High detergent oil for a 1940 LaSalle

[Jamurray]

I'm changing the manifold gaskets on '40 LaSalle, and this gave me the opportunity to inspect the valley after removing the two valley covers. The valve stems, the lifters, and everything else looks clean with no accumulated gunk.

I didn't know what oil previous owners had used, so I didn't know how much sludge coated the engine's inner surfaces. I've been using non detergent oil with Lucas zinc additive since 2014, but I'd like to use high detergent oil from now on.

Is there any reason why I shouldn't?

Jack Murray

[Fred Pennington 25635]

I really hate this topic, Some of the most contentious threads I have ever read revolve around "What oil to use".
Your 40 LaSalle was built without a filter and any add on filter takes a side trip as far as the oil is concerned and is questionable as to effectiveness.  It used to be common practice non detergent oil was used without filter and detergent with filter.
Theory is the dirt settles in the non detergent and stays suspended in the detergent oil for the filter to remove.
Today the experts say  15/40 Diesel oil works best in old engines. It has higher zinc for wear protection and if changed frequently the detergent is not a problem and controls sludge.

This fits well with what aircraft engines have done for ever.  Non Detergent for break in and detergent after break in.

[LaSalle5019]

Yes, use an ashless dispersant oil - often referred to as detergent oil.  Detergent isn't really a great term as it conjures up some super cleaning oil. It isn't going to clean out old sludge deposits.  All AD oil does is keeps new contaminants suspended in the oil rather than settling out on parts or the oil pan. Most of the contaminants that make the oil look dirty over time is carbon from the combustion by-products. 

As far as a zinc additive (ZDDP) - save your money. ZDDP was not even around when your car was built. It was not until high compression engines with high valve spring pressures were designed in the 1940s to support the war that the additives were needed. Post war automobile engines began to be introduced that used the learnings from the war to create more power and those engines required a balanced zinc and phosphorus content to reduce wear issues. Running a high ZDDP content oil will not hurt your engine but it certainly is not needed. What will hurt is adding too much ZDDP, like using Valvoline VR1 and using a ZDDP additive. If you want to step it up a bit and buy synthetic oils those are about the best you can get.  My problem is, without an oil filter, the carbon content from combustion does not get filtered out and the oil gets pretty dirty in 500 or 1000 miles so I like to change my oil fairly often.  I stick with mineral based oils in my 1939 LaSalle for that reason.