Follow Up Question on Diesel Pre filters

Submitted: Wednesday, May 28, 2014 at 09:10
ThreadID: 107983 Views:3235 Replies:7 FollowUps:14
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Hi All,

A follow up question on the recent discussion on secondary filters on new CRD Diesels. I get the pros and cons of placing the secondary filter before or after the factory filter so don't want to revisit that discussion as it was well covered in the recent posts.

I have a Stanadyne FM100 pre filter on my Ranger. The factory filter is, I believe, a 20 micron filter with alarm.

Is there any issue with me running a 5 micron size filter in my pre filter? i.e. a pre filter smaller in size than the main filter. Some posts seem to suggest the pre filter should be a larger size than the main filter resulting in progressive filtering as fuel moves through the system.

I realise that using a smaller filter as a pre filter could pretty much make the factory filter redundant but my aim is to get the benefits of a 5 micron filter without having to deal with the disadvantages of installing a filter after the factory filter.

Any thought would be appreciated.


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Reply By: Member - Frank P (NSW) - Wednesday, May 28, 2014 at 09:25

Wednesday, May 28, 2014 at 09:25

One issue with using a finer filter either before or after the factory filter is the possible effect on fuel flow. The engines do not like the flow to be restricted. If you go this way you need to find out what capacity (in litres per hour) filter you need.


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AnswerID: 533299

Reply By: Ross M - Wednesday, May 28, 2014 at 10:58

Wednesday, May 28, 2014 at 10:58
Peter F9
I doubt very much that your factory Ranger filter is 20 microns in size.
For a CRD engine it is hardly worth having a 20 micron as that will allow contaminant sizes which will destroy the system quick smart.
It is more likely the OE filter is around 5 micron as is the Dmax and others, some a bit smaller.

If you draw a circle of eg, 20mm then you can draw many 5mmdia circles in that circular space with gaps in between. So 20micron NO. I would be surprised if it is.

Thinking of the circle sizes, that is the sizes the contaminants get through, so if the size is smaller, and with some filter clogging happening there will be smaller gaps for the rate of required fuel flow to get through without significant restriction.
Therefore as the filter you choose is smaller in micron size, you have to have a corresponding increase in filter medium area size, so no significant restriction is going to occur.
As the finer, more efficient filter is being used it will hold rubbish and begin to restrict. Without sufficient area it will soon restrict and have you, for ever changing expensive filters.

Filter life, usage time/km, contaminant loading/catching/essential flow rate are all items worth considering. Anyone who recommends a filter for a purpose should have a full grasp/understanding of the variables and essential requirement.
Nearly all sellers of that stuff do not know much about them. Only "this is the one we sell" and it is good, take my word for it.

Choose one which fits your purpose and also make sure it is also a Dewatering filter to catch emulsified water, without that you are basically wasting your time as water WILL get into the system. We are trying to minimize the chance of that happening, aren't we?

The bigger the filter area you choose means the flow rate is better and the actual filter membrane flow rate is slower and therefore allows for more chance to catch rubbish and dewater at the same time, instead of hurrying through the filter.

5 micron of a suitable flow and area will be ok. At least 140L/h min, bigger the better.

This applies whether it is before OR after the OE filter.
AnswerID: 533307

Follow Up By: Peter F9 - Wednesday, May 28, 2014 at 11:29

Wednesday, May 28, 2014 at 11:29
Thanks Ross, good comments. Yes both filters have dewatering filters and bowls. A follow up question on flow rates. Is the flow rate requirement affected by having two filters in line? Say for example the Ranger requires a 140L/H flow rate. Would it be sufficient to have both filters rated at 140 or do I need to go higher because I have two in sequence? Thanks P
FollowupID: 816638

Follow Up By: John and Regina M - Wednesday, May 28, 2014 at 11:31

Wednesday, May 28, 2014 at 11:31
My new Triton standard filter is 10 micron with water alarm.
I have added a 2 micron after it.
FollowupID: 816639

