Using vegetable oil for chainsaw bar oil

I've been using used cooking oil as chainsaw bar oil for the last few years. It seems to work fine, but there are some risks to look out for.

The oil I use comes in these 20 litre drums new, then is used for deep frying, then put back into the drums. I filter it into 5 litre tins like the one on top - the rats can't chew thru a steel container

What's wrong with normal bar oil?

Chainsaws use a "total loss" oiling system to lubricate the chain as it slides along the bar: oil is pumped into the chain slot at the top of the bar base, and most of it is lost into the sawdust by the time the chain has travelled around the circumference of the bar. If you want to use your sawdust for composting, you might think about this bar oil that's mixed in: over time the sawdust will be reducing in volume as it is oxidised away biologically, so the oil will become more concentrated, along with any additives or contaminants. Mineral oils are gradually decomposed by microbes, but we don't know how quick or complete this is with our chainsaw oils. "Bio" chainsaw oils, made mostly from plant oils, seem to be required in some European countries, but aren't common in Australia. 

Chainsaw oil is also quite expensive: around $5 to $10/litre, depending on how big a drum you buy. To avoid this cost, there is an old bushie tradition of using sump oil (used oil from car engines) instead of bought bar oil. "It was fine lubricating the engine for the last 1000km, so what's wrong with using it in the saw?", is a reasonable question. I've occasionally used sump oil in the past, especially in the external oiler for my Alaskan mill, but sump oil is worse than new mineral oil as a sawdust contaminant: it is laced with all sorts of toxic chemicals from the petrol and combustion, and I certainly don't want it in our garden. 
Interestingly there is some discussion about the health effects of breathing in oil mist from chainsaw bars - again, I'd rather not be breathing old sump oil. 

Using vegetable oil

A few years ago, with all these questions about bar oil in my mind, and after a few google searches to assure me I wasn't the first, I started cautiously by using some out-of-date vegetable oil in my electric chainsaw. The saw is small, so the risk seemed less. Nothing bad happened over the next couple of years: the saw worked fine, the bar didn't seem to wear, so I tried using veggie oil in my petrol saws. 

I now get 20 litre drums of used canola oil, out of a deep frier, from my friend who has a cafe (he otherwise has to pay for old oil to be removed). I strain this oil thru a seive (to remove old chips etc.) into 5 litre steel fuel cans, from which I put it into the chainsaws. I use this oil in all my saws, from the big Stihl 090 milling saw, to the little Stihl 024 thinning saws and the electric saws. 

What can go wrong?

Rats

The biggest risk from using veggie oil comes from it being undoubtedly food - there is even a scent of hot chips in the forest as I work, some days. This makes it attractive to rats, and in our sheds amongst the rainforest, we have an abundance of native and introduced rats, who will chew anything they think is getting in the way of a feed. I only store the veggie oil in steel containers, because plastic bottles are easily chewed. Most 20 litre steel drums have a plastic bung near the bottom for screwing in a tap. I screw a metal BSP plug into this to make it hard for rats to chew at the plastic. 

I once made the mistake of leaving the lid out of a chainsaw's plastic oil tank, and later found the female thread nearly chewed away by rats trying to enlarge the oil filler hole and get to the puddle of veggie oil inside. The plastic external oiler tank on my Alaskan mill was chewed to pieces after I used veggie oil in it. Now I've made a stainless steel tank from an old water bottle. 

Bush rats chewed this hole in my Alaskan mill external oiler!

If you're using a saw with a plastic body, veggie oil could get a hole chewed in your plastic oil tank if you're not careful (generally, professional saws have a metal oil tank, consumer saws have one of plastic). 

Bar and chain wear

The biggest worry to most saw users will be that the veggie oil doesn't do its lubrication job well. Some people worry that without the sticky additives, the oil will be flung off at the bar nose, and that the oil won't have the lubricating properties the chain and bar need. 

