Primary and Secondary fuel filter question

[dhays]

Hi All,

I've searched a bit and couldn't find any consensus on this.

I have a Yanmar 4JH4AE engine. The Yanmar has a spin-on 10 micron secondary filter on the engine. As installed by Catalina, it has a Racor 500FG filter as a Primary filter using a 30 micron filter. Yanmar recommends replacing the secondary filter every 250 hours or yearly.

There has been some discussion among C400 owners as to whether a 10 micron primary filter would be better than the 30 micron primary filter. This raised a question in my mind and since I'm completely ignorant about diesel engines, I thought I would ask here.

It is possible to put a vacuum gauge on the Racor filters to determine when the filter element is getting clogged enough to warrant replacing. The idea is that when the vacuum pressure reaches 7-10 mmHg, the filter element is providing enough resistance to fuel flow that it should be replaced. This allows you to only replace the filter when it actually needs replacing rather than doing it every 250 hours or yearly.

That sounds fine and dandy, but if the Racor is only filtering down to 30 microns, that doesn't tell you much about the state of the secondary 10 micron filter. This means that you would still be faced with the task of replacing the secondary filter yearly or every 250 hours since you don't know how many particles under 30 microns passed through the primary filter.

So, what about putting a 10 micron filter on the Primary? This would mean that your primary filter is doing most of the filtration work. If you had a 10 micron filter as primary and a vacuum gauge to tell you when to change it, in theory you would only be changing the primary when it needed it. You could change the secondary as well at the same time, but likely it would really need it then since the primary was doing most of the filtration anyway with the secondary acting only as backup.

Really two questions.
1. Is there any advantage to using a 10 micron primary instead of a 30 micron primary?
2. What actual utility is there in using a vacuum gauge to tell when the primary filter needs replacing?

Dave

[chef2sail]

We have the same 10 micropn secondary and 30 micron racor primary set up as you on our Yanmar g30f. The 10 Micron filter if used as a primary will be too small and will get clogged very frequently as we have tried that before. We have a vacum gauge on the 30 filter, but I still change the filter every 50 hours or so as its quite simple and only takes about 2 minutes and doesnt require the whole system to be primed. We do change the secondary 10 micron every 200 hours, but honestly it has been pristine every time we have.

My philosphy is that the small amount of money spent on filters is worth it so as not to have larger prolems later so what I do may be overkill, but it has worked well on a 28 year old engine so far.

Dave

[dhays]

Thanks for the feedback Dave. I agree that the Racor is really easy to change.

If you replace it every 50 hours, what does your vacuum gauge read before you change it? Just curious.

If the 10 micron filter clogged up quickly as a primary, doesn't that mean that the secondary is getting clogged quickly as well with a 30 micron primary?

Dave

[chef2sail]

Doesn't seem to choke off fuel or clog when weuse the 30 like the 10 does. We read 9/10 on the gauge
Dave

[noelex77]

I thought the 4jh4ae had a 2 micron secondary filter.
Anyway I have a 10 micron primary without any problems

[noelex77]

Originally Posted by chef2sail

Doesn't seem to choke off fuel or clog when weuse the 30 like the 10 does.
Dave

That means that the junk that used to clog the primary filter is now cloging the smaller secondary filter or worse getting into the injectors.

[dhays]

Originally Posted by noelex77

I thought the 4jh4ae had a 2 micron secondary filter.
Anyway I have a 10 micron primary without any problems

For some reason I had thought that the filter was a 10 micron filter. Now I can't find any reference that indicates what the filtration is for that filter. You could easily be correct. If it is a 2 micron filter, I would be even more tempted to go to a 10 micron primary filter.

[noelex77]

I am relying on memory as well, but I think 2 micron is correct for the secondary. There has been a lot of discussion in previous threads about the ideal primary micron filter size. The consensuses IMHO seems to be 10 micron with a small and approximately equal number of supporters for 2 and 30 micron.

[charisma94]

I have a 4JH2CE with a 10micron primary RACOR & a 2 micron secondary on the engine. I'm pretty consciencious with tank cleanliness however. Watery & sludgie tanks would be an issue with the 2 micron. Clean your tanks and go for the finer filters, your engine will love you for it! IMO 30 micron as way to big, small marine diesels don't want to be more than 10 micron.