Cooling problem
 

300e 2.8 M104 engine.
The temperature stay at 100-105 C when ambient temp is over 85 F.
Even if I am driving on the Hwy at 70Mph it does not go lower than 100 C.It is a permanent cicle of the auxiliary fan.
But if I am in trafic and the engine is ideling the car cools down to 87 C in about 5 Min.
I have done the folowing:
New fan clucth ,new radiator, new termostat, flush the coolant with genuine MB fluid.
Also I have changed one of the auxiliary fan that was bad. The aux fans work fine. They start when the A/C is on, in first stage and at 105 they go in second stage .
I don't Know wat coud be. Most of the people on this forum claim that a soon as the car is driven at hwy speeds the engine should cool down.Mine is the other way.....!!!!!!

Possibly there is a problem with the temperature gauge, maybe it is inaccurate?

Gilly

if the car is idling (like in traffic) its not building much heat in comparison to driving at freeway speeds.
conversely, while idling in traffic there is little airflow through the radiator while there is plenty at freeway speeds.

i surmise that there must be some kind of blockage thats preventing air from flowing freely through your radiator at high speed, and that the coolant capacity is enough to cool the engine when the engine isnt producing much heat. leaves, insects, other debris could be in the fins of the radiator or the AC condensor, preventing airflow. i say check there first. clean out as nec, and observe for any changes in temps.

Replace the pressure cap, too!

Check for a soft lower radiator hose -- if it's mushy, it can collapse at high engine speed, reducing cooling capacity. This usually only happens with a non-pressurized cooling system (bad pressure cap).

If you also get some coolant spill or brief boiling noise when you shut off hot, for sure it's a bad pressure cap.

Otherwise, it's time to check for coolant flow (difficult on this car) -- you may need to use an infared thermometer to check radiator temperature, it may be plugged from residual crud from the cooling system (bummer!).

Peter

Re
 

All the hoses are ok and the radiator is new not insects or debris that can block it.
The presure cap on the coolant reservoir is also new.
Coud be a small leak in the coolant reservoir that release the presure?
It look old to me.
I am trying to replace it .

I am completly puzzled.
Thank for your help, and maybe you guys have more Ideas.
I was reading some postings that the termostat can be installed wrong or the fan wings are installed backwords. Do you belive in that ?

You could have a bad thermostat. These days, with parts made who knows where by anyone, quality is going to hell fast, so bad ones new in the box are not unheard of. I recommend you stick with Behr or Wahler only, get it at a good independent, the dealer, or here at FastLane. DO NOT buy one at AutoZone, etc, they usually are junk.

Yes, the coolant tank can leak, the plastic gets old. Check the hoses for pressure after it gets warm on the highway. Wrap a rag around your hand so you won't burn yourself, and squeeze the upper radiator hose. It should be quite firm. If it smashes down easily with sounds of moving coolant from the tank, you have a pressure leak. Usually have coolant loss on stopping with this problem, though.

I would also check for a blown head gasket. Does the coolant tank hold pressure cold? If so, pretty good chance the head gasket is leaking, and this will cause overheating on the highway.

So will dragging brakes, though.

I suppose it's possible to put the fan on backwards, but this would cause overheating all the time.

Peter

Check your af/h20 ratio.
No more than 50/50 mix
If you have high af ratio, it will not transfer the heat back to radiator well.
Other possible is air bound...

re
 

head gasket is out of the picture because I have done it 10 months ago,and there are no simptoms related to this.
Also it seams that the system holds presure the radiator hose is firm(hard) and when is cold and open the cap it release presure(fsssssss).
I am goin to change the termostat but I know is Behr.I will never put any think from aftermarket.
Does anybody know wat it suppose to be the temperature at hwy speds with the ambiant temp 85 F?
How can I check the accuracy of the gauge?

It is possible that the head gasket is leaking. What I have noticed over time is that a majority of technicians will use a "cookie cutter" pad to clean the cylinder head mating surface prior to reinstalling the head. I also noticed that some technicians are not completely satisfied with the surface unless it is shinny! With an aluminum head it takes little effort to actually remove material, a couple of thousands here or there when using a rotating disc is not something that can be easily detected. When cleaning the surface I believe some technicians have a tendency to become focused on removing “stains” (which can be .003 to .007 deep into the material) rather than the material which effects the sealing quality of the mating surfaces. I have encountered a number of situations now where the only solution was to remove the cylinder head, disassemble the valve train as needed, and have the cylinder head machined. I had one head that had to be replaced due to the surface being badly damaged from an over zealous cookie cutter operator.

1) The fact that your engine runs warmer on the highway implies that it is getting hotter while driving.
2) The fact that it is cooling down in traffic implies that it is capable of cooling itself sufficiently.

I just went through this uncomfortable process with a friends car, the cylinder needed to be machined due to the imperfections and now the engine temp is rock steady at 85-C. Valve job performed within the last 2 years………….IMHO I would encourage switching to a wood scraper (finishing scraper) when cleaning the cylinder head surface, it is faster.

I agree completely with the last post, my guess on reading your statement that there is cold pressure was a bad head gasket or a cracked head. Since cracked heads are rare on the M104, I'm betting the gasket has failed, either for the reasons listed above or by the use of a defective gasket (some aftermarket ones are problematic).

Overheating under load with cold pressure is a sure sign of exhaust in the coolant.

Peter