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Surely some internals of the engine will be running "dry" for a short time after a filter change i.e. until the filter becomes full and passes oil. However the makers do not suggest priming the new filter. Priming a filter is a messy job that I have always done, but my question is, am I wasting my time?

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I've never seen an owner's manual or service manual for a passenger car/truck/van that advises priming an oil filter either, as you said in your question too. So if the manufacturers don't say to do it, then you don't need to do it.

If your oil filter is in such a place that you can add some oil & get it attached without easily spilling oil all over the engine, floor, or yourself, then it couldn't hurt.

But many engines I've seen have the oil fill cap on top of the valve cover. Especially if there's only one valve cover (inline 4 or 6-cyl), when you pour in new oil it will be flowing down through the engine anyway.
So when you start it a minute later (as recommended in service manuals I've seen before "topping it off") there will be some oil coating some of the engine, probably a lot more than if it had been sitting overnight. Along with fresh oil and a still-warm engine, I don't think there will be enough extra wear to worry about.

I wouldn't risk spilling oil everywhere, so I don't do it. And mechanics I've seen & talked to don't do it either. I wouldn't say you're wasting your time, but I think you could be spending it more productively doing something else.

  • The problem with your theory of oil "flowing down through the engine anyway", the areas this will cover (while good) are secondary lubrication areas. The primary lubrication areas, such as bearings, are what has a lack of lubrication while the engine starts up. These are the areas which suffer the most and where the most damage to the engine occurs during startup. Priming the oil filter minimizes this. To me, mechanics who are saying this to you are being lazy. Spend an additional 30 seconds and put some oil in the filter. Save the yourself or the customer a ton of wear over time. – Pᴀᴜʟsᴛᴇʀ2 Oct 26 '18 at 11:22
  • @Pᴀᴜʟsᴛᴇʀ2 That's probably true, but a little's still better than none. When changing the oil, the engine was probably running 20min ago so there should still be lots of oil on all the surfaces anyway (probably more than after sitting overnight or for a few days). The best would be an oil pump that could be turned on before the engine, maybe a small secondary pre-start pump... – Xen2050 Oct 26 '18 at 14:36
  • "Probably better than none" ... Since you are going to put most of the oil down the hole anyway, this makes your suggestion moot. It still means you have zero oil pressure for several seconds while the filter fills, which increases wear. Pre-filling, or at a minimum, wetting the filter, will give you far less "dry" time on the engine, which will reduce wear in the end. – Pᴀᴜʟsᴛᴇʀ2 Oct 26 '18 at 14:40
  • I basically suggested doing nothing... Anyway, do you know of any studies showing there is more wear during that ~1 second than compared to a normal start, especially with an already warm engine? It "makes sense" there should be, but maybe the residual oil from the engine still being warm virtually eliminates wear (that's one excuse I've heard for engines that turn off automatically, like at stop lights) – Xen2050 Oct 26 '18 at 15:01
  • And, I would basically say back to you, show me studies which show it doesn't. And, if you haven't looked, it takes far longer than ~1 second for the oil light to go out during first startup after oil change ... and that's with filling the oil filter. To think there isn't an issue with excess wear during this time is foolhardy at best. With that, if you'd like to discuss this further, we can pick this up in The Pitstop. – Pᴀᴜʟsᴛᴇʀ2 Oct 26 '18 at 15:23
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If you can prime it, you should. I mean, if the filter sticks out sideways, there is just about no way to prime it and not make a mess. I have a car where I have an element filter which goes in the top of the engine. There is no way to prime it (as the oil would just run back down into the engine anyway). The reason you prime it is to try and minimize the amount of time the engine is ran without oil. The shorter the better (obviously). Always make sure you put new oil on any seals which are on the filter as well. This will help for a proper seal.

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    To minimise mess but maximise priming I add just enough oil saturate the medium e.g. start with 2cm deep and roll the filter around, all enough time to be absorbed, then add more etc. If you get it right you can screw on the filter before oil seeps out. – Warren Hudson Jan 11 '15 at 1:27
  • I thought running an engine dry was punishable by death.... why then do the makers not suggest priming? – Warren Hudson Jan 11 '15 at 1:31
  • @WarrenHudson Remember that normally most of the oil will have pooled in the sump anyway, so many parts of the engine start dry no matter what. If you ever get a car with an oil pressure gauge, you may be surprised at how long it takes to reach operating pressure. It's only seconds, if that, but the engine is definitely started! – Dan Jan 12 '15 at 12:17
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    Yes, the advantage of priming is small but it IS significant. Unlike the mechanics, I let the oil drain for an hour minimum and often overnight. You would be surprised how much more you get out (I once measured 300ml.). When you prime you add just enough to saturate the filter medium and rotate/tilt to do so, then there is no mess when attaching. I believe the fresh oil goes directly to the filter before anywhere else so priming minimises the dry start effects. There's a term for this and it is "best practice" and it is one reason I do my own all changes. – Warren Hudson Oct 26 '18 at 9:05

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