97 E320 Overheating?
 

Just in the last couple days, the car's dashboard water temp. indicator has been travelling beyond the 100 degree mark, and has been fluctuating. When the meter showed 120, I turned the car off, and sniffed around under the hood. I would have expected to smell some steam, and feel the engine heat, but it didn't feel any warmer than it usually is right after I stop it. The aux fans were going overtime, but that doesn't seem to affect the temp reading that much.

As I drive, it goes up and down, and often it is reflective of how I'm driving, as in going down when I'm rolling due to the general air cooling, then climbing up when I'm not moving much, but this morning, even though I was going 60mph, and had been for a few minutes, the temp was not going down.
Last night, again when I was sniffing under the hood, I felt the water reservoir housing, and it didn't feel as hot as I would have expected it to feel for a supposedly 120 celsius fluid, and opening the cap, there was not much pressure that vented.
Unfortunately, I don't have a good thermometer to measure the actual fluid inside the housing, but I will be going to a shop this afternoon to have them look at it.
I'm just trying to get an idea of what possibilities there are for the problem. Could it just be a temp. sensor that's going out? Or could it be that the coolant is not flowing properly? Not sure. Any ideas?

Hi,
there is always a chance that the gauge got haywire or just a bad ground.
If you can, try to measure the temperature at the thermostat housing.
There are low cost infrared thermometer, perhaps at a Harborfreight near you.

If you measure about the same temperature as indicated by the internal gauge, then it is time to investigate more.

Careful, in most cases I know of, the head gasket(s) was on it's way out.
Another check one can guestimate, but is probably too early in your case, a builtup of grey/greenish gunk on the oil filler cap could indicate water contamination withint the motor oil.
This usually goes along with higher coolant pressure and the pressure release mechanism at the water reservoir would indicate that. The level in the reservoir, could be higher than usual.

The level looked normal in the reservoir from what I can tell. The guy that changed the oil said there's a small leak, and some gaskets on the top of the engine (straight 6) need to be changed.
I recognized last night that I really needed something to measure the temps at various parts...

Also have a look at post 14. The thermostat bridge broke leaving the t stat in this position. See post 12 on how to enter HVAC data screens. It uses the same sensor as the dash gauge but it is in American units and an actual number.

http://www.peachparts.com/shopforum/tech-help/355880-95-c280-overheating.html

You mentioned the aux fans, but what about the main cooling fan (between engine and radiator)?

ricochetv1, it helps to indicate the mileage on your vehicle when asking for members to diagnose problems. If the thermostat hasn't been replaced recently, or never, recommend installing an OEM thermostat for starters. I experienced a sudden overheating problem, similar to yours, with a 104 engine and a new thermostat resolved it immediately.

I suspect your mechanic advised replacing the valve cover gasket to stop a slight oil leak, typically at the back of the engine.

It was the thermostat. The mechanic took the housing off, and the thermostat was stuck closed. I replaced that and the temp. sensor, since it was right there beside the thermostat, and no addtl charge for the labor... I guess the valve cover gaskets are next on the list.

Bet you were happy to find just that broken.....

Leaking coolant now...
 

I definately, was, but now it seems I have a small high-pressure coolant leak. I do not know where it's coming from. I suspected it's coming from the thermostat housing, but I didn't see, smell or feel anything coming out of there.
#1 - Is there something out there I can put in to the coolant that will help give a telltale?
#2 - I've heard of putting grated ginger into the coolant to plug up the leak. Any opinions on that?

The car uses green coolant.

In general, I am not too thrilled about any goo inside the cooling system, there are probably a number of others that aren't either.
With this stuff in the cooling system it can clog smaller passages and holes, but a side effect could be, disallowing the right amount of coolant to flow, most likely in the radiator.
Plus, in my opinion this would only be a temporary solution!
If your coolant has the green stuff in it, then you have already something colored.

Is the indiated coolant temperature, back to nominal?

It is hard to find a leak that is hidden, thats for sure.
Perhaps, a local auto parts store has a pump that can be attached to the sytem. You may be able to rent it.
It can pressurize the system to it's nominal pressure and a bit beyond. Can be done while the engine is cold and is safer to investigate.
Also make sure, the radiator cap is the correct one!! It could be just steaming out...

If it loses pressure and you can't find it leaking out anywhere, there is only one other way to go!
Check your oil freqently for water contaminants.

If you can't find anything on the floor, the leak could also be somewhere in the really hot areas. Evaporating before it can hit anywhere. Perhaps, the heat exchanger itself has a small leak, or near the engine block a hose clamp etc.

Same stuff ( plus a few more things ) that is in Bars Leaks Tablets. This can also be gotten at GM dealers. It is factory approved for seepy leaks.

It won't clog heater cores or rads and is stealth once mixed. Be sure to grind it up before adding to rad and then drive right away to keep it from settling.

I found the leak... It's shown in the attached picture, and that is on the back side of the radiator closest the reservoir tank.
Is that something I can fix with epoxy or something? Or have someone spot weld it? The hole seems to be right next to that clip, or clamp, since the fluid shot straight out from it. If it was coming from behind it, I figure it would have spluttered out all over the place, instead of straight out.

It's only leaking when the thermostat is open. I proved it by squeezing the thermostat intake hose to force it open. It started shooting out coolant, then stopped when I let go of the hose.

I don't know what kind of success people have had patching the plastic tanks of 19-year-old radiators.
You can pick up a Nissens for like $150, and replacing it will be similar to the W124 described here: Pelican Technical Article - Mercedes-Benz W124 - Radiator Replacement

I think "Hirnbeiss" suggested the right thing.
The plastic may be brittle in other spots and it may become a never ending story.