Oil Pressure Drops After High RPM

DoubleDingo said:

I just did a cold check on the 81. Yes, I need to change the oil, and I also see it's a half-quart low. But it covers the entire area, not just a remnant. The photos you posted it looks like remnant of oil. This cold check is popping the hood and checking the oil level without any engine rotations, and not wiping the dipstick, it shows how everything settled in and at what level since I drove it last week.

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Yes the pic I just posted is cold no wipe. So extremely low then? Damn. I guess that is the  real issue.

Don't excommunicate me guys.

Dont rule out that maybe the sending unit is bad

JamesSam said:

Don't excommunicate me guys.

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No Soup For You!

Definitely change the oil and filter now and check for shiny bits in the drain pan. I've never cut open a filter, but that may be a good thing to do as well.

My oil pressure dropped due to low oil (duh) mine is burning it up a bit and discovered some engine oil under the truck most recently. At least i think its engine oil, need to actually you know, take a close look at it.

Checked the dip stick after that and ruh roh shaggy i added some more and bingo back to normal. The oil underneath appeared after i garaged it a couple of months ago. Not related to my low oil pressure i described above.

I was also thinking that dip stick looked like there was basically nothing on it.

legopnuematic said:

5-30 is too thin in my opinion for a run of the mill small block or big block.

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It's a recommended weight for 1990 350 TBI, So at least in 1990 they were designed for that oil weight

JamesSam said:

Yes the pic I just posted is cold no wipe. So extremely low then? Damn. I guess that is the  real issue.

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It looks like there is way below minimum, if it's on a cold engine and it's parked on level ground then it's most likely what dipstick has collected from a dipstick tube on a way up.

Once you rule out low oil level then there is a possibility that something is going on with the gauge too. However knocking is telling it's an oil issue.

legopnuematic said:

5-30 is too thin in my opinion for a run of the mill small block or big block.

10-30, 10-40, 15-40, 20-50 for these old mills.

Personally 15-40 in everything I own. The 76 has 20-50 VR1 in it, but was 15-40 before the last oil change.

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^This.
Although I have a bunch of extra 5-20 or 5-30 I forget. Used it in the C10 350 when I changed the oil. But the engine is new and runs around 60psi until warmed up and still 40-50 when the engine is hot.

@JamesSam it does sound like low oil pressure. May be time for a New oil pump. Idk. Been a lot of years since I messed with old Chevy motors much. The 2 small blocks and 1 big block I have are all low hours

WFarm said:

Just for comparison, my oil pressure is at 60 PSI immediately after starting cold. On the highway after the engine is at normal operating temp it settles in the mid 50 PSI. When I stop at a stoplight when hot oil pressure drops to around 30 PSI.

This is a Mk IV 454 running Amsoil Z-Rod 10W-30 full synthetic oil.

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Similar with my (purported) low hr 454, original GM crate replacement from back when mark VIs were new and the new no name drop in rebuilt 350 in the c10 and the Vortec 350 in the boat with 450hrs.
By comparison, I’ve had a lot of old arguably wore out motors years ago that were more like 30psi cold and low at warm idle. Never lost one to no oil.
But they were generally throw away rust bombs that were not worth any more than keeping them roadworthy enough to get from a to b.

You have oil cavitation. You pump is working too hard. Thicken up the oil.

We use Castrol 20/50 high mileage full syn (keeps seals form leaking)

My body has 345k miles, and I do not know how old the gauge is, but I have changed the sending unit for oil and water.

Since we dont know how miles are on it, or if its the OEM motor.

Oil pressure is 40 at idle, 65 under power.

I am seldom looking under the hood of my 2007 CRV and my wife's 2015 Highlander. I constantly check on the truck. Oil, transmission, coolant. Always looking for leaks. Currently the radiator or it's hoses(fairly certain the lower hose needs a re-clamp after all that last radiator stuff I posted) are leaking but not enough to stop operating correctly. I have not seen oil leaking. I replaced the sending unit myself about a year ago and it was not causing issues. The last time I had the oil changed I had the gasket on the pan resealed(I had the garage do it not me) because it was seeping. The engine doesn't smoke, and I love that. It is original to the truck and I have only put about 7K on it. 148 when I bought it and it is approaching 155. Which is why I was basically having to convince myself that it needed oil badly. Looking at the dip stick oil would deceptively be up in between the add 1 quart and full dots but only on one side of the stick(IDK! It was really throwing me off) so being nervous about it I was reluctant to pull the trigger, then when the guage and strange sounds began I started to realize I needed to get to the bottom of it. Now I am about 1000 miles off from next oil change. The longer I have the truck and do things to it the more I realize I can frett less and know to more confident. I love the truck and am always afraid of doing something that would destroy the engine or transmission or anything else. I plan to change the oil myself this time and want to switch to something like the Amsoil Z rod for high mileage engines, and likely thicker oil with more zinc as suggested by you fine folks. No Stabilizer with this change. I will be looking for oil burning more often now, confidently. I want to be doing more to my truck but our budget and time do not allow me to. I am often envious of what I see a lot of you all accomplish on your rigs. I am appreciative of all of your feedback. Will be posting next updates. ASAP.

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When you get to the knock stage pull 1 plug wire off at a time and put it back on and if the knock goes away on any of the cyl. well...not good. I use plug boot puller pliers for that. Indicates a rod bearing bad. Cam bearings also may be bad. A lot of oil pressure is maintained in them. My 2 cents. Hope it helps.