Oil Filter and Oil Pressure


IHC in the early to mid-fifties.

Golden Jubilee
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Post Mon Jun 17, 2019 7:42 pm

Re: Oil Filter and Oil Pressure

Agreed. My employer bought some used Cummins powered vehicles and there was an external bypass filter system installed that complimented the full-flow system.
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Golden Jubilee
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Post Tue Jun 18, 2019 5:52 am

Re: Oil Filter and Oil Pressure

As far as oil pressure, over on The AMC Forum there have been EXTENSIVE discussions on the subject. The rule of thumb there is that if you have 10 psi per 1000 rpm through about 4500 rpm, your oil pressure is good. So 10 psi at a 650-700 rpm idle is nothing to sweat, based upon those guidelines.
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Golden Jubilee
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Post Tue Jun 18, 2019 12:50 pm

Re: Oil Filter and Oil Pressure

cornbinder89 wrote:To be clear, and fair, some heavy diesels do use a bypass system like Dean describes, The Cummins Big Cam 3 comes to mind. They have a piston pressure valve that opens to the bypass filter when the pressure rises but they flow a lot more thru the bypass filter then the engines we are talking about.


Thanks guys for correcting my misinformation. :oops: I guess other systems are not quite as much like diesels as I thought.

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Golden Jubilee
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Post Tue Jun 18, 2019 2:15 pm

Re: Oil Filter and Oil Pressure

Yeah, the oiling systems on these old trucks was pretty basic. The filters were add-on to the original design.
I have an old GM Diesel 6-71 that has two big bypass filters on it and no full flow. The Luberfiner was a popular add on bypass for heavy diesels and that also only had a fix restriction. It wasn't until the engine mfg started incorporating both the bypass and full flow filters into the design from the get-go do we see them pressure regulated.
The Cummins Big Cam 3 bypass flows a lot more oil than the Luberfiner did. The Big Cam 4 used the single filter with the bypass inside the full flow. I know the early Series 60's had 3 filters, I don't remember if they were 2 bypass and one full flow or the other way around.
The Spinner ii is another bypass that has a regulator built in, but there it is because if the pressure is below 30 PSI it doesn't spin fast enough to do anything.
In most cases, the media used for full low and bypass will be different, the bypass will be depth media with a large pressure drop to filter to a much finer degree, Full flow is all about removing the biggest particles with minimum pressure drop.
Most of the British buses just had a big centrifugal type bypass filter, and we never lost an engine to lube problems, It took a pocket knife to scrape the dirt out of the filter cup, it was so compacted in there!

Rusty Driver
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Post Wed Jun 19, 2019 1:36 pm

Re: Oil Filter and Oil Pressure

When I first drove mine a few weeks ago I was worried about the pressure. Idling in the garage even after getting good and warm it was around 15. After I drove it a few miles, hot idle was only 8. Freaked me out until I read 10psi per 1000 rpm. I'm not idling 800 rpm so I guess I'm good.

Golden Jubilee
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Post Wed Jun 19, 2019 3:25 pm

Re: Oil Filter and Oil Pressure

In an old motor with higher miles, oil pressure, whether high or low may or may not be a problem. An oil pump moves the oil from the pan into the engine. A high pressure may indicate a restriction to the flow. Lower pressure with an sign of oil flowing to the rockers is a good thing.
Pumps move volume. Restriction to the flow makes pressure. Pumps do not suck. Atmospheric pressure moves more oil into the pump to balance the low pressure behind the pump.
It is important for a person to understand the "no suck rule" before they try to work on a carburetor. In the simplest of rules, a carburetor is a kind of low pressure fuel injection. The fuel is propelled by the atmospheric pressure and pressure difference made by a venturi.
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