Hydraulic Fluid Instead Of Engine Oil??

[iansterling]

my idiot teen friend was running low on engine oil so filled it up and ran his car on hydraulic fluid, it's an old 1970 beetle 1500cc. it's still running.. I have told him to get it emptied out and flushed out with clean oil and engine flush at least twice. will this have done much damage?

[bhg481]

Difficult to say, but taking your advice will minimise the damage. It reminds me of the time many years ago when a colleague came to work confused; he'd changed his engine oil but found the oil was way above the correct level even though he'd filled it with the correct amount. We discovered he'd drained the gearbox and filled the engine.

[Buenchico]

I have to admit that I'm not always too fussy about the oil I put in my car. For example, if I'm running a car that officially needs 10W40 but I've only got 5W30 to hand to top it up with, I'll probably just chuck that in anyway. However I think that switching to hydraulic fluid might be step too far!

Found on Quora (as a response to a similar question):
"Normal hydraulic oil is based on the exact same base stocks as mineral engine oil! I should know, I spent 20 years formulating lube oils for major oil companies! ISO 100 mineral hydraulic oil would be equivalent to SAE 30 motor oil and ISO 46 VHVI would be around 20W-30. But the hydraulic oil does not have the detergent and dispersant additives to keep your engine clean. Hydraulic oil is about the same as 1950’s engine oil and would be OK to use in an emergency to get you home. If you used it for longer than a few days, you would start to form deposits in the engine that would clog oil ways and block your hydraulic valve lifters. Also you may find that the engine will show some signs of excessive wear, particularly on the cams and valve gear".

I agree that it would clearly be best to replace the hydraulic fluid with proper engine oil a.s.a.p but, if it was me, I wouldn't bother flushing the engine. I doubt that having a very small amount of hydraulic fluid left in there could do much harm.