Follow Up By: Peter F9 - Wednesday, May 28, 2014 at 12:56

Wednesday, May 28, 2014 at 12:56
Trying to find out what micron size is in the OE Ranger filter has been interesting to say the least! My Ford dealer has no idea! Would anyone know the micron size of the standard Ford Filters in the 3.2ltr PX Diesels? Thanks P
FollowupID: 816642

Follow Up By: Ross M - Wednesday, May 28, 2014 at 13:55

Wednesday, May 28, 2014 at 13:55
Peter F9
Two filters in series will of course add some restriction, BUT, since the effect will be minimal and less than a clogged filter anyway it shouldn't affect the system at all because it is still within it's operating parameters.
However, if the additional filter is before the OE filter and also bigger flow rate than the OE, then the restriction effect would be even less noticeable.

Johns & Reginas filter , being 2 micron is good to have but it has to be of a flowrate/area which doesn't affect the normal flow rate. If it will block with the stuff that goes through the stated 10 micron OE filter if sufficient hits it.

All these systems have to have a flow rate to supply AND also to provide adequate cooling flows for the High Pressure pump. You can use a small filter but it won't pass the cooling flow required in addition to the usage flow.

If you ever get a restriction indication, then the cooling flow aspect has been compromised for a period of time/KM before the alarm.

With the 2 micron after the OE it is a good thing BUT, you will only get a restriction sensing if it is the OE filter blocking.
If the New filter is restricting, the first indication you will get of a restriction, is if the engine doesn't want to work well as that position negates the OE restriction sensing the new one is blocking,
FollowupID: 816647

Follow Up By: Peter F9 - Wednesday, May 28, 2014 at 14:03

Wednesday, May 28, 2014 at 14:03
Yes Ross I tend to agree which is why I'm not looking to put a new filter after my OE filter. I want the OE blockage and water sensors to work as intended, as you suggest.
FollowupID: 816649

Reply By: Brian - Wednesday, May 28, 2014 at 13:03

Wednesday, May 28, 2014 at 13:03
gday Pete ,
i'm no expert on this but thought i would add my two bob's worth , is it worth fitting a 1 micron filter ( toilet roll type ) still utilising your standard filter ?? I have heard of them being used on diesel trucks for fuel as well as for the oil , with them being used on the oil they are a bypass system , but not sure with fuel as someone has pointed out the flow rate is important .
Not sure what state you live in but Jupiter Steel in either Palmyra or Myaree WA are agents for them ?
Would be interested to hear from other forum members or guests who have have one fitted and if so where it is fitted ??
Good luck mate
AnswerID: 533310

Follow Up By: Peter F9 - Wednesday, May 28, 2014 at 13:42

Wednesday, May 28, 2014 at 13:42
Thanks Brian, very good point. I'm starting to think that it may be better, as you say, to try to run a finer filter element, (2 micron or so as John above suggested) in the OE filter and keep the pre filter at 10micron or so - provided I can get the appropriate flow rated filters.

I'm having difficulty finding out if there are different filter elements available for the OE Ranger Filter or for that matter what the standard OE filter element rating is!.

For what its worth Stanadyne literature recommend a 30 micron pre filter and 5 micron primary.
FollowupID: 816646

Reply By: Emerging I.T. - Wednesday, May 28, 2014 at 14:21

Wednesday, May 28, 2014 at 14:21
Pre Filter should always be larger than the final filter. I had 2 micron to 2 micron on my Cummins diesels on my boat, I inherited it that way. Changed to 10 micron pre filter and kept the final filter as 2 micron. I had various diesel mechanics implement this as standard practice. I think Marine filtration is slightly different but the same principles apply. I am a bit out of the loop as to what people are using on their 4x4's however and would like to know what specific filtration has been developed for 4x4's or people who are often susceptible to dirty fuel. We encountered this once on a boat trip to King Island, we re-fuelled there and suffered power loss on our trip home which was when it was discovered our filtration was not set via best practices.
AnswerID: 533315

