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  #1  
Old 01-10-2002, 04:25 PM
moedip
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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??

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  #2  
Old 01-10-2002, 04:55 PM
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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.
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  #3  
Old 01-10-2002, 04:58 PM
BlackE55
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Agreed. Last summer was hot here in the midwest and even sitting at long stop lights the 560 never hit 90.
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  #4  
Old 01-10-2002, 05:21 PM
moedip
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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?
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  #5  
Old 01-10-2002, 05:24 PM
moedip
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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???
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  #6  
Old 01-10-2002, 06:15 PM
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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.
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78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
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97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k
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  #7  
Old 01-10-2002, 06:20 PM
Mattman
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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.
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  #8  
Old 01-11-2002, 09:09 AM
moedip
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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
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  #9  
Old 01-11-2002, 12:56 PM
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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...
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  #10  
Old 01-11-2002, 02:17 PM
moedip
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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.
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  #11  
Old 01-11-2002, 02:34 PM
Mattman
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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.
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  #12  
Old 01-11-2002, 02:59 PM
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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...
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  #13  
Old 01-11-2002, 03:00 PM
moedip
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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
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  #14  
Old 01-11-2002, 03:45 PM
moedip
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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?
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  #15  
Old 01-11-2002, 04:06 PM
moedip
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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????

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