oil tank drainage

[keith burks]

i have 80 sc that if left to set for a while, it will drain the tank into the block, starting is very smokey until the oil is scavenged out of the bottom end, i have looked at the book and it looks like the oil pump has two sides in and out is there some kind of check valve in there failing or something. how do i repair this problem

[tharbert]

You say "set for a while." Leaking of oil into the sump is normal as is a puff of smoke at start-up. Oil typically leaks through the pump and bearings back into the sump until they reach equilibrium...no check valve. The scavenge side of the pump immediately starts sending oil to the pressure side (1976 - the oil bypass mod) upon cranking the engine and empties the sump probably in a matter of seconds.

How long is "set for a while.? If you drive it two days in a row, is there smoke the second day? You don't mention anything about the condition of your engine. What's your oil consumption, ~1000 miles to a quart? High mileage engine? Worn pump and bearings would contribute to oil leaking into the sump. Worn rings would contribute to more than just the normal puff of smoke. Recent oil change? Could it be overfilled?

In any event, you could try a higher viscosity oil. That will certainly slow the flow from tank to sump. And, the best suggestion would be to drive it more!

Post pictures and you'll get better answers!

[tharbert]

Good explanation below on how oil in sump can cause smoke at startup. Worn seals and guides would make it worse:

Originally Posted by Speedy Squirrel

The explanation I was given is as follows.

As a flat engine, the exhaust valve points in a downward direction (see picture). The area around location 16 can, in some cases, be below the surface of oil that is collecting in the lower valve cover. If that is the case, on shutdown, the engine can draw oil though the exhaust guide/seal. It will hang around in the cylinder until it either drains past the rings, or gets burned on the next start.

The amount of oil in the lower valve cover depends on a number of factors, like level of oil in the sump, fill level of the oil system, viscosity and temperature of the oil, operating speed of the engine, and so on.

[turbo nut]

Rothsport sell a check valve that goes in the S hose. We have used it many times with no issues.

[simsalabim]

Not to hijack or anything, but if one wanted to remove the lower valve covers, is it necessary to drain the sump and/or tank first ? or if the engine were cool, would the amount of oil under the covers stay the same ?

[Heinz911]

If you tilt the car sideways the amount of oil that will come out is limited. Else there is quite some oil that will flow from the case through the oil return tubes.

[safe]

or start the engine for 15 seconds, then the oil pump has scavenged whats in the engine to the tank.

[RedCoupe]

Simsalabim, what Heinz911 means is that if you want to remove the lower valve covers, as for a valve adjustment, you don't have to drain the oil out if you only remove one side at a time. If you have one side of the car up on jack stands and the other side on the ground, you won't lose oil when you take the valve covers off of the higher side.

[simsalabim]

Thanks, I get that but I was wondering about removing both lower covers (getting them milled for flatness). It strikes me that if I were only to drain the sump, the amount of oil left under the covers would be the same regardless of whether the tank was also drained. I even wonder about the need to fully drain the sump as well ?

[RedCoupe]

Never tried draining just the engine without draining the tank. I know that when the car sits for a period of time, the tank oil level and the oil in the engine sump reach a sort of equilibrium, but if you take a couple of quarts of oil out of the system (i.e. drain the sump) would the equilibrium oil level in the engine be low enough to remove both bottom valve covers without spilling oil? Very good question!

[RedCoupe]

Actually, I think that there's more than just a couple of quarts in the engine when it has sat for a long spell, so draining the sump could make a significant difference. However, if I had fresh oil in the car that I didn't want to waste, I think I would just thoroughly clean the drain plugs and drain the tank and engine into clean buckets and not worry about spilling oil when I pulled the lower valve covers. But, simsalabim, if you try draining the sump without draining the tank, please report back!

[cgarr]

I would be interested to know how the check valve works for this application?

[simsalabim]

I suppose I could check the tank level while cold, drain the sump and then check to see how the tank level changes .... If it does not change, and/or stabilizes before the sump is fully drained, I would think we would be at equilibrium and good to go. I realize it is not very difficult to simply drain the whole system, but I am curious, and why take the time to drain and refill if not needed ?

[safe]

Originally Posted by simsalabim

I suppose I could check the tank level while cold, drain the sump and then check to see how the tank level changes .... If it does not change, and/or stabilizes before the sump is fully drained, I would think we would be at equilibrium and good to go. I realize it is not very difficult to simply drain the whole system, but I am curious, and why take the time to drain and refill if not needed ?

If given time you will have more oil in the sump than in the tank. if the lower valve covers are removed for a longer time, most of the oil (I guess 5 quarts) will be on the floor.

The dipstick has about 2 quarts between min and max, so quite quickly it will be "out of range".

[simsalabim]

Thank You Safe.

So, it sounds like the tank will always be trying to fill the sump to a certain minimum level ?

And, that any oil in the sump will always find a way (rings, valve seals etc.) back under the lower valve covers regardless ? I would have hoped that the ring and stem seals would prevent most of this (especially when newly refitted), but maybe I'm wrong ....

I would have at least thought that after a sump drain, most of the oil would drain out of the valve cover reservoir and then back out of the sump. Then, it would be quite difficult to re-fill the valve cover reservoir in a non-running motor. It is most likely (and quite expectedly) that I am missing something quite basic here ... as such, I appreciate the patience of all on this forum. Is there another avenue into the cam boxes other than those mentioned ? What if I were to fit an aftermarket check valve between the tank and the motor ?

