No/Slow oil pressure in cold weather - temporarily fixed by new filter..what's up?

[Big6ft6]

91 TBI 350 in k2500 175k miles. Good cylinder pressure in all 8 cylinders, but does burn quite a lot of oil (builds up on plug, no blue smoke though)

• In warm weather I don't notice any problems
  
• In cold weather, when I start my truck the oil pressure gauge takes a long time to show ANY pressure. (Like 5 minutes!).
  
• When it finally starts to register it is slow to come up and never reaches normal full pressure
  
• If I change the oil/filter, the problem is instantly fixed. Even from a stone-cold start I get instant, full pressure right away. But the fix is only temporary. After a few hundred miles,...I am back at the same spot.
  
• I've tried many brands filters.

Is there any hope other than my engine is slowly disintegrating and clogging filters? Is the no/low pressure what would be expected if my oil was being forced through the bypass in cold weather? Would love thoughts on what is happening and why. Thanks All.

 

[dyeager535]

Probably in the wrong section for this...not that you won't get help, just that the "injection" forum really revolves around fuel injection specific issues. I'd use the general forum FWIW.

With key in run (not started) if you disconnect the oil pressure sender wire, what does the gauge do? Then, if you ground that wire to the engine, what does it do? Should react immediately by pegging high/low depending on ground/open. If it does, then you've ruled out the gauge/wiring.

Your sender could be suspect, but it doesn't really sound like it since changing the oil solves it.

What weight oil are you running? As far as I'm concerned no weight oil should make this difference you are seeing, but if you are running 20-50 and it works fine in warmer climate a lighter oil might help. Not going to help the burning though.

I doubt the filters are getting clogged. If it were that bad, cutting the filter open would show it plugged up with coked oil (looks like tiny pieces of coal), and normally that doesn't happen. From the very abused 305 I bought, it just ends up coating all the innards of the motor, to the point of clogging all the drainback points. But unless you disturb the buildup, it tends to stay in place as it's very hard.

 

[Big6ft6]

Thanks DJeager, using 5W-30 oil. I cut one of my filters and nothing jumped out at me, but I wasn't sure what I was looking for, but definitely not caked with anything.

Last winter when this first started I did replace the sender assuming that was it to no avail. I then used a mechanical oil gauge in the port above the filter to confirm the zero pressure was in fact real (it was...unfortunately).

maybe I'll move to the regular section...i was curious where to go.

 

[4X4HIGH]

The oil pick-up tube could be clogged or the pan smashed against it. I would venture that it being clogged before the pan smashed though as you said changing oil/filter cures it for a short while. FWIW I use nothing but Wix oil filters.

 

[eagle mark]

If the filter was plugged wouldn't the oil go through the bypass?

Something is really wrong?

 

[chicken joe]

i have the same problem when the temp is below 0, on my 76 with fluid guage, takes 3-5 min befor i get any reading. for me this is why, i have a rod knocking and i have been running 20w50 since i bought it a year ago. im prety sure once it warms up my engine isnt going to last much longer. my pressure started normal at the begenning of winter and now the best it gets when totaly warm is 20-25.

 

[Big6ft6]

What is weird is I don't have the problem all summer. At least I never noticed, it really seems to be tied to cold weather. And once I warm the truck up even in the cold temps, if I stop at the store for 15 minutes and start the truck back up I get instant oil pressure. The zero pressure only happens if it gets totally cold...like sitting over night.

Someone else suggested some sludge build up near the pick-up and when it gets cold it gets really thick. When I do an oil/filter change with warm oil, draining the warm oil washes the sludge away from the pick-up for a while, but after driving the sludge builds up again near the pick up and in cold weather the sludge just gets really thick block the oil pick-up.

This is about the best possibility I've heard yet.

 

[eagle mark]

If your mechanical gauge really shows no pressure for that long cold? I'd be pulling the pan...

If you have no pressure the motor would also be making a lot of noise like lifter taps...