oil consumption benchmark for rebuild engine

[dede911]

Hi,

My 3.2 engine (on CIS injection) has been rebuild ca 6000km ago by a well known local Porsche specialist. During trackday's I got worried about oil consumption.

Because is not easy to get a reliable measurement, I decided to put 1000 road km's on the clock, mainly motorway use; driving around 125 km/h (around 3000rpm).

Oil consumption is 0.75 l/1000km on 15W50 synthetic
There is a small leak on the left bottom valve cover. No stains on the garage floor, but oil burns off on the SSI. No idea about the leakage. Cover has to be machined or replaced.

What do you think about the oil consumption?
Is this normal for e fresh engine?

Thanks,

André

[Jesse16]

Normal, no problem. Check the plugs if you want to feel better. If no smoke or puddles, don't worry.

[Reiver]

Seems high to me for a rebuilt motor. 25.3 oz for 623 miles when cruising is what I got on my 3.0 after 230 k miles and no rebuild.
I've a rebuilt 930-10 with 10k miles and use about 6-8 oz. in 3000 miles. I know that's a great figure but the builder was/is meticulous about tolerances and break in.

[Jcslocum]

You're at about 1qt per 1000 miles. Not bad and with a leak. Consumption is affected by driving style, temp and type of oil. Not wanting to start an oil jihad, but making a change to another oil, maybe non synthetic would help.

[kodioneill]

Use cenpeco not synth.

[Discseven]

Andre... a minor detour from your main interest...

I've heard that switching from synthetic to dino oil once a TRANS has used synthetic is not a good idea...

Is this info incorrect?

If it is correct... why would it not hold true for the engine as well?

[dede911]

Hi,

There are a lot of opinions about oil types and brands...

For me most relevant is the viscosity. That why I mentioned I used 15W50.

What I like to know from this community is the oil consumption for a rebuilt engine, so that I can really benchmark my own consumption.

This can help me to decide if it makes sense to ask my engine builder to ask his opinion....

Let the data coming.

Thanks

André

[osl]

Sounds a little on the high side to me. I'm getting around 0.5l/1000miles on a 230k miles engine that had a top-end rebuild plus new piston rings at around 170k over 12yrs ago..
15/40

[brads911sc]

Are your internals stock or you have goodies like JE pistons in there...

[Reiver]

A few questions?
Are the cylinders and pistons Nicasil? Did you break the motor in and has the oil consumption been the same from break in?

[Jesse16]

My post about "no problem" is based on my engine (216k miles now) being rebuilt about 25k miles ago. Was smoking alot on decel and dripping everywhere. Top end I did it myself but Anchor did the heads and another shop took the bottom end apart and installed my new rings when I didn't have what I thought were the best measuring tools.
Mine uses now about 1 qt/1000 miles which while not "low" is very normal. I'd say the 1 qt/2000 plus engines are far between.
Again, does not smoke at all, has zero leaks and the plugs look great meaning its simply burning slowly away which is very normal. I'm very pleased.

[Reiver]

Jesse,
I politely disagree. A good engine builder should do better than that on a total rebuild.
If you are running flat out all of the time, as you would in a DE track day then high oil consumption is understood.
Normal driving on a rebuild should not be a qt. in 1 k., at least I wouldn't be happy with that as the odds of holding that usage are slim and you don't exactly have a cushion.
Our host recommends looking at a rebuild issues at that mark of 1qt/1000 miles....I don't really agree with that but would be not so happy if I was there directly after the infusion of so much time/cash.
The guy that rebuilt my 930-10 gets hardly any usage in his rebuilds....only use maybe 8-10 oz between 3k oil changes and that is his norm. This is after about 10k miles.
I was getting about 600 mpq +/- on a 230 k unopened motor and figured that was pretty damn good for the miles.
If you had 150k on it I'd say you were doing just fine...25k, not so much.

[dede911]

Hi,

thanks for your replies so far.

Pistons are as far as I know no JE's, according to engine builder high comp.
Cilinders have 11 ribs, so I suppose Nikasil.
I can not compare oil consumption immediately after break in and know,because I usually don't drive a lot only on street. Mostly a mixture track/street.

Plugs have a very nice color.
Power was good: 235hp
Torque was very good: 305Nm
And indeed on track, the engine goes very strong, most 3.2 carrera's are no problem.

My concern is indeed that the rebuild was not cheap. I don't think that the oil consumption will further improve...
I'm also afraid that the engine builder will tell that this is normal, case closed...

Looking forward to further comments.

André

[Jesse16]

Just back in the office, of course all reply's politely done, I appreciate it. Having read many years of others stating their usage, I think even the factory when new, wouldn't fix a new engine using at my rate. I guess my thought is what is it that a "good" builder does to reduce usage? Other than new P's and C's, mine is "new". I had a guy that signs all his engines here in the Carolinas do my "bottom end" work after I did the Top which other than the heads is just a bunch of bolting and sealing. Guess I did OK as it has never leaked or otherwise.
I'd be interested to hear from someone in the business whether there is any magic to make a non-oil using engine. My thinking is that other than getting the rings right and really going after the cylinder wall to ring interface with extreme care, that's it. I did do a break-in routine as recommended. I think anyone that builds for a living is realistic about the variability and understands 25+ year old air cooled engines vs. modern water pumpers. There is no benchmark.
I'm expecting my oil usage to remain constant for 100k+ miles until the valve seals fail again or I develop leaks. Minor oh yeah, I've done lots of DE's and never noticed any additional usage as a result. Probably because its just not that many miles driven.

[Reiver]

Jesse,
The guy that rebuilt my 930-10 pays a great deal of attention to the valve guides. He has made a unique tool for removing them so no 'meat' is taken off the head around the guides and spends a lot of time insuring exact tolerances on each. He grinds his own seats and valves.
He only uses factory rings on rebuilds that he sources from Porsche or Brumo's (same thing really).
The top end is where the oil usage will come from.
The 930 bottom ends are bullet proof if you change oil regularly...as a matter of fact he's never had to use anything but stock sized bearings when rebuilding unless the motor/crank was abused (improper oil or change schedule).
You are using oil either at the guides or your oil rings are seated in a manner to allow some bypass...and probably pretty evenly distributed between cylinders so it is really not a 'problem' as your plugs look fine.
In my limited experience oil consumption above 5-600 mpq had no effect at all on performance...my 230k mile 930-16 ran like a top with great leak down numbers, very strong...I drove it 1700 miles to do the change out and got 23 mpg /680 mpq and spent most of my time at 70-85 mph. (Az,Nm,Tx route)
Honestly speaking your consumption may remain the same for who knows how long.
The only reason I changed motors was I knew at that many miles if I needed work done it would only make sense to do a total rebuild ($) and I wanted a Howard Freeman built motor. It was also a pita putting oil in every 600 miles or so...watching it etc as it is a daily driver.
The euro spec I liked too.

[theiceman]

I get about 3000 miles before I have to add a quart, so I never have to add oil as it is time to change it again. I would not say 1qt per 1000 is rebuild time, but I would be concerned if I had just had a rebuild.

I don't track at all however.