Again, thanks for the feedback.

cheers

[cmonref]

Quote:
Originally Posted by Speedy Squirrel View Post
The explanation I was given is as follows.

As a flat engine, the exhaust valve points in a downward direction (see picture). The area around location 16 can, in some cases, be below the surface of oil that is collecting in the lower valve cover. If that is the case, on shutdown, the engine can draw oil though the exhaust guide/seal. It will hang around in the cylinder until it either drains past the rings, or gets burned on the next start.

The amount of oil in the lower valve cover depends on a number of factors, like level of oil in the sump, fill level of the oil system, viscosity and temperature of the oil, operating speed of the engine, and so on.

I do not understand how oil from the rocker end of the exhaust valve can travel from the valve-head-end of the guide into the cylinder. Wouldn't it drain into the heat exchanger -- even if the exhaust valve is open -- and not the cylinder? I can see that an oil level in the intake valve area would drain into a cylinder if the valve is open or pool on the valve head awaiting the next opening.

[Walt Fricke]

I share Craig's interest in how a one way valve in the S hose is going to work. If it is a regular one way valve, either it will prevent all oil from the sump from reaching the oil pump (so that can't be right), or it will prevent all oil from the pump side from draining back into the tank (which, even if possible, is not a cause for concern.

So maybe the valve has a very carefully chosen spring which will hold a ball or flap closed against the gravity pressure of a full tank, but when the suction of the pump comes into play, will open?

Race car guys with a big oil tank mounted in the front of the car by the big front oil coolers will sometimes run the return line through the cockpit, and include a ball shutoff valve in that line. The driver closes it right after he shuts off the engine in the paddock. That will keep the engine sump with rather little oil in it - the oil which slides down the internal surfaces, maybe a little residual out the bearings. But he for sure has to remember, every time, to open it when starting the motor. One guy had a switch which disabled the ignition when the valve was in anything but the full open position. It got a hair out of adjustment, and shut his engine down on the track!

On the question of how oil from the tank makes its way, with the engine off, into the engine sump, my theory is that the gravity head of that tank oil is high enough for oil to move out through where the unsealed shafts in the oil pump are exposed to the engine innards. And similarly, out the scavenge side (having gotten there through the same unsealed rod bushings (really drillings, as most pumps have the rods just spin on the pump case material)) into the engine sump. Additionally, I suspect there is enough head, at first anyway, for this oil to move past the pump gears and into the oiling system, and thence into the main bearings and rod bearings. I am a bit dubious about that part, as it has to climb fairly high if it is to do this. But it for sure finds a way.

I think it is seldom that a guy really needs both lower covers off at once, as you do. So inquiring minds may not have experimented with seeing how low drawing down the tank you need to go, right after having run the motor for a while, to prevent this bleed back from rising above the level of the bottom of the oil return tubes. I know I have only used the "jack a side way up" approach outside of an oil change.

But you will be performing a noble experiment, whose results we all will eagerly await.

[simsalabim]

Great feedback as always.

Something tells me that a guy like Henry at Supertec may have a pretty good idea what that check valve actuation pressure is ... From there, I would think it a pretty simple calculation as to the head pressure developed by a given viscosity and volume of motor oil, between the tank and the valve.

Being a simple mind, I think I will perform the most basic experiment(s) first. While it might be interesting to start with a just shut down motor, I think it is just as useful to start cold. First, I will open up the sump drain and close it again once the oil flow stabilizes to a trickle and then record the volume of oil drained as well as the amount of time it took. Next, I'll wait a suitable amount of time (suggestions?) and repeat the procedure. I'll do this until no more oil collects in the sump. While I would imagine some deviation, depending on the type and condition of each oil pump out there (as well as the oil type and ambient temperature), in the total volume of oil and time to "equilibrium", it should not vary too much so that the information is irrelevant.

Depending on what I find, I might progress to closing my eyes and removing those covers..... Yes ?

Thanks, as always

[Walt Fricke]

Results will vary depending on how you jack the car up. I'm guessing you will jack up the rear, set jack stands on both sides, and remove both rear tires for better access. This will result in a forward tilt, making the front return tubes the preferred drain. But perhaps you have a lift, so the engine remains level? Or are a masochist and determined to do things with the car just sitting on its tires?

Your approach is nicely quantitative.

But suppose that you never quite get to equipoise? There is scant room above the exhausts to put pans to catch oil. When I jack a side way up, I am comfortable just putting rags on the exhausts. That's because I always get some oil spilling, and also because I am not going to have the covers off for very long. Just long enough for the up and down of rotating the engine and setting the lash. Will the rate of discharge fall off sufficiently exponentially that you can calculate when only ragable amounts will come out in the time needed to have the covers trued?

[simsalabim]

That's why they call it an experiment I guess ... I will start with as fixed and repeatable conditions as I can. I tend to choose my masochistic events carefully, so I believe the car will be jacked as you call out. I really cannot see how eventually the drainage will not cease, but that's how we learn right ? If things go south during the time it takes to get the covers back, I will simply drain the tank, lick my wounds and consider if it's worth installing an oil shut of valve or some other tactic.

I still believe that if complete drainage was not needed, there might be some real advantages in performing certain relatively common maintenance activities ...

I'll start the process this week and report back.

Thanks