The Stovebolt Site Forums The Shop Area Engine Shop external full flow filter -261

I bought a spin-on Kit from Deve's technet using a WIX 51515 filter and installed it. Everything seemed to be fine last summer when it was hot except that the oil pressure is a bit lower than with the previous engine; about 28PSI compared to 35PSI. I'm also running 15/40 oil rather than 20/50. The engine has a new Melling oil pump and tight bearing clearances, low end of spec. In summer, the oil pressure does not vary much whether cold or hot except at hot idle (250 deg oil temp) pressure is ~15 psi. I interpreted the change in oil pressure to the fact that the gauge connection is on the low-pressure side of the filter so there is the pressure drop across the filter to consider. I'm also running a Franz toilet paper bypass filter in parallel with the gauge connection. Franz paperwork says it has a restrictor.

Now the real head scratcher and cause for concern is that now it's winter (high for the day was 15 and the low was about 5 and it's been like that for 3 weeks now) and it takes more than two minutes for the oil pressure to come up. The gauge shows nothing for 30 seconds or so then slowly creeps up. It seems to me that the filter's bypass valve should open under these conditions and provide flow despite cold oil. I'm assuming this filter has a bypass valve and one spec I found indicated that it filters something like 11 to 15 microns. That's pretty fine for a full flow filter, so I can see where there might be considerable pressure drop with thick oil. But running all that time with no indicated oil pressure bothers me.

Anyone have any experience with full flow filters on Stovebolts? Should I just not worry about it or go to a coarser filter?

A full flow filter on a stovebolt engine is a solution looking for a problem. It sounds like your oil is a bit too thick for the climate, or your filter media is woven a little too tight. At least you also added a bypass filter to clean up the oil efficiently. I'd suggest one oil change using 10W-30 oil to see if the pressure comes up quicker. If so, you need to run thinner oil in cold weather. If you don't want to deal with the hassle of changing the Frantz filter element, spin on filters down to the 1 micron range are available to use in the bypass system. They're normally used for hydraulic fluid or Diesel fuel, etc. DO NOT use a tight weave filter in a full flow application.
Jerry