Thoughts on cooling a model engine with oil instead of water

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xander janssen said:
Hi,

In order to reduce potential issues with corrosion due to various materials (aluminium, steel, brass), I was thinking on using oil instead of water/glycol to cool my model engine.

According to Wikipedia, there are advantages and drawbacks on using oil.

Wikipedia oil cooling

I my opinion, the drawbacks e.g. lower specific heat, can degrade at high temperature do not hold for a model engine.

How do you think about this?

Regards,

Xander
Click to expand...
There was a popular tractor in the early 20th century that ran on heavy kerosene and because it needed to run hotter than a traditional water cooled tractor ( pressurized systems weren’t used that early) it used a cooling oil instead of water. It was called Rumley Oil pull. Many people think it was because it ran on a kerosene but many tractors did at that time.
https://www.dieselworldmag.com/feat.../#:~:text=At about 5.5:1, the,well under 15:1).
 
Giving this some more thought, what about silicone oils? They have very good thermal stability and the heat transfer properties seem similar to those of mineral oils. This of course assumes one does not simply use the sump oil as coolant as well.

Based on their specific heat capacities, it looks like one would require about four times higher coolant flow rate with oil as compared to water. The thermal conductivity of oil is also lower, so the difference in temperature between engine and coolant will also be somewhat greater.
 
That Rumely article that Billp66 posted is interesting.
I use to run my John Deere model H on diesel, and like the Rumely article mentions, that worked very well if the engine was hot and not idling.

Also interesting to note how Rumely used modulated water injection to offset the problems with operating on kerosene or diesel.

And the kerosene line was routed through the exhaust pipe, for fuel preheat, which is very clever.

Rumely was very creative in their engine design.
Three part carburetor which atomized kerosene, gasoline, and water.

.
 
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I have several Gehl skidloaders that use hydraulic (46 ) oil in the engine. the hydraulic system and the engine both use the "radiator" for cooling. Works well in this application.
 
Unlikely model engines see any kind of duty or dis use that corrosion concerns would be a primary reason in the choice of cooling mediums. Oils and Glycols beat out water on a maintenance basis and liquid cooling introduces a system in need of reservoirs, pumps and plumbing in your model.
 
What about using the fuel to cool the cylinder liner? I am kicking around the idea of a diesel that runs on a vegetable oil. That will require a combustion chamber temperature of 500°c to burn cleanly and the fuel would have to be 100°C + for a viscosity in the diesel oil range.

I was thinking water cooled with a tube heat exchanger but cooling the oil resivoir and having ready hot oil seems simpler.
 
The Rumley Oil Pull tractors used oil for coolant. Closed system with a radiator. They wanted the engine to run hotter that they could with water, and were probably concerned about freezing also. You will have to size the cooling system larger to account for the lower specific heat of oils as compared to water.

Might also want to be careful what types of oil you use, vegetable oils polymerize and act like a sticky paint in the presence of oxygen, and at higher temperatures they might do that quicker than at room temperature.
 
I was thinking mostly copper pipe (iron plus any oil = bad for peroxide formation) and a simple dessicant positive air flow on the reservoir.

Build up on the cylinder liner is something I'm still researching.

A hydraulic cooling oil with a heat exchanger to the fuel oil is another thought.
 
The Ignoble Troll said:
I was thinking mostly copper pipe (iron plus any oil = bad for peroxide formation) and a simple dessicant positive air flow on the reservoir.

Build up on the cylinder liner is something I'm still researching.

A hydraulic cooling oil with a heat exchanger to the fuel oil is another thought.
Click to expand...
In my experience copper and its alloys have a habit of reacting with vegetable oils and biodiesel over time. You get a film of greenish sludge building up on the parts. Better to use stainless steel, or regular steel where it isn't suitable.

Anyway using fuel as coolant is possible, in fact fighter jets use this method frequently. But they don't hold fuel in contact with hot parts for long or cool it in a radiator, instead the fuel is recirculating constantly back to the tanks where the very large mass of fuel on board acts as a heat sink.
 
Nerd1000 said:
In my experience copper and its alloys have a habit of reacting with vegetable oils and biodiesel over time. You get a film of greenish sludge building up on the parts. Better to use stainless steel, or regular steel where it isn't suitable.

Anyway using fuel as coolant is possible, in fact fighter jets use this method frequently. But they don't hold fuel in contact with hot parts for long or cool it in a radiator, instead the fuel is recirculating constantly back to the tanks where the very large mass of fuel on board acts as a heat sink.
Click to expand...
Iron and steel are actually the worst for most oils as Fentons reactions spur polymerization of the oil via radical formation. If steel wasn't just so dandy, it wouldn't be used in hydraulics.

Now I'm going to have to do some tests on oil and copper.

But that would be derailing this thread, so I'll desist.
 
xander janssen said:
Hi,

In order to reduce potential issues with corrosion due to various materials (aluminium, steel, brass), I was thinking on using oil instead of water/glycol to cool my model engine.

According to Wikipedia, there are advantages and drawbacks on using oil.

Wikipedia oil cooling

I my opinion, the drawbacks e.g. lower specific heat, can degrade at high temperature do not hold for a model engine.

How do you think about this?

Regards,

Xander
Click to expand...
On aircraft engines they did use oil and air cooling.

Water is very good coolant for engines.
The problems with oil is the sulfur in the oil under heat it turn to sulfuric acid.
Back to square one.

They have found distilled water is best for reducing corrosion.

Dave
 
SmithDoor said:
On aircraft engines they did use oil and air cooling.

Water is very good coolant for engines.
The problems with oil is the sulfur in the oil under heat it turn to sulfuric acid.
Back to square one.

They have found distilled water is best for reducing corrosion.

Dave
Click to expand...

