W210 1999 E300 Thermostat - PeachParts Mercedes-Benz Forum

packerfan · #1 08-18-2017, 10:51 PM

Not sure why but cabin heat is not very hot when climate control is switched to "High". The needle on the temp gauge is about 1/8" below the 80 deg.C mark when driving on the highway. I am wondering if my thermostat is faulty or if I need a radiator flush?
What things should I be testing?

torsionbar · #2 08-19-2017, 12:05 AM

Low cabin heat, low engine heat, sounds like a failed thermostat. I think MB recommends new engine coolant every 3 years in these cars.

ESchwab · #3 08-19-2017, 02:16 AM

You get high temperature readings if your radiator is not working properly. You get low temperature readings if your thermostat is bad and remains open all of the time. The thermostat should not open until the coolant in the motor is above 80 degrees C. It may be that your thermostat is open all the time and the coolant never gets above 80 degrees on the highway, when your cooling system operates most efficiently.

When you have a bad thermostat, you get high temperatures if the thermostat is stuck closed or does not open properly; you get low temperatures if the thermostat is stuck open.

It's also possible that you gauge does not register correctly. I have a '98 e300, and my gauge registers high most of the time. The reason I know is that I bought an infrared thermometer at Sears and get readings of 80 to 90 degrees from that thermometer of water going into the radiator when the gauge registers well above 100 degrees. You might buy an infrared thermometer. There is a huge price range. Harbor Freight has them at below $20; Sears has models that sell for around $40 and near $70; and Amazon sells them at the full range of the prices.

Like torsionbar, I suspect that you have a bad thermostat. The thermostat is at the bottom of the motor in that bell housing where the coolant from the radiator enters the motor. It is not hard to change; the major problem is the aggravation of draining the coolant. I changed mine yesterday.

jake12tech · #4 08-19-2017, 02:57 AM

Hi packer... went through this a few months ago and it was a bad thermostat. They are supposed to be done every 3 years. It wouldn't be a bad idea to do a coolant flush as well. Also order the kit so you have to gasket. The job calls for half hour, I get them done in 15 minutes.

packerfan · #5 08-19-2017, 09:40 PM

Quote:

Originally Posted by jake12tech

Hi packer... went through this a few months ago and it was a bad thermostat. They are supposed to be done every 3 years. It wouldn't be a bad idea to do a coolant flush as well. Also order the kit so you have to gasket. The job calls for half hour, I get them done in 15 minutes.

Hello again my friend!
I will change the thermostat and see what happens.
I have read somewhere that the drain plug in the bottom of the radiator is made of "plastic", if this is true I should order a new one of those as well in case the old one cracks on me?

packerfan · #6 08-19-2017, 09:43 PM

Quote:

Originally Posted by ESchwab

You get high temperature readings if your radiator is not working properly. You get low temperature readings if your thermostat is bad and remains open all of the time. The thermostat should not open until the coolant in the motor is above 80 degrees C. It may be that your thermostat is open all the time and the coolant never gets above 80 degrees on the highway, when your cooling system operates most efficiently.

When you have a bad thermostat, you get high temperatures if the thermostat is stuck closed or does not open properly; you get low temperatures if the thermostat is stuck open.

It's also possible that you gauge does not register correctly. I have a '98 e300, and my gauge registers high most of the time. The reason I know is that I bought an infrared thermometer at Sears and get readings of 80 to 90 degrees from that thermometer of water going into the radiator when the gauge registers well above 100 degrees. You might buy an infrared thermometer. There is a huge price range. Harbor Freight has them at below $20; Sears has models that sell for around $40 and near $70; and Amazon sells them at the full range of the prices.

Like torsionbar, I suspect that you have a bad thermostat. The thermostat is at the bottom of the motor in that bell housing where the coolant from the radiator enters the motor. It is not hard to change; the major problem is the aggravation of draining the coolant. I changed mine yesterday.

I like the idea of an infrared thermometer, I was trying to figure out a way to test the engines temperature.

jake12tech · #7 08-19-2017, 09:47 PM

Quote:

Originally Posted by packerfan

Hello again my friend!
I will change the thermostat and see what happens.
I have read somewhere that the drain plug in the bottom of the radiator is made of "plastic", if this is true I should order a new one of those as well in case the old one cracks on me?

It shouldn't crack. They don't normally at all. My bets on the thermostat. When you replace it's going to be Air Bound. Make sure to bleed it defrost on high, overflow cap off. 2000rpm for 2 minutes. You'll tell when it's good.

shertex · #8 08-20-2017, 04:49 AM

Quote:

Originally Posted by packerfan

I have read somewhere that the drain plug in the bottom of the radiator is made of "plastic", if this is true I should order a new one of those as well in case the old one cracks on me?

Yes, have a new one handy. On mine, the knob broke off....I had a time of it getting the plug to come out.

97 SL320 · #9 08-20-2017, 08:39 AM

For radiator drain in general, some are threaded and others 1/4 turn the pull out so be aware of that.

I've had the thermostat bridge break and disc stay partly open. It would run hot at idle / low speeds and cool when driving. The hot running was due to the bypass not being blocked off by the thermostat and the cool due to it being stuck open. If the pin had completely come out of the bridge and stat shut , it would have overheated at all times.

Look at my post 5 here 1995 e320 running hot

ROLLGUY · #10 08-20-2017, 12:25 PM

You may or may not know this: When you fill it with coolant, be sure to fill through the upper radiator hose, as well as the expansion tank.

packerfan · #11 08-20-2017, 03:35 PM

Quote:

Originally Posted by ROLLGUY

You may or may not know this: When you fill it with coolant, be sure to fill through the upper radiator hose, as well as the expansion tank.

Thanks for that tip ROLLGUY, no I did not know that.

ROLLGUY · #12 08-20-2017, 04:06 PM

The Tstat is located in the coolant flow before the engine (not after, like in the old American made cars we are used to). The only way to get coolant on the other side of the Tstat is through the top rad hose and into the engine. If not done this way, there will be air on the hot side (engine), and coolant on the cold side (expansion tank and rad). The Tstat will not open.