Over filling with Oil - What causes the engine to burn oil?

[Mark B]

I am trying to identify an issue with an engine that has gone form burning no oil to burning excess oil in a matter of 40 miles. I do have a few things to check, oil filter is old and wasn't changed with the oil (don't ask, amateur mistake, breather pipes to crankcase and head and also look in the cylinder head around camshafts.

My question, why does over filling with oil cause oil burn?

Does it increase oil pressure, therefore pushing oil past seals?
Does it cause oil splash, therefore pushing past piston rings?
Does it overfill cylinder head therefore leaking past valve stem oil seals?

Can anything else cause any of the above? For example, damaged oil filter causing an increased oil pressure?

I have a lot of investigations this weekend, but I don't believe I have oil burn from a worn engine. I do know the engine was over filled with oil by 1.7L though (not by me, I will hasten to add)

As I say, I will be checking breathers, oil capacity, oil filter and wipping cam cover off to checking valve stem seals.

Any thoughts?

[paintman]

Vehicle make, model, engine & mileage?

[Mark B]

It is just a general question, but...

It's a Lotus Elise with a Ford Duratec Engine fitted. To add more info, I did put in a 2nd hand engine in which on the rolling road spat out the dip stick. At the time, we assumed this was due to the O ring being loose/weak. On the road it was fine except under high revs/ throttle. I did 4k miles in it and it was fine, except under high revs, high throttle. Last winter I pulled this engine and bought a 30k mile Ford Fiesta ST engine. I spoke to the guy selling it, it had been pulled from a crashed car the week before and had no issues. I had this in my car running within a month, so I don't believe it got dry as such.

This engine, on the rolling road also spat out the dipstick tube, this was when oil was added and over filled due to the dipstick marks not being right as the car runs throttle bodies and the tube is modified due to space. So, when over filled, it was spitting oil up the dipstick, the oil was then drained and correct volume added back. Once this was done, I drove the car home without any oil, albeit a slow drove home for 35 miles. I then fixed a few other bits and wanted to take it back to the RR, on the journey after 20 miles the oil burn was just horrendous, so I turned around, drove home, slowly and by the time I got home I had a blue cloud following me, under all conditions, tickover, dipping the clutch from 2k revs, half throttle 3k rpm... etc.

I cannot get my head around it being rings, they don't wear that quickly.. or do they? I do need to check levels and oil filter and obviously do a compression test, but I am just wondering what could cause pressure build up to spit a dipstick tube out and possible be the cause of oil burn.

[paintman]

Mark B said:

It is just a general question, but...

It's a Lotus Elise with a Ford Duratec Engine fitted. To add more info, I did put in a 2nd hand engine in which on the rolling road spat out the dip stick. At the time, we assumed this was due to the O ring being loose/weak. On the road it was fine except under high revs/ throttle. I did 4k miles in it and it was fine, except under high revs, high throttle. Last winter I pulled this engine and bought a 30k mile Ford Fiesta ST engine. I spoke to the guy selling it, it had been pulled from a crashed car the week before and had no issues. I had this in my car running within a month, so I don't believe it got dry as such.

This engine, on the rolling road also spat out the dipstick tube, this was when oil was added and over filled due to the dipstick marks not being right as the car runs throttle bodies and the tube is modified due to space. So, when over filled, it was spitting oil up the dipstick, the oil was then drained and correct volume added back. Once this was done, I drove the car home without any oil, albeit a slow drove home for 35 miles. I then fixed a few other bits and wanted to take it back to the RR, on the journey after 20 miles the oil burn was just horrendous, so I turned around, drove home, slowly and by the time I got home I had a blue cloud following me, under all conditions, tickover, dipping the clutch from 2k revs, half throttle 3k rpm... etc.

I cannot get my head around it being rings, they don't wear that quickly.. or do they? I do need to check levels and oil filter and obviously do a compression test, but I am just wondering what could cause pressure build up to spit a dipstick tube out and possible be the cause of oil burn.

In the bit I highlighted what you say doesn't make sense. You talk about a 35 mile drive without any oil. Is this a typo or did you drive it without oil?

[stevieturbo]

So both times it spat the dipstick out, the 2nd engine you know nothing about, and as above, you drove it 35 miles with no oil ?

Seriously ???

On the first aspect, it just sounds like your breather system is fked up, hence excessive crankcase pressure.

On the driving home with no oil....really no response to that one.

[Mark B]

So, when over filled, it was spitting oil up the dipstick, the oil was then drained and correct volume added back. Once this was done, I drove the car home without any oil BURN, albeit a slow drove home for 35 miles.

Sorry, that would be one missing word changing the whole meaning of the sentence

See above, so the 35 mile drive home was "without any oil BURN" not "without any oil"

Oops.

So, back on topic, I am somewhat concerned about the breathing and possible high oil pressure... Can this really have an impact on oil BURN?

\sat here feeling amused / embarrassed...

[Steve_D]

What makes you think you have high oil pressure?

