improving the performance of a mercedes school bus

The video was a little altered because of my android battery needing a reboot LOL. All I wanted to show you was the severity of the leak at the charge air cooler. The gaping split on the core was causing a major turbo boost drop and producing the engine code 2631 “turbo boost performance”. This is a very common code with the Mercedes MBE 900 diesel engines.

Mercedes Engine Codes A Regular Occurrence

The emission controlled Mercedes engines in our fleet have been keeping us busy with emission and engine codes. The DPF filters are now a common maintenance step since they have to be serviced or replaced every 125,000 KM. The soot levels are high so the emission components are gumming up more than anything else causing failures.

All of our 2007 and 2008 buses running these engines are coming due because of the mileage or we will jump on them when they stop self maintaining themselves as directed by the engine control unit. If the soot level builds up faster than normal that indicates the diesel particulate filter requires cleaning.

If we send it away to one of the shops for cleaning it may fail the process and we will be stuck buying a rebuilt unit. They cost us $800.00 while the cleaning process (both stages) run around half of that cost. We thought of keeping one of the cores to have it on hand for the next job but the core charge is over $2400.00 so we send them back for obvious reasons.

Charge Air Cooler Removal

Removal of the charge air cooler requires a few steps with the removal of the power steering cooler. The 2 upper hoses and bottom mounts make this job not a bad operation. Since the leak is on the inside of the core of the cooler we have to wait until it’s removed to inspect the damage.


As you can see in the photo it’s a bust as far as repairing this core. Most of the time it’s not a successful repair because of the fragile core tubing that also has the cooling fins attached. After contacting the dealer it’s going to be 7 to 10 days delivery time from Memphis which is the typical location of major replacement parts for the Thomas buses we’re running.


I’ve ordered 2 charge air coolers so we’re ready for the next failure which I guarantee will be happening sooner than later. We buy these buses with the exact same specs and in groups of 5 or 6 on average.

Some components usually fail at around the same time within a month or so of each other. It’s happened several times since I started working on these buses 20 years ago. If we get another bus the same year with the same code you can bet that we will be testing the charge air cooler for leaks. To quote that popular saying us techs use all the time “you learn by experience”.