Hello everyone,

I have a 1994 C280, and having overheating problem since the water pump leaked and was replaced. I had the coolant flushed after the pump replacement because I noticed that the shop used the regular green antifreeze, and the temperature was above 100 at all time and the belt was stretched.

Now the temperature gauge shown around 80 while the car is moving, and raised to near 110 when stopped after the Benz shop replaced the belt, tensioner and others. The hoses are still burning hot when touched from the outside, and the fenders are very hot from the outside as well.

Could this be the thermostat's problem? Where is the t-stat located in the 1994 C280 model? Any picture to help locate it will be greatly appreciated. I think I may do this myself to avoid another big bill.

The auxiliary fans kicked in only when the temperature got to 110, and turned off right after it cooled down slightly. I don't know whether or not the cooling fan run at higher speed when the temperature got above 90 or not.

Your help will be very appreciated.

Golden

follow the upper radiator hose (the big fat one) to the front of the engine - it will be attached to the thermostat housing. three bolts to take the housing off. when you pick up the new thermostat - check that you have a new gasket included because the old one will be shot...

__________________
joE
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"
http://banners.wunderground.com/bann...L/Key_West.gif

This happened after the water pump was changed? Was that all they changed other than the coolant?
If so, they may have installed an after-market water pump that simply doesn't measure up.

I can't say for sure about MB, but if you put a factory Honda pump next to some of the after-market varieties, you'll see a big difference in vane design.

Something to think about.

if you want to look at thermostats-then go to the fastlane section of this website and go into the online catalogue section-then enter the year,make and model of your car and you will get close up pictures of the t-stat,the o-ring gasket and prices.
good luck.!

Thank you so much for your folks' lightning speed respondses. I love this forum, and learned so much from everyone.

Before the pump leaked badly, the temperature gauge stopped at 85 at all time whether or not the AC was running. After the pump was replaced, engine run hot all the time, and promted me to flush the coolant after I read from the treads that MB coolant is either clear or orange in color. Wrong coolant used with the aluminum MB radiator may be the cause for the high temperature, I thought.

So, I brought the car to a euro car shop other than the local MB dealer mainly because it was quoted about half the cost. The pump cost plus labor. Sounded reasonable, but end up costed me almost twice as much by the time everything was done. My belt was streched loose due to may be the poor workmanship for fastening, or too hot in the engine compartment that cause the belt to badly stretched because wrong type of coolant used.

I will give the thermostat a shot, and thank you all for being so kind to help. I assume that the dome shape half cube which is connected to the upper hose located at the top of the water pump will be the housing of the thermostat.

Was the thermostat's characteristic changed after overheating occured? Just curious !

By the way, is there any modification in resistor change for the boosted HP just like some treads suggested? Or the 202 chassis (C280) does not have the resistor as other models that were discussed?

Golden

1994 C280, Red hot with cream interior 106K miles
2000 ML 320 Silver
1991 190E 2.3

Hi,

Suggest using a factory or at least OEM replacement thermostat.

Replaced my less than one-year-old t-stat with an OEM replacement. Much better performance! Solved most of the hesitation problem and car runs far smoother. Gauge rarely goes over 87c degrees. (Make certain you buy the correct temp. unit.)

Search on thermostat replacement on this forum. Good procedure for my 1990 300E. Might work for you too. It took me 15 minutes and very little loss of coolant.

Good luck,

Hunter

PS: Gas mileage went way up as well.

Thank you Hunter,

I got my part from FastLane. Try not to mess around .

Any one has the C280 vacuum schematic? I am trying to find out where is source for the vacuum leak that causes the air to cool the windshield instead of human from center vent. Who knows, cars has its own intelligence !

Golden

1994 C280, Red hot with cream interior 106K miles
2000 ML 320 Silver
1991 190E 2.3

Hi Golden,

You are welcome.

As for your AC problem.

Suspect the ACC unit first. My car had the same problem but intermittently. Vacuum seems to work so I suspect the ACC unit is on its last leg. Pulled it and resoldered the joints and board. That helped but oddly enough, the t-stat replacement helped as well. Go figure.

Is the problem on your car intermittent or all the time?

Regards,

Hunter

Hello Hunter,

The air vent problem is constant. It always get to default mode (cooling windshield) as soon as the car is started. When the car is running at night with very little surrounding noises, I could hear the sizzle sound under the dash. I think the vacuum connection may be bad at the actuators area. I had tried to look into the problem by opened the side panel under the glove box, but couldn't reach the inside to see. I was too cautious to poke further before I understand the structure of the under dash. I had the tendency to screw things up worse everytime I did something, and caused extra works. May be I should start to remove the radio and look from there. I need to learn the procedure to get the radio panel removed though !

