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Old 15-04-2020, 16:59   #1
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Must Oil Filter Be Filled After Oil Change?

I've always heard this, and done this, but is it necessary? It can make a little mess.

Perhaps it depends on the engine. I'm thinking that oil flows from the oil pump through the oil passages to the various lube points in the engine, and then to the oil pressure relief valve (which is what causes the oil pressure needed at those lube points). The oil (then with less/little pressure) flows through the oil filter.

Is this generally right? It would then follow that it wouldn't matter if the filter is filled at startup, or not. But if the oil flows through the filter first, or at least before the pressure relief valve, having it filled initially would be important.

I do notice that it takes longer for oil pressure to rise after oil change than it does normally, but thought that is because oil passages don't completely drain until all oil is drained.

Got time to think about stuff now, thus the question.
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Old 15-04-2020, 17:13   #2
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Re: Must Oil Filter Be Filled After Oil Change?

In some cases, it is going to be physically impossible to fill the oil filter before installing because they install "upside down" or "sideways" This is a dumb design choice, but it happens.

There is no reason to do this. Just follow good procedure: Fill with the amount of oil specified by the manufacturer, run the engine for a few minutes, and then check the level, topping off if needed.
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Old 15-04-2020, 17:17   #3
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Re: Must Oil Filter Be Filled After Oil Change?

Quote:
Originally Posted by ggray View Post
I've always heard this, and done this, but is it necessary? It can make a little mess.

Perhaps it depends on the engine. I'm thinking that oil flows from the oil pump through the oil passages to the various lube points in the engine, and then to the oil pressure relief valve (which is what causes the oil pressure needed at those lube points). The oil (then with less/little pressure) flows through the oil filter.

Is this generally right? It would then follow that it wouldn't matter if the filter is filled at startup, or not. But if the oil flows through the filter first, or at least before the pressure relief valve, having it filled initially would be important.

I do notice that it takes longer for oil pressure to rise after oil change than it does normally, but thought that is because oil passages don't completely drain until all oil is drained.

Got time to think about stuff now, thus the question.
No need to fill an oil filter

Do wipe fresh oil on the new oil filters O ring before installation

The filter that is worthwhile to fill is the fuel filter
Saves much time when bleeding the air from the system
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Old 15-04-2020, 17:50   #4
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Re: Must Oil Filter Be Filled After Oil Change?

In general, oil flows from the pump to and thru the filter, then into the gallery which feeds the crankshaft, the overhead, and the rest of the engine lube points. Pressure relief valves are typically in the gallery or in the filter housing itself.

If you can fill the oil filter before you install it on the engine block or on its filter head, that's worth while doing, as it saves a few seconds without oil flow.
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Old 15-04-2020, 17:54   #5
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Re: Must Oil Filter Be Filled After Oil Change?

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Originally Posted by ggray View Post
... I'm thinking that oil flows from the oil pump through the oil passages to the various lube points in the engine, and then to the oil pressure relief valve (which is what causes the oil pressure needed at those lube points). The oil (then with less/little pressure) flows through the oil filter.

Is this generally right?
No, not quite right. In most engines, the pressure relief valve is actually part of the oil pump. Oil flow is from the sump, through the pump, through the filter, and then out to the lubrication passages in the engine, draining back to the sump.

The oil filter sees the highest pressures in the system, which makes sense because it is the biggest restriction to flow.
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Old 15-04-2020, 17:55   #6
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Re: Must Oil Filter Be Filled After Oil Change?

The Cummins Onan MDK model generator service manual states that the oil filter should be partially filled so that oil gets to the engine parts sooner after startup..
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Old 15-04-2020, 18:11   #7
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Re: Must Oil Filter Be Filled After Oil Change?

There have been arguments made that pre-filling the filter can introduce contaminants that bypass the filter (since you generally pour your fill oil in the "clean"side of the filter). CAT and Cummins have issued advisories against pre-filling. This is from the CAT C3 series manual:

Quote:
NOTICE
Do not fill the oil filters with oil before installing them. This oil would not be filtered and could be contaminated. Contaminated oil can cause accelerated wear to engine components or engine damage.
These CATs have the oil fill on the sump itself, so if you introduce contamination during the fill it then goes to the filter. Those of us who pour the oil down through the engine don't get that same benefit.