The sulfur that produces sulfurous acid/sulfuric acid requires moisture, or a process that creates moisture, to produce acid.

Just hucking a wet rusty iron bolt into a vat of pristine oil with an open atmosphere is enough to produce acidification.


Dry headspace venting is a great way to keep oil dry. If the oil is dry and stable, not already contaminated with polymerization products, it should stay dry and stable.

Polymerization is autocataltic so once it starts... that's why mixing 1L of old petrol with 10L of new petrol equals 11L of old petrol.
 
""
The sulfur that produces sulfurous acid/sulfuric acid requires moisture, or a process that creates moisture, to produce acid.

Just hucking a wet rusty iron bolt into a vat of pristine oil with an open atmosphere is enough to produce acidification.


Dry headspace venting is a great way to keep oil dry. If the oil is dry and stable, not already contaminated with polymerization products, it should stay dry and stable. ""

Thank you ! 👍👍👍 .
 
Various oils, such as machine oil, gear oil, engine oil, cooking oil, have additives suited to their main application. Some - like engine oil, are heavily loaded with corrosion inhibitors, particularly the anti-acid compounds, that combine with the acids from blow-by gases to prevent corrosion within bearings, etc.
Also a major issue is the electro-potential from different metal combinations in the flow of the fluid around the engine. These electro-potentials will electrolytically corrode the Anode material. So the countermeasure is to use a sacrificial anode, like a piece of zinc, and install in the region you most want to protect from corrosion. The oil will have some stuff, but the zinc anode will help prolong the anti-corrosion ability of the oil by using the corrosive acids first.
But the cooling system is without blow-by gases I guess? - so should not be as bad as the crankcase, so why not simply use decent quality (SF/CC or better) engine oil for cooling? And add a zinc anode (ships chandlers sell them in various forms to stop corrosion of ships, particularly bronze screw propellers).
K2
 
Steamchick said:
Various oils, such as machine oil, gear oil, engine oil, cooking oil, have additives suited to their main application. Some - like engine oil, are heavily loaded with corrosion inhibitors, particularly the anti-acid compounds, that combine with the acids from blow-by gases to prevent corrosion within bearings, etc.
Also a major issue is the electro-potential from different metal combinations in the flow of the fluid around the engine. These electro-potentials will electrolytically corrode the Anode material. So the countermeasure is to use a sacrificial anode, like a piece of zinc, and install in the region you most want to protect from corrosion. The oil will have some stuff, but the zinc anode will help prolong the anti-corrosion ability of the oil by using the corrosive acids first.
But the cooling system is without blow-by gases I guess? - so should not be as bad as the crankcase, so why not simply use decent quality (SF/CC or better) engine oil for cooling? And add a zinc anode (ships chandlers sell them in various forms to stop corrosion of ships, particularly bronze screw propellers).
K2
Click to expand...
To have electrolytic corrosion you need two dissimilar metals electrically connected to each other and in contact with an electrolyte. Oil isn't conductive so the latter does not apply, no electrolytic corrosion should occur unless the oil somehow gets contaminated with lots of water.

In marine applications we often use anodes, but they only work on items that are in contact with the same body of water the anode is in contact with! So they do nothing to help your rigging which gets covered in drops of spray but isn't immersed (ok I've immersed my rigging many times, but I didn't intend to...). What my dad taught me to do was approach the electrical connection side of the problem in those cases, for example by putting insulation between metal parts. Often that takes the form of duralac brand anti-corrosion paste. We also often use monel rivets rather than stainless steel because they are less aggressive towards aluminium.
 
Water is used in the vast majority of commercial cases not only for its heat capacity, but its other heat transfer properties such as thermal conductivity, and viscosity. Water is a great heat transfer fluid, oil, not so much. Note I said commercial applications. In our models, maybe it's not a great hardship to make the radiator twice as big. In other special cases, whatever works. My dad wanted to eliminate the wing mounted oil coolers on the Rare Bear 77 race plane (world's faster prop plane) as they caused too much drag. So the oil coolers became a coil in an open water tank in the fuselage that boiled off during the race. In our special cases, we can do anything that works that would not make sense for a commercial product.
 
GreenTwin said:
We need to see that.
Click to expand...

Nerd1000 said:
To have electrolytic corrosion you need two dissimilar metals electrically connected to each other and in contact with an electrolyte. Oil isn't conductive so the latter does not apply, no electrolytic corrosion should occur unless the oil somehow gets contaminated with lots of water.

In marine applications we often use anodes, but they only work on items that are in contact with the same body of water the anode is in contact with! So they do nothing to help your rigging which gets covered in drops of spray but isn't immersed (ok I've immersed my rigging many times, but I didn't intend to...). What my dad taught me to do was approach the electrical connection side of the problem in those cases, for example by putting insulation between metal parts. Often that takes the form of duralac brand anti-corrosion paste. We also often use monel rivets rather than stainless steel because they are less aggressive towards aluminium.
Click to expand...

You can get corrosion on past contamination on certain metals (say steel) where the oxide and metal have different potentials. The oxides of certain metals, plus air, will also create the chance for the polymerization reaction of the oil which creates H2O or H+ or O- or worse HO- which further drives electrolytic or acidic corrosion as well as attacking the oil.

This is where additives like BHT, citric acid, ascorbic acid etc, can be your friends as they terminate the oils reactions by IIRC dropping in some hydrogen to cease the reaction.

It's neat that antioxidant acids can be used to stabilize reactive oils like bio diesel fuels.

I have seen corrosion in aluminum pumps caused by iron oxides from rust elsewhere in the system that was transported to the Al.


The above assumes poor practices.

Maison jars arrive today... still have to finish designing the experiment.

I'm also used to working with mineral oils so re-reaserching veggie oil reactions is taking time.
 
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