Hydraulic Oil vs. Motor Oil

I think you and your friend are both right. You should definitely avoid detergent engine oils. The closest ISO Viscoscity grade to SAE 10W is ISO46. This should work in your dozer.

The suggestion to go up to ISO68 may have been suggested because higher in-use viscosities will improve efficiency and productivity of the equipment. The typical drawback of switching to a higher visc grade is degraded performance at start-up and cold temperatures leading to possible cavitation.

To get both you need a multigrade hydraulic fluid that has improved low temp as well as high temp performance. I would avoid the 10W20 fluid because multigrade engine oils are not shear stable enough for hydraulic applications.

You should look for a shear-stable, hydraulic fluid formulation with a viscosity index of at least 150. Some manufacturers sell products labeled MEHF (Maximum Efficiency Hydraulic Fluid) that meet the performance level you are looking for.

Hope the helps,

-Doc

Not sure if your familiar with Texas Refinery Corp. or not but we offer a oil specifically designed for that type of equipment. It's called Pro-Tac IV and is actually a Caterpillar TO-4 and Allison C-4 equipment spec transmission fluid as would be found in dozers and other heavy equipment. It's available in SAE 10, SAE 30 and SAE 50 viscosity's.

If it's only needed for a hydraulic system I would suggest a ISO 32 hydraulic oil. Here's a list of approximate ISO to SAE viscosity's:

ISO 22 = SAE 5
ISO 32 = SAE 10
ISO 46 = SAE 15
ISO 68 = SAE 20
ISO 100 = SAE 30
ISO 150 = SAE 40
ISO 220 = SAE 50

Several differences between bespoke hydraulic oils and engine oils(monogrades)
Antiwear performance in engine oils is better due to higher levels of ZDDP. Engine oils are pro emmulsion wheras hydraulic oils are better at shedding water.
Monograde engine oils SAE 10W are readily available usually in appropriate specs which include CAT TO2 and Allison C3 and have hydraulic performance tests.
Oils with CAT TO4 , Allison C4 are usually much more expensive and have no benefits in hydraulic systems over CAT TO2 products.
See no reason why ISO 46 hydraulic oil can not be used with some good antiwear credentials like Eaton Vickers M-2950-S(Mobile) similarly SAE 10W with CAT TO2 etc. Suggest you do not use SA 10W type product which does not contain any antiwear additive.If this is the current product in use would go to non detergent ISO 46 hydraulic oil as above immediately.

Thank you for the informative posts.