All of our Navistar conventional school buses come with the Espar Hydronic 5 (E-Guardian) diesel coolant heater. The impact switches that came with the heaters are very sensitive and would pop when ever the bus went over rough roads.
We did a partial fix by using a hole saw and reaching in to the heater housing and resetting the switch. This was a hassle but necessary to keep them operating. Low and behold the engineers at Espar came out with a new impact switch and harness that does not cut out over rough road.
The part numbers for this unit are below. There are 3 harness options and just one impact switch. Impact switch number: 252800705050OZ . The harness that fits the Hydronic 5 we have is 25280070100200OZ. The International dealer can get you the parts or anyone who has dealer status for Espar.
A great advantage to getting Espar heaters is the software is free to download. Go to the Espar website to get the software. The heater comes on in cycles starting with the blower and fuel pump then the electrode to start the burner.
The fuel used is minimal about 1/2 a cup of diesel per hour. With anti idling laws around schools these heaters preheat the buses long enough to get the interior temperature up fast. They operate for 2 hours at a time during each cycle. The faster a diesel engine can warm up saves fuel due to less warm up time in the morning.
If you are interested in these heaters it's possible to install them after factory with a complete install kit. You just have to get a fuel feed from the tank and hook up the coolant plumbing and electrical. Our shop installed a Webasto heating system on an International conventional bus because it was parked out of town and we wanted more assurance that it was going to start in cold weather.
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Below is a video I did on setting the 7 day timer on an Espar