Why to use CAV diesel filters?

[Markus]

Winter seems to be long and there's time to think so here it goes:
Why do we use CAV-type of filters as pre-filters and not the similar screw-on-filters as the engine fuel filter (Delphi HDF496 and like)? I believe changing the CAV pre-filter to such a screw-on-filter would have the following pros:

• Much quicker to change if needed underway
• Much easier to change without spills
• No separate gaskets to loose, misalign, etc
• Air leaks less likely due to reduced amount of sealing surfaces and parts
• One less spare part to carry as both primary and secondary filters would be identical

cons

• Cost: maybe 2 eur more per piece... 
• Cannot think of anything else

Some people switch from CAV to Racor at a huge expense whereas the mounts for M16x1.5 threaded filters are maybe 15 eur.

Thread is now open for comments! 

[sy_Anniina]

Secondary filter is more 'coarse' like 10 microns or so while the  primary filter is finer like 2 microns. Like the idea but still 2 different spares to carry.

BR

Tommi
s/y Anniina

[Yngmar]

Our Chinese copy of a Racor was cheap and is still doing fine after a couple years. These make it very simple to change filters (without having to drain the fuel). Last time I stocked up filters they cost about €7 each. Seems an obvious choice. Some also have two installed with a switchover valve.

[Laysula]

Just swopped mine for a spin on filter for those exact reasons. I also made sure that the filter head incorporated a priming pump to make bleeding easier.

[Salty]

If I’d kept my boat instead of selling it, I would definitely have removed the CAV filter. The Chinese copy of a Racor filter, as Yngmar has mentioned is of a simple design where changing the filter element is very easy, and which with very little effort on the operators part allows the filter element to be withdrawn and changed with almost no risk spillage of oil into the engine compartment. The filter element comes out through the top of the device which makes life easier than the CAV filter where the element fits into the bottom, and with only one seal rubber to change there is far less risk of diesel fuel leaking into the engine bilge area. Indeed, I made up a fuel polishing system using one of those Racor style filters, and fitted it with its own pump into an old rectangular motorcycle pannier box I had. The box had its own carrying handle, so that it was easy to transport to and from the boat which was lifted ashore each winter. Once there the fuel onboard would get several days of polishing before the start of the next season.
With no boat now, the polishing system is surplus to requirements.

[Markus]

Secondary filter is more 'coarse' like 10 microns or so while the  primary filter is finer like 2 microns. Like the idea but still 2 different spares to carry.

This is usually the case, but I am not sure if there is really any benefit to it? So why not just use "2 micron" identical spin-on filters for both?

Our Chinese copy of a Racor was cheap and is still doing fine after a couple years. These make it very simple to change filters (without having to drain the fuel). Last time I stocked up filters they cost about €7 each. Seems an obvious choice. Some also have two installed with a switchover valve.

I assume you mean something like this: https://www.aliexpress.com/item/33011720348.html
That's probably also a good choice. The very slight reservation I have for this type is that it's still a bit more complex than the spin-on filters and it's one more filter to have on stock. It also has the glass bowl and some other parts that may break with really bad luck, although that glass bowl gives also means to visually inspect fuel which is a bonus. And with that kind of price carrying even a full spare filter housing is not a problem... Will have to reconsider this option as well 

I should have probably added a photo to my original post, but I was thinking of just a simplest possible filter head like this, capable of taking the same type of filter as the engine spin-on filter. I suppose it does not get more simple than this, although you loose the glass bowl as means of inspection.

https://www.aliexpress.com/item/4001107907520.html

[tiger79]

I should have probably added a photo to my original post, but I was thinking of just a simplest possible filter head like this, capable of taking the same type of filter as the engine spin-on filter. I suppose it does not get more simple than this, although you loose the glass bowl as means of inspection.

The glass bowl on a CAV filter contains filtered fuel and any water which has settled out in the filtration process.  There shouldn't be much (if any) water, so inspection isn't going to tell you much.

