cat fuel filters

Genesis said:

Just stick a vacuum gauge inline with the pump (after the filter.) Trivial, and inexpensive.

Racor rapes you because they make things for the "marine" market, where the usual is to screw you to the tune of at LEAST 300%.

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Thanks Genesis -- good idea. Yeah, I used to live on my sailboat and everything was an order of magnitude more expensive once labeled "marine."

Not difficult really. Most diesels (TDIs are not an exception) flow enough fuel with return that irrespective of the power level the restriction doesn't change THAT much. If you're in trouble filter-clog wise you'll see it even at idle.

Genesis said:

Not difficult really. Most diesels (TDIs are not an exception) flow enough fuel with return that irrespective of the power level the restriction doesn't change THAT much. If you're in trouble filter-clog wise you'll see it even at idle.

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Well, interestingly, in this case, I didn't feel it at idle. Pretty much only on relatively aggressive acceleration and with a limiter-like bog down around 3K RPM in all gears.

I'll be interested to see how things go with the rest of this tank of fuel. I hope I don't have to drain it!

Yeah, that's how clogs like that work -- but you WILL see it if you have a vacuum gauge. Trust me on this one -- owned a fairly large diesel-powered boat for quite a while, and although the engines would idle fine and run under low power, you still could easily tell there was trouble if you looked at the gauges.....

I have my Cat filter running after 36K miles. No problems yet.
But the clear prefilter shows junk in it. I imagine smaller particles are caught in the CAT filter.
I used biodiesel, but some of my containers had bits of leaves, stuff like that.

I am also using some old kerosene to cut the biodiesel and to extend the fuel...
So I will use it for a while, then change out the CAT filter.

Will report how it goes.


ON a side note, I used to work as lab manager for major oil lab. I actually climb all sorts of oil company farm tanks, large and small, large oil cargo ships, and one thing I can tell you, is that the bottom of tanks of all cargo tankers, delivery trucks, tank farms, large mixing tanks, etc, is a layer of mud, sludge, water and leaves and other unknown contaminants.

Good thing most oil companies pre filter the fuel a bit, but again, the filters themselves are sometimes dirty, and minor contaminants do get into gas stations/ diesel stations.

Remember, the bottom of those tanks have sludge and water, so find out when your fave diesel station gets fresh diesel, and fill up about 2 days after delivery. You dont want to fill up immediately after delivery, since the new fuel sloshes inside the fuel tank, and stirs up all the settled dirt and sludge and water , into the new fuel....creating a mixture of poorer quality fuel. Wait a few days for the contaminants and water to settle .

You dont want to use the bottom of the tank , where fuel can be mixed up a bit due to churning and could have some sludge get absorbed into the layer

Reporting back: No further problems and the vehicle continues to run excellently. I don't know that it was the CAT that was clogged -- could very well have been the little clear pre-filter. Regardless, all is well once again in TDI-land. This thing runs like a gem.

I have run my Cat filter just over 180k with no problems. When I changed it out I put it in service in my garage furnace (still there now) I have a vacuum gage on it and there is less than 3in of vacuum.

I think that the data shows that these filters would last a long time in our cars. My biggest concern, however, is with water collection. Jay, it would be instructive to find out how much water has been trapped in that filter.

UhOh said:

I think that the data shows that these filters would last a long time in our cars. My biggest concern, however, is with water collection. Jay, it would be instructive to find out how much water has been trapped in that filter.

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I changed my first CAT filter after almost 100k miles. I found no water and virtually no visible contaminates either. Considering that I burned some rather "questionable" old fuel when I first installed the CAT filter I was surprised.

Hadn't really been concerned with water until I discovered that, for some mystical reason, one of my tractors seems to be (it's relatively new) a water magnet: fortunately it has a sensor AND a drain. Although water isn't good for any diesel it's especially bad for CR ones.

It would seem I was mistaken about the 180k miles on the filter. I checked my maint records and had put that filter on shortly after I bought the car in 2010 at 71k and did not change it until 3-2016 at 321k. That's 250k miles on the filter. I don't remember any water in the filter when I changed it. I couldn't believe I left it on that long but I had bought 4 filters years ago and still have 1 left on the shelf (1 was used in my previous Beetle).

In my other three TDIs I had left the OEM fuel filter system in place and changed those in a more timely manner. In between changes, during oil/filter changes, I would open the water collector drain valve on the bottom of the fuel filter. Never got any water out of any of them in an amount that was detectable, nor was there any found at the end of their service life upon dissecting them. Apparently we get pretty decent clean fuel around here most of the time.

jayb79 said:

It would seem I was mistaken about the 180k miles on the filter. I checked my maint records and had put that filter on shortly after I bought the car in 2010 at 71k and did not change it until 3-2016 at 321k. That's 250k miles on the filter. I don't remember any water in the filter when I changed it. I couldn't believe I left it on that long but I had bought 4 filters years ago and still have 1 left on the shelf (1 was used in my previous Beetle).

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Damn dude...that's crazy! I don't know why after running mine a fraction of that, replacing it solved my problem. I can only think that sometimes, one picks up some bad fuel (water?) and it becomes clogged prematurely.

OlyTDI said:

Damn dude...that's crazy! I don't know why after running mine a fraction of that, replacing it solved my problem. I can only think that sometimes, one picks up some bad fuel (water?) and it becomes clogged prematurely.

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That's the purpose of the filter. Most of the time it's probably not needed, but when the random bad batch of fuel gets added it (hopefully) does it's intended job to protect the rest of the sensitive fuel system.
I'm sort of amazed at how "clean" most of the fuel must be. After 100K miles and thousands of gallons of fuel passing thru it there was very minimal contamination/particles visible in my filters. Someone I know well drove their 7.3 Powerstroke 175K miles before changing the fuel filter. It wasn't cut open and dissected, but never caused a clog before being changed. Lots of fuel went thru that thing.

I ordered the cat filter and the filter head yesterday. Micron rating from cat dealer said 1-2 microns. So who is counting? way finer than the VW. On our big commercial fishing boat we use top of the line Racors and they come with a pressure gauge. You note the initial pressure and write it on the filter with the date. Every time you change the oil you note the pressure. When it changes from the initial you put in a new filter. If the fuel was clean we could go years between changes. These were big detroit diesels, 6-71 and 8-71's. If we got a load of cruddy algae fuel we could go hours or days. But the key point was you change the filters when they begin to clog. No need to change sooner. The racors were great because they had clear plastic bowls. If you got dirty fuel with algae or water you saw it immediately. I'd put racors in if I had the room . The cat takes a 1-14 thread if memory serves. Cost was $49 free shipping and comes with one filter. Lots of filters interchange with it, Wix, donaldson , NAPA etc.

Today, I changed my Cat filter , after about 62.000 miles. It was not clogging at all, but It has been 9 years , so I said, waht the hell , might as well.

Poured out the fuel in the old filter, and on the bottom last bit there was sludge, some water, and some rust and brown particles. I do use old fuel and old gasoline and biodiesel and other peoples old diesel, mixed with new diesel,.............

Poured Diesel Purge and some other additives into the new filter, and installed, and immediately started it up, no problems.

I think if you use reasonably good diesel fuel source, a CAT filter will last over 80,000 miles.......or more.