Should I use heavier oil in my vintage engine?

Question:

I own an old Ford truck with a Y-block engine and ever since I purchased the truck it has lost some oil pressure after completely warming up. I currently use 30 weight oil (not HD). I also add ZDDP. I believe the engine has quite a few miles on it. Is this the correct oil to use, or should I change to 10W40 weight oil? Would this help if the engine is loose? I have a difficult time deciding which oil viscosity to use in older engines.

Answer:

In general, the oil viscosity you choose should correlate to the ambient air temperature range your vehicle will be operated in and the internal condition of the engine. Using a heavier weight oil in any engine, including one with a lot of internal wear and correspondingly large bearing clearances, will normally yield higher oil pressures at all engine operating temperatures. While this makes drivers with oil pressure gauges feel better it usually doesn’t do anything to help the engine and certainly doesn’t fix the underlying problem that is causing low oil pressure in the first place. Under normal street driving and operating conditions all typical passenger vehicle engines, including those with a lot of wear and large bearing clearances, do not suffer from low oil pressure. In other words, the fact that an engine has 10 or 15 psi oil pressure at idle when hot, is not normally the problem and the lack of higher oil pressure will not hurt the engine. Instead, the problem is the excessive bearing clearances and high internal wear that’s causing the low pressure.