Diesel Engine In Frame MaxxForce DT

imported_John Whelan - June 3, 2017
If you told me we would be rebuilding one of our MaxxForce engines in six years I would have laughed and then went into total denial. There's no way a school bus carrying 60 or so children operating 4 to 5 hours a day would be enough to wear out a diesel engine. I could see a highway truck and trailer with a 140,000 lb load having issues but a school bus who would have thought?

When there is a legitimate cause to the failure that makes a world of difference. With this DT model they have a weakness which is the EGR cooler. Our 2011 and 2012 models have gone through several coolers to date. Now we have to be very aware when there is a coolant loss issue. After getting a few EGR coolers replaced under warranty the writing was on the wall.

I caught a couple of these failures through oil samples which indicated high levels of potassium in the oil which is coolant. The cause was the EGR cooler with a failed inner core allowing coolant in the oil and exhaust gases into the coolant. The first sign of a problem was the coolant blowing out the surge tank due to pressure build up so I instructed the driver to leave the rad cap off of the surge tank so there would be no more coolant loss and drive the bus back to the shop.

But the amount of time you allow this engine to run with coolant in the oil could contribute to washed down cylinder walls and premature wear. The number six cylinder in the video has a totally worn down liner caused by lack of lubrication. Experiencing this for the first time has taught us a big lesson. If there is any sign of internal coolant loss we will have to immediately check the EGR cooler for leakage.

It's a weak spot with these models and going a long time without any action repairing this problem will cause the same outcome. Since we have ten of the MaxxForce DT diesel engines in the fleet obviously this problem will happen again. The repair costs on this job with engine tools and rebuild parts will be between $6,000 - $7,000.

This doesn't include the labor which we don't count since the job will be done by our shop. An unfortunate turn of events with these diesels but we will have to adapt and keep on top of them since we now know their weak spots.




School Bus
Diesel Engine
DT MaxxForce