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

[Northern Banana]

My car has the std Caterham dry sump system fitted, post engine rebuild I have a problem with the DS system blowing too much oil into the catch tank.

 

When the system finally finds its level and I look down the neck of the conning tower the oil is approx 2-2.5 inchs below the base of the tower. This is too low, proved after 50 miles when more oil is required.

 

Current thoughts:

 

Too much oil is being pushed in the DS res and can only escape to catch tank (when running with right oil level getting good pressure 65 psi at idle - 72 psi when driven).

Any thoughts as to why this may occur.

 

Does the DS system need a baffle to prevent too much oil being sent to the catch tank. Has anyone else needed to fit one? If I tried this route any suggestions as to what baffled design may consist of.

 

Gold star if anyone has the correct answer - as I am supposed to be at the club trackday a week on Weds at Cadwell.

 

Northern Banana.co.uk

 

Edited by - paul aram on 29 Apr 2005 22:18:37

[Peter Carmichael]

the oil is approx 2-2.5 inchs below the base of the tower. This is too low, proved after 50 miles when more oil is required.

 

What do you mean by *more oil is required*? Lots of us run our oil levels about where you are describing, which is probably about 10 inches of oil from the bottom of the tank.

 

[John Howe]

If you do a search on this subject you will find a reference to how deep the oil should be.

 

Suggest you get a long, narrow rod and insert it down the tower until it is sitting on the floor of the oil tank. Measure the depth of the oil and compare that with measurements you find in your search.

 

If you are getting too much oil blowing out could you have over filled the tank - how much did you pour into the engine to start with?

 

JH

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[Northern Banana]

Peter,

 

After a while (with the oil at the level described) the oil pressure falls away.

 

When topped up slightly it is fine again - so I am guessing that over time too much oil is blown into the catch tank , leaving insufficent in the system to push oil from the res to the oil pick up connector at the front edge of the sump.

 

 

 

Northern Banana.co.uk

[robmar]

Paul - is that oil pressure going down under load/driving or when idle?

 

if the later then that is normal as the oil gets hotter

 

Edited by - robmar on 25 Apr 2005 11:52:10

[Northern Banana]

JH - Was filled with around 5.5-6 litres, but with top ups and catch tank emptying unsure what volume will be know.

 

Just from a visual cue, the level appears lower than prior to the rebuild and I have now got this issue that over time the system doesn't appear to be retaining enough to maintain oil pressure.

 

Northern Banana.co.uk

[Mike Bees]

The level of oil in the DS tank won't have any significant effect on oil pressure unless it gets so low that the pickup (at the bottom of the tank) is sucking air.

 

Mike

[thinfourth]

what was changed in the engine rebuild?

 

If piston rings did you run them in on mineral oil or did you go straight to synthetic.

 

As you might be getting too much air/gas into engine meaning the dry sump system has to vent it out and it is taking oil with it.

 

Sod the heater wheres my shades

[Peter Carmichael]

After a while (with the oil at the level described) the oil pressure falls away.

 

Does it drop away suddenly? At what rpm? Is the oil level still the same when you next check it? Have you changed any of the breathing arrangements during the rebuild?

 

[Johnty Lyons]

I'mwith thinforth on this one if it was a rings rebuild and you used synth and treated it with care youve got blowby always use mineral and thrash the nuts of it.

[Northern Banana]

Answers to the various questions:

 

TF/JL: Still running in only 320 miles completed, on mineral oil - not exceeded 4,000 rpm yet.

 

PC: connected a new catch tank (Mocal) but hoses and vents kept the same. The pressure falls away very quickly to 15-20psi within rev range of 1,5000 - 4,000 then I switch the engine off quick.

 

MB - Does the engine oil pump create a 'pull action on the oil from the DS res, or does the system rely on gravity/weight of fluid to push oil to the ppick up connector. I do feel that supply to the pick up is the issue given that a 0.5 ltr top up address the oil pressure (for a while).

 

 

Would it be OK to trial a plug in the top of the catch tank hose with a small hole (to allow air to vent).

 

Northern Banana.co.uk

[Northern Banana]

DP

 

Edited by - Paul Aram on 25 Apr 2005 18:47:56

[Mike Bees]

I think the pump must pull.

 

Mike

[SLR No.77]

Pump pulls - despite the additional pipework etc, the connection into the belltank is effectively the same as the pick-up pipe in a wet sump setup

 

Stu.

[SLR No.77]

.......... didn't V7 SLR have issues with a similar problem recently - seemed to centre around a possible redesign of the coning tower arrangement? This problem is not uncommon

 

Stu.

[Jason Plato]

did you remember to put the circular spacer with the 2 O rings between the sump pan and the engine block ?

 

The internal Rover oil pump draws the oil from the bellhousing tank . The exact volume and level wont affect pressure so long as you have a "reasonable " ammount in the bellhousing tank ( 10 > 11.75" from the base )

 

I sounds to me like you have a more fundamental problem which needs investigating by an experienced engineer who knows the dry sumped K system before you do any damaged to the engine .

