So, tonight I changed the oil in my 951 in preparation for winter storage... *sigh*. I also fixed my power steering. I have been driving without that for 6 months. What a pleasant change that is!!!
Anyhoo, I have been having intermittent problems with no oil pressure on startup. Sometimes the gauge will register pressure quite quickly, but I will hear lifter clatter for 30 seconds or so, sometimes the gauge will be slow to rise (and it sounds like I have no oil pressure, so it's not an electrical problem). The worst case of which it took almost a full minute for oil pressure to build. I was midway through s***ing my pants that time. Anyhoo, when I fired it up to pull it into the garage (it was already warm from a long drive immediately prior), I noticed lifter clatter again. Not good. After removing the oil filter, I find the check valve to be jammed about half-way into the oil filter, cocked at a very severe angle.
This was on a Mahle filter, not an OEM porsche one. Usually I have been using OEM ones from the dealership on the 951, but I only had this one left-over, so I gave it a shot. It was a short OCI anyways (~600 miles).
I don't know if anybody has ever had this happen before, but I was absolutely shocked. I have no doubts in my mind that this was the source of my oil pressure problems.
Has anybody ever had the check valve fail in a Mahle (or an OE one for that matter) before?

The filter was completely dry, and dribbled virtually no oil. Despite having been run about 20 minutes prior (fixed the power steering and drained the oil cooler before I pulled the filter). This may have been a function of the tilt the car was on (driver's side was jacked up ~1 foot), since the drain from the filter is on the passenger side, but I suspect this was also due to the check valve.

That said, the engine sure starts a LOT better with some Mobil 1 10W30 in there instead of castrol GTX 20W50 (for breaking in my new rings), and it drives so much better with the power steering connected. No matter what people say, a car with a power rack just doesn't feel right without the pump being driven. I've driven enough cars with manual steering racks to know how they should feel.

 

Sounds like a good case for using that stock filter. Always seems a few more bucks than others that fit, but that's for the valve, I figure. Better if it works!

Setting the way-back machine...

Years ago I rebuilt the engine on my Riviera. In the process I threw out the air injector pump and the bracket for it. Oops. That held the PS pump. For two years I drove that massive beast with no PS. Actually felt new upper-body muscles develop. Finally fabbed something and later scored the correct bit off eBay.

 

Any chance you can take a picture of what the check valve look liked? Im kinda interested in the mode of faliure on it.

 

I have, and I have written about it here in the past and everybody here acted like I was a retard. I was going to write it off to the fact that at least one time when it happened with a Mahle filter it was one for a 928 which supossedly doesn't have an anti drainback valve like the ones for 944s. But at least one other time I had the same problem (dry start) and it was with a standard 944 Mahle filter. I have NEVER had the dry start issue with a Mobil1, Fram, Purolator, STP or K&N branded filter, only with the Mahle and that stupid C&M cartridge filter unit I tried a few years ago. BTW, the Porsche filters you buy at a dealer are marked "Made in the US" and are most likely made by Champion, who also makes the STP filters.

 

Dude, No "supossedly" about it; 928 filters don't have drain back filters. They mount from below and stay full naturally.

 

Makes sense to me. I didn't bother to look or cut it open and check. It kind of annoys me that some online retailers used to sell these to the 944 crowd based on the extra filter capacity. I'll have to check my receipts to see how many of the standard 944 Mahle filters I have used to this point.

 

i too have heard that about mahle filters, which is a shame because ive always heard they are a good filter to use.

 

Here's a couple of pics for reference as I happen to have a few brands of filters on my garage shelf. They all have a check valve, each one a little different in design. Not evident from looking at them which ones perform better.

 

Check valve and anti-drainback valves are not the same thing. Check valves are there to allow a bypass so oil can still flow if the filter media gets completely clogged. This prevents dangerous high pressure inside the filter housing as well as allowing continuous oiling of the engine internals. They are usually spring loaded in some way.

An anti-drainback valve is included in filters for cars were the installed filter is oriented in such a way that the oil would drain back out of the housing and allow dry starts if the valve was not there. They are usually a simple flapper ring of some sort of rubber.

In that picture, the anti-drainback valve is barely visible through the outer ring of perforations in each filter. The check or bypass valve is visible through the center

 

Actually, the anti-drainback is there to keep oil in the passages, and not flow back to the filter. And the check valve in the oil filter has no DIRECT affect on oil pressure ie. it does not regulate it, as said before it just by-passes the filter if it becomes clogged.

Mark

 

I think it depends on the orientation of the installed filter. On our cars it helps keep the filter primed and, as you elude to, holds a bit of a lock on oil already in the oil passages.

It was pretty easy to see what a bad anti-drainback flapper looks like on the C&M filter housing. The heated oil would cause it to take a set over the first couple hundred miles and it would never seat sealed again once set. I suspect that is something that also happens on some of the Mahle filters that go bad.

 

Our cars have the bypass valve (aka relief valve) in the oil cooler assembly. The flaps and center valve are both to keep the engine primed and the filter full.

 

I wish I could take a picture, but I threw the stupid thing out due to pure disgust. I will not use another Mahle filter unless it is a life or death situation. The valve in the middle was jammed most of the way up the filter, and twisted very severely. I'm fortunate that it didn't destroy the filter media, and cause some collateral damage.

Interesting side note. Going from Castrol 20W50 conventional to Mobil 1 10W30, I actually have higher oil pressure. This was completely unexpected, but I understand why. It seems to be from the reduced friction of using a thinner oil. I believe this is a good thing. Also the car idles so much smoother, and revs much more freely when cold. Amazing the difference the proper oil can make.

 

That sucks. I have always used the mahle filters. What a bunch of bull****. Especially since it is such a pain in the *** to do an oil change on our cars.