Q&A / Tech

Mailbag: Low Oil Pressure and How it Affects Your Engine Bearings

 

Q: I was wondering if you could answer a few questions for me:

  1. Could low oil pressure (15-20 psi) spin a main bearing or otherwise ruin an engine?
  2. How can you avoid low oil pressure?
  3. How long would it take for low oil pressure to spin a bearing?

A: Here are the answers to your questions in the order you asked them:

  1. Low oil pressure combine with high RPM can indeed spin a main bearing, but most likely a connecting rod bearing would go first due to lack of oil.
  2. A good way to help prevent low oil pressure is to Plastigage all bearing clearances to make sure parts were machined properly before you assemble the engine.
  3. How long it takes low oil pressure to spin a bearing depends on things like rpm, bearing clearances, temperature, engine load, oil viscosity, and main cap or bolt flex. The basic rule of thumb on oil pressure is to have 10 psi of pressure per thousand engine rpm. At 4,000 RPM, for example, you need 40 psi of pressure. At 15 to 20 psi, 2,000 rpm would be the max before you start damaging the engine.
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One Comment

  1. It is most likely the low oil pressure was a result of the bearing going bad ,if a bearing turns it can block the oil passage causing the pressure to drop.

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