"P0128 - Coolant temperature below Thermostat regulating temperature"
 

Hi all,

My girlfriend has a 02 C230 coupe as well and her car keeps throwing the following error code:

"P0128 - Coolant temperature below Thermostat regulating temperature".

Its happened twice now and Ive cleared the errors but is it something to worry about? :nix:

Anyone run into this problem?

Thanks guys..

You probably need a new coolant thermostat.

https://mbworld.org/forums/c-class-w...need-help.html

Perfect! That was easy.

Any idea if there is a DIY around somewhere? Ive tried searching and cant seem to find one.

Thanks.

Bring this one back from the dead. My wife's car is having the same code thrown as well only we've had the thermostat changed and it still pops up from time to time. I'm beginning to wonder if the sensor itself is malfunctioning? Her car has 114,xxx miles now and other then that has been cool, knock on wood :D

90% sure it's the coolant thermostat. Buy one online, and DIY. It's extremely easy to replace. 2 bolts at the front of the engine block. Search the forum with my name. There's a thread where I've posted some part #s and stuff.

You will also need a jug of MB coolant to mix, as you'll lose 1-2L of coolant once you pull this part out of the engine block.

Coolant thermostat - not "level" thermostat. There is no such thing.

^ You are correct, good sir. Brain fart. Engine coolant thermostat it is.

Ironic that this thread was bumped.

My car just threw this error this morning.

Here's the thread with the DIY: https://mbworld.org/forums/c-class-w...edan-w203.html

But, RMeuropean only carries the 90 degree version. I don't live in a very cold climate and even a hot climate, so I assume I need the 87 degree? But from other threads it looks like people are having difficulty finding the 87 degree. Has the 87 degree been discontinued? Will the 90 degree be ok?

^ That must means your coolant runs 3C hotter. You are right, nobody carries the 87C version anymore, not even Canadian dealers.

If you think about it, it makes no sense why they even bothered making 2 versions, which is probably why they discontinued the 87C version. The only difference between the 2 is that your coolant runs 3 degrees Celsius hotter at the high end during normal operation. This is completely irrelevant to the ambient temperature from an engineering perspective. You want your engine to get hot enough, period. Doesn't matter if you're in Sweden or Saudi Arabia.

Everyone now seems to carry the 90 deg C thermostat. It can do no harm. Will give very slightly better engine efficiency.

Ironic that this old thread that I started 2 years ago got bumped now...exactly when Im looking for the coolant DIY.

Thanks for the link nlpamg.

haha, the world goes round in circles :)

Thanks for the link! Y'all have motivated me to do the work. Been getting/resetting P0128 for about a year now, seem to get it about 9 minutes after startup on cold evenings when I don't hit any traffic.

If I were, I wouldn't have driven the car for a year with P0128/thermostat issue. Although, we are told that thermostats on these cars usually get stuck in open position, it can get stuck in closed position and it's a matter of minutes before serious damage to engine occurs. Fortunately, replacing thermostat is relatively easy.

Past is past, please take care of that problem ASAP. :)

Mine did it at exactly 100k miles. Part was $29 and yes I had to go with 90C thermostat. 22k miles and almost a year later and no further issues.

Okay... I just ordered the thermostat kit from Parts Geek. Plan is to install it next weekend. Thanks!

Just a tip once you get the the black housing for the thermostat. I sprayed lots of WD-40 around it and pulled it out with my bare hands. That junk was stuck on there . Took me 40 mins just trying to pull it out. Use a big flat head to help push it out.

Driving home from work today I noticed my CEL came on and it's the P0128 error as well. Can someone point me to the right part number ? I have the 2002 C230 Coupe Kompressor. Also how much different is it using that DIY that was posted by nlpamg I opened the hood and looked my engine and it is not the same as the 03. Any help appreciated.

I signed up for the EPC tool to look at the diagrams but I can never figure out how to search for anything using that tool.

I have an extra coolant thermostat i had bought awhile back. I got it from Partsgeek.com If you want I can sell it to you just name a price and shipping. accept paypal. The box is unopen too actually.

Here is the extra thermostat I have, it is actually sitting in front of me. Just cut the shipping box open. Double check the part number on the page if it matches up to your vehicle. If you need it , just let me know I can ship it USPS to ya.

The thermostat sits in front of the engine. Just look at your radiator top big hose on your driver side. Follow it to the engine, it will lead you towards the center. That is where your thermostat sits in that black plastic housing. Take off your air filter front housing for better view. THen you will take the 2 bolts off and disconnect the hose from the plastic black housing by pulling the clamp up and using a flat head to gentle pry it loose. It will then leave you with the black housing left on it. I hope your arms are strong, because its hard as hell to yank off. Use some wd40 and a flathead to help you pry it loose.

Picture

https://mbworld.org/forums/attachmen...sedan_w203.pdf

Click here and download instructions with pictures, this will help you.

Hey guys, i got this code last week, but cleared it with my scanner and it hasn't come back. Should i worry about it? or no need to do anything unless it comes back? thanks!

I got this too the other day as well and its the second time :rolleyes: Sounds like we definitely need to change our thermostats and Coolant temp sensors.

Roland - just watch your temp gauge. If the car is running cooler than normal & taking a long time to warm up to operating temperature from a cold start then change the thermostat.