Copyright 2019 Discovery Owner's Association, Inc.

Overheating Problems

If everything is working properly on your D, you really should never encounter any overheating problems, even in the hottest weather on the longest grade. NOTE - Well, may that is a bit of an overstatement. At higher altitudes where the air is thin, the ability of the atmosphere to accept heat is reduced, especially if the ambient temperature is hot. So, under these conditions the coolant may reach 210 degrees Fahrenheit, which is the trigger point for the "Check Engine" or "Stop Engine" lights. If this happens, try downshifting and operating at less than full throttle. It is best to monitor your coolant temperature with your VMSpc and take action to prevent the coolant from rising to 210 degrees. Cummins is very specific about the cooling requirements of their engines and requires every motorhome manufacturer that uses their engines subject each model to a strenuous test before Cummins will allow them to use their engines. It appears as if the radiator has been increased in size on late 1999 model D's.

So, what if you have an overheating problem?

Here are some things to check:

  • Check your thermostat. Some late 1998 and early 1999 D's were delivered with defective thermostats
  • Make sure that your coolant is 50% water and 50% coolant. Having more than 50% coolant seriously degrades the ability of your coolant to transfer heat.
  • Make sure that you do not have a leak and that you have the proper amount of coolant in your system.
  • A common problem that is overlooked is the Charge Air Cooler. If this is dirty, the turbo will not get cool air and this will cause your engine to overheat. Periodically, spray it with Simple Green and hose clean. Be careful if you use a power washer as the fins are easily damaged. After 10,000 - 20,000 miles, you would be surprised at how much gunk you can get out of there! Click Here for an article by Leo Everitt for an alternative cleaning method.

This is not meant to be an exhaustive list of possible problems. If you want to contribute other ideas, please advise the webmaster.


The DISCOVERY OWNERS ASSOCIATION, INC, was formed to promote the sharing of information and the camaraderie of fellow Discovery motorhome owners. Membership in the club is limited to owners of Fleetwood Discovery motorhomes.


Website Questions
Email Webmaster
Membership Questions
Email Membership Coordinator