 

Can you post some pitures of the oil pipes and the routes you have plumbed them .

 

Dave

[Peter Carmichael]

I agree with Dave. A last check would be to run with a 25-35psi oil pressure switch instead of the notoriously unreliable sender.

[Northern Banana]

Dave & Co,

 

No pics but basic explanation of oil sys plumbing.

 

Hose from bottom of DS tank in gearbox bellhousing connected to pick up pipe connector at front of sump pan.

 

My understanding then is across to the filter, past the pressure sender and into the engine internals, before dropping down into the sump.

 

Hose from rear of sump pan, to push on connector at rear of DS scavenge pump.

 

Hose then from top of DS scavenge pump back to connector of DS conning tower to complete the system.

 

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

 

 

Where is Oily when you need him?

 

 

Northern Banana.co.uk

[oilyhands]

Hi Paul,

 

Just a couple of observations about the oiling system.

 

The oil pickup as removed had deposits of silicone sealant inside, the original pressure pump was quite the worst condition oil pump I have seen to date. So it's likely that with the fully ported 'as new' pump, clear pickup and ported block oilways you are delivering substantially more oil than prior to the rebuild.

 

This may have an impact on the oil circulation through the DS tank, it might be an idea to damp/baffle the conning tower to prevent returned oil from just bleding out of the breather.

 

oily

[Northern Banana]

Oily / others,

 

If a baffle of some sorts in the DS tower is the way to go any suggestions as to what a potential design may consist of?

 

 

Northern Banana.co.uk

[Jason Plato]

it should be capable of doing the job without any modifications , as in numerous other instalations

 

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South Wales AO

[John Howe]

I keep coming back to this posting as it currently appears to be a riddle. I have to agree with Dave Jackson.... that the CC system works and therefore should not need any form of modification. The problem must lie elsewere...

 

Since the scavenge pump gather at "say" twice the rate of the basic pump, then it can only gather from the sump what has been deposited there. What is dumped there comes from via the enngine's basic oiling system.

 

I am not convenienced that excess crankcase pressure will cause this problem, but the simple answer here is to run a breather from the cam cover to the dump tank and thereby allow some of the pressure out of the engine via the head and not the scavenge pump.

 

Paul, can you offer an indication of the depth of oil in the Bellhouse when you top up - it has been suggested that 10-11" is a good yard stick. If you have enough oil in the bellhousing then there is either a gravity feed problem to the pump or the pump is not moving enough oil through the engine.

 

Could it be that too much is being retained in the bellhouse and causing the return from the scavenger unit to overfill into the dump tank... I don't really believe this, just thinking out loud.

 

JH

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[thinfourth]

Now i get a good suck when i run the engine without the oil filler in the cam cover. So if you were getting excess gas into the crankcase then you would have less suck them me. So from here there is two experiments open to us

 

Run a engine with same oil system and measure crankcase pressure which might give some indication of the amount of blow past or leakage we are getting in your engine.

 

Experiment 2 i remove the filler cap and rev the engine and see if the dry sump system spits out oil with the extra air in the system.

 

Sod the heater wheres my shades

[V7 SLR]

Don't modify the conning tower. I tried and it caused the oil to syphon into the catch tank.

 

You *could* try adding a baffle plate between the bottom of the conning tower and the main tank. I was going to try this but I appear to be venting NO oil at the mo so I'm leaving it alone.

 

Before my most recent rebuild, my DS system vented a noticable amount of oil. When the car was new it vented NO oil. My engine was generally unwell before the most recent rebuild (bent valves and worn rings). The excess venting was what led me to investigate a baffle for the conning tower but this was a baaaaad idea.

 

When my engine was venting a lot, the level would often go down so much that I noticed oil pressure drop significantly when idling or when braking. During the problem with the conning tower baffle the engine dumped about 2.25 litres out of the 5 litres I filled up with into the catch tank (and over my feet). With less than 3 litres left in the engine/tank in total, the pressure drops were very apparent.

 

It's now sorted and vents NOTHING again. The bottom of my Mocal tank is clean.

[Northern Banana]

Sorry V7 just need to clarify.

 

Are you saying that post rebuild you are now not venting any oil (compared to when the engine need attention). Or have you needed to make any further modifications since your rebuild to stop the excessive venting?

 

Another question:

 

You have the Mocal catch tank - which I feel has a reduced ability to breath compared to the old plastic Caterham solution. Are both of your vents blocked up in the cam case?

 

Only thing I can think of, is the Mocal tank acting as a syphon??

 

The only other consideration I have is that the oil pressure release valve is sticking open dumping oil into the sump and allowing the DS scavenge pump to get ahead of the engine oil pump and fill up the DS tank. Only flaw in this arguement is that I should see a dip in oil pressure when the valve opens- and I don't.

 

 

 

Northern Banana.co.uk