What oil to use in these flathead engines?

[Ken Bartz]

At our Plymouth Club meeting we had some discussion about what engine oil to use in our old cars. Well, it is obvious to us that you would not use a detergent oil in an old car that has many years of sludge build up inside the old flathead engine. Therefore, you would use a “straight weight” oil such as 30W. But then, with a freshly rebuilt (clean) flathead would you use a detergent oil (10W30) in it? How much would these bypass filters that we have on our cars have an effect?

Then the discussion turned to the “High Milage” oil that the companies have come out with. What are peoples opinion of them?

Then someone said that we should STAY AWAY FROM the “API Standard GF4” as noted on the API label. Why is that?

One guy says to use diesel engine oil. But that stuff costs so much more. What is the scoop on using diesel engine oil?

Finally, is there an oil company that I can go to their web page to get the “real story”? I would like to use this information to publish in our club’s newsletter.

[Brad Lustig]

I use regular off the shelf oil (with detergent) with no problems. Havoline 10w30 I believe. A few people here are using the diesel oil now with good feedback.

[Dennis Hemingway]

I have been using 20-50 Castrol Oil in my 48 P-15 for years with no problems.

Dennis:cool:

[Lou Earle]

I have used it all in various old flathead cars. All seems to work just fine. I have had no trouble with detergent oil "dislodging" sludge ever. and I have e run it in cars that were 1/2 inch deep in sludge in the pan.

Lou

[captden29]

i use straight 30 detergent and have no problems. my car has about 63,000 miles.alot of talk about diesel oil because it has an additive that has been removed from regular oil that is good for the tappets. almost any oil today is better than the oils of yesteryear so they all will do a good job. dennis

[Tom Skinner]

Ken,

I use 30w non-detergent NAPA oil.

Then in the gas for each tank full of gas I add 1 (8oz) bottle of Lead Substitute from STP (also sold at NAPA), and 8oz of Marvel Mystery Oil,

(also sold at NAPA). A sort of Cocktail if you will in the gas that makes my

1948 Chrysler Royal (250.6cu.in.) 6 Cylinder Flat Head run like a sewing machine. It only has 53,900 original miles on a never opened engine.

If I rebuild it, which I hope to do in the next 5-10 years before I retire

I will probably start back with 20w oil just like the Service Maintenance

Schedule calls for in the book. I owned a 48 Royal in the 70's and drove it as an everyday car. The rings went, and I rebuilt it myself and used 10-30w oil

then the rings went out again every 10-15,000 miles.

Now that I know engines better I believe the sleeves had excesive taper, thus my problem, but alas I sold her in 84. I think straight weight is the way to go.

Tom

[Norm's Coupe]

Ken,

I use 10w30 detergent oil in my engine. Of course my engine is all new inside so had no sludge buildup to worry about. Rebuilt the engine in fall of 1998 and have been using 10w30 detergent oil ever since. I use Penzoil brand oil only in it. I do not use a lead additive in the gas tank. It's not needed since we have hardened valve seats. If anyone wants a bottle of that, I have almost a full bottle. They just have to pick it up. Was using it in 1995 before I found out I didn't need it.

[Guest rockabillybassman]

The reason for using diesel oil is because it contained zinc (ZDDP), a necessary feature which has been legislated out of regular oil because it is a pollutant. ZDDP is not needed for modern engines, but flat tappet engines need it. However, as of this year, even diesel oil no longer has it.

The good news is that our engines really dont need it. The guys who are suffering are the Chevy SB owners who replace their cams with aftermarket ones. Nearly all aftermarket cams are ground from billet made in China. This stuff is a lot softer than good old American or Canadian steel/iron and desperately needs the correct ZDDP ratio to prevent premature cam failure.

As for the straight weight argument, there has never been any proof either way as to which is better.

[Plymouthy Adams]

I will agree with the Chevy cam to some degree..not all the time is the metal fatigue due to poor material or workmanship..it is a product of over building for the street and improper break in..most of these boys will put in high lift cam, super heavy springs so as not to float at the revs they will NEER run on the street and then idle these babies to a ground powdered metal just to hear them chop. IF you think you need a engine of this nature..DO install normal daily driver stock grocery getter spring and break in the cam right..then after break in..change to the higher tension..however I still don't recommend racing hardware on the street driven car that will idle or pull a AC at low rpm etc....dollar for dollar more money is spent on a Chevy engine in the valve train area than anywhere else on the engine so they can be on par with either the Mopar or Ford stock design. These are such a major flaw in the GM and just recently have they copied the 1957 Mopar poly block heads of the 318 for performance and durability...