On the fuel filter side, Cummins does specifically state, in bold letters on their website:

Quote:
Remember: 3 micron on-engine, stage 2 filters, should never be pre-filled.
CAT on-engine filters come with a "pre-fill deterrent" to prevent pre-filling and "risk debris reaching injectors".

Pre-filling the Racors, sure, pre-filling the on-engine fuel filter not recommended.
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Old 16-04-2020, 04:24   #8
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Re: Must Oil Filter Be Filled After Oil Change?

Especially on diesels...... If it’s a sideways filter, wet it out by pouring oil into it to soak the paper element. And leave as much as you can without spilling.

Diesels have high pressure so they fill fast but by wetting them out it helps to eliminates air bubbles passing through the system.

My truck diesel takes 2 quarts of oil to fill it. Imagine the time it would take to fill it up.

I even do this on gas engines. It will help prolong the life of the crank bearings.
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Old 16-04-2020, 05:05   #9
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Re: Must Oil Filter Be Filled After Oil Change?

It certainly doesn't hurt to fill the filter if you can. I make a point to at least partially fill it on any engine where I can still install it without a mess. When it's at a bad angle, I don't worry about it.
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Old 16-04-2020, 05:09   #10
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Re: Must Oil Filter Be Filled After Oil Change?

If people are worried about a dry oil start, you can always spin the engine over without starting for a few seconds until the low oil pressure light extinguishes or the oil pressure gauge displays a decent pressure.

Usually a lot easier than filling the oil filter.
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Old 16-04-2020, 05:32   #11
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Re: Must Oil Filter Be Filled After Oil Change?

On some side mounted filters, they drain when shut. Not my Yanmar but so on my Toyota. Diesel vs gas. The compression ratio on diesels are very high compared to gas motors. More chance to spin a crank bearing on a diesel.
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Old 16-04-2020, 06:19   #12
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Re: Must Oil Filter Be Filled After Oil Change?

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Originally Posted by SVHarmonie View Post
No, not quite right. In most engines, the pressure relief valve is actually part of the oil pump. Oil flow is from the sump, through the pump, through the filter, and then out to the lubrication passages in the engine, draining back to the sump.

The oil filter sees the highest pressures in the system, which makes sense because it is the biggest restriction to flow.
There you go. I had a misconception of the function of the pressure relief valve, which is why I thought it (as well as the filter) was located as I speculated. Google just helped me understand this better.

So it seems it would be good to fill the filter (as much as possible) after the oil change. I know some other posts here suggest that contamination could occur doing this, so will consider that.
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Old 16-04-2020, 06:22   #13
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Re: Must Oil Filter Be Filled After Oil Change?

A lot of worry about nothing.

Probably better to warm the engine a bit beforehand to get the crud mixed into the oil and it drains better.

If you just ran the engine, all the parts are lubed up already, so 5-10sec for oil to start flowing once every 3 months, isn't going to cause any harm.

Doesn't hurt if you want to pre-fill but it isn't going to hurt anything.

PS: Also not buying the idea that putting fresh oil in has the potential to introduce contaminants...new oil shouldn't be loaded with contaminants.
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Old 16-04-2020, 06:22   #14
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Re: Must Oil Filter Be Filled After Oil Change?

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Originally Posted by DougR View Post
In general, oil flows from the pump to and thru the filter, then into the gallery which feeds the crankshaft, the overhead, and the rest of the engine lube points. Pressure relief valves are typically in the gallery or in the filter housing itself.

If you can fill the oil filter before you install it on the engine block or on its filter head, that's worth while doing, as it saves a few seconds without oil flow.
Thanks; making sense now.
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Old 16-04-2020, 06:27   #15
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Re: Must Oil Filter Be Filled After Oil Change?

I always thought so, then one day my mechanic was sitting with me. He was working on something while I was changing the oil and filter. I was doing this and said "You know you don't need to do that, right?"

I think this is one of those things that used to be an issue many years ago, and has long since been resolved. Now we continue the process out of superstition and habit.
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