Re. oil temp. Understood, thx.The max temp per vm motori of 284 is sump temps aka in the oil pan. The derate temp of 268 F is post oil cooler which is whats measured. When coolant comes back from the radiator it’s typically around 30-50 degrees lower than whats displayed on most engines the displayed temp is at the return for the water pump which is hottest.
We'll probably never agree re. our oil cooler, but I do have the Ram engineer on my side on that.
30-50deg of temp drop sounds high. I've taken an IR gun to radiator inlet/outlet hoses and AL bits many times and the temp drop across the radiator is much less than that. Water is moving pretty fast thru the coolant system. There wouldn't be enough time in the radiator to drop so much temp.
I went looking for some numbers to remind myself how pressure and anti-freeze impacts boiling temps. The bottom line is that we have become accustomed to coolant temps pretty darn close to the boiling point of our coolant.
The boiling point of water goes up only slowly with pressure, and once the coolant is out of the engine, the system isn't under much pressure. Sure, anti-freeze has an anti-boil but the standard 50/50 mix only gives you about 15deg of protection.
The chart below shows how pressure increases the boiling point of antifreeze. Note 236deg for 50% solution at 4psi. There's got to be parts of the coolant system that are as low as 4psi because the pump is sucking and the pressure at the radiator inlet will be only barely higher.
The chart below indicates that the boiling point of antifreeze at 4psi is 236deg and pressure in the hose between the engine and radiator inlet is not going to be much more than that. As coolant temp increases, so does pressure due to microboiling. That's good in the sense that increased pressure helps keeps coolant flashing at bay, but the increased pressure also stresses gaskets and hoses leading to premature failure. So when your EVIC says your coolant temp is >225deg, consider how close you are to bad things.
Sure, it's not a crisis because engines aren't blowing up every day due to coolant overheats, but it does seem to be a thin margin of error. We know that coolant related things fail on these trucks, and here we are talking about the coolant system putting unusual stress on bits.
Situation at high altitudes is worse. A mile of elevation and you lose about 25% of air pressure. That would drop the boil point by about 8deg.
21.2 KB Views: 7
27.3 KB Views: 5