Detergent or Non Detergent oil? 1954 Chevy 235 inline-6

[DHBWA]

There are thousands of vintage Mustangs with rope type rear main seals that are using Mobil 1 without any complications. A hundred or so having pasted thru the vintage shop I worked at.

Just what I was going to say…Also a ton of older
Dodge and Buicks with rope rear main seals…It’s a trick to install those properly….

 

[CR94]

Our '54 manual-transmission 235 tended to collect gray sludge (or lead byproduct?) in the housing of the optional partial-flow oil filter. Pressure lubed, solid lifters, 115 claimed "gross" horsepower. (The Powerglide version had hydraulic lifters and claimed 125 hp.) It always got detergent oil of the latest, greatest grade.
I became acquainted with three other 235³ Chevys---my parents' '55 pickup and '61 Biscayne, plus my landlady's '55 car, which had no oil filter and went well over 100k miles.
By the early '60s, they were claiming 135 hp. However, the '61 seemed much slower than the '54.

 

[72C10]

The only time I would run non-detergent oil is during engine break-in.

 

[supton]

The only time I would run non-detergent oil is during engine break-in.

Why? lower cost of oil that will be immediately drained out within hours?

 

[72C10]

Why? lower cost of oil that will be immediately drained out within hours?

Detergents tend to compete with Zinc and Phosphorous, which you want in higher quantities during break-in, especially in a flat-tappet cam. Lower levels of calcium would be ideal. Maybe not zero, but definitely not your normal levels in high detergent oil.

 

[vwmaniaman]

I think if you plan to use detergent oils I would start with maybe half of the oil change being with non-detergent and slowly each change add more detergent oil.

 

[supton]

Detergents tend to compete with Zinc and Phosphorous, which you want in higher quantities during break-in, especially in a flat-tappet cam. Lower levels of calcium would be ideal. Maybe not zero, but definitely not your normal levels in high detergent oil.

Ah, ok. The chemistry is beyond me but sounds reasonable.

 

[Brons2]

I recently acquired a 1948 Chevy 3100 pickup truck. It was originally equipped with the 216 Stovebolt inline 6 engine but spent many years getting worked hard on a farm. At some point, the farmer removed the original 216 engine and replaced it with a 1954 Chevrolet passenger car 235 inline 6.

I suspect the 235 had been rebuilt at some point prior to the previous owner (to me) purchasing the vehicle 10 years ago. The engine block and head have been painted a non-factory color, and it carries very high oil pressure (30-50 psi, depending on RPM and temperature). It is also very quiet, mechanically, and burns almost no oil.

The previous owner to me (who purchased this truck 10 years ago) ran nothing but non-detergent SAE 30 oil in it while he owned it - believing that the truck still had the stock 216 in it. He put at least 6000 miles on it, with an unknown number of miles being on the truck and 235 engine previous to him purchasing it from the farmer.

I've heard horror stories about switching to detergent motor oil in old engines because it can loosen sludge that can plug up oil passages. However, as I stated, this engine has been rebuilt at some point. I inserted a bore scope camera into the oil pan thru the drain plug but could not determine if there was any sludge laying in the bottom of the oil pan due to inadequate lighting.

The question is: would it be safe to use a modern detergent motor oil in this engine at this point? I will, of course, be adding the recommended amount of Zinc/ZDDP due to the presence of a flat tappet camshaft.

I have gone through quite a few of these 235s back in the day. 30-50psi is normal with the high pressure bearings and oil system. If it was a low pressure system, 30 would be on the high side and 5-10 psi normal at idle.

As for whether to run detergent or not, take the valve cover off and if it's clean run detergent oil. We ran dino 20w50 in these after rebuilds back in the day in the machine shop I worked in, but I would recommend diesel 15w40 nowadays, or diesel 10w30 in a cold climate. You don't need the additive with the diesel oil, and you probably wouldn't need it even with PCMO, the valve spring pressure run in these is quite low.