500SEL running hot at all times
 

My 500SEL is running too hot for my flavor.

I have done everything I could to make the engine run cooler but no good results yet.
I flushed the system several time, installed a new visco fan clutch (Behr/China crap), new radiator, new water pump and new thermostat.

Still the engine is running at 90-100C degrees at all times.
The thermostat is the OE 84 C but still temperatures still running 10 degrees higher. Ignition timing is to specs.

The electric fan come on very often and I am at a loss.


My other Mercedes stay cooler and are much more stable around the thermostat temperature and a few degrees higher.

I have not changed the temperature sensors.

Any ideas what the problem might be?

Martin

you sure the gauge is accurate?

you sure the new fan clutch works as advertised.

I cannot confirm that the new visco fan or the old temp gauge are working properly.
How can you tell?

not an endorsement, just an example-

https://www.amazon.com/Thermometer-58%E2%84%89-1022%E2%84%89-Instant-Read-Non-Contact-Temperature/dp/B07KB4S9KJ/ref=asc_df_B07KB4S9KJ/?tag=hyprod-20&linkCode=df0&hvadid=564707962680&hvpos=&hvnetw=g&hvrand=11286549795268674386&hvpone=&hvptwo=&hvqm t=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9011785&hvtargid=pla-1569543240433&psc=1

shoot the top hose and the thermostat housing, along with where the temp switch for the gauge screws in.

when the car is cold, does the fan spin or is there resistance? when hot and running should be a definite fan noise, better at 3000 rpm or so. hold your hand close to the engine and feel the breeze. drop to idle and still hot, breeze should drop off according to rpm. you should always feel some breeze when the clutch is hot and working. shut off and spin fan. waaay too much resistance to spinning, maybe just move a blade or so and that's it. any looser and the clutch isn't hot enough or the clutch is defective. had problems with chinese clutches and usually use just behr, sachs or oe. was there a more expensive behr available? could be a bargain line behr has now. behr part numbers would tell me.

lastly, make sure the entire core of the radiator has heat hot in the top, approx 15 degrees cooler at the lower hose. a new radiator should be fine, never seen a bad one out of the box, only leaky.

also, were radiator and clutch listed for "tropical" applications. a euro car may not have to capacity to cool off in the u.s. almost always different specs and parts for euros and u.s. cars. i would've tried 560sel numbers to see if they are different than what you found for yours.

90-100C is perfectly normal. Its the way the cooling system on these cars was designed. I'm not sure about the specifics of your model, but the clutch fan on my '88 190E 2.6 does not fully engage until 100C and the twin aux. electric fans engage at high speed at 105C. Operating temperatures up to 110C are considered normal.

Emission controlled engines beginning in the late sixties were designed to run hotter because higher operating temperatures reduce emissions, and 200-230F (about 95-110C) is considered normal especially in warm/hot weather and stop and go driving.

Some owners get so concerned they shut down the AC, but the engine might actually run cooler in low speed traffic because AC cooling demand will cycle the electric fans at low speed, which also benefits engine cooling.

A 50/50 blend of ethylene glycol with a 15 psi pressure cap boils at about 265F (about 230C).

If it works don't fix it!

Duke

Hi porkface,
I ordered the thermometer, makes sense to measure and understand the
real temperatures.

I also saw that the gauge in the dash is jumping /jerking around some.
Not sure what this could...so it is jumping for instance from 95 to 100 and the back within probably 10 seconds. I have not seen this in any of my other Mercedes cars.

Martin

i work on an 81 300td that does the same needle jump on the temp. i think it's in the gauge but i can't have the car long enough to find out. that period car did not have harness issues, that's why i suspect the gauge. in the old days, i'd just pull 1 from aonther car and try it. not now, though.

duke 2.6 makes a good point about normal. being a kjet car, you want the highest normal temp for the highest control pressure. not enough temp and it will run a little richer than it could. really, that's true of any design fuel injection.

Check the electrical connection for the gauge for corrosion.

Thanks,

jumping gauge needle:
I'll check the gauge terminals for corrosion, need to pull the instrument panel anyhow soon because my odometer quit (total miles and . I'll need new plastic gears it seems.
I just don't know the size of the second or third plastic gear.

temperatures between 90 and 100:
If the temperatures between 90 and 100 are acceptable and okay..... I need to confirm these temps by measurements . I have the new laser light thermometer and will test the temperatures at the thermostat housing soon.

aux fan starting at 95 C:
With the 105/110C switch the aux fan should not start before temperatures reach 105C correct? However my fan is starting before the needle is reaching the 100C mark, probably at 95. This would mean that the fan switch is probably questionable.

Martin

Try opting for a 79*C thermostat for the summer months and swap back to the 84*C during the cooler months. Also, check this guy's video out: he works on these MBs and has a ton of info for you
https://www.youtube.com/watch?v=Ts6CZ7lMJlM&t=7s

Thanks for the link and your are the first one who is suggesting a 79C Thermostat.
Do you know where I can get this thermostat?


I was already suspecting the gauge having an issue. And I bought an infrared thermostat in order to check if the temperature shown in the dash can be verified with the measurement.

Pierre is stating that the temperature should not reach the 100C mark.
And I agree!
All my other Mercedes don't do this and stay around the thermostat temperature or slightly higher (probably up to 5 C higher). I'd very rarely see
90C.

He is also mentioning an air lock at the sensor meaning the sensor cannot sense the water temperature correctly because the probe is in air and not the water... However I don't know why the 'sensed' temperature then might be higher.... because the enclosed air cannot be hotter than the water unless there was a sudden water temperature drop while the air might be still hot...However a sudden temperature drop is probably not realistic.

As the radiator, water pump and visco fan clutch are all new ... the 79C thermostat might be a good option.

Martin

With the coolant/water the temp will be lower than air because air that is compressed or under pressure is hotter. Go to FCP euro and type in your car year and model then search for the thermostat. Even if it's the same one 84*C click on that and then scroll and look for the fitment section. Then you will see several different years and models that all will use that thermostat. Then what you do is just a reverse search for one of the models listed that use that thermostat and see which model offers a lower temp thermostat. I believe I saw a 1981 380 SL as using the same thermostat, but I'm not sure. Anyways, go check it out. Good luck.

Hi Ismalley,

Not sure if I understand the search.
all the 380s and 500s from 1980-85 used that thermostat 84C #1162000215
If I reverse search for these cars, yes the very same thermostat will show up.
Martin

It means, if you know that your car shares the same thermostat as all those other models, then instead of searching for a thermostat for a 500SEL, you go search for a thermostat for any of the other models. Not necessarily on that website.

w:

Enter this in the eBay search line:
"79C Mercedes Thermostat"
Take your pick.