed to idle at these conditions.

Interestingly, under some stop/go conditions, the engine will run cooler with the AC on than it will with it off. With AC on, the elcetric fan is on low speed and helping cool the engine. With AC off, only the mechanical fan is trying to cool the engine, and the electric fan will allow it to reach 115 before it turns on to help.

Since new, my 300SE in 90-degree weather has run about 85-90 on the highway, or in light traffic. But, in heavy traffic jams, it will slowly creep up to 115 whether the AC is off or on, then cool to 105 as the hi-speed fan turns on.

I personally think a good-working system will not get over 115, as the high-speed fan should provide adequate air flow under virtually any conditions when it turns on at 115 (or thereabouts).

DG

My 1988 300SEL is an original Florida car and it has the underhood insulation. I know mine is an I6, but the highest I have ever seen the temp was slightly above 80°C. It will go there when the engine first warms up, then it falls back down to 80°C.

In traffic with the AC on, my 300SEL would normally creep up to the mark in the picture...some people said it was fine, others said something was wrong... :\

http://img.photobucket.com/albums/v2...1205713783.jpg

S-Class Guru has remarked on the thought that occurred to me as I read the symptoms you described, particularly that you could jump the aux fan and that would keep your temps under control. Low fan speed is triggered by a pressure sensor set to actuate the fan at 20 bars (or is it 15?) of compressor pressure, while the high speed fan is triggered by a temp sensor set to actuate high fan at about 105C. Given all of the other repairs to the coolant system, I'd go straight to the 2 sensors responsible for aux fan operations.

Additionally, Jim Forgione has devised a clever little device called Cool Harness, designed with Mercedes' known overheating tendencies in mind. Search this forum, there are threads. It functions by actuating the high fan speed at either 92C, 95C or 98C of coolant temp (depending on which variant you buy), regardless of what the A/C is doing at the time (i.e., whether the low fan is on or not). In other words, it starts the high fan some 8-15 degrees before the factory specs would start it. Installs very easily in place of the bipolar plug coming off the CTS. If you're interested, his website is at this URL:

http://www.k6jrf.com/MB_S500.html

Be aware that the a/c low fans are most commonly mis-diagnosed as a bad high side pressure switch. One jumpers the sw. and gets low fan ,verifying low fan circuit, so he assumes a bad sw. The actual cause is not the sw. at all , but rather a slightly low refrigerent level. No low fan is the first complaint on a car that has a small refrig leak. The a/c still works, so it is not suspect, but in fact the high side never reaches the aux fans cut-in spec b/c of low refrig level. VERY COMMON.
The complaint is as yours, with rising coolant temps in traffic and at idle w/ac , where airflow is needed the most. The condenser heat passively increases the Thermal Load on the radiator and you wind up waiting for the coolant High fan to correct. That should be at 105C cut-in, but by that time with no low fan , the coolant will continue to climb..
As stated , many choose to bridge the coolant sesnor to a lower cut-in, but the place you want to be looking is if your low fan comes on when the a.c is on and there is a high thermal load conditon..such as stop/go traffic.
If No low fan, simply jumper the high side pressure sw [ the one with the pig-tail leads] ..if the fan then works, the sw or refrig level is suspect..if still no fan, then the culprit is the fan circuit itself, with first check being the fuse, and next being the dropping resistor behind the headlamp.

I would think that w/ the Aux Fans on continously, the eng temp shouldn't be higher than 90C even w/ the A/C on.

I agree, except under High thermal load conditions...
A good , old fashioned cond/radiator fins clear/clean might be also in order....
and a good flush. You would be surprized what crap gets in between the rad and condenser ....the more airflow you can get , the better.
A/C guys check those regularly...

Let me redo that ..

"GOOD " a/c guys .........

My car, with new Radiator and proper fluid and new temperature sender will commonly show over 100 C (maybe that 105 shown up there in that picture) but a quick check with a Infrared thermometer never shows more than 91 C. My problem appears to be with the gauge itself. It will jerk up there and then jerk down fairly quickly and sometime read normally for a while. It is inconsistent. Could be grounding or could be a voltage issue to the gauge. Don't know, but I can live with it as long as I know the real temps. One of these days I will mess with it and fix it.

Check it with an infrared Thermometer and confirm its really correct before you do anything else.

Gauge/sender check is to put a 38 ohm resistor in place of the single wire.sender...that equates to 100C on gauge.
Radio Shack....99 cents . Use a close tol. one.
I have one made up in the tool box for instant gauge testing............

Guys, I stand corrected; looking at Johnathan's photo, it appears that's about the temp that my high fan turns on (105, not 115).
In my '86 manual, it lists a thermal fan switch 105-115, so I assumed it turned on at 115 and off at 105. Maybe at 115 it goes into hyperspeed - ha.

Arthur is right on about the junk that can collect between the condensor and radiator.

I had the infamous low-speed resistor burn out. I thought it was the pressure switch, as stated above, but when I dug down and looked at the resistor, it was pretty obvious (wire fried). I ran a secondary wire from the low-speed relay to the resistor to permanently solve that problem.

DG

S class

<In my '86 manual, it lists a thermal fan switch 105-115, >

That is where you went off track.
The 86 schematic can not be used b/c they used a 105/115 temp sw.

The '88 and up do not use the 105/115 sw...they use a two wireThermistor sensor that triggers the ACC Panel at 105 cut-in, and that triggers high fan. The R factor decreases as the temp increases .. [ neg./ coef. thermistor] ..that is what allows one to change the cut-in of high fan by bridging that sensor...the R in parallel drops the Total R of the sensor, so you get a lower cut-in.
But you were absolutely correct on all other aspects and I comend you.........................Archieves

<Maybe at 115 it goes into hyperspeed - ha.>>


Actually, The 115 is a/c compressor cut-out if temp gets to 115.
The fan is the 105 section of that sensor.

