Special Limited Time Offer – Join Today and Receive our RV Foundations Course FREE for One-Year! Valued at $127.Ā 

Oil Contamination in LP Gas Systems

Oil Contamination in LP Gas Systems 1

Liquid propane gas (LP) packs a large amount of energy into a small package. As a result, itā€™s an economical choice for RVers, and it is used for heating, cooking and to power the RV refrigerator when AC power isnā€™t available. My wife, Mao, and I run our business for six months of the year from our RV, never using shore power!

The story begins when we were camped at Boomerville, in Quartzsite, Arizona, for the annual January get-together. Mao and I were performing installations of our product, Fridge DefendĀ®. A group of folks was gathered around having a good time, seeking knowledge and sharing stories while I worked. This is simply the way we Escapees operate, and we love helping other RVers in need. That is what we are about! A gentleman came over and asked me if I was an RV tech. I said, ā€œNo, but I can help you with your refrigerator if you have an issue.ā€ I finished my work and went over to investigate his problem.

I learned that he began having problems with his propane system after he filled his LP tank. He had replaced his LP regulator but did not know why it had failed. His main issue was his refrigerator. When he found that it was not cooling on LP, he was wise enough to discontinue its use. I say wise because he could have created a dangerous situation by continued use. Iā€™ll cover this issue more later. Being Boomerville, we were all boondocking. He was able to power the refrigerator with his generator, but no one wants to run a generator all day and night as itā€™s too much exhaust and noise nuisance for happy neighbors!Ā 

Visual Inspection

Oil Contamination in LP Gas Systems 2
One Must Be Qualified To Perform a Pressure Test

Because the refrigerator worked on AC power but not LP, the first thing we did was open the burner housing to perform a visual inspection. We found there was brown oily residue below the burner. This was the proverbial smoking gun! We immediately understood why his LP regulator failed and why his refrigerator was not working on LP. When his tank was filled, he got a batch of oil in the LP. Itā€™s rare, but it happens. The oil can get into the system and destroy the LP regulator, plug burners and filters.

This was the first time we have witnessed such an extreme case where oil actually came out of the refrigerator gas jet and collected on the bottom of the burner housing. The refrigerator was at least 18 feet from the tanks, and it takes a lot of oil to flow this far.

Ordinarily, oil contamination in the LP system is checked for in one of two ways: The first and most scientific method is to do a pressure test somewhere in the LP lines to make sure that the pressure regulator is supplying 11 inches of water column (11″ WC) gas pressure. The LP bottle and regulator are to the left. A drawing of a manometer attached to the LP regulator test port shows the principles behind the pressure test; the purple represents the water in the manometer. One must be qualified to perform this pressure test, so we will not go into manometer details here. What is to be understood from this drawing is that, if the pressure is 11″ WC at the regulator, and then the manometer is moved to the fridge solenoid-operated valve (SOV) ā€˜gas jet pressure test portā€™, and say 8″ WC is measured, then lower pressure is measured. The probable cause is a plugged SOV gas filter.

Cleaning the Filter

This brings us to the second method. After reading the above, one can understand what can go wrong, and then go directly to the suspected problem. This is exactly what we did. We were not carrying a manometer with us; we knew that there was an oil contamination issue by the evidence in the burner of the fridge, so we proceeded to go directly to the LP filter within the SOV valve.

We disconnected the LP supply line from the SOV valve after turning off the LP gas at the tank and bleeding off the residual pressure by lighting a burner on the stove. Once the inlet line is removed from the SOV valve, the Norcold refrigerator SOV has a foam filter that can be removed with a toothpick. (For most Dometic refrigerator SOVs, the filter is ceramic and has to be cleaned in place by flushing with 91 percent isopropyl alcohol.) The Norcold filter was placed into a glass jar with 91 percent isopropyl alcohol.

Finally, because of all the oil in the burner housing, we knew that the LP jet was contaminated. This was quite evident when, after removing the line from the SOV to the gas jet, oil began running out of the line. Once the jet was removed, we could look through it into the sunlight to see how restricted it was. We put it into a glass jar with the 91 percent isopropyl alcohol to soak. Naturally, we flushed out the line from the SOV to the jet, but it was getting dark and we had to finish our job before we lost light.

To finish the job, we installed the Fridge DefendĀ®. Why? As mentioned above, when the fridge is not cooling, it is because the boiler on the refrigerator is overheating. The only way to tell that the boiler is overheating is to install the Fridge DefendĀ®. Thus, as stated above, the owner of this fridge was wise, because he could have overheated his boiler to the point that it ruptured. This is how refrigerator fires occur.

How Fridge DefendĀ® Helped

You may ask, with the propane supply partially blocked by oil, how can the fridge overheat? If the blockage was complete, and there was no flame at all, it wouldnā€™t harm the fridge. However, because of the design of the boiler, too little heat is almost worse that too much! If the flame is too low, the reduced heat at the boiler will still boil off the ammonia without causing the necessary pumping action, leaving the cooling system stalled. No circulation in the cooling system will allow the boiler to run dry and overheat.