Reply By: bluefella - Wednesday, May 28, 2014 at 14:54

Wednesday, May 28, 2014 at 14:54
I would suggest a 30 or 20 micron as the pre filter. I think the primary job of the pre filter is to catch the larger stuff and more importantly to trap any water allowing for a early alarm before the primary, letting the primary filter do its' job of catching the fine bits. this way you can be sure there is no restriction in fuel supply.
AnswerID: 533317

Reply By: Member - Leigh (Vic) - Wednesday, May 28, 2014 at 16:48

Wednesday, May 28, 2014 at 16:48
Hi Peter, I consulted a diesel specialist whose company does rebuilding of pumps and injectors etc. He advised me not to go below 30 micron. For me I use a CAT filter that is rated at 150 micron (basically a bag in the canister) but I use it primarily for its water separation ability and have connected an alarm. I too was concerned with limiting flow but concluded that the factory primary filter was good and safe enough to filter the end product. I just want to avoid water like my life depends upon it!! hope this helps? Cheers
AnswerID: 533325

Follow Up By: Ross M - Wednesday, May 28, 2014 at 17:48

Wednesday, May 28, 2014 at 17:48
Leigh (Vic)
That diesel specialist advice is in stark contrast to many other diesel specialists. Since a 60 series Toyota has a filter of 30 micron as OE, the belief is: For CRD far smaller is better as a prefilter ie 5micron to 10micron so it still strains it and the particles which get through it are many times smaller. A 30 micron will let through a vastly larger cross section sized piece of dirt than a 10 micron will. The ratio isn't 3 to 1 as initially thought. How many 10 sized holes can you fit in a 30 sized hole????

If you have a large micron pre filter and the OE becomes damaged etc, the size coming through a 30 micron will total the fuel system and provide no insurance at all.
Not a sound piece of advice at all IMO. it is only my opinion.
FollowupID: 816661

Follow Up By: Member - Leigh (Vic) - Wednesday, May 28, 2014 at 19:40

Wednesday, May 28, 2014 at 19:40
Hi Ross, thanks for your response. My objective of separating water, whilst not impeding fuel flow, and providing an earlier alarm against water have been met by my system. Filtering is not my primary concern, I'm happy for the OEM filter to perform that final duty on my CRD Prado.

As for the "60 series" and my 6cyl Troopy these appear to be more tolerant of poor fuel and in any event injectors are relatively cheap when compared to CRD/Direct injection. I am happy with the OEM set-up on the Troopy (it has a pre-filter as standard) and it is only serviced according to the Toyota maintenance schedule with OEM parts. I think we are looking to achieve different outcomes.

Your suggestion that my earlier comments are, "not a sound piece of advice" is probably deserving of a polite retraction. Cheers
FollowupID: 816675

Follow Up By: Peter F9 - Wednesday, May 28, 2014 at 20:36

Wednesday, May 28, 2014 at 20:36
Thanks Leigh, your probably close to the money for my requirements as well. My Diesel mechanic and Stanadyne say the same as your diesel specialist and Stanadyne should know given they are an OE supplier of injectors and pumps to a lot of the big machinery and auto companies.
My worry also is with water so I think a good 30 micron pre filter with water extraction capabilities is what I'll go with and let the OE primary filter do its thing on the rest.
Having said that I will not be doing much very remote stuff where I will be at higher risk of contaminated fuel. If I was I think I would go down Ross' route with a heavier duty system.
Thanks everyone for their comments much appreciated.
FollowupID: 816678

Follow Up By: AlbyNSW - Wednesday, May 28, 2014 at 20:51

Wednesday, May 28, 2014 at 20:51
Peter there are just as many incidents of contaminated fuel in the built up areas as the remote suppliers
Also do you have a warning buzzer on your FM100? I think that is an integral part of the system
FollowupID: 816679

Follow Up By: Ross M - Wednesday, May 28, 2014 at 21:00

Wednesday, May 28, 2014 at 21:00
Some people are reporting their diesel specialist says a 2 micron is ok, other say, apparently a 150 micron is ok. Still others mention 30 is ok.

