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Oil in air lines
After finding black engine oil in the air I bled from the rear bleed port and in the air dryer, it seems obvious it’s time to replace the engine mounted air compressor. After I replace the compressor and air dryer cartridge, what action should I take to remove oil from the air lines? Blowing solvent through the line from the dryer to the rear bleed port while it’s disconnected seems innocent enough since residual solvent won’t find its way into any Norgren valves or other critical components to swell “O” rings, but what if I find oil in other lines? Do I stand a chance of making the potential problem of gummed up valves worse by attempting to clean oily air lines? Would you experts out there just blow clean dry air backwards through disconnected line segments or leave bad enough alone and just watch for oil at the valve exhaust ports? I would anticipate that engine oil might make Norgren valves sluggish in cold weather or cause the rubber rings to swell and stop the shuttle valves altogether, but what other problems are likely if the oil has gotten past the air dryer? How much of a nightmare may I be facing?
Is there enough cost difference to warrant shopping for a heavy compressor at a local truck parts shop instead of having one shipped from Prevost Parts? Thanks for any answers or comments you might have for a newbie who is about to get a comprehensive air system education.
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12 Replies
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Ron,
Do you suspect the oily air got beyond the Wet Tank?
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Tom, I haven’t investigated past the air dryer. I may be allowing my fears to get the best of me, but it seems like the parking brake got easier to move. I haven’t checked all Norgren exhausts for evidence of oil either… too cold to work outside right now. Is any level of oil contamination of the air dryer acceptable? Air pressure is normal, not sluggish in returning to 120 PSI. What’s the criteria for condemning the compressor?
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Nice visit yesterday: back to subject. compressor -to air dryer-to wet- tank then air is distrubited through outlet half way up tank. = unless this tank is over 40% full of oil/water you should not have much past it. sounds like you still have life left in that compressor. When your recovery time starts to get slow then start looking. Just remember you usually run in realy hot heavy load conditions where higher than normal oil usage is normal. Bob
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Nice visit indeed, Bob. I don’t know why I failed to bring this
up then. Your description of the wet tank makes me feel better because I’ve
never found more than a trace of liquid in it. However, the engine bay bleed
valve air flow is often nearly stopped by gobs of oil coming out. Is this
normal? Recovery time is the only criteria for replacement? Mine seems fine! Is
there an average mileage one can expect before a compressor rebuild? I’ve got
350K on mine. -
Ron,
You are correct in being concerned about potential downstream damage from oil, but before I push the panic button I would drain the air tanks in sequence. I agree with Bob that it is unlikely you have oil migrating past the wet tank, but by draining your tanks in sequence (call up your pneumatic diagrams and follow the air path) you will know where evidence of oil stops.
I think your coach was a seated coach, so I suspect your air tank configuration will be unlike a motorhome, but you should be comforted in knowing that the last place oil can get to is the Norgrens because only after the brake tanks are satisfied will air go to the aux tank, and then onto the Norgrens. I would be more concerned with moisture from an aux compressor unless the coach has a good water trap or dryer downstream from the aux compressor and before the aux system.
If an air system has problems from excessive oil passing the compressor you will know without cracking a petcock. Look at the area around where the air dryer spits and if you see oil on the frame of the coach then you know oil has passed the dryer. The dryer cartridge is going to catch both oil and water and the oil will coat the element making its function as a dryer useless. To gauge the health of the compressor service the dryer, and drain the wet tank as well as monitoring if new evidence of oil is seen on the frame. I have about 250,000 miles, change the dryer cartridge every 2 years and never see oil on the frame or drain more than a tablespoon of an oil / water mix from the wet tank. My oil water mix is a milky tan color. Any engine driven compressor will pass some oil. The key is not letting the oil get ahead of the cartridge service life. At that point you do have to do something.
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Ron,
Not familiar with the H, but on the XL’s the rear air valve fills all tanks, brake and aux air and mine has a check valve to prevent a loss of air through the valve. This line is connected to the dryer.
