My 300E never reaches 80C when on the highway - PeachParts Mercedes-Benz Forum

glpro160 · #1 06-24-2010, 11:02 AM

My 300E MY 1991 never reaches 80C when on the highway. Fan clutch is still working. So is the thermostat. Some people say the optimal temperature is around 90C. Might there be something wrong with my dear 300E?

tjts1 · #2 06-24-2010, 11:07 AM

If its sitting just a hair below 80C at highway speeds, you probably have a 79C thermostat. I wouldn't worry about it. If its much lower than that, your thermostat might have failed.

anthonyb · #3 06-24-2010, 11:31 AM

I believe these cars came with an 87 C thermostat.

tjts1 · #4 06-24-2010, 11:53 AM

They did come with 87c tstat but a lot of people swap in 79c thermostat because of all the over heating issues these engines have, myself included.

glpro160 · #5 06-24-2010, 12:04 PM

Some say for the engine to be in its best state operationally and economically it must be around 90C. Engine parts have gaps between them and those gaps can only be filled up only when at 90C as metal parts thermally expand. Under 90C the parts stay loose with each other and that give more chance to parts' wear. Under 90C also makes the ignition harder thus reduces fuel economy.

I like to run cool engine but the above logic sounds reasonable.

tjts1 · #6 06-24-2010, 12:18 PM

Running at 79c doesn't make a whole lot of difference to be honest. I'm getting the same ~30mpg on the highway with a 79c thermostat that I did with a 87c thermostat. Last tank was 32.5mpg. I did notice that it pings less on 87 octane under high load than it did with the 87c. Mercedes used a hot thermostat to reduce emissions, not for fuel economy. I would keep the cold thermostat.

glpro160 · #7 06-24-2010, 12:27 PM

Quote:

Originally Posted by tjts1

Running at 79c doesn't make a whole lot of difference to be honest. I'm getting the same ~30mpg on the highway with a 79c thermostat that I did with a 87c thermostat. Last tank was 32.5mpg. I did notice that it pings less on 87 octane under high load than it did with the 87c. Mercedes used a hot thermostat to reduce emissions, not for fuel economy. I would keep the cold thermostat.

What about engine wear? How much does it do with the engine wear?

What W124 are you running? The best I ever got is 24mgp.

tjts1 · #8 06-24-2010, 12:48 PM

I have a 190e 2.6 manual with the same M103 engine found in the 260e and 300e 2.6. No idea about engine wear but 79C (174F) is not an unreasonable operating temperature. I'm more worried about the 100C + spikes these engines seem to have in hot weather and slow traffic. I've read too many blown head gaskets and overheating stories to allow my engine to get into that temperature range. If the temperature was getting stuck at or below 60C, then I would worry about engine wear.
cheers
Justin

glpro160 · #9 06-24-2010, 12:54 PM

Quote:

Originally Posted by tjts1

I have a 190e 2.6 manual with the same M103 engine found in the 260e and 300e 2.6. No idea about engine wear but 79C (174F) is not an unreasonable operating temperature. I'm more worried about the 100C + spikes these engines seem to have in hot weather and slow traffic. I've read too many blown head gaskets and overheating stories to allow my engine to get into that that temperature range. If the temperature was getting stuck at or below 60C, then I would worry about engine wear.
cheers
Justin

Thanks, Justin. Your explanation is convincing to me. There must be a reason that people make 79 thermostat.

I just post another thread on ABS malfunction indicator. Go check and share if you have any thoughts.

JamesDean · #10 06-24-2010, 01:27 PM

Does it take a long time to warm up?

You might need to replace the thermostat and do a coolant flush.

I had to do this on my 300SD. It took forever and a day to get anywhere near 80C. New thermostat and a flush later. It heats up just like it should

My 190E 3.0 heats up in no time and stays a little north of 80C all day long, without ac. Ac doesnt work so cant say what it does when that is on.

ps2cho · #11 06-24-2010, 03:22 PM

Do you guys think it would be wise to go to a 79C thermostat since I am moving from California to Arizona?

tbomachines · #12 06-24-2010, 03:37 PM

I used to have the same problem, sometimes the temp would drop close to 60 on colder days. Replaced the thermostat this weekend and it is dead on 90* (have heard Behr is a bit on the hot side) all the time with the exception of sitting in traffic this afternoon where it began to rise in the 90-95*F heat.

tjts1 · #13 06-24-2010, 04:25 PM

Quote:

Originally Posted by ps2cho

Do you guys think it would be wise to go to a 79C thermostat since I am moving from California to Arizona?

It will help a bit but the more important part is to make sure that your viscous clutch fan is working property. The cool harness modification would be more useful.

glpro160 · #14 06-24-2010, 09:59 PM

Quote:

Originally Posted by JamesDean

Does it take a long time to warm up?

You might need to replace the thermostat and do a coolant flush.

I had to do this on my 300SD. It took forever and a day to get anywhere near 80C. New thermostat and a flush later. It heats up just like it should

My 190E 3.0 heats up in no time and stays a little north of 80C all day long, without ac. Ac doesnt work so cant say what it does when that is on.

It takes around 10mins in the city to reach 80C, I always use lower gear until it reaches 60C, i.e. I use 2nd gear when 3th gear would be used in operating temperature.

If 80C and 90C don't make a lot of difference in economy and engine wear so I would stick to the 80, as the risk of wire harness damage is lower.

tjts1 · #15 06-24-2010, 10:04 PM

10 minutes seems a bit long to reach 80C. Once on the freeway is the gauge really really close to 80c or somewhat lower? You might still have a bad thermostat.