Water contamination in my LeRoi Dresser 500 oil.

by Tim
(Duncannon PA)

There appears to be water contamination in my LeRoi Dresser 500 oil.

I have an older LeRoi Dresser air compressor with a Dresser 500 2 stage pump. I only use it occasionally to run my sand blaster.

I have a smaller Speedaire compressor for shop air.

I went to use it yesterday and checked the oil. The oil was the color of honey mustard dipping sauce (originally it was a light honey color). I drained it and flushed the case with kerosene then used shop air to blow out any remaining kerosene. I refilled it with Valvoline 30 weight non detergent oil. Then I ran it for 3-4 hours while I used the sand blaster. I occasionally had to allow the compressor some time to catch up.
I noticed that water was dripping from what I believe is a pressure relief valve on the line going into the high pressure piston. When I was done for the night I let the compressor cool down and checked the oil. It looked like dipping sauce again. I drained it and flushed with kerosene again. This time some black chunks of stuff came out too. When I drained the tank approximately 4-5 OZ of water came out. It was pretty humid yesterday with temps in the high 80's.

Is this amount of water/condensation in the crankcase indicative of piston ring failure? Is this pump generally worth rebuilding ($300 in parts) or should it go in the next scrap run?

Thanks for your time.

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Jul 24, 2017
Water in oil
by: Tim in Duncannon

I would think worn rings if it's that bad. Running it hard in a humid environment doesn't help either. I only ran mine every 4-6 months on a sandblasted. The condensation would cause the valves to stick and the unloaded would just puke air. Had I run it every day it may not have been a problem. That compressor was a PITA to deal with. Really should have had a 10hp motor on it but that's not very practical in a residential single phase environment.
The Kellogg 335 that I mentioned earlier is way easier to deal with. I rebuilt the whole thing with hand tools, a cylinder hone, and an $80 parts kit. Much happier with it.

Jul 23, 2017
re: "anonymous"
by: Doug in s.d.ca.

As mentioned below, could be rings, dunno what valve you might mean.

You might change the oil again and run it unloaded for awhile, see if it gets milky that way.

If it does get milky unloaded, then probably lo side rings.

If it doesn't, then gets milky loaded, it's probably rings hi side.

Jul 22, 2017
Water in the oil
by: Anonymous

When checking the oil, I found it to be milky white. I drained and refilled with 30w none detergent. After an hour or so of use I checked it again and it was milky white again. Leaky valve?

Sep 15, 2015
no more...
by: Doug in s.d.ca

Well, it was a valiant effort. Sorry it didn't work out.

But knowledge of the parts and tool problems is useful nonetheless.

Thanks for keeping us informed, and good luck with the new(er) machine.

Sep 15, 2015
No more Leroi Dresser Compressor.
by: Tim in Duncannon

Soaking everything in a 50/50 mix of ATF and acetone seemed to free up the unloader piston a little bit.

I built a tool to remove the HP unloader assembly.

I managed to snap a 1/2" drive Harbor Freight(yeah...I know) breaker bar with 4 feet of pipe on it and not budge the unloader assembly.

At that point I had had enough.

I sold it on CL for basically the price of the tank and the casters it was sitting on(2 bills).
The Dresser needed too many special tools. The parts were too expensive. There is virtually NO information available for these pumps. Too many issues to be worth my time.

I bought a 3 phase CompAire Kellogg 335 on a vertical 80 gallon tank. Parts are relatively cheap and plentiful. It doesn't appear to require any special tools to work on it. There is a fair amount of information available for it. UPS should be bringing me a Baldor 5hp single phase compressor motor by the end of the week. Hopefully the Kellogg isn't messed up. But if it is I can very likely fix it
Thanks for your help!

Aug 29, 2015
by: Doug in s.d.ca

Maybe 4-5 for type 30, but we generally figure more like 3-4 @ 90 PSI.

Parenthetically, I needed a 1 3/8 to get a plug out of a tank, and was dismayed at the prices, then I thought of Rock, found it for <$10 US, shipped as against 25+ other places + shipping.

Happy hunting.

Aug 29, 2015
by: Anonymous

I hadn't thought of Rockauto. Thanks! I'm pretty handy around the shop and I can probably make two of the tools I need without much trouble. The hard one is the valve retainer tool. I'll check it out.

There is an IR 242 for sale about an hour from me that I might check out. I have heard that those only put out about 15cfm @ 100 psi though. I've also heard that the rule of thumb on type 30 compressors is 4-5 cfm per hp but no idea at what psi.