A spin-on filter has advantages in that it's quick and easy to fit, and has no separate O-ring seals to worry about.  If you fill it with diesel before fitting it, there'll be minimal bleeding to do.  If you buy a filter head with a built-in primer pump, the whole process will be easier.

[PEA-JAY]

Nothing will convince me to change from the CAV 296 setup on my 39C. I have had several years of problem free use on different boats thanks to this trusty filter. Do however beware of cheap replacements. I buy only Delphi brand filters.
Spill free replacement is just a matter of planning, unscrewing the unit from the engine compartment wall which gives full excess. Just prepare a bowl to receive the unit once you have dismantled it and the job can be completed in the galley. Afterward the diesel goes back into the tank!

[Salty]

In my opinion, the advantages of the Racor system are as follows:-
1. the only part that needs to be undone in order to change the filter within, is the top cover, one T shaped screw that can be opened or tightened with fingers only, no spanners needed, and only one rubber seal to replace, (comes with the new filter).
2. with the top cover removed, fuel spillage is unlikely to occur because the rest of the filter body below the top cover remains liquid tight.
3. removing the filter can be done easily by gently withdrawing it upwards allowing the fuel within the filter to drain down into the main body of the device, so no spillage.
4. unlike the CAV filter which requires both hands to remove and replace its various parts while also trying to support yourself within the side entrance to the engine compartment, with the Racor filter system gravity actually works with you rather than against.
5. In regard to the sight glass on the Racor filter, it is actually plastic, so whilst it could arguably become broken, one would have to be particularly ham fisted to achieve breakage.
6. the sight glass like many other filters allows the user to see if there is any water accumulation within it, same as with the CAV filter and like that filter, water to be drained off using the drain provided One of the filters suggested in the previous responses does not have the benefit of a sight glass.
7. once the filter has been changed, unless the bowl has been partially or fully drained, then the filter will have remained full of fuel on completion of the change. This then eliminates the need or expense of looking for a filter system with a pump, or fiddling around with the manual fuel pump on the engine. (I never needed to use the manual pump anyway as there was always enough fuel in either the primary or secondary fuel filters to get the engine up and running again). In the event that the filter body had been drained or partially drained, because the last piece to be put back in place is the top cover, the bowl can simply be topped up with fuel from a jug before the lid is put back on and secured. With the filter full of fuel and the lid screwed back down, no further priming in regard to that filter is needed.
The only negative point is that the Racor system is marginally larger than the CAV. As for the number of different types of filters carried as spares onboard, I started off with three, and whether I had a CAV or a Racor filter I would still have only three different types of filter, so nothing gained there or lost, and the whole job done without a spanner in sight unless draining from the bottom take off point is needed.

[JEN-et-ROSS]

Having read through these comments I'm now sold on the Racor system, it's far easier.
 So I've ordered a Racor to replace our old CAV, a Chinese copy yes, but they do look well made and since many expensive established brands are often made in China anyway and only then do they acquire the brand 'Logo' and a colossally high price required for OEM parts.
 So, In my opinion there's a good chance they're made in the same place.
A good example of this is an EGR valve I recently replaced on my wife's MX5. (A horrible job as the little bugger was mounted low down at the rear of the engine, about 2mm from the bulkhead)
Mazda wanted £150+.
A 'Chinese copy' from eBay was £27, So I thought I'd take a chance...
When I compared the old duff one with the new it was perfectly plain they had been made in the same factory.  ..QED

[Markus]

Good input from everyone! I tried to distill all of this into a table below to allow for comparisons.

	CAV	Racor	spin-on
Cost of filter housing / eur	20	200 (OEM) / 30 (copy)	20
Filter availability	excellent	good	excellent
Cost of OEM filter / eur/pc	5	15	7
Inspection possible (dirt)	no	yes	no
Inspection possible (water)	yes	yes	no
Ease of changing filter	poor	good	good
Tools required	yes	no	no
Risk of air/diesel leaks	high	low	very low
Needs bleeding	yes	no	yes

*spin-on refers to Delphi HDF496

I think based on the comments from Yngmar & Salty I am starting to slightly prefer the Racor system over spin-on filters.