CorvetteRules

First cold start of day for my 91 starts immediately, but has a second of knock. Any suggestions on an oil additive I can try to eliminate it?

Kevova

Oil filter with check valve.

RetroGuy

And of course use Mobil 1 full synthetic oil. I like 10/30W. I use Mobil 1 and sometimes the best Fram filter made for synthetic oils. No knocks in the morning even after sitting for 7 days straight.

84 4+3

sounds like a checkvalve issue.

CorvetteRules

Great thought, I wasn't even thinking that direction.

bpan

I'd probably suggest ditching that Fram filter. Cut one open one day and you'll see why. Try a WIX.

Kevova

The deal is anti drain back valve to reduce oil from leaking down. Fram came out with a filter with check valve before GM. If you have basically a stock engine PF1218 or equivalent it's the higher capacity truck filter. Wix does make a version 51060XP.

RetroGuy

Isn't a check valve to prevent drain back in a horizontally or upside down mounted filter??? The '96 LT1 has an oil filter position that holds the oil in it, vertically mounted.

auburn2

I would think all oil filters have anti drainback valves today. In any case if you changed the filter and it is still happening, it is probably not do to the filter, more likely a bad oil pump or gunk in the engine which is delaying pressure getting to the lifters.

I don't really think there is any problem with FRAM filters, or any other filters, as long as you change them. I have yet to see any oil analysis results showing one filter being better than another over a normal oil change interval.

People complain about the cardboard end caps, but several oil filter companies claim they bond to the media better than the metal caps and leak less around the joint between the endcap and filter media. The media also flows more cold than a filter with a metal barrell, meaning more of the oil is filtered and less bypassed when the engine is cold.

auburn2

But there is oil above the oil filter in the oil galleries, that will exert a head pressure on the oil in the filter and without a drainback valve it will push oil out of the filter and back through the pump into the pan as those galleries drain down into the filter.

Kevova

Around 1993-4 some Chevrolet 5.0 and 5.7 had a condition of cold start knock. It was attributed it to oil system leaking back. GM was recommending fram filters until AC Delco developed a filter to replace the pf 25 and 35.