# Used motor oil: Into the oil furnace? (attn: chaparralv8)
**URL:** https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272
**Category:** Factual Questions
**Created:** [January 23, 2005, 6:24pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272 "2005-01-23T18:24:51Z")
**Posts on this page:** 11
**Page:** 1
### Author:  [@Scruloose](https://boards.straightdope.com/u/Scruloose)
#### Post date: [January 23, 2005, 6:24pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/1 "2005-01-23T18:24:51Z")
Rather than hijack [this thread](http://boards.straightdope.com/sdmb/showthread.php?t=298404), I’ll just start a new one, for hopefully a wider audience.
In his oil changing instructions, **chaparralv8** said that used oil could be put into the tank of an oil furnace. Really? Here in the Northeast, _everyone_ has oil heat, and I’m surprised that I’ve never heard of this. So I’m trying to think if there are any reasons why this would be a good or bad idea. Not knowing much about oil furnaces, I ask the teeming millions: Is this a good idea? Why or why not? If it is, how much would be too much?
Thanks!
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### Author:  [@jayjay](https://boards.straightdope.com/u/jayjay)
#### Post date: [January 23, 2005, 6:30pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/2 "2005-01-23T18:30:03Z")
Everything I’ve look at online so far says that used motor oil can be _re-refined_ and used as heating oil. Meaning, take the used motor oil to an oil recycling station so it can be sent back to the refinery and re-released as heating oil. I imagine there are problems with viscosity, impurities, and just the gunk that made the oil need to be changed in the first place. You’d probably ruin your oil burner if you did this straight from the car.
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### Author:  [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)
#### Post date: [January 23, 2005, 6:30pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/3 "2005-01-23T18:30:19Z")
Although there are waste oil furnaces, some differences exist between them and a home oil burner. Given that you have a filter between the burner pump and the oil supply line, I’d be concerned about crud from the crankcase blocking that filter.
The only fuels I’ve ever put in an oil burner were #2 home heating oil, diesel fuel, and kerosene.
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### Author:  [@Scruloose](https://boards.straightdope.com/u/Scruloose)
#### Post date: [January 23, 2005, 6:30pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/4 "2005-01-23T18:30:34Z")
Oh, and **chaparralv8** , I certainly didn’t mean this as a “CITE?!?” put you on the spot posting. My apologies if it comes across that way.
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### Author:  [@astro](https://boards.straightdope.com/u/astro)
#### Post date: [January 23, 2005, 6:49pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/5 "2005-01-23T18:49:32Z")
Some opinions here
Mixing Used Motor Oil With Home Heating Oil
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### Author:  [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)
#### Post date: [January 23, 2005, 7:57pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/6 "2005-01-23T19:57:00Z")
I used to.
I stopped after I realized that the thick UMO would raise the viscocity of the heating oil to a point where the fuel wouldn’t pass through the burner injector orofice.
Now, I use just enough UMO to make 2-stroke gas for my lawnmower and leaf blower…the rest I take to be recycled.
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### Author:  [@aahala](https://boards.straightdope.com/u/aahala)
#### Post date: [January 23, 2005, 8:30pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/7 "2005-01-23T20:30:05Z")
I know it would be wrong for me to try it. My wife has drawn the line – no more home experiments involving anything flammable, explosive or poisonous.😃
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### Author:  [@Scruloose](https://boards.straightdope.com/u/Scruloose)
#### Post date: [January 23, 2005, 9:40pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/8 "2005-01-23T21:40:39Z")
> [@aahala](#):
>
> I know it would be wrong for me to try it. My wife has drawn the line – no more home experiments involving anything flammable, explosive or poisonous.😃
Yeah, but the line’s only drawn if she knows about it, right?
So, I gather from the responses, and **astro’s** link, that you _could_ put used motor oil into the tank, but it’s probably not best of options. Got it. As I’m _still_ cleaning up soot from a burner burp almost 3 months ago, I think I’ll pass on this option.
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### Author:  [@beltbuckle](https://boards.straightdope.com/u/beltbuckle)
#### Post date: [January 24, 2005, 4:06am UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/9 "2005-01-24T04:06:27Z")
For what it’s worth, we had a oil furnace abou 15 years ago. My dad used to dump motor oil from oil changes into it for years, and we never really had a problem with the furnace. This was probably a few gallons a month max, so I imagine when you mix it with hundreds of gallons of heating oil it doesn’t make a big difference.
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### Author:  [@Stan\_Doubt](https://boards.straightdope.com/u/Stan_Doubt)
#### Post date: [January 24, 2005, 4:44am UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/10 "2005-01-24T04:44:01Z")
**Beltbuckle’s** post about dilution obviously makes a lot of sense. Certainly a gallon or so of motor oils cannot affect the viscosity of a home oil tank full of #2. People are pretty anal about oil changes and modern cars shouldn’t really circulate wear deposits in engine oil. If you are really concerned about particulates, you can filter the oil thru a synthetic fiber filter or even a dust mask prior to burning it. As far as contaminants go, remember that thousands of people burn this shit year round in their automobiles.
That said, If you are not familiar enough with your oil furnace to know what the injector nozzle looks like, this is probably not a good idea anyway. How much are you really saving? A gallon of heating oil is pretty cheap-is it worth f@$#ing up your furnace and paying for a service call if you clog your nozzle with piece of grit to save two bucks?
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### Author:  [@BinDerSmokDat](https://boards.straightdope.com/u/BinDerSmokDat)
#### Post date: [February 13, 2019, 7:31pm UTC](https://boards.straightdope.com/t/used-motor-oil-into-the-oil-furnace-attn-chaparralv8/286272/11 "2019-02-13T19:31:19Z")
I bought my house in September 1999. My father would put used motor oil in the heating oil tank of our childhood home so when I did my first oil change in my new house, I did the same.
So after nearly 20 years, with the same furnace and the same fuel oil tank, I’ve never had an issue. i no longer change my own car oil but I do it for several motorcycles, snow blower and lawnmower.
I don’t do it because I’m cheap, I do it for convenience.
I no longer have to pour waste oil into a jug and then cart it down to the auto store for recycling, risking a mess in the trunk, spilling, etc.
Most heating oil tanks are 275 gallons with some being 330 gallon.
That means if you dump an average 4 quart oil change into a tank of fuel, that is 0.36% to 0.30% used oil percentage with a full tank of fuel.
Even if you have a 1/3 tank full of fuel that is 1.09% to 0.91% used oil percentage!
That small amount makes no difference to the fuel oils viscosity and as long as you aren’t letting chunks of crud/build-up from the oil pan itself entering the tank, your fuel filter can handle the extra suspended material.
You should be changing your fuel filter once a year at a minimum during the annual maintenance. Mine is a large spin-on style that looks a lot like a truck oil filter. It has always handled the extra motor oil with no issues.
I can’t imagine the smell from my chimney smells any different to anyone with less than a percent of used motor oil in the mix. I know I don’t smell it.