Concerned over M103 engine temperature - PeachParts Mercedes-Benz Forum

ps2cho · #1 09-07-2009, 01:14 PM

My 300TE runs consistently at 100C with A/C on even on the freeway when the temperature is 90F +

I could have sworn that it got worse after replacing my thermostat. I am just concerned over premature warping over the head as I only did my top end rebuild about 8k miles ago. I hardly want to revisit that anytime soon considering how meticulous I was over the whole process.

So my first question -- How many different variants of the thermostat's are there? How can I tell what mine is? Would it be written on it somewhere?

My fan clutch is working fine as I hear it spin up and slow down once I get to the freeway, but it spins high around the town all the time.
I've done the engine temp sensor for CIS, but not the one for the cluster (is this one also connected to the fan clutch? or does the CIS-one do that?)

Anybody know which variant the one on fastlane is?

Thanks,
Robert

alienman · #2 09-07-2009, 07:37 PM

Hey ps2cho,

I think the two most common thermostats are the 79c and 87c. I'm not sure where my mechanic got the 75c unit, but that one and its replacement have the temperature rating stamped on the thermostat. I bought the replacement at a local shop so I could examine it before purchase.

My fan clutch engages in town a lot as well, but I think the fan clutch is operated mechanically. If I'm not mistaken, the sensors on the head are for CIS, gauge, and AUX fan.

tinypanzer · #3 09-07-2009, 07:43 PM

If you're suspicious of your thermostat, you can always take it out and boil it along with a candy thermometer and see if it is in fact opening when it should.

Ivanerrol · #4 09-07-2009, 08:45 PM

Your fans should have no effect at highway - Freeway speeds. The airflow through the radiator does the cooling. Make sure you have the OEM or Behr thermostat. The erzatz ones work O.K. but the washer/O-ring that comes with them is often suss. You can buy the correct O Ring at your local stealership for very little money.

Have you done a reverse flush on your radiator? Make sure there is no crud buildup between the radiator and the AC condenser. Make sure you have new radiator hoses. Any air leak will give you higher temperatures.

The M103 even with the AC on should have a lower temp than 100 degrees at highway speeds.
What temp does you car operate at freeway speeds without the AC?
If you turn the heater up does the temp come right down?

ps2cho · #5 09-07-2009, 10:59 PM

I'll have to test those above...

When I rebuilt my head I replaced all the coolant hoses and completely flushed the radiator, block and heater core...The radiator is only about 3 years old.

I just looked it up and I have the 87c Behr one. Where can I find the 79c one other than the stealership?

#6 09-08-2009, 07:01 AM

Did you get the air burped out of the system after the thermostat replacement. I may be getting my models mixed up, but I'm pretty sure that there is a bleed screw on the thermostat housing on your car. It is used when filling coolant WHILE ENGINE IS COLD!

Ivanerrol · #7 09-08-2009, 07:33 AM

Quote:

Originally Posted by LarryBible

Did you get the air burped out of the system after the thermostat replacement. I may be getting my models mixed up, but I'm pretty sure that there is a bleed screw on the thermostat housing on your car. It is used when filling coolant WHILE ENGINE IS COLD!

Not all thermostat housings have this bleed screw. The other way to bleed is to loosen the bolt on the head closest to the front of the engine just over the first injector.

In the image below you can see the bleed screw on top of the thermostat. If you don't have this you can see the referenced bolt in the background near the injector

Oracle12345 · #8 09-08-2009, 12:09 PM

believe it or not you want the engine to run hotter since it will perform better. Engineers specified that thermostat for a reason. The hotter the engine runs the most efficent in terms of combustion and fuel economy.

my 190E gets around 100c when its really hot out when im sitting at a light but on average day it runs steady at 90C when im crusin

anziani · #9 09-09-2009, 11:42 AM

Remember that you have to get the oil temperature above 212F (100C) to cook off any condensation. If not, you make sulphuric acid. Not a good thing. So the closer you run at 100C, the better.
Anziani
'93 300CE 175K
'95 E420 117K

kwontumspeed · #10 09-09-2009, 02:30 PM

100 is normal in these cars. I wouldn't worry about it. Even 105-110 isn't a problem. You're not going to be doing any kind of damage to your heads at the stated temps.

ps2cho · #11 09-09-2009, 07:55 PM

Quote:

Originally Posted by kwontumspeed

100 is normal in these cars. I wouldn't worry about it. Even 105-110 isn't a problem. You're not going to be doing any kind of damage to your heads at the stated temps.

I mean she never overheats and I've never seen above 110C, I am just concerned about premature head warping. On cooler days (70-80F) she sits right on 90C...but being in Southern Cali, above 80F is commonplace.

ps2cho · #12 09-09-2009, 08:04 PM

Quote:

Originally Posted by Ivanerrol

Not all thermostat housings have this bleed screw. The other way to bleed is to loosen the bolt on the head closest to the front of the engine just over the first injector.

In the image below you can see the bleed screw on top of the thermostat. If you don't have this you can see the referenced bolt in the background near the injector

No I did not bleed the system. Maybe this is the problem then? Do I need to drain the coolant again or just pop that bolt?

I don't have a plug on the thermostat housing.

Oracle12345 · #13 09-09-2009, 10:19 PM

Quote:

Originally Posted by ps2cho

I mean she never overheats and I've never seen above 110C, I am just concerned about premature head warping. On cooler days (70-80F) she sits right on 90C...but being in Southern Cali, above 80F is commonplace.

no need to worry about it, the metal is being normal. Google the thermal properties of metal