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Webasto 90st with a 60 a day habit


davids3511

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I'm not using it in a boat. I'm a window/commercial cleaner by trade and recently purchased a 3 year old cleaning system that includes a Webasto 90st. It heast a coolant tank which in turn heats the water we use to clean buildings/windows/solar panels/clading etc.

 

It behaved perfectly until one day the batteries ran out of charge, I though I'd get more then two days from 2x Numax 120Ah batteries wired in parallel but no. I noticed the smoke first before the water pumps died. Since then its smoked on and off. It will run ok for a few hours and then it'll look like the van is on fire. Some days it smokes from the first moment, other days it is fine for 6 hours then its smoking again.

I've had it out and checked it over. The burner looks in good shape, a minimum of coking. The oval hole in the bottom of it where the glow pin passes underneath was almost coked over though. I cleared that thinking it would resolve the problem and it did for a day but then it was back. Today I've connected it to a known good battery and it ran fine for about an hour but then the smoke started. Not awful but at times it was quite heavy. Not being a boater I dont have a network of people who I can trust to look at this thing and not replace stuff that doesn't need replacing. Any ideas on what might be wrong? I've also siphoned out all the fuel and filled again from another source just in case of water in the diesel. Any help gratefully received.

webasto.jpg

Edited by davids3511
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Have you checked the temperature sensor? If the sensor has been used in fresh water without corrosion inhibitors they VERY quickly corrode and will cause intermitent burning before eventualy failing as they short out. Easily unscrewed at top of unit and  replaced.

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14 minutes ago, mrsmelly said:

Have you checked the temperature sensor? If the sensor has been used in fresh water without corrosion inhibitors they VERY quickly corrode and will cause intermitent burning before eventualy failing as they short out. Easily unscrewed at top of unit and  replaced.

It's a coolant system but will check it anyway. Cheers. 

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35 minutes ago, mrsmelly said:

Have you checked the temperature sensor? If the sensor has been used in fresh water without corrosion inhibitors they VERY quickly corrode and will cause intermitent burning before eventualy failing as they short out. Easily unscrewed at top of unit and  replaced.

Just checked it now. Clean as the day it was installed. 

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53 minutes ago, Mike the Boilerman said:

Hmmm so combustion is failing.

Have you measured the battery voltage while the fuel vapour is being emitted?  

Constant 12.03v apart from 1/4 second on startup where the voltage dropped to 9v but then revolver ed to 12.03

Just now, mrsmelly said:

was worth a try. we used to go through them like hot cakes. :cheers:

Appreciate the suggestion, I'm out of ideas myself. 

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2 minutes ago, dccruiser said:

The last time my ebby failed due to being coked up it took almost 2 hours going flat out to clear out all the excess fuel from the non starts ... covered half the marina in smoke before it eventually cleared and ran well again.

 

Rick

It does run clean for extended periods sometimes. I don't think it's a hangover from when I cleaned the glow pin off. 

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30 minutes ago, davids3511 said:

It does run clean for extended periods sometimes. I don't think it's a hangover from when I cleaned the glow pin off. 

Was just a thought .... the battery voltage you measured at 12.03 .... what is the rested battery voltage without the heater running? batteries may just need a really good overnight charge.... as you have ruled out fuel and the glow pin and burner chamber....

Rick

 

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19 minutes ago, dccruiser said:

Was just a thought .... the battery voltage you measured at 12.03 .... what is the rested battery voltage without the heater running? batteries may just need a really good overnight charge.... as you have ruled out fuel and the glow pin and burner chamber....

Rick

 

Rick, it's resting at 12.41, battery charger showing fully charged. Not great but not terrible. 

Edited by davids3511
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Another long shot, have you checked all the internal and external connections for damp? i ask as i have just serviced my ebby and found damp in the connector block to the ecu ... also the resistance of the glowplug and flame sensor

glowplug should be around 0.360 ohms cold (25 deg C )

Flame sensor between 2.6 and 3.4 ohms cold (25 deg C )and 12 to 15 hot (800-1000 deg C )

Just a thought if either are out their perameters it might cause poor combustion

 

Rick

 

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8 minutes ago, dccruiser said:

Another long shot, have you checked all the internal and external connections for damp? i ask as i have just serviced my ebby and found damp in the connector block to the ecu ... also the resistance of the glowplug and flame sensor

glowplug should be around 0.360 ohms cold (25 deg C )

Flame sensor between 2.6 and 3.4 ohms cold (25 deg C )and 12 to 15 hot (800-1000 deg C )

Just a thought if either are out their perameters it might cause poor combustion

 

Rick

 

Cheers Rick I'll get it apart and check them. Wasn't sure how to check they were functional. The flame sensor is covered in a very thin layer of solid crud that won't budge. 

I'm also thinking maybe ecu damage. There is a water pump right behind the ecu that was leaking for a day about 6 weeks ago so should be no damp left but maybe water got into ecu.

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1 hour ago, dccruiser said:

For mine i use an old electric toothbrush with some cillit bang ... others use caustic soda particularly in the combustion chamber but i have never found the need to, the cillit bang and electric toothbrush bring it up like new.

Rick

Went to test the glow pin and the tiniest sheath of metal came off the tip. Not sure I'd that's normal, it's hollow so not a lump of the pin, just a tiny bit of melted metal. 

IMG_20170911_190453.jpg

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2 hours ago, dccruiser said:

Another long shot, have you checked all the internal and external connections for damp? i ask as i have just serviced my ebby and found damp in the connector block to the ecu ... also the resistance of the glowplug and flame sensor

glowplug should be around 0.360 ohms cold (25 deg C )

Flame sensor between 2.6 and 3.4 ohms cold (25 deg C )and 12 to 15 hot (800-1000 deg C )

Just a thought if either are out their perameters it might cause poor combustion

 

Rick

 

OK, glow plug is .5 and flame sensor is 3.6.

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51 minutes ago, WotEver said:

Probably ok then... apart from the bit that fell off. 

 

53 minutes ago, WotEver said:

Probably ok then... apart from the bit that fell off. 

It was more like the tip had been dipped in solder and that came off, it didn't seem to be part of the actual glow plug. It didn't feel like metal either, when I squeeze it, it was almost crystalline but I can't tell if you're being sarcastic and it's obviously goosed and needs replacing.

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2 minutes ago, davids3511 said:

 

It was more like the tip had been dipped in solder and that came off, it didn't seem to be part of the actual glow plug. It didn't feel like metal either, when I squeeze it, it was almost crystalline but I can't tell if you're being sarcastic and it's obviously goosed and needs replacing.

Nope, not being sarcastic... I have no idea what it is/was either but I'm guessing that either it shouldn't have been there or if it should, that it shouldn't have fallen off. For the minimal cost of a new one it can't hurt to try. 

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Assuming this device works in a similar way to a conventional boat webasto I can't imagine the fault being anything to do with the glow plug. The glow plug is only operated during the ignition sequence. 

The problem. We have here is combustion continues correctly for an hour or more then fails. The task is to find out why. The only reason I can imagine is fuel starvation after an hour out so leading to the flame extinguishing, rapidly followed by resumption of the fuel supply injected into a hot combustion chamber hence the clouds of vapour from the exhaust. The flaw in this line of reasoning is there would normally be a flame detection function to cut off the fuel in the event of combustion failure. 

Consequently I conclude there must be two consecutive failures occurring (combustion, then flame detection), OR, I'm barking up the wrong tree entirely. 

 

 

 

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