I used to own a radiator shop. A couple of points that I'd like to toss out..... Between my partner and I we have many years working on vehicles. I have only seen one water pump that caused overheating. The fins on the impeller had corroded away. My partner had only seen one other..... the impeller had gotten loose on the shaft and wasn't turning at shaft speed. Yes, a water pump can cause overheating but it is very rare.

Another is how a cap affects the cooling systems performance. The basic purpose of the cap is to pressurize the system. Each pound of pressure raises the boiling point approx 2° (F). Higher pressure does not increase the efficiency of the system. It merely keeps the coolant from becoming steam. I ran my 450SEL up hwy 15 through Cajon Pass to Barstow, CA at over 70 MPH with the a/c on without the cap even on. This was on a warm day. Only found that the cap was off when I stopped to get gas and it spit some coolant out due to heat soak heating the coolant to the boiling point. No change of operating temp.

A radiator can appear to be good but may have reduced efficiency. Scale can form on the inside of the tubes and reduce the heat transfer from the water to the tubes. Often this can't be seen and the radiator may flow quite well. If the radiator is like the ones in my 500SEL and my junk 420SEL it's an aluminum core with plastic tanks and one row of giant tubes. And these radiators don't have a cap on the top where you can see down into several of the tubes. The tubes can get scale built up on the tube walls without really affecting flow. Unlike typical radiators used in the 60s, 70s and 80s with multiple rows of smaller tubes that are much more prone to flow restriction due to scale accumulation and will show reduced flow quicker with scale accumulation. The second thing that happens is loss of tube to fin contact. In a copper/brass core radiator where the fins are soldered to the tubes the tubes try to become round as pressure in the system builds and eventually this breaks the solder bonds. I don't know how they bond the fins to the tubes in the aluminum radiators. I'm assuming a thermally transmissive adhesive. But reduced radiator performance may not be readily obvious and may only show up in marginal situations (such as a hot day). In it's beginning stages it's pretty hard to isolate a radiator with reduced efficiency without a known reference.

Karl M.

I forgot to mention about my experience with ignition timing. As some of the other posters mentioned something about timing and mixture. Retarded timing can cause all sorts of problems including: poor performance, poor gas mileage and the engine may run hotter than normal. Maybe quite a bit hotter than normal. And a continuing buildup of heat even at idle. (DAMHIK) Doesn't hurt to check your timing.

As one of the other posters remarked, running lean can cause an increase in operation temperature. If it's this lean you will probably also notice knocking from detonation. PROBABLY but maybe not.

Karl M.

if your aux fans are coming on when you temp climbs to 110c but your temp is not coming down you might need to flush your system and add a fifty fifty mix of mb coolent along with an addative called water weter this helps in heat transfer in cooling system do to bubbles forming in water. Water wetter helps prevent this an aids in heat transfer for better cooling.. a lot of guys who have these. cars in hot climates use this product to help cooling of the engine..
Bob

I think that the suggestions that point to verifying that you are even overheating at all are on point.


I like the idea of using a 38 ohm resistor to verify that your gauge reads 100c. That's a good check. Follow up by measuring the resistance of the temp sensor (The single pole one that goes to the gauge) at ambient and comparing it to the chart to make sure it's accurate.

I recently replaced temp sensor, it was 20 degrees off. It was reading just over 60 when the temp was really just over 80. That's typical of negative temperature coefficient sensors, they tend to drift higher in resistance, registering a colder than actual temperature. It is possible for them to drift the other way, but it isn't as common in my experience. It is also possible for the gauge circuit to be off, so that's why I really like the 38 ohm resistor test.

If you've verified that your gauge is accurate, and you're still experiencing heat rise, check the thermostat. We'll assume the radiator is good since it was replaced recently.

Using an IR thermometer (or a $1.99 digital meat thermometer taped to the hose), measure the temperature of the top hose coming out of the water pump after the thermostat. Start the car from cold and let it run. What you want to watch for is when the thermostat opens, the temperature should rise quickly on the thermometer. Now, the water coming out of there should be no hotter than the temperature rating of the thermostat when the car is first warming up. Under load is another story, but what you want to verify is that the thermostat is opening up at the right temperature from a dead cold engine. Also, note the dash gauge temp reading at the moment that the thermostat first opens. Compare that to the rating of the thermostat. You'll know quickly if something doesn't jibe.

If the water coming out of there measures much hotter than the thermostat rating, then replace it. You can also squeeze the hose to "feel" the flow, and assess if it is restricted or trickling. It should start out slow and begin to flow fully as the motor heats up. Watch out for belts and fans. Also, a lot of folks are missing part of their fan shroud and aren't even aware that there is a second ring shaped piece that snaps into the main shroud. That could lose you a lot of efficiency, but that shouldn't be an issue at cruising speed. That will get you hot at a stop light.

Yes, a blown head gasket is possible, but would probably manifest other symptoms as well. I'm betting something simple if you're not having other serious issues or noticing oil in your coolant.


-tp

Temp suggestion
 

If you convert 110 celsius to fahrenheit you get 230 degrees. I don't know for sure about Merc's being aluminum and all but, 230 is not that unusual on modern engines. Most people don't understand that the pressure cap is there to raise the boiling point of the coolant so that it can run there without boiling off the coolant. Tom