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Oil from Air Tank Blow-Offs


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Since I've owned this truck, every time I blow off the air from the air tanks, a lot of dirty black oil comes out, mostly from the front tank of the three.

Here is a photo of how it looks:




All that black oil coating the gravel came from one short blow-off. As you can see the two aft tanks don't blow much oil if any.

Is this a sure sign that my air compressor is toast?? I had the air dryer replaced around 2000 miles ago; this didn't help the issue at all.


Another question, while I have the long fairing off, I'm thinking of replacing the lanyard-pull poppet valves with small ball valves. I know the lanyards are supposed to make it easy to bleed the tanks by reaching in through the battery access door, but in reality it's kind of a PITA to locate each one and yank it. I'm thinking it may be just as easy to reach under the fairing's bottom edge and turn each ball valve, one at a time. Part of my concern here is that the poppet valves don't seal reliably; sometimes I need to wiggle the cable a few times to seat each one. But the main concern is that the poppets blow the oily dirty water and air mixture all over the back of the fairing and the aluminum extrusion tends to direct the blast forward all over the tire.


If I use a short 90-deg "street" elbow, then the ball valve, the blast direction can be more inwardly directed.


Any chance these poppet valves are 1/4 NPT thread??



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Thank you SO MUCH for responding. That's what I thought as well. Is it possible the oil has been in the air tank for years, due to an earlier dryer failure?

Could my new air dryer have become saturated within a few days of driving, due to excessive oil entering the air stream from the compressor?

Finally, what do you think of my idea to replace the "poppet" valves? Am I the only one who is unhappy with getting the black oil blasting all over my left front tire when I bleed the tanks, as well as on my shoes (if I'm not careful to stand with my feet WAY BACK and leaning forward to reach the valve lanyards)?

I'm thinking this blast of oily air is not normal...



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That oil is "crawling" all over the system. The decissant cartridge should remove normal amounts, but it might be overloaded with oil from a worn out compressor. Not uncommon, but not a good sign. Reman compressor should fix it.

And the multiple tanks are not "wet or dry", they are primary and secondary tanks, servicing different parts of the air system.

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And the multiple tanks are not "wet or dry", they are primary and secondary tanks, servicing different parts of the air system.

I suppose I used some slang terms when I referred to the "wet" tank, but it is properly called the supply tank.


The first of the three tanks found on our trucks is generally referred to as the wet tank. I suppose because IF there is any water/oil in the system it is likely to collect in this first tank. The other two tanks are the primary and secondary, each serving different parts of the system.


You should not have ANY oil or water in the system if you have a properly working compressor and air dryer. At most a little bit of water, but I have rarely seen that in any truck I've driven if it was in proper condition. As an example. I had my Volvo 610 for 10+ years. There was never a drop of water even in the first tank. And I have never gotten anything out of my 780 in the two years I've had it.


As Jeff said, you have an issue - (I'm sorry I'm stating the obvious....) :(

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Same as Jack here, no fluid at all from tanks on our truck. I did replace air dryer assy and cartridge a few years ago.


About the drains, I put new ones in several years back due to they were sticking. Cheap to buy at the Volvo dealer. But I ran new long cables (I think they came with the valves) to them and tie wrapped them in place inside batt door. Now just grab each cable and pull. No issue at all.

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