Aug 28, 2015
by: Doug in s.d.ca


Try the universal tools for front end hubs and stuff. It's dependent on the exact size that fits or is close enough.

Aug 27, 2015
unloader problem
by: Anonymous

After some more investigation It seems that the HP unloader valve is stuck in the unload position. When I hold my hand over the LP side of the intercooler and spin the flywheel it sucks air in and pushes half of it back out. I have it soaking in ATF and acetone right now. Maybe it'll free up.

Where did you find sockets for the valves for cheap? The only ones I could find were $85 and $147.

Aug 23, 2015
water in oil
by: Doug in s.d.ca

Sorry to hear my fears confirmed.

Depending on the exact size, looks like you can get a socket for the valves for as little as $12, but you'll probably want to go $25 or so for a decent one. Try rockauto.

Good luck and thanks for the update.

Aug 21, 2015
by: Tim in Duncannon

It will probably depend if I can get the valves out of the heads whether I junk it or not.

Just from my experience with engines the scoring in the HP cylinder is too deep to hone out.

If I could find oversize rings or an over-sized piston I would get the cylinder machined. So far I haven't found anything like that.

To the best of my knowledge it is a pressurized lubrication system. I'm not sure how or if that correlates to the rust in the cylinders.

I think part of the problem is that the crankcase vents to the intake side of the LP cylinder and not to atmosphere.

I'm watching CL to see what comes up. I'm also looking out for parts for the 500.
It is a bummer that it was let go but I could understand how it would go unnoticed.

I'll post up any further findings.

Aug 20, 2015
by: Doug in s.d.ca

I wonder if the rings would seat if you honed out the lip (I think that's what you said) on the HP cylinder. (there's no sleeve, is there?)

I also wonder if this is pressure lubed - seems like the HP side might not have gotten lubed or the rust and stuff wouldn't happen.

Maybe hang on to it and look for a pump with a good HP cylinder?

I'm sorry, this is just sad...

Aug 20, 2015
Pulled the heads
by: Tim in Duncannon

I disassembled the compressor last night. I was unable to remove the exhaust valve on the low pressure head or either valve on the high pressure head.

The low pressure exhaust valve looks like it requires a 2 1/8" socket which I don't have. A flat pipe wrench and 3 feet of cheater pipe wouldn't move it. The same thing happened with the other 2 valves.

I removed both heads and the condition of the gaskets leads me to believe that this was taken apart before.

The LP cylinder looked pretty good with about 70% cross hatching still visible and no rust visible. It could be honed out and re-ringed and be good to go.

The HP cylinder is another matter. The top of the piston is rusty and the cylinder walls have a "mottled" appearance with no visible cross hatching. There is some very light scoring that could be cleaned up by honing it.

The bigger issue is that there is a 1" long circumferential score mark that easily catches my fingernail about 4" down in the bore on the lower side of the cylinder. The bore would need to be machined to correct this.

It would appear that moisture collected in that cylinder and rusted that area. The piston then broke the rust free and left a gap.

My biggest concern would be how to prevent that from happening in the future. I don't see how to do that unless I run the compressor only in the winter.

At this point I could do what the PO did: put it back together and put it on CL.

The difference will be that I will let prospective buyers know that it makes air but should be rebuilt and will price it accordingly. Or I will junk the pump and look for a replacement.

I could rebuild it but I think the rings on the HP cylinder would wear very quickly due to the previously mentioned scoring.

Any further input would be appreciated.

Aug 18, 2015
by: Doug in s.d.ca

Tim -

Exactly. Looking forward to your findings.

Aug 18, 2015
Follow up question.
by: Tim in Duncannon

Thanks for your input Doug in s.d.ca! If I understand you correctly, the intake valve on the high pressure cylinder may not be sealing correctly and allowing high pressure air to back up into the low pressure cylinder. This makes sense because the low pressure cylinder exhaust side seems to run pretty hot. It sometimes gets to 305* but usually runs around 250ish*. I keep a box fan turned on hi blowing across the pump when I use it.

I'll probably pull the heads this weekend. I'll keep you posted on what I find.

Aug 18, 2015
water in oil
by: Doug in s.d.ca

Sounds like the hi side isn't sealing on the intake, allowing high pressure toward the lo side, possibly getting past the rings on lo side along with water. That would explain reduced output, too.

I know 250-300 bucks is a nice piece of change, but a new one anywhere near as good as this one is gonna probably at least a grand.

So, I'd at least pull the heads to see how the cylinders look, and if good, rebuild.

YMMV - let us know how it goes, please, and good luck.

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