Oil preassure

[colinb]

I have a problem, but to start firstly, has or is it possible for the preassure relief valve on the pump to suddenly stay open so on full bypass and when the engine is shut down and restated to work as normal and then when it feels like it to go open again, a proper quandry this one, i have come to this conclusion since the latter has happened to me a couple of times, have checked sender and guage and seem ok, i am pretty sure it is the pump as i felt that there was definatly a preassure loss in the way the engine reacted.
So has anyone had the pump reacing like this at all.

Colinb

[wilf]

That could happen, if there was dirt in the bypass valve/spring area, or if the ball or "tadpole" itself has worn so that it sticks. Not unknown.

What engine?

[colinb]

Hi Wilf,

One day we will speak when i have no problems, anyway its a 350sbc, happened to me twice on saturday sudden preassure loss , stop engine wait ten mins and its up again, i even thought that there could be something floating around in the sump.

I think the best thing is probably drop sump and check pump, what do you think?

Colinb

[wilf]

Colin - it is possible that you are somehow emptying the sump, especially if you have a HV oil pump fitted. All the engine oil could be sitting up in the heads, oil pump sucking on air.

This is mainly a Ford BB isue, but HV oil pumps can do this to other engines as well.

Lastly- are you sure that you do have enough oil in the sump anyway? How did you decide where the "full" mark on the dipstick would be?

And even more lastly - too much oil can have a similar effect - crank runs through the oil, foams it, result = loss of pressure.

Have fun sorting this out now.

[kurrmet]

Originally Posted by wilf leek

Colin - it is possible that you are somehow emptying the sump, especially if you have a HV oil pump fitted. All the engine oil could be sitting up in the heads, oil pump sucking on air.

This is mainly a Ford BB isue, but HV oil pumps can do this to other engines as well.

Lastly- are you sure that you do have enough oil in the sump anyway? How did you decide where the "full" mark on the dipstick would be?

And even more lastly - too much oil can have a similar effect - crank runs through the oil, foams it, result = loss of pressure.

Have fun sorting this out now.

I can concur with Wilf as I had to fit 7 quart sump to ensure that all the oil did not end up in the heads and none in the sump.

This is one a 383 chevy.

Best of luck sorting your problem

[colinb]

Well thanks you two, some very interesting facts and ones i had not thought about. The oil level was determined by the dip stick mark already there, but isee where you are going as has this been marked according to the sump fitted. The oil pump is an unknown quantity until i ask the previous builder, but in thinking back if it was the oil up in the heads then how long would it be for the oil to travel back down to the sump. Does the oil have to be at a certain temp or just hot to froth. Question ? if we were to try and graduate the correct level in the sump by looking at the engine from a side elevation say guaging from the block/sump joining line, what would be the ideal oil level.

Colinb

[wilf]

Colin - unfortunately, I don't think there are definitive answers to your questions, but here are some ball park ones:

If the oil was all up in the heads, it should drain back down to the sump in a couple of minutes after engine shutdown. (warm engine)

Oil can froth at pretty much any temp, so far as I am aware.

Empirically, I would expect to set "max" oil level about 1" lower than the bottom of the crank counterweights. So without knowing the dimensions of your crank, I couldn't suggest where this point might be down from the sump/block joint. Maybe someone with better/more recent build experience of a sbc, or maybe an engine builder could give you that measurement.

How much oil does it take to go from empty to the current "full" mark?

[Purple AK]

Please note that I know nowt about owt But I notice that most US engine builders include in their specs "relief work to increase oil flow back to the sump" Maybe there is a clue here

[colinb]

Thanks Wilf,

I put 6litres origionally in it and this did not include the remote filter and piework that ad already been primed, the full mark was covered on the dip-stick and as far as i was told 5 quarts should suffice. Iam just checking the mark on the D-S in relation to its position in the sump and it does seem low, so i will try and detail the depth more accuratly, the oil in de head seems to be getting to me, speak soon and let you know.

Colinb

[h8jse]

Originally Posted by colinb

Thanks Wilf,

I put 6litres origionally in it and this did not include the remote filter and piework that ad already been primed, the full mark was covered on the dip-stick and as far as i was told 5 quarts should suffice. Iam just checking the mark on the D-S in relation to its position in the sump and it does seem low, so i will try and detail the depth more accuratly, the oil in de head seems to be getting to me, speak soon and let you know.

Colinb

Just a thought....... I know as much about this as Chris does, the max/full mark on the DS... is it for an engine running without an oil cooler? do you run an oil cooler? does the oil pressure drop when the engine is hot? if you do/it does the max/full level on the DS might be just under the full/max level for an engine with cooler? does that make sense ......I'll get me coat.....