I've been told tractor trailer drivers periodically monitor the ph of their diesel engine coolant. If so, why has this not been an issue for so many auto owners that never change engine coolant. The example given is in the presence of dissimilar metals maintaining a proper ph is critical to prevent rapid corrosion.
Thanks,Rob
if you change it on time you don't need to worry about pH
why has this not been an issue for so many auto owners that never change engine coolant
Of course it's an issue. If you never change the antifreeze then you get all kinds of problems. Sludging, failing water pump, holes in the radiator, etc...
It depends on quite a lot of variables. What the components of the coolant are and what material the block/ head and head gasket are made of are the big ones. I do chemical work for a living, unrelated to cars. I'll try to explain it.
Aluminum is more corrosion resistant than cast iron, meaning it will react more slowly to certain acidic or alkaline solutions than cast iron. Cast iron is also more resistant to certain solutions than aluminum. Cast iron is what they used for engines back in the day. Now, they're predominantly aluminum to save weight. I don't believe diesels have gone this way, they take a lot more pressure than gasoline engines. They're likely still cast iron or steel.
Leave water in a cast iron skillet that isn't seasoned and see how long it lasts before it rusts. It'll develop rust within a few days. Leave aluminum in the same water bath, and it will never rust. Aluminum forms oxides that adhere to metal underneath, oxides of steel and cast iron do not, it develops flaky oxides, which is what we call rust.
Aluminum oxides do react with certain acidic and alkaline chemicals, chlorine violently reacts with aluminum, for example, and much more slowly with cast iron/steel. You can use hydrochloric acid to strip rust off steel and cause minimal damage to the metal underneath, if not left on for a significant period of time. Don't try it with aluminum, it can blow up. Heat also increases the reactivity of metals and caustic chemicals, which is something engines that engines always produce.
Nobody uses acids to cool engines, but this is a general idea.
Long story short, it depends on what the chemicals in the coolant degrade into when they break down, and how aggressive it is at corroding the components of the engine. It takes a long time to eat through most engines. It's not like if you go a year or two past the change interval, It'll eat through your engine. It takes a long time, but it eventually happens.
Diesels I'm not really familiar with, galvanic corrosion is possible at certain pHs with certain metals. Steel fall victim to galvanic corrosion, so I would assume this is the case.
