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ZR-1 ZR-1 ZR-1 ZR-1 ZR-1 ZR-1 ZR-1 Haibeck Automotive Technology
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An LT5 Filter Comparison As published in 1997 It May Be Time For More Than Just A Simple Filter Replacement See the note at the end of this article for the latest filter recommendation dated June 2005 I have discovered that there is a defect in the design of the PF970C oil
filter. The anti drain back feature does not function properly. This becomes
apparent when a used filter is removed, it weighs about the same as a new
filter. When a used Fram TG3985 is removed it is noticeably heavier because it
is filled with oil. If the same filter is cut open adjacent to the base plate,
it can be observed that the outer cavity of the filter, the area between the
filter element and the case, is filled in its entirety with oil. An empty oil
filter requires the engine to run for an additional period of time in order to
fill the filter before oil pressure can be developed. On my '93 LT5 it takes
about 1.4 seconds to refill the PF970C at startup. Average Time Required to Build Oil Pressure to the Center Tick on the ZR1 Oil Pressure Gauge: PF970C 7.5 Seconds TG3985 6.1 Seconds The measurements were made at an ambient temperature and engine temperature of 75 degrees. The timing started when the cranking began. The numbers are averages, based on 10 starts. The oil was 10W-30 Mobil 1. Early LT5s are programmed to have a slightly longer cranking time before the ignition is enabled. The run time with no oil pressure is reduced by about 20% with the TG3985. Over a long period of time, this may result in a significant reduction in engine wear. The quicker oil pressure buildup has an effect on cam chain tensioner noise at startup. With a PF970C filter, I encountered cam chain tensioner noise several times a year. I drive my ZR-1 nearly every day during the summer. The TG3985 reduces the incidence of cam chain tensioner noise to about once per year.. The problem with the PF970C is with the oil anti drain back valve. Because of a design flaw, it has a small leak. It is interesting to note that when a used TG3985 was stored with the base oriented in the down position for a month, less than a drop of oil leaked out. For reference, I have obtained selected engineering specifications for comparison. The PF970C specifications were supplied by the AC filter customer service manager at my local GM zone office. The TG3985 specifications were supplied by the Fram filter engineering division. The filtration specification indicates that the TG3985 can capture smaller particles than the PF970C. This is probably of little significance since the LT5 was certified for durability with the 25 micron rated PF970C. The flow rate specification shows that the TG3985 has a lower flow capacity, though the difference between it and the PH970C diminishes if equal pressure differentials are considered. The engineer at Fram expects that bypassing will not occur if the filter is kept clean by replacing it at conservative intervals. The local GM Zone AC/DELCO service manager does not believe that a drain back leak exists in the PF970C design. He was not interested in receiving any specific information describing the problem. The TG3985 is white in color but can be painted gloss black to maintain the
esthetics of our beautiful LT5’s. PF970C Filtration, 25 microns. Flow rate, 6.6 gallons/minute at a pressure
differential of 3 psi. Bypass pressure, 9-12 psi. Case size, height 4.3", width
3.7". TG3985 Filtration, 10 microns. Flow rate, 3 gallons/minute at a pressure
differential of 2 psi. Bypass pressure, 9-12 psi. Case size, height 3.7", width
3.6”. I recommend the use of the TG3985 over the PF3985 because the TG model is
constructed with premium quality materials. I don’t recommend the DG model
because it contains a Teflon additive that might be detrimental to the engine if
used repeatedly. Fram no longer markets the TG3905 filter in the Chicago area. A good filter
that is available in this area and works correctly is the Bosch 3401. Auto Zone
parts stores stock the Bosch 3401. A plus feature of the 3401 is that it is
colored gloss black like the PF970C. The Mobil 1, M1-207 is also a good choice. The anti drain back valve seals normally. The filter is white in color. Serious LT5 owners will want to paint it black. It is rather expensive. It's available at Auto Zone stores.
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