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FUTURE_OF_GM

A simple question, but a good one.

10 posts in this topic

How much excess oil does it take to float the valves in a small block Chevy?

I added a bit too much oil to my '68 Camaro (1/2 quart) and while I was draining it, I got to thinking; how much is too much? Would a half a quart over be enough to float the valves or would it have to be significantly more?

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Hmmm, a half quart overfill likely won't cause too much trouble. Any more than that and I'd say that you would be asking for it.

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i don't think it'd be a valve float problem, but more of a foaming oil problem.... from too much hitting the crank all the time.....

I thought valve float was when you rev it so high the valve never fully closes before it opens again.

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i don't think it'd be a valve float problem, but more of a foaming oil problem.... from too much hitting the crank all the time.....

I thought valve float was when you rev it so high the valve never fully closes before it opens again.

It is.

But I also heard that you could run too much oil pressure and float the valves in a motor with hydraulic lifters. I guess the lifter would fill to the point where the valve would not close and thus be burnt.

I know oil pressure isn't all that dependent on the amount of oil, but anyway...

It's not a trick question, it's just something I started pondering... I mean, I've never seen it happen but I've heard of it and it just got me thinking.

Is it a myth?

Edited by FUTURE_OF_GM
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I'd say yeah, it's a myth.

AFAIK, "valve float" happens when RPMs get way too high.

Too much oil causes other ills.

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i'd think to high oil pressure would mean something else.. and maybe pump cavitation. just finished a semester of fluid power.

the hole in hydro. lifters...i'm not familiar enough with what the difference is... but i'd think the oil pressure would have to be upwards of 300psi to move something that has such a small contact area to the valve assembly.

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Valve float indeed is caused by too high an RPM to allow the valve to fully close- it's a byproduct of cam speed/profile vs. valve spring pressure.

I do not believe it's possible to exceed the designed oil pressure capacity in hydraulic lifters.

I have never heard of oil pump cavitation- water pump yes, but not oil. However, yes: the crank can aerate the oil in the pan if the level is too high- but I would think it very unlikely to so completely aerate the oil than the air bubbles get down to the sump and get transfered to the oil pump.

The oil gallery pressurizes via the oil pump speed/clearances- having another 1/2 quart in the sump will not increase the pressure any- it's on the neutral 'side' of the 'circuit'.

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I'm agreeing with everyone else on this one, it wouldn't float the valves, it might add a few bubbles to the oil, but that's about it.

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Yeah, myth.

Add too much oil and you won't raise your oil pressure to the point it will push the lifters solid, it just won't happen.

Poor/weak valve springs sure......

I've heard of oil pumps cavitating... I've heard of fuel pumps cavitating... neither will have anything to do with valve float.

Windage in the crankcase being caused by overfilled oil I can see, that's why windage trays and crank scrapers are used, but engines without these parts don't seem overly concerned about relatively low rpms and no windage trays or scrapers...? Aeration won't be an issue unless you are pulling F1 rpms IMO.

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