Still, if you allow for the restriction with a suitable capacity filter I would imagine water will tend to romp through a 150 micron filter quite a bit easier than a 5 micron one asked to be also dewatering.

I agree with Odog, what do people believe?

Most systems are meant to be doing a job.
Stanadyne seller a pushing 2 micron filters.
150 micron will ensure plenty of large stuff gets to the OE filter, thus reducing the insurance you have.

I don't think all the diesel specialists are reading off the same page. They can't be with the wide variety of possible solutions they are suggesting to people.
Some are good suggestions and others aren't.
I still think some advice is poor and leaves the owner at greater risk than necessary. A situation which is easily rectified.
FollowupID: 816680

Follow Up By: Peter F9 - Wednesday, May 28, 2014 at 21:35

Wednesday, May 28, 2014 at 21:35
Ross I hear what your saying and respect your view. I understand the issues involved. Sure smaller filtration is better but to me it becomes a game of diminishing marginal returns. For my application, and I stress its only my application, a 30 micron pre filter and 5min primary filter will get me 95% the way I want to go. And its sure better than the OEM solution only.
Sure added smaller filters may be better but then again I could put 10 filters on and not get 100% protection. So it becomes a call based on cost vs the diminishing extra benefit vs the risk of contamination. And yes, as Alby points out, I could get a bad batch of fuel in suburban Chatswood, Sydney. But again the risks are lower than filling up on the Canning from a rusty drum thats been sitting in the hot sun and cold nights for a month. And I won't die getting home from Chatswood station!
If I was setting my vehicle up to tackle the Canning then it would be a different matter and, as I said above, I would look at a different system.
Lets not turn this thread into another "all experts are idiots unless they agree totally with what i say" as often happens on this site.
The fact is that there is a range of opinions that are equally valid and its up to the individual to decide whats right for their particular situation.
Thanks again for everyones advice.
FollowupID: 816685

Follow Up By: Member - Phil G (SA) - Wednesday, May 28, 2014 at 21:43

Wednesday, May 28, 2014 at 21:43
All the sellers I came across are pushing the 30 micron filters in the FM100.
I agree with Leigh, I view the prefilter as merely a water separating device where the water sinks to the clear chamber and is easily seen and drained.
FollowupID: 816686

Reply By: Member - Odog - Wednesday, May 28, 2014 at 16:50

Wednesday, May 28, 2014 at 16:50
I'm not that mechanically minded, but have the water watch fitted on my 150 prado, but think maybe better to have a filter/dewater type instead/in place of the water watch, I have heard they are good for there purpose, and it was recommended to me, but who really knows?
Have also heard of running 2 fine filters side by side, as in splitting the fuel flow to over come the restricted flow rate? What do you do? Too many options, one says this, someone else says that...
Should maybe by a pushy...
Cheers. Odog
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AnswerID: 533326

Follow Up By: Ross M - Wednesday, May 28, 2014 at 18:28

Wednesday, May 28, 2014 at 18:28
I think you have to get past the hype and the marketing of these things and purely concentrate on what works best for a CRD engine.

Fine is good but must have is big area/flow rate for less restriction.

WW is great and sensitive but doesn't stop water. just warns and you do the saving of the system if caught in time.

2 filters in parallel is more effective for flow, crap catching and dewatering and sump catching than a single, but is more expensive.
Not so costly as you think, if you use some Local brand names.

Some diesel and 4wd house people, sell what they want to push at shows. Worst place to buy a filter because it is unlikely you will get an informed person or one who won't sell it to you if it doesn't suit.

A Filter on the Camel Back water bag is good if using a pushy though.
FollowupID: 816665

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