I have been having a peculiar issue with my Aqua-Hot system in our coach. I experienced a smoking issue back in June when the wife and I were on a trip to Grand Teton NP. Upon arriving home I decided to do a service on it, which consisted of replacing the fuel filter, fuel nozzle and cleaning the combustion chamber. After performing the service it appeared to be better for a trip or two but they were fairly close together trips.
The coach had set for about three weeks before we headed to Ouray in August. Upon arriving at our campground in Ouray, I fired up the Aqua-Hot and noticed a slighty smoking situation. Although much less than previously detected it was still there but different. The unit would fire up going through the normal startup procedure and would not smoke immediately, it would run for approx. 45-60 seconds then start emitting a very slight white smoke from the exhaust for about another 60-90 seconds. After which it would clean up and burn completely clear for the remainder of it's burn cycle.
I decided to rebuild the solenoind plunger as it is a serviceable component and sold in "kit" form. It comes as a plunger, spring and pintle along with an O-ring for the solenoid stem. I replaced this in August upon arriving home from our annual Ouray trip and while I was in there I decided I would check the fuel pressure. I believe I posted some pictures of this procedure earlier in my thread.
Prior to testing the fuel pressure I decided to fabricate a pressure gauge setup. These pressure gauges can be purchased from Aqua-Hot but they are a bit on the spendy side. I just decided to use an old nozzle and make one in house.
I disassembled an old nozzle assembly.
Chucked the nozzle up in the lathe and faced off the end.
Fuel nozzle cleaned up after facing, drilling and tapping the end for an 1/8" NPT thread.
I then purchased an inexpensive 0-200 PSI gauge and a 4" piece of stainless with 1/8" NPT threads on either end. Upon inserting the test gauge into the nozzle stand I made certain that the fuel pressure was exactly @ 145 PSI +/- 5 PSI. When I first opened up the cabinet I did however notice a few drips of diesel fuel hanging off of the fuel fittings and the intake horn for the blower housing was a little damp with diesel fuel. I thought this to be odd because there should be no fuel on the blower housing side of the fuel plate, everything fuel related should be on the nozzle side. My suspicion was a leaking fuel pump as it is driven off of the gear driven from the blower motor. However, generally speaking when a fuel pump leaks it will generally emit a continuous white smoke, not intermittent.
Here is the gauge threaded into the stand where the nozzle resides and ready for testing.
The pressure checked out so I put the unit back together and fired it up. It smoked just a small amount but that is normal after a service as diesel fuel can pool in the nozzle assembly.
Next trip out to Yellowstone in September I again noticed the white smoke upon initial startup again. Very slightly and my wife mentioned that she didn't notice it. But I did, and I found it to be embarassing.
I absolutely HATE it when something of ours is not just so. I found it hard to relax as it irretated me to no end.
Upon arriving home I decided to pull the Webasto burner completely out of the coach and get it on the bench where I could disassemble it and try to locate the problem. I had a theory, but it was only a theory. My theory was that the fuel pump was starting to leak and pooling a very slight amount in the blower housing, but not enough to give continuous white smoke. Upon startup, there was no fuel pooled near the nozzle so that is why it fired up smoke free. After running for close to a minute it must be pushing that pooled fuel out into the combustio chamber where it was getting burned, resulting in the white smoke. Once that extra fuel was burned in the combustion chamber it would clean up and burn clear/clean the rest of the cycle. Then depending on how long it sat between burn cycles it would smoke if sat for a day or more between cycles, or burn clear and clean if only a few hours between burn cycle. This was my theory and I felt good about it but wanted to tear the unit apart and locate the source of the fuel leak.
Webasto unit out of the coach and on the workbench.
Webasto unit separated and the bottom side of the fuel plate.
Here is the original grease/lubricant that has hardened and doesn't appear to be lubricating the fuel pump drive gear any longer.
Here is the assembly with the blower housing removed.
Here you can see where there is diesel fuel pooled on the blower side of the fuel plate. It appears as though the fuel pump input shaft is leaking.
The blower housing was wet with fuel as well. I originally detected diesel fuel at the intake opening last month.
After removing the blower impeller you can see the fuel coating the assembly.
The Webasto completely disassembled for a thorough cleaning. I also put together a parts list.
Composite blower houseing cleaned and set aside ready for re-installation.
I placed my order with Roger Berke and the parts promply arrived two days later. When I was disassembling the blower impeller assembly I noticed that the bearings had diesel fuel coating them. The unit is now 13 years old and I didn't want to risk the chance of the fuel washing the lubrication out of the bearings. The unit was still nice and quiet with no adverse sounds but while I was in there I opted to replace the two bearings on the impeller shaft.
I also ordered a new large O-ring to seal off the blower housing as the original one crumbled upon removal.
I replaced the fuel pump, which came as a kit with new banjo bolts, crush washers and high pressure fuel line from the pump to the nozzle stand. I also replaced the nozzle stand although I don't think that was causing any issues, the seat was just appearing a little worn and I figured I was this far into it. These units can be purchased remanned with a core charge but they are around $3500.00 and I figured I could do just as good a job rebuilding it as anyone else so I opted to merely purchase the parts and rebuild it myself.
Here is the unit completed and ready for re-installation back into the coach. Look at how nice and pretty and clean everything is. Looks great just for it to go into a basement compartment and never be seen again.
Here is a closeup of the business end after adjusting the electrode gap to proper specs. I have installed an old nozzle just for the picture.
Pile of old parts.
Here are the new Donfoss nozzles. These are the replacement for the older style of nozzles but are the same .35 GPH flow rate.
After a successful re-installation and several test runs it appears to be smoke free and ready for many more years of operation.
Mike.
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Linear Mode
