The Espar is back in action. In and effort to add to the knowledge base of the forum, the following is a summary of sorting the Espar DW5Z in my 04 T1N Sprinter and some other lessons learned.
Recap:
About 4 years ago, I replaced a bad Flame Sensor and the Espar has worked w/o issue since then. I ran the Espar about 5 months ago to exercise it as some have indicated that they need to operate regularly. A couple of months ago I tried to do another maintenance run cycle and the Espar would not start (or do anything) and the cover over the temp sensors looked somewhat warped.
Data Points:
I removed the Espar and checked the following; hardware appeared operational and values in range.
[Ambient Temp of 70 degrees]
Glow Pin resistance = .9 Ohms
Flames sensor Resistance = 1.1 K/ohms
Cold Sensor Heat Exchanger - 9.27 K/ohms
Hot Sensor Heat Exchanger - 9.03 K/ohms
Espar Fan spins freely with 9 volts applied
Intake and Exhaust hoses are free of obstruction
Disassembled burner chamber and sprayed carb cleaner into the D-chamber / fuel wick.
I have not heard of dosing pump failures so I just made sure that it was connected and did not test it. Given that the Electronic Control Module has made it this long, I guessed/hoped that it was ok, but did not rule it out as the culprit.
Hypothesis: Given the failure rates of the Electric Circulation Pump, the fact that mine was the stock unit, and the warped plastic cover, I speculated that the ECP had failed causing an overheat fault and corresponding lockout. However, the vexing part was that I could hear (and feel) that the ECP was still working with the REST function on but I questioned whether it was actually moving sufficient coolant (I did not disconnect the hoses to confirm). Even more vexing; generally speaking, the Espar does not require the Electric Circulation Pump when the engine is operating. Given that my Espar ONLY operates with the engine on (i.e. no bypass or 7 day timer), then why would failure of the Electric Circulation Pump cause the Espar Hydronic to overheat?
Theories:
Aqua Puttana - "The mechanical coolant pump output varies. I believe that engine speed is a factor. Idling too long without the Electric Pump operating may reduce flow in the Eberspacher heater enough to cause overheating.”
Midwestdrifter - "The heater is designed around having coolant flowing through it. If it starts up and gets to temp with no coolant flow, it is entirely possible for the burner temp to overshoot by a significant margin before the temp sensor catches it. Plus even if it sees the overheat and cuts the fuel, there is still a fair bit of fuel in the vaporizer/burner which will still keep making heat for 10-15 seconds. It is possible that the heater might shut down due to overheat with just the engine circulated coolant. However it would not be likely to overshoot, and would restart once it cooled down."
"Depending on how the heater is oriented, there may be a air/gas bubble around the temp sensor if there is no coolant flow. Such a gas bubble could prevent accurate temp sensing. That is not an issue if there is any coolant flow, which would likely purge the bubble.”
Based on the foregoing data, theories, and the medical diagnostic adage “when you hear hoofbeats think horses not zebras” (i.e. go with the odds)- I elected to replace the Electric Circulation Pump since it is a high failure rate item. After a fuse pull reset, the Espar fired up.
Lessons learned:
1. Apparently, the ECP can still appear operational (sound/vibrating) but have insufficient flow for the Espar such that it causes it to overheat even though the engine is running.
2. The Espar did not fire up until I got the fuse pull sequence correct. The Espar fuse pull reset requires:
a. Start the vehicle
b. Turn on the Espar with the bacon button.
c. Pull the #1 and #6 fuses
d. Turn the Espar off
e. Replace the fuses
f. Turn the Espar back on and wait a minimum of 3-4 minutes
3. When you first turn on the ignition and the ECP starts up, it makes a loud buzzing sound until the coolant reaches the pump.
4. A diagnostic tool would be worth it's weight in gold if you plan on keeping a stock Hydronic Espar unit.
*Bonus points - Working on the Espar and or Electric Circulation Pump is a great time to do a coolant service if you are due. I removed the Espar and ECP after draining the radiator. Based on refill volume 2+ full gallons (1 gallon Zerex G5 and 1+ gallon distilled water) it appears that a near total evacuation was accomplished w/o the hassle of removing the block drain plug.
**Double Bonus points - If you have not done so already, changing your Glow plug Relay module is easy while the grille/headlight assembly is out and you are messing with the Espar etc.
Thank you all for your input!