Also the air flow completely sent to the windshield during aceleration. Air will get back to the side vents after 2 to 3 seconds of leveled speed. This has been a pain in the you know where when the hot temperature in central Florida climb to 98-100 degrees in the summer.

The MB dealer has done the repair on this before when the car was under warranty and the control pushbuttons did not even change the air flow as you wanted it to, i.e. to the floor, or to the windshield.

Hope to get these mistery problems fixed once and for all.

Couple of general comments:

1. TStat would be my first choice ... it may seem weird, but lots of folks how have the coolant system "opened" (fluid drained out) seem to have problems with tstats when the system is resealed and filled - is there a failure mode?

2. Type of coolant is not likely to make a major difference in temperature. It will, long term, likely mean some problems.

3. Proper ratio of coolant to water is likely a bigger factor in cooling efficiency than type of coolant.

4. Is there a failure mode for the viscous clutches during R&R& i.e. are they stored in a manner that causes problems? I recall my new one had a warning to store vertically vice laying them flat ... on the other hand they were shipped flat?

5. Within reason, I can't imagine a minor vane difference being enough to make a cooling problem.

5. Finally, there could simple issue of system not being pressurized. Start at the cap and work down through the system looking for leaks. Cap is about $5 ... if yours is more than 5 years old, give it a try.

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

Thanks George and everyone,

I will replace the thermostat that just received today from FastLane. (What a lightning speed of service they have there, ordered yesterday late afternoon).

It seems like not that much difficulty to replace the t-stat, but I need better understanding before the work.

I have a few questions and need your kind advice:

1. Is it neccessary to replace the 3 bolts with new ones?

2. Do I need to drain the coolant slightly before open the t-stat housing? If I open w/o draining, how much coolant will be lost?

3. Any other precautionary procedure that I have to be aware of?

I feel like a dummy when come to working on cars again after 20 some odd years especially the newer and more complicated vehicles. When the repair bills runs high and the wallet is going flat, need to know how to D.I.Y. It is better learning late than never though.

Thanks again for all your advices, and this very valuable technical forum.

_______________
Golden

1994 C280, Red hot with cream interior 106K miles
2000 ML 320 Silver
1991 190E 2.3

you don't have to replace the bolts. if your thermostat lifts out , it won't take 15 seconds to replace it with the new one and you won't lose a lot - maybe a pint of coolant. if you take longer, you might lose the contents of the reservoir but not much more. when you take off the housing just make a note of the thermostat's orientation to avoid putting the new one in backward.

__________________
joE
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"
http://banners.wunderground.com/bann...L/Key_West.gif

I'll post a pic of the engine bay on a C280 with the thermo

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Hi Golden,

Here's how I changed mine:

With a cool engine, place some newspaper below the car and a towel or two to cover the belts as much as possible.

I made certain the gasket was already on the new t-stat.

Loosen coolant overflow tank cap. Do not remove it. Loosen so your hear the pressure being released.

Squeeze top radiator hose with one hand as much as you can and while holding hose tight, tighten cap on tank. Let go of the hose. This gets most of the coolant away from the t-stat.

Remove three bolts. Pay particular attention to the thermostat and how it's positioned. Top and bottom. I read someplace that the the little hole (at least there was one on my replacement) on the middle rim should be facing the firewall.

Remove housing and quickly remove old t-stat noting the placement of the unit as it comes out. Up and down and position of little hole. Place new unit in and double check the position.

Carefully replace housing and press straight down to seal.

Put in the bolts and tighten them up by hand. I watched the housing seat while tighening the bolts. Hand tight but a torque wrench can be used.

Wipe up any fluid on the engine and fire it up. Look for leaks as it warms to operating temp. Be sure to run it to operating temp and let it idle for a few minutes. Turn on the AC too.

Took me about 15 minutes.

That should do it:-)

Good luck,

Hunter

Only thing I would add is to replace the coolant lost with water initially - this saves cost of more coolant - UNTIL YOU ARE ABSOLUTELY SURE THIS SOLVED THE PROBLEM.

If the new tstat did fix the problem, then drain a bit (your choice of methods) and add appropriate amount of coolant. I have heard a lot of variance in temperatures shown on the gauge that I think are related to the mix of coolants.

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg