UPDATED : Dry Sump Sys - Blowing too much oil into catch tank

[V7 SLR]

Post rebuild I am not venting any oil, compared to when the engine needed attention, correct.

 

I have a different cam cover to you which has only one breather, however this is blocked off.

 

The Mocal ought to be sited at the same height as the top of the conning tower. Mine's on the bulkhead. It can only syphon if a liquid is in the pipe between the breather outlet of the conning tower and the Mocal.

 

I never really understood *why* mine vented so much previously. The top of the conning tower (the removable bit where you fill it from) ensures that any oil entering through the tangiental inlet does not immediately go up through the breather, however the modification I made to alleviate the venting I used to suffer only made it worse. I concluded that the breather is probably marginal, insofar as when everything is working well *it* too works well but as soon as something's *not* working well, it misbehaves.

 

Even when my engine wasn't in the best of health, the engine had a net vacuum (created by the scavenge pump) therefore there was no excess pressure forcing oil out.

[Peter Carmichael]

Like John, I keep coming back to this thread.

 

Paul, you are convinced there is something wrong. You are convinced that the "right" oil level is above the oil level that the system settles to, but you have described an oil level that is absolutely *correct* in terms of by the book checking of oil levels.

 

Therefore...

 

... why haven't you found out where the oil is when you get the symptoms of loss of pressure? If the pressure side of the engine oiling system is working correctly then the only possible explanations are ...

 

a) the DS tank has somehow emptied itself into the engine

b) the oil is somehow massively aerated (except noone else ever gets this with the conning tower DS)

c) the sender is kaput

d) the pressure side of the system is actually kaput

 

So at the risk of repeating myself, have you ...

 

...checked the oil level according to all the advice given in the 7FAQ article written here 🤔

 

... checked the oil level immediately after shutting down after seeing the oil pressure drop on the gauge 🤔

 

As for:

have replaced the pressure sender - so unlikely that 2 have failed

 

Ahem. Not at all unlikely IME.

 

 

[Northern Banana]

Gents,

 

Thursday night will re do all measurements and provide pics. I am going to empty the oil sys, remove all hoses and try some alternatives (i.e old catch tank, opening up cam cover breathers).

 

Does anyone know if Halfords/Machine Mart sell a suitable manual pressure gauge?

 

I really want to try and prove or disprove whether the DS tank is filling up or if it is somehow the motion of the oil return pipe/aeriated oil which is causing the problem.

 

This may have to be something as simple as a clear piece of polythene held onto the opening of the conning tower with elastic band or jubilee clip to see what happens at sustained revs.

 

 

[oilyhands]

Paul

 

I have a manual gauge I can loan you.

 

Oily

[oilyhands]

One thing that occurred to me Paul, when I rebuilt your engine the sump drain for the DS had no strainer and as a result a lot of the large chunks of silicone used for sealing the sump pan had been sucked up into it. I wonder whether any of this may have found it's way into the tank and/or pipework and might be causing a problem?

 

Have you cleaned out the pipework and DS tank?

 

Oily

[Northern Banana]

Oily,

 

Yes all pipework has just been removed and dry sump tank emptied, including removal of blue plate.

 

Update on what I have done tonight - however I haven't solved the problem!!

 

So I knew confidently re levels and pipe work, I emptied the oil removed the hoses, check and cleaned then and removed filter. Reconnected everything.

 

I also replaced the the Mocal catch tank with the old plastic catch tank.

 

I filled up the DS tank to a level which measured 12 inch from the bottom of the DS tank.

 

Started the engine - 64 psi of oil pressure and nothing in the catch tank.

 

Ran the engine for around 30 secs then switched off.

 

Checked the level in the DS Tank and it had, as expected, reduced as the oil had being pulled around the system. Topped it up until it measured 12 inch from bottom.

 

Started the engine again, pressure OK and nothing being blown into the catch tank.

 

Repeated and added a touch more oil to 13.5 inch - when engine next started a small amout was blown into the catch tank but pressure was still fine.

 

Went out on a small run, after 2 miles oil pressure drops, hovers for a while (20 secs) around 15 psi then back up to 64psi.

 

Turned for home, as approaching oil pressure drops again hovers around 9 psi (maybe 30 secs this time) then back up to mid 60's psi.

 

Gets home swaps sender and checks levels nothing extra in the catch tank, approx 12inc in the DS tank.

 

Goes for a run exactly the same happened.

 

So in summary:

 

The change in catch tank may have addressed the expelling of too much oil (but more likely down to only very short runs).

 

I am now getting intermitent drops in oil pressure. Some may think this is down to a sender, however I will disprove that one when I borrow one know to be working tomorrow.

 

Is this now pointing to the oil pressure release valve coming into operation. If so what causes that?

 

Final test tomorrow (apart from the 3rd sender) is to unplug the cam vents to see if they have an impact.

If that doesn't work then, then I heading back to MK. ☹️

 

Northern Banana.co.uk

[Peter Carmichael]

The single thing you appear not to have done is...

 

... when the oil pressure drops, kill the engine and immediately measure the oil level in the DS tank.

 

It might be that you just didn't mention it.

 

BTW, 12 inches from the bottom of the DS tank is more oil than anybody else manages to get in there for hot running. I run closer to 10 inches. Filling to 12 inch depth I would be unsurprised to find oil exiting to the catch tank... but I never have pressure difficulties.

[Northern Banana]

PC - unfortunately never hand a suitable moment to do this, eithe rin traffic or condisitions didn't permit. When I got home and test thought down to 8.5-9inches.

 

Although since have made progress

[Northern Banana]

Progress has been made, although I am not sure that my assumptions are 100% correct, they may or may not be inter-related.

 

Having changed from the Mocal catch tank back to the caterham plastic version, the amount of oil being deposited in the catch tank reduced. This maybe down to breathing abilities of the Mocal tank.

 

The more significant change however was that when the engine was rebuilt a straining gauze was fitted to the hose connector which is the pick up for the DS scavenge pump. Prior to the rebuild this was not in place - DVA adding it as extra precaution. The gauze however was quite restrictive to the oil flow, evident by the fact that when I took out the connector a surge of oil was released from the sump pan.

Another possible impact is that the DS pump is not working at an optimum rate.

 

In my humble (and very limited technical opinion) it is possible that the fitting of the strainer reduced the ability of the DS scavenge pump to circulate oil, with more volume being retained in the sump - this in turn may have been a variable issues dependant on engine and pump speed.

 

All I know is that I managed 150 miles yesterday with no low oil pressure, good oil level in DS system and little oil in the catch tank.

 

Oh and I let the engine have it's head - and at 5,500rpm it really rather fast! Roll on 7,500rpm 😬

 

 

Northern Banana.co.uk

[Chris__]

Good to hear you've got this sorted Paul

[Peter Carmichael]

If a gauzed pickup prevents the scavenge from keeping up with the pressure pump, the scavenge pump is bu&&ered. Replace it ASAP rather than continue running without a gauze in the pickup. Initially running without a gauze might be an explanation of why the scavenge pump is currently in no fit state.

[SLR No.77]

Just to add - I think there are differing gauzes for the different pumps - gold or purple

 

Stu.