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Another Oil Pressure Question

I

IndianaRed

Member
I've always thought oil pressure should be higher in lower temperatures.

Yesterday morning when I started my 4.8 Chevy at 0 degrees it started right up, but boy it wasn't happy, click, click, click. Probabaly a lifter? It had done that once or twice before, but just for a second or two. This time it did it for quite a few minutes. Scary sound. Then all day yesterday and today I noticed my oil pressure was running low. Checked oil level, fine. I run Lucas in it all the time and figured that should help with cold starts, but maybe it was just too cold for anything to help? But I'm thinking the Lucas makes it a little thicker/heavier. Someone told me these 4.8's do that a lot, but I wonder.

So today I changed the oil, mostly to see if there were any shavings in the oil. It looked good, and instead putting 5w30 back in, I went down to 5w20. Drove it around some and the pressure was back up to where it should be.

So thicker, cold oil won't come up to pressure as well? Seems backwards to me.
 
I've seen in cold weather that the pressure relief valve will stick open and not reseat itself. This will cause oil pressure to stay low.
 
Not a lot of difference between 5-20 and 5-30. It can be common to have a little ticking at start up in the cold. The best way to check for any metal is to cut the oil filter open and after squeezing the oil out in a vice, look for metal shavings in the filter material. You can buy, or some places will do it for you, an oil filter cutter. It's like a big tubing cutter. Getting an oil sample analyzed is a good idea also. Dave
 
Ya, but this was worse than what you would expect. Very solid click, almost a clack or clang, but not quite, and went on for 5 minutes as the oil just would not move.
 
I have noted a decrease in oil pressure sometimes on a very cold engine. I think the oil is just too thick to pump and flow properly. If it is very cold I tend to drive away very slow and easy for a mile or two until things start to warm up just a little. If oil gets old and diluted it can get thin too and not show good oil pressure. This happened a lot more with older carburated engines than with injected engines I think. And probably more with gas than with diesel.
 
The oil is too thick to flow through the pickup screen when it is cold. Is lucus like STP? The noise is a collapsed lifter. The cold oil is too thick to fill it up till it runs awhile.
 
Yes, but after it warmed up it still didn't seem to want to flow. Doing 60 on the highway I was still 15 pounds lower than normal. Maybe that's the 0 degree temps cooling the pan that much? I don't know, doesn't seem likely and I'd never had that problem before when it's been cold. But I had the Lucas in there which I know thickens it up some. Just wanted something thinner that might flow better.
 
Yes, cold oil will make higher pressure. Much higher... but it simply gets dumped across the relief valve in the pump body. The net result is that the rest of the engine is starving for oil. The pressure sensor being somewhat higher up than the relief valve will see a lower pressure, and it is right, as are the rapping lifters.
You did the right thing by dropping the oil. I guess if it's desparate cold then mabey 5W20 is in order, but I probably would have went with 5W30 minus the Lucas.
While I suppose it's good as a viscosity improver in an old worn engine, if yours is still in good shape and tight, all it's doing is starving the engine for oil because cold thick oil can't flow.

Rod
 
You should try running a good synthetic oil. I prefer Amsoil but Mobil 1 is good also. I run a 0w-20 in our Denali and my '95 Chevy 350. Run 5w-30 in my '96 6.5L diesel. Pours like water even with a -40 windchill. I gained 1 mpg when I changed over too plus I go 15k between oil changes. The '95 lives outside and I can tell it cranks over much easier, the other two are spoiled and live in a 72 degree garage.
 
I used Valvoline motor oil for awhile in the early 80's. When it was 10 to 20 below zero, I would drive my 69 Ford (360 V8) for over 5 miles before the oil pressure would come up to normal.
I switched to Texaco and now to Mobil and have never had that problem again. I figured the Valvoline was too thick to go into the oil pump.
 
Cold weather causes the oil pump to "cavitate".It cant pull the stiff oil in through the pickup screen so it runs out and doesnt pump anything except air for an instant.A thick additive will make this worse when it gets real cold.Lifter clatter could be because the oil was so thick it wasnt going through the passage good enough to pump up the lifters,or oil was so cold that it was all getting pulled out of the pan and not getting back to be picked up again quick enough starving it for oil.Also if you tear down a motor thats had STP run in it,it will be worn out everywhere.Thick oil and cold weather are hard on bearings and motors.Might be different if the car was in a heated garage every night or plugged in to a block heater.
 
IR much as I hate to admit it, t-40 is right, on the subject of block heaters, at least in chevys. A neighbor just had a push rod go through his lifter on a 4.8, I think. Chevy has a history of lifter and oil related problems lately, might have to do with the unions, or maybe its just GB's fault like everything else!
 
Well, that's the thing about synthetic oil, it is soo thin.
It you run too thin of oil, you have very low oil pressure. Also, never run synthetic in a brand new motor until it is broke in. Thin oil also will find any leak spots you might have. I like Mobil 1 10W-40 for most things and have used 20W-50 for my drag car - very nice!
 
Thanks Rod.

It usually takes 5w30, so wanted to go just a little thinner. Seems to be better now, but then it's quite a bit warmer now too. Left the Lucas out too.

B
 
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