HELP can i put hydraulic oil as engine oil ?

[Stealth Camper]

Two cars and a Dodge pickup. Ford 4.6L w/ 230,000 miles. 70 Cutlass w/ 260,000 miles. Ram Diesel w/ 230,000 miles.

When all my engines were young, I used to run straight weights, but since so much older, and straight getting so hard to find around here, I just use 10-30 or 10-40. I think I know the diesel oil has some high temp additives and extra detergents and some stuff for viscosity stabilization, so the conclusion I jump to is that it would be at least as good as regular motor oil for the gas engines. Anything way out of line about that??

I think that mine are WAY over the hump, except for the diesel.

The only engine I don't want to use it in is the Harley. That has low volume/high velocity system that I think is fundamentally different from the others. But the oil can does say SE/CC at 10-40, so maybe ????

Delvac is about $11.00 and change per gallon here. The car oils are $14, so I am being incentivized to change.

I think Honda and Toyota missed the memo about the 75th percentile. Only the American companies seem to have gone that way. Sad. But I really can't complain; I have never had an engine go out on me before I as ready to get rid of the car anyway. Except the Cutlass. It threw a rod here some time back and I am going to keep it, so will be doing some engine work. It's a rust bucket, so am going to enter it in the Rat Car
category at the car show! It will win hands down.