I installed a lanyard on my wet tank to drain often and I get a little mist of oil (almost a smell and little liquid) when draining the tank. Every bus I have owned has had this trait and I consider it normal.
If you don’t have a drawing for your H, go here: http://prevostparts.volvo.com/technicalpublications/pdf/d140199rh_fr.pdf
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Ron, 350,000 miles on a compressor it’s due for a change you got your money out of that one
Clifford
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Jon, I will unpush that panic button and do a methodical search for evidence of oil. Your words are comforting since my dryer is not slobbering oil everywhere and I don’t have an aux compressor putting moisture into the system. Yes, mine was a seated coach. Like you, I’ve gotten only a little tan oily water from the wet tank drain. For now, I will change dryer cartridge often and monitor the wet tank closely to protect everything downstream. I think Tom put his finger on the source of my panic when he mentioned the check valve in the bleed/fill line (I don’t see it on my drawing). Fragments of the shattered one-way plastic valve on the air cartridge I changed may have gotten into that check valve to give me the indications that have caused me so much concern. Thank you, Tom. I’ll clean the line thoroughly and give the check valve special attention or replace it. Then I’ll follow Clifford’s advice and replace the compressor… when the snow is not blowing around me. Thanks guys for all your help.
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Ron,
Maybe Clifford can eleborate, but if my memory is correct on another site I read where rebuilt compressors had little of the reliability of the new ones and some owners were not viewing the lower price of a rebuild as cost effective.
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Check for rebuild tag? If you haven’t owned coach since new it is hard to tell. Guess I’m a little slow to replace until signs of loss of use are evident. I do not know how much oil we are talking about.Could always start search for replacement and store it away until yours starts to loose efficiency. Sounds like it is still coming up quickly. I know your dragging your shop around with you. Your choice. Watch prevost for monthly deals on Aircompressor. I’m sure there are good rebuilders out there. I only trust my local guy that I can lay hands on. or do it my self. Clifford or Jon might have someone they trust. Bob
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BTW Ron………we need to have a serious conversation. What is the deal with snow blowing around you? You need to be where the sun is shining and it is warm.
That’s why Mr. Prevost put wheels on these things.
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Bob, I’m almost certain the compressor is original (14 years old) with two storage periods of more than a year each with no engine running. There’s no rebuild tag. The last time I checked recovery time (90-120 PSI) I believe it was around 30 to 45 seconds, but I can’t locate my log right now. The coach airs up within a few minutes from a zero/zero indication, so I don’t think air output is degraded. Since I found less than a teaspoon of oil in the base of the dryer and just a little tan water in the wet tank, I feel I overreacted to a tablespoon or so of thick black oil coming out in spurts from the air bleed valve in the engine bay when I opened it. Even more disconcerting is the fact that it spurts oil, then the air stops flowing completely! I thought the line was plugging up, but now believe the one-way valve in the line has small pieces of plastic in it from the air dryer and needs cleaning or replacement. The front bleed valve (in the bay under the driver’s seat) sprays a continuous fine mist of water with no oil. From what you tell me about the wet tank, I could probably wait until I routinely drained a quart of thick brown oil and water before replacing the compressor, but I’d rather err on the side of caution. I’ll watch for new ones on sale at Prevost Parts or elsewhere and replace it if it gets any worse. You’re right, keeping heavy spare parts is a luxury I had to give up to live mobile. No rock collections either. 🙂
Jon, this is the coldest I’ve been since I left Ohio as a teenager. Brrr! But it wasn’t planned that way. We were on our way to southern Arizona for the winter when test results caught up with us showing she had to be home in central Illinois in February for a medical procedure. We were able to divert to central Florida for a month before heading north. Now it will be March before my tires are no longer frozen to the tundra. Eleven degrees tonight…yikes! Send any extra heat this way.
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