Factory oil pressure gauge fluctuates while braking

[vma1788]

Long time lurker, first time poster.

69 c10 with factory cluster. While braking the oil pressure gauge drops. Under, relative, hard braking it will drop all the way down. No audible knocking, oil level good with not old VR1 20w50.

Is this just an overly sensitive gauge? Doesn't really make sense unless its just the slosh and the sending unit temporally goes dry?

Old pic, pre wheel change now on 15x8 rallyes.

[Jrainman]

20/50 oil is some thick stuff , what engine is in your truck

[hamjet]

Is it a fly-by-wire gauge or oil tube fed gauge? My bad, gauge uses tube.

[geezer#99]

What does the gauge do when you're under extreme acceleration?

[LockDoc]

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Welcome to the board....

I would say that your pickup tube or filter screen has dropped off of the oil pump. My Blue '67 with the 454 would do that when you turned a corner hard or braked hard or accelerated hard. Try putting an extra 1/2 or full quart of oil in it and see what it does. If it doesn't do it then you will need to pull the pan and check the pickup tube/filter.

LockDoc

[vma1788]

Originally Posted by LockDoc

-
Welcome to the board....

I would say that your pickup tube or filter screen has dropped off of the oil pump. My Blue '67 with the 454 would do that when you turned a corner hard or braked hard or accelerated hard. Try putting an extra 1/2 or full quart of oil in it and see what it does. If it doesn't do it then you will need to pull the pan and check the pickup tube/filter.

LockDoc

Excuse my ignorance, ive seen you post this before, but what does the pick up tube have to do with it? Wouldnt that result in constant low oil pressure? where is the factory oil press sender located?

motor is a 468 big block with unknown internals (purchased the truck with it)

[geunther]

Originally Posted by vma1788

Wouldnt that result in constant low oil pressure? where is the factory oil press sender located?

Under normal driving, the bulk of the oil would be located such that the pick-up tube could get the oil. Under vigorous driving, the bulk of the oil can move to a different location in the pan, moving away from the pick-up tube. The screen moves the pick-up point closer to the bottom of the pan, where some oil may remain even under vigorous driving. If the screen came off, then the tube can't reach the oil when you are under hard braking.

[Ol Blue K20]

The pick up tube is designed to pick up the oil from close to the oil pan. The pump intake is submerged without the pick up but not a lot. Corners, braking, hard acceleration can leave it exposed to air instead of oil resulting in cavitation or airation.

[davepl]

In my '69 with the 307 I'd get the light (non gauge truck) would come on during cornering, and I figured that was related to the pickup tube, but it didn't come on under hard braking, which is weird now that I think about it.

I wound up keeping mine a little overfull, which isn't the right solution, but I was 17. It also burned so much oil that I had all my friends save theirs so I could run it. And it eventually maxed out at 45 downhill because it was so tired.

Is it possible for the pickup screen part to fall off and the tube itself still attached? Mine seemed like that, as if the whole thing fell off, you'd imagine it'd suck air the whole time.

[VetteVet]

Here's a few pictures of my engine with the pick-up tube off. And one with the new engine I had to put in because it flat lobed the cam. You can see the difference and how the oil pump could cavitate if the pick-up fell off.














This one is not a real good picture of the pick-up. It sits right on the bottom of the oil pan so it's easy to see how it could cause the oil pump to cavitate if it fell off.

[davepl]

You're right, I visualized it wrong - without the pickup it'd still grab from the top of the sump, but likely grab air under slosh. I didn't think the pump went that far down, but I guess it does!

[vma1788]

Thanks for the images guys. Before I drop the pan, where in the pressure sensor located? Do I have to yank this thing out to pull the pan or is it a motor-in-the-truck ordeal?

[67 chevelle]

if it is off , put a tack weld on it , when you replace , so it does not happen again

[LockDoc]

Originally Posted by vma1788

Excuse my ignorance, ive seen you post this before, but what does the pick up tube have to do with it? Wouldnt that result in constant low oil pressure? where is the factory oil press sender located?

motor is a 468 big block with unknown internals (purchased the truck with it)

As far as the pickup tube, what they said ^^^^. And like I said in my previous post if you over fill it with oil that should let you know if that is the problem....

There isn't a sender unless you have a dash panel with lights instead of gauges. The oil gauge is mechanical so the pressure is read directly from the port on the block.

LockDoc

[davepl]

I think he said he's got a big-block, in which case those are down by the oil filter, but it shouldn't matter.

I was always paranoid about tacking the pickup tube on because I'd heard that heat could ruin the spring. So I'd take them apart first... and I also brazed them for some reason rather than welding (dissimilar metals maybe?)

I have no idea if a little tack welding would really hurt the spring inside, but it can't hurt to take it out. Unless you forget to put it back in I suppose!

Anyone know if you can drop the pan in a truck with a big block simply by raising the motor? I've never tried.

I do know my grandfather did new rings and bearings in his '63 Biscayne without pulling the motor. He was a heavy duty diesel mechanic and I guess you get used to working in place, but I thought it was kind of cool. How he compressed the rings to get them up into the bores I really don't know... Pretty sure that would have been a 6 though.

[LockDoc]

Originally Posted by davepl

I think he said he's got a big-block, in which case those are down by the oil filter, but it shouldn't matter.

I was always paranoid about tacking the pickup tube on because I'd heard that heat could ruin the spring. So I'd take them apart first... and I also brazed them for some reason rather than welding (dissimilar metals maybe?)

I have no idea if a little tack welding would really hurt the spring inside, but it can't hurt to take it out. Unless you forget to put it back in I suppose!

Anyone know if you can drop the pan in a truck with a big block simply by raising the motor? I've never tried.

I do know my grandfather did new rings and bearings in his '63 Biscayne without pulling the motor. He was a heavy duty diesel mechanic and I guess you get used to working in place, but I thought it was kind of cool. How he compressed the rings to get them up into the bores I really don't know... Pretty sure that would have been a 6 though.

I dropped the pan far enough on my '67 1/2t with the 454 but it was a pain in the arse. I couldn't get the pan all the way off though.

(I modified my previous post on the port)

LockDoc

[vma1788]

Well, my flex plate shattered and my bellhousing snapped a few ears off so im busy replacing that but I will drop the pan once I get the trans back in.

Rear sump, stock capacity pan, BBC- LOOKS like I can drop the pan pretty easy.... thoughts?

[vma1788]

TTT ttt

[biketopia]

give it a whirl. you should be able to drop it enough to at least check to see if that's the problem. probably see in their easier too with the trans and flex plate out of your way as well.

[SoCoC10]

What about air in the line to the gauge? Its easy enough to have the engine running and just crack the nut on the back of the gauge and let a little oil out until you get a steady reading on the gauge.

[biketopia]

only reason it should have air in the feed line is if it's super low on oil, or sucking air at the pick up.