Does Propylene Glycol cause motor oil to coagulate?

It is well known that ethylene glycol when mixed with motor oil will cause catastrophic engine failure. The mix coagulates to a brown-mud that fails to lubricate. But, will a Propylene Glycol / motor oil mix also cause a failure?


The few articles I have been able to find refer to glycol/oil mix. The [ethylene](https://www.machinerylubrication.com/Read/193/oil-glycol) seems to be [implied](https://www.machinerylubrication.com/Read/735/glycol-oil-ball-engine). It appears the glycol reacts with the additives in the motor oil. At the micron level, this mixture is very abrasive. I am not finding any info on how Propylene Glycol reacts with engine oil.


I heated a Propylene Glycol/motor oil mixture to boiling. It never coagulated. When it cooled, the mixture separated. I repeated the same with ethylene glycol/oil mix. That mixture failed to coagulate as well. Again, when it cooled, the mixture separated.


Oil pumps generally run in the 20-30psi range. I doubt pressure is needed to cause the coagulation as the oil pan is typically full of mud when an engine fails.


I'm wondering why I can't get the mixtures to coagulate. Does anyone know if Propylene Glycol/motor oil coagulate?




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The oil/coolant mixtures sat for a week. Both versions had separated. When agitated, the mixtures would quickly separate. The ethylene version showed signs of mud at the interface layer. The propylene version was very dark in color. Very close the same shade as the oil, but with no sign of mud.
When the ethylene version was heated (not to boiling) and agitated, it quickly emulsified into thick mud. When it cooled the emulsion held.
When the propylene version was heated and agitated it showed signs of emulsification but when the agitation was removed it would quickly separate. When cooled the separation was more pronounced. It did not coagulate the oil.




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Both the EG and PG are a 50/50 mix with water.
Update: A week later:
The ethylene glycol (EG) is still fully emulsified. It is showing signs of separation but is still fully incorporated.
The propylene glycol mixture has coagulated to mud. There is a layer of oil sitting on thick layer of mud with no sign of any unincorporated PG.


Both ethylene glycol and propylene glycol do coagulate when mixed with motor oil.


