I cant find an answer in the Haynes manual.

Does anyone know for sure if the 280ZXT engine oil pump system is a bypass type or a non bypass type???

Thanks

Definitions:

A bypass type system, found in most passenger cars, has a pressure relief valve in the oil pump body that will supply oil to the engine when the backpressure in the oil filter reaches a certain level, about 10PSI. This system ensures that the engine will receive oil if the filter becomes clogged. In most vehicles, the oil pump is capable of supplying way more pressure than the filter can handle and sends the majority of the oil to the engine leaving a small, but important, volume of oil to be filtered. This is also called a sidestream loop design and is used successfully in many automotive and industrial applications. The filter does not see more than 10 PSI or so and does not need to built to withstand the entire system pressure.

A non-bypass system is one that sends the entire volume of oil through the filter before entering the engine. These type of systems are usually modified factory systems or other speciality systems that are put into use because there are special circumstances that demand 100% filtration. Extremely dirty off road racing or mining equipment situations come to mind. The oil filter must be robust enough to take the full system pressure.

 

I was reading about the oil pump in Z's last night in the How To Modify and Race your L Series Engine Good Book.
I believe it would be of the bypass type but I am not 100% sure I know that by replacing the spring inside the pump you can make it so that it can have around 70psi at idle which is recommended for race apps where rpm reaches above 7000rpm.
Not sure if this will help.
I would recommend the book but as it explains lots of L engines and pros and cons and what not to and what to do.
The Haynes book is very vague.
Gav

Gavin,
Melbourne
Australia
73' Datsun 240z