Turbo Underboost and Overheat
Thread Starter
Newbie
Joined: Mar 2023
Posts: 1
Likes: 0
From: NJ
2015 C300
Turbo Underboost and Overheat
Hello everyone,
I always use this site as reference but I never posted anything.. until now because for the first time I’m getting frustrated with my car. I have a 2015 C300 with 87k miles. I’ve owned this car for 5+ years
About 2 weeks ago, my car felt like it was stagnant at 60 mph; not accelerating efficiently. It felt weird for about a second and then I received the “coolant too hot turn off engine” message. I pulled over, turned off engine.. there were no leaks. took it to a trusted mechanic who replaced the thermostat. We did placed it on park, with AC on high, running for 30 minutes…to test and temperature does not reach past 90. Fan is working properly and cooling is not an issue.
My car is still reaching max temperature on a daily basis if I drive at a speed of 60+ for 20 mins or more. It drops and raises and fluctuates for the entire commute, but my car has not reported an error message telling me to turn off the engine.
A week after the thermostat was replaced, I’m driving my car and decide to put it into sport+, i realize it’s driving differently and the check engine light pops on. After scanning the message P0299 Turbo Underboost pops up. I cleared it and have driven 300+ miles since then without it popping back up yet, but my car has been whack to drive. It’s sluggish and the temperature continues to fluctuate only at high speeds.
what do you think it could be? Do you think there’s any way the issues are also related ?
I always use this site as reference but I never posted anything.. until now because for the first time I’m getting frustrated with my car. I have a 2015 C300 with 87k miles. I’ve owned this car for 5+ years
About 2 weeks ago, my car felt like it was stagnant at 60 mph; not accelerating efficiently. It felt weird for about a second and then I received the “coolant too hot turn off engine” message. I pulled over, turned off engine.. there were no leaks. took it to a trusted mechanic who replaced the thermostat. We did placed it on park, with AC on high, running for 30 minutes…to test and temperature does not reach past 90. Fan is working properly and cooling is not an issue.
My car is still reaching max temperature on a daily basis if I drive at a speed of 60+ for 20 mins or more. It drops and raises and fluctuates for the entire commute, but my car has not reported an error message telling me to turn off the engine.
A week after the thermostat was replaced, I’m driving my car and decide to put it into sport+, i realize it’s driving differently and the check engine light pops on. After scanning the message P0299 Turbo Underboost pops up. I cleared it and have driven 300+ miles since then without it popping back up yet, but my car has been whack to drive. It’s sluggish and the temperature continues to fluctuate only at high speeds.
what do you think it could be? Do you think there’s any way the issues are also related ?
MBWorld Fanatic!
Joined: May 2021
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Likes: 200
From: Plainfield IL
Amg C43
MBWorld God!
Joined: Dec 2019
Posts: 32,224
Likes: 6,281
MBWorld God!
Joined: Dec 2019
Posts: 32,224
Likes: 6,281
I make that mistake all the time when trying to find the thread and then posting it when I came across something that might be related to OP of other threads' questions, don't think about it too much : ) We are all just trying to help.
MBWorld Fanatic!
Joined: Jun 2012
Posts: 1,229
Likes: 188
From: Toronto
2022 E53 AMG
First problem I see if that that they guy that changed your Thermostat, didn't place new coolant but used your old. Second like many modern cars, you need to pressurize the Coolant system which removed all the air out of the system.
Also the turbo getting stuff maybe because of a vacuum hose, so check to make sure that there is a hose connected.
Good Luck.
Also the turbo getting stuff maybe because of a vacuum hose, so check to make sure that there is a hose connected.
Good Luck.