I haven't noticed any increase in wear, but I understand I'm not doing a controlled experiment: I'm not running 2 saws with different oils, doing the same amount of work for several years, to see what happens. So it's possible that I am getting more bar wear, and will pay a price for that. However the savings of 100s of $ in bar oil will easily pay for a little more bar wear. Certainly the type of bar oil is nowhere near as important as chain sharpening and bar maintenance: I see many badly worn bars that have only had expensive bar oil on them. 

This report https://www.fs.fed.us/eng/pubs/html/98511316/98511316.html

shows very good results from veggie oil-based bar oils, but they are commercial oils with additives, not just straight from the fryer like mine. 

Oil drying on the chain or in the tank

Veggie oil could be a problem for the occasional chainsaw user. It does dry over time, so if you haven't used the saw for a couple of months, the chain can be a little stiff with dried oil. On the bar this isn't much of an issue: it usually runs itself free pretty quickly, or occasionally needs a little spray of kerosene and oil (homemade WD40) to loosen.
I imagine this could be a problem in the tank, thru the filter, and in the pump, if left for a very long time. I've had enough experience with linseed oil in furniture finishing to know how hard it is to clean off excess dried oil - it doesn't dissolve in normal solvents. So far I haven't had any problems inside my saws. 

Different oils have different drying characteristics: olive oil doesn't seem to dry at all (we've used the same olive oil containers for years without any sign of drying), and some dries quickly. The repeatedly heated (in a deep fryer) canola oil I've been using seems to be very quick to dry into a hard varnish. 

Oil drying on the engine cylinder

The most serious concern I've heard about using veggie oil has been in a youtube video by Andy Reynolds (in the last minute of the video) (Andy's chainsaw maintenance and repair videos are really good). Andy says that veggie oil is swept thru the engine cooling fan and gradually deposits on the cylinder fins. There it will bake on, reduce the cooling effect of the air, create hot spots on the cylinder, and cause an engine to seize (this can happen just from sawdust buildup alone). 

I think Andy is speaking from experience, and I'm looking out for this. Any old saw will show some oil, usually mixed with fine sawdust, on the flywheel side of the cylinder fins (which should be cleaned off to improve cooling). Given the drying nature of veggie oil, I can imagine the buildup of "frying pan varnish" if not managed carefully. 

Here's the bottom side of one of our old cast iron frying pans, showing an impressive coating of cooked-on oil. This wouldn't be good on a chainsaw cylinder.

I make a habit of removing the cowlings after a few hours use and blowing with compressed air, plus if necessary scraping with a screwdriver (and potentially wire brushing?) to ensure the fins are clean.

Here's the cylinder on a Stihl 024 I've run with veggie bar oil for several years, but neglected to do a good clean (shared use, away from home). The worst oil buildup is on the flywheel side of the cylinder, where the air, sawdust and mixed-in oil get blown in. These old 024s are particularly oily as they keep pumping even on idle. I'm pleased to say it didn't have any cylinder overheating problems before I gave it a good scrub. Methylated spirits is good for cleaning off dried veggie oil, but this baked on stuff wasn't easy. It would be worth trying some stronger solvents (maybe acetone?) to see if they are more effective with the well-cooked oil. It would also be good if I clean this saw more frequently.

Veggie oil won't affect electric chainsaws in the same way, but it's worth looking out that the air slots are clear and that there's no buildup of oil and/or dust inside the motor. 

Conclusions

For me, as a frequent chainsaw user, and happy to be a bush mechanic, used veggie oil seems very worthwhile. We use all the sawdust we can collect: in our garden, in composting toilets, for neighbours' chook houses, we even sell it in bags, sometimes for house cat litter. Sawdust is a valuable resource and biodegradable oil makes it safe to use. 

The biggest risk to using veggie oil appears to be burning onto the cylinder, which I expect to be able to manage. If I can manage that, the savings and benefits seem well worth it. 

Here's another web page on using veggie oil:
https://learn.eartheasy.com/articles/using-vegetable-oil-to-replace-chainsaw-oil/