oil loss/ diagnostics

cantdecide

A question and a sub-question

I've just checked my oil level and despite the fact that it was serviced about 3 months ago it took almost a litre of oil- I haven't done more than 1500 miles. It hasn't been running well for a few months and I'm wondering if the two things are related.

I know I'm going to be told to get a diagnostic check to be sure and I will asap but is there different kinds of checks? I saw a very sophisticated system where the various readings were displayed and the mechanic was able to diagnose a weak MAF reading. Most of the time I hear about stored faults but will all these systems give the same info? should I find out if my mechanic has only cheap generic equipment??

peasant

disappearing oil won't necessarily show up on diagnostics.

A worn engine will simply burn it without registering faults (other than high exhaust values), it may just run out of a cracked seal somewhere, or a hole in the sump.

It's more a matter of actually looking/investigating than diagnosing, so a mechanic with brains and eyes instead of expensive computers should do just fine.

Darragh29

cantdecide wrote:

A question and a sub-question

I've just checked my oil level and despite the fact that it was serviced about 3 months ago it took almost a litre of oil- I haven't done more than 1500 miles. It hasn't been running well for a few months and I'm wondering if the two things are related.

I know I'm going to be told to get a diagnostic check to be sure and I will asap but is there different kinds of checks? I saw a very sophisticated system where the various readings were displayed and the mechanic was able to diagnose a weak MAF reading. Most of the time I hear about stored faults but will all these systems give the same info? should I find out if my mechanic has only cheap generic equipment??

If your car has an oil consumption/loss problem, it is usually one of, or a combination of, three different problems, none of which need the use of diagnostics equipment to diagnose:

(1) You either have a problem with your piston seals, causing excess oil to pass the seals and enter the combustion chamber, where the oil is burnt. Consider the job of (and the cost of) rectifying this problem to be akin to open heart surgery for your car, probably costing well over 1k, depending on make, model, etc.

(2) Alternatively you have a problem with your valve stem oil seals and the oil is passing these seals down from the top of the engine and entering the combustion chamber and is being burnt off this way. Cost of resolving this problem if probably not much less than option (1) above.

(3) The third option is that you might have an engine oil leak, in which case you will most likely have a puddle of oil in your driveway. Will cost you less to fix but you didn't mention any obvious oil leaks in your op so I guess this isn't a runner.

The only diagnostic equipment you could to point to either (1) or (2) being the problem would be to put the vehicle on a gas analyser and if you detect excess HC and CO, you "may" have the problems outlined above, however you also "may" have other problems, for example a problem with your cat.

Is there any sign of excess blue smoke from the exhaust? You need to get someone to do a dry & wet compression test on the engine to confirm or eliminate option (1) above. After getting this done, you should know whether you are dealing with problem (1) or else looking at problem (2), in the absence of problem (3) being a runner, unless you have a visable oil leak.

Lastly, does your engine have a turbo? If it does, there could be an option (4)!

cantdecide

that's a pretty comprehensive answer guys thanks.

The last time I had similar bad running, it was down to a weak MAF sensor and but mainly a knackered lambda sensor in my 325i. I recently passed my NCT and the results were

740rpm @110 degs: CO- 0.01% & HC- 0ppm
Lambda: 1.011 2730rpm : CO- 0.01% & HC- 16ppm

It's a 2.8 V6 non turbo with 111k miles with no visible signs of smoke and when serviced, my mechanic said he was very happy with it.

I was starting to think the poor running was due to a serious problem but it is very intermittant. Yesterday it ran as well as it ever had before deteriorating again.

But will all diagnostic equipment work the same way? Even if it is burning a little oil due to wear, i would like to get to the bottom of the poor running.

Mr.Diagnostic

cantdecide wrote:

But will all diagnostic equipment work the same way?

Simple answer is no, but like most things to do with cars it is a bit more complex than that.
The diagnostic machine, no matter how good or bad it is does not fix cars. The man pushing the buttons must have the required knowledge to go along with the right equipment to be effective.
You are lucky to have a VAG from a diag point of view. They are the easiest make to write software for so every tool covers them at least pretty good.

cantdecide

But they will all give detailed information about the car's running for interpretation? ie, is there simpler diagnostic systems that will show only faults or faulty sensors and give no more info?

ps, are my NCT results okay?

cantdecide

would the wrong oil be a possible cause?

there's pretty much no smoke from the exhaust. My brother followed me as i floored it and there was pretty much nothing to report.

rebel.ranter

What yyear is your 325i? In the e36 I believe Semi Synthetic is recommended, in the e46 it was Fully Synthetic e.g.Castrol Edge.
Six cylinder BMW engines can be hit & miss when it comes to oil comnsumption. They are known for it. Some do & some don't.

Mr.Diagnostic

cantdecide wrote:

But they will all give detailed information about the car's running for interpretation? ie, is there simpler diagnostic systems that will show only faults or faulty sensors and give no more info?

ps, are my NCT results okay?

Even the weakest system should give quite a lot of detail on any VAG car.

Your NCT results are spot on.

Mr.Diagnostic

cantdecide wrote:

would the wrong oil be a possible cause?

there's pretty much no smoke from the exhaust. My brother followed me as i floored it and there was pretty much nothing to report.

Under a litre in 1500 miles is not that bad. Are you sure the level was correct to start with? What mileage is on it?

cantdecide

rebel.ranter wrote:

What yyear is your 325i? In the e36 I believe Semi Synthetic is recommended, in the e46 it was Fully Synthetic e.g.Castrol Edge.
Six cylinder BMW engines can be hit & miss when it comes to oil comnsumption. They are known for it. Some do & some don't.

MY fault- the '92 325 is my previous car and I was using it for comparison. I checked it regularly because it was so old but it never needed a drop outside of servicing even