Detection of slow coolant leaks into engine oil or ATF

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Aug 2, 2002
Coolant reacts chemically with engine/transmission oils to form an acidic sludge, so it may not test positive as Ethylene Glycol. The best way to detect slow coolant leaks is to look for trace amounts of common coolant additives. These are the ones to look for and they vary by coolant type.

Trace Element - Chemical Symbol:

Sodium - Na

Potassium - K

Silicates - tests as "silicon"/Si

Borates - tests as "boron"/B

Molybates - tests as "moly"/Moly

You may note that some of these like boron and moly are also common oil additives, so you need the baseline oil analysis data on the formulation you are using to determine if significant contamination is present. Other key things to look for are accelerated bearing - Pb/Cu/SN - wear and abnormal increases in viscosity and total solids/oxidation. If the leak is slow, the water in the water/coolant mixture will normally evaporate and is the last thing you'll see. If pure water is present > 0.5%, these levels of coolant additives will generally be in the hundreds of ppm and will be very noticable. The oil may also look like a milkshake at this point, from the oil/water emulsion that forms ....

Yea and if you wait until the oil analysis detects "glycol", you may have a long wait.
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