two filter flow

[sdan27]

When an engine comes equipped with two oil filters, does the oil flow through one filter and then the next or is oil flowing through both and on into the engine at the same time? Is it always the same or up to the manufacturer's discretion?
I was changing the oil in a farm truck with a Ford 7.8L diesel that has two filters on it and noticed one of the filters was hot to the touch and the other was much cooler, making me think the cool one had already plugged and the oil was simply bypassing it.

 

[Colt45ws]

One may be full flow and the other may be bypass. Are they the same number?

 

[sdan27]

Yes, they are the same number. I thought about it some more and I'm guessing the oil has to go through the one filter and right into the other. Seems to make more sense than the option.

 

[Gary Allan]

I don't know why they would run them in series. I guess you could do it, but it would make more sense to run them in parallel. Like with some fuel filter setups you will have a primary that may be at one micron level then a secondary that's finer.

I guess this would work if it was some redundancy type thing. The first in line just plugs up and the flow bypasses it at that point. This would have to be the case if you're getting one cold filter. If they were truly in line, both should be warm/hot.

One way to test this out is to replace the cold filter and see what happens.

 

[sdan27]

I took the time and looked through an engine manual and found that oil flows into both filters at the same time and then on to the oil gallery ( at least on the IH DT466 and Cat 3208 we run, not positive on the Ford 7.8l but it's probably the same ). I changed both filters when I changed the oil but, don't like the thought that half the oil wasn't even getting filtered. Have to watch a little more carefully in the future.

 

[Gary Allan]

What are the part numbers for the filters? They may not have bypass valves built in. The 5.9 Cummins doesn't have an in filter bypass. It's in the engine (something like 50lb PSID required to open). That is, all of the oil may have been going through the single filter. It would be an odd case that the one filter would completely clog and run cold.

I had a bypass filter running in parallel with a full flow. Even then, with the bypass effectively simulating a mostly plugged filter, it got warm. As the full flow aged, the flow through the bypass increased and fully enveloped it.

 

[Herz]

Would'nt running 2 filters in series cripple flow to the engine?

 

[Gary Allan]

He doesn't have that situation apparently, but you could set it up that way if you wanted to. It wouldn't necessarily make much sense, but if you wanted to do it you could. You would just factor the full PSID and bypass capability into the oil system and the filter.

That is, suppose you an only effectively bypass 2 gallons a minute with a fully saturated filter without collapsing the media. You reinforce the media to withstand 50lbs ..but put a 10lb bypass valve in it. Now you can pass the required gpm with a 50% fudge factor (what ever that volume may be). Effectively it would turn the first filter in line into a bypass filter with the second filter being the full flow up to the point it started bypassing due to loading.

That's the simple view that I can pull out of my behind. It would make no more sense than doing two in parallel in terms of length of service ..or so I reason at the moment. If you've seen as many alternative ways one can perform a given process as I have ...I imagine someone explored this line of reasoning somewhere. Look at all the wrong things that Fiat and Peugeot did over and over again ..perhaps expecting different results??

 

[sdan27]

I'm using two LF3443s on that unit. They have about a 20 psi bypass in the filter. I also run an LF777 bypass filter on that unit too. Looking to change the full flow filters to LF3656s next oil change as they are a little taller, with the same bypass setting and microglass filter media.