We buttoned up the job during a beautiful Quartzsite sunset, started the fridge on LPĀ and checked for normal boiler temperaturesĀ on the Fridge DefendĀ® display.Ā Satisfied, weĀ headed into the desert to enjoy the evening.

The next morning, we called to see how theĀ evening went with the repaired refrigerator.Ā Well, we had an unhappy customer because the Fridge DefendĀ® turned the fridge off during the night. We explained that the jet and/or the filter was probably plugged with oil again, resulting in overheating of the fridge boiler. Hearing our explanation, the customer was pleased to find that the Fridge DefendĀ® had done its job by protecting him and his RV.

We went out to the RV again and did our best to flush as much oil out of the lines as possible and suggested that the owner have the system flushed again if the problem continued.


Oil contamination can be a problem in LP gas systems. It is introduced during a fill of the LP bottle, and the oil can plug jets and filters in the LP system. Oil in the LP system is particularly dangerous for Dometic or Norcold refrigerators because they have a filter in the SOV valve, and the gas jet is very small. Oil accumulation in the LP jet or filter can result in the fridge cooling unit boiler overheating, and only the Fridge DefendĀ® by ARP can protect the fridge if this happens. The oil contamination can be cleaned out of the system by disassembly and flushing with 91 percent isopropyl alcohol. Acetone can also be used to clean the pipes, but you must not let it touch any rubber or plastic parts. Be sure to leave the LP system open long enough for the solvent to evaporate. If you know that you have oil contamination in an LP bottle, when the bottle is empty the valve can be removed, and the tank can be turned over to flush and drain the oil.Ā 


Paul & Mao Unmack

PAUL AND MAO UNMACK are mechanical engineers. Paul ran an automotive repair business in Red Lodge, Montana, for 20 years before receiving his engineering degree. He has practiced nuclear, fire suppression and industrial process control systems design. Mao designed pressure vessels for ammonia plants, in China, for 12 years, then came to the U.S. to get a masterā€™s of welding engineering. She designed biodiesel plants and worked for a government- funded research and development organization. Paul and Mao run the entire ARP control business while taking on engineering consulting gigs.Ā 

5 Responses

  1. Paul & Mao… good article. I have a Mr Buddy propane heater connected to a 100 lbm propane bottle with ~ 20′ of propane compatible hose linking them (the only regulator in the circuit is the mfg supplied one on the Mr Buddy heater). I am getting oil in the heater tubes which effects the flow thru the orifice and causes the burners to shut off due to the thermocouple not getting adequate heat. if the oil is coming from the 100 lbm bottle, how did it get into the bottle in the first place?

  2. Hi George, the oil is put into your tank when it gets filled. Oil contamination is generally from the bulk propane plant. I am told that the positive displacement gear pumps for transferring the LP have oil misters to lubricate them. Other than LP being a petroleum product, I am told this is where the source of the oil is.

    Stay safe, Paul and Mao Unmakc

  3. I have read that oil often enters the propane tank when the tank is being overfilled. Fillers are supposed to leave space in the tank for heat expansion and leave a place for the propane to evaporate into. If the tank is overfilled with liquid then oil can easily be pumped into the regulator and on into the lines. So, overfilling tanks is the most common culprit.

  4. I have the same problem with my mr. heater little buddy. I got the oil from a Blue Rhino exchange tank, so over filling was not an issue as they notoriously under fill their tanks. However, the tanks have to be hydro-static tested from time to time to make sure they still have structural integrity. The process involves totally filling the tank with liquid and pressurizing it to a high test pressure. For some types of pressure vessels they use water but for propane tanks they use oil. improper cleaning after testing can also leave oil residue in the tanks and exacerbate the oil fouling issues with filling. There are little inline filters for these small heaters that are suppose to help. I don’t know if there are any for plumbing in to RV lines seems like some one should make one.

  5. I believe a fact check needs to be posted for ‘D Willemin’. A “hydrostatic test” is where the tank is put into a test vessel, the secondary test vessel is then filled with water. The tank within the test vessel is then filled with air. The amount of expansion of the tank is then measured by the water pressure in the test vessel.

    Maybe they changed the procedure?

    Stay safe, Fridge Defend

Leave a Reply

Your email address will not be published. Required fields are marked *


Limited Time Offer

Join Today & Receive RV Foundations FREE!

$127 Value!


Sign up for Escapees RV Club News and Never Miss a Thing!

Find Your Community at Escapees Events!

Learn to RV with Escapees!

Whether you’re a part-time or full-time RVer, you can learn to RV with our in-person and online training.Ā 

RVers Boot Camp is your in-person opportunity to learn directly from RVing experts.

RVers Online University allows you to learn at your own pace from the comfort of your own home or RV.

Never miss a post.

Sign up for Escapees RV Club News now!