Generally speaking, the various fluids used in an automobile’s engine should stay within their perspective systems. However, in real life, that’s not always the case. There are numerous ways that leaks can start, and given the number of fluid-based systems in the average automotive engine, there are lots of leaks possible. However, one that you’ll want to watch for very carefully is coolant/water mixing with the engine oil, commonplace when purchasing cheap engines online.

What’s the Issue?

If there’s coolant or water mixing with the engine oil, it’s a bad sign. Most commonly, it’s a sign that there’s a blown head gasket. However, other problems can cause this too, including a cracked block and compression issues. The problem here (aside from the obvious leak and potential for damage) is that antifreeze alters the properties of engine oil. It actually thickens the oil, making it harder to flow through oil channels and lubricate the engine.

How to Detect Coolant in the Oil

So, how do you detect coolant or water in the engine oil? The gold-standard test is to remove the oil filler cap and look in the filler neck/under the cap for white or light brown buildup. This CAN indicate coolant leaking into the engine oil, but it’s not a guaranteed accurate method. The problem here is that condensation can build up within an engine and cause discoloration around the filler cap. This is particularly true with vehicles that are only driven short distances (daily drivers or cars that are only driven rarely). In order to dispel condensate buildup, you have to heat the engine to a certain point and then maintain it.

A better method for detecting coolant contaminating engine oil is to look for “milk chocolate” on the oil dipstick. When coolant mixes with engine oil, it creates a light brown liquid that looks an awful lot like chocolate milk. If you notice this on the dipstick, there’s a problem and you need to diagnose it. Finding the leak can be tough to do, though, unless it’s something pretty obvious like a cracked block. Check for head gasket leaks, and if necessary, do a leak down test on each cylinder.

In most cases, replacing the head gasket or repairing the compression problem (coupled with a thorough cleaning of the buildup within the engine) will do the trick, but that’s not always the case.

Worst Case Scenario

In the worst-case scenario, you’ll need to talk to your customer about engine replacement. A crate enginewould be ideal, but remanufactured and even salvage engines can be good options, particularly if your customer has a limited budget.