Steve

[PaulKemp]

I suspect you still have a crankcase breather valve fitted that only releases pressure under vacuum from the inlet and have this piped to a catch tank
The result of this is the crankcase does not breath, pressure builds up and is released wherever it can find a way out, rings possibly, and is probably the cause of the dipstick flying out

[Mark B]

Steve_D said:

What makes you think you have high oil pressure?

Steve

I don't, but I am wondering if high oil pressure could give oil burn. I will be taking the aftermarket (Raceline) Oil Filter adaptor and oil filter off to check they're both OK. If not, this may be giving high oil pressure.

My initial question was how and why does having excess oil then lead to oil getting into the chambers to be burned.

Can high oil pressure force oil past valve stems for example or are they just in an oil bath in the head?
Does excess crankcase pressure force oil up past piston rings?

[Mark B]

PaulKemp said:

I suspect you still have a crankcase breather valve fitted that only releases pressure under vacuum from the inlet and have this piped to a catch tank
The result of this is the crankcase does not breath, pressure builds up and is released wherever it can find a way out, rings possibly, and is probably the cause of the dipstick flying out

I am starting to feel this too.. I will be investigating the PCV, although as far as I am aware I successful dremeled it out meaning the crank case is open to atmospheric pressure. I then pipe the exit to a T piece with the cam cover vent to a catch tank, which has an exit via a filter to atmosphere.

[DVandrews]

High oil pressure won't blow out seals , crankcase pressure is more likely to do that, oil pressure is contained within the oil circulatory system which exits via the sides of the crank bearings, cam bearings and follower bores. It will very rarely impact on oil consumption, only on engines which have oil cooling sprays to the underside of the Pistons could it have an impact and this is likely to be small.

Dave

[Mark B]

DVandrews said:

High oil pressure won't blow out seals , crankcase pressure is more likely to do that, oil pressure is contained within the oil circulatory system which exits via the sides of the crank bearings, cam bearings and follower bores. It will very rarely impact on oil consumption, only on engines which have oil cooling sprays to the underside of the Pistons could it have an impact and this is likely to be small.

Dave

Perfect, thanks Dave just the sort of answer I was looking for.

As I know you know about these things, could a blocked oil filter which doesn't have a release valve cause a back pressure also increase crankcase breathing?

[DVandrews]

Crankcase pressure and oil pressure are entirely separate and one is not influenced by the other. There are no seals on the engine that contain oil pressure other than the one at the base of the oil filter. A blocked filter will compromise the bearings and bores as there will be restricted oil delivery. Inadequate lubrication can wipe out the rings, but by then the bearings will have long since failed.

Daves

[phumy]

Mark B said:

It is just a general question, but...

It's a Lotus Elise with a Ford Duratec Engine fitted. To add more info, I did put in a 2nd hand engine in which on the rolling road spat out the dip stick. At the time, we assumed this was due to the O ring being loose/weak. On the road it was fine except under high revs/ throttle. I did 4k miles in it and it was fine, except under high revs, high throttle. Last winter I pulled this engine and bought a 30k mile Ford Fiesta ST engine. I spoke to the guy selling it, it had been pulled from a crashed car the week before and had no issues. I had this in my car running within a month, so I don't believe it got dry as such.

This engine, on the rolling road also spat out the dipstick tube, this was when oil was added and over filled due to the dipstick marks not being right as the car runs throttle bodies and the tube is modified due to space. So, when over filled, it was spitting oil up the dipstick, the oil was then drained and correct volume added back. Once this was done, I drove the car home without any oil, albeit a slow drove home for 35 miles. I then fixed a few other bits and wanted to take it back to the RR, on the journey after 20 miles the oil burn was just horrendous, so I turned around, drove home, slowly and by the time I got home I had a blue cloud following me, under all conditions, tickover, dipping the clutch from 2k revs, half throttle 3k rpm... etc.

I cannot get my head around it being rings, they don't wear that quickly.. or do they? I do need to check levels and oil filter and obviously do a compression test, but I am just wondering what could cause pressure build up to spit a dipstick tube out and possible be the cause of oil burn.

If you have modified the distick tube, how do you now know what it the correct level in your car/sump?

[Mark B]

I know where the marks are for the full level. Unfortunately the garage didn't.

I couldn't keep the standard dipstick as the Jenvey throttle bodies are in the way. I does need to be addressed, but hadn't at this time hence the garage over filled it. I don't in any way blame them for this.

[hman]

he doesnt - thats why it got overfilled - then he drained it all out and put back in the correct amount.

[stevieturbo]

Mark B said:

My initial question was how and why does having excess oil then lead to oil getting into the chambers to be burned.

You're starting off with the completely wrong assumption as to what has caused any oil to get burnt, hence the topic is pretty much senseless as long as you continue to pursue that line of questioning.

[hman]

I can give you my experience of this - someone I know was advised to fill their car up HALFWAY between min and max.

The car started up and began leaking oil - a Lot of oil .

Dipstick was checked - it had been filled HALFWAY up the fking dipstick.

Oil wasnt burning but it was pissing out of everywhere when running, fixed by draining out 2 litres of surplus oil - no ill effects.