Here is a project we were working on involving a block heater replacement on a Thomas C2 conventional school bus. In this video you will be able to see the tight spot that you need to get in to accessing the block heater element.
This is an MBE 900 Mercedes diesel which is inset under the firewall and the dog house is not easily removed. So it involves an eye ball on a stick. This being a 2008 bus it is the most difficult models out of all the years to work on for this operation.
The MBE went emission controlled in 2007…you will notice the extra hardware on the inlet section on top which is part of the EGR system. Along with the EGR there is a DPF (diesel particulate filter) that collects soot and periodically cooks out the particulates that build up.
The DPF muffler has sensors on it that monitor heat and pressure differential that sends a signal to the MCM (motor control module) to start the regeneration.
This is accomplished by a fine mist of diesel fuel injected into the exhaust system downstream that creates an extremely high temperature in the exhaust system. This heat causes the soot build up to break down preventing harmful gases (oxides of nitrogen) to enter the atmosphere.