45: Detergent Oil vs. Non Detergent Oil = Hot Topic

Definition:  DETERGENT OIL 

In essence, detergent oil was designed to cleanly scrub down your crankcase* and take all that debris to the oil filter. It "suspends" those gunky particles so that they can be taken to the oil filter – and of course the oil filter traps and collects that gunk to help keep the engine clean. It’s the circle of life in engine speak.

*A crankcase is the housing for the crankshaft**

**Crankshaft: Click here to see a neato Wikipedia animated clip explaining what and how it works 

Definition: NON DETERGENT OIL

Non-detergent oil does not hold the particles in suspension so the gunky stuff tends to settle out in the bottom of the oil pan--where theoretically--it would be drained out during a routine oil change. 

Most automobiles built early-on and through the 1940’s did not have oil filters; (This would be Abbey) subsequently, they used the oil available in that day which was non-detergent oil (or just “oil” as detergent oil hadn’t been invented yet). 

The Discussion:

A big problem today is what to use when you get a vintage vehicle, so the rule of thumb is: 

If it doesn’t have an oil filter and you aren’t going to overhaul it, use a non-detergent (or non-suspense) oil … then just wait until a good overhaul to switch over. Or not... (wait, what?)

People who have these old vintage vehicles and use detergent oil before tearing in and completely overhauling an engine may not realize that the newer stuff will probably dissolve that sludge at the bottom of the oil pan and start to circulate all those particles through the engine causing rapid and excessive wear. 

With the low miles that these old cars generally get driven, and with the proper oil the engines should last a long time, but with the wrong oil, the wear will be so rapid on the engines that they will eventually need to be rebuilt, and that can be expensive if you want to stay o-r-i-g-i-n-a-l. 

Let’s face it, you probably won’t be taking the old gal (and by old gal I mean the vehicle) for a cross-country road trip unless you overhauled the engine right?

Seems simple enough, right? Wrong... (What?)

The topic of non-detergent oil vs. detergent oil is a HOT one and everyone weighs in on it. 

A good public discussion thread with many opinions can be found HERE and worth the read. 

Another view offers specifics in favor of non-detergent oils: HERE

You can still buy non-detergent oil from various auto parts stores but you have to ask for it. It will typically be marketed as compressor oil, available in 30W, 40W and some dual weights.

So, to recap:

(1)   No oil filter or not doing a complete rebuild of the engine - use non-detergent oil

(2)   Filter, or just completed an engine rebuild - use detergent oil (Or not)

(3)   Do whatever you want and see what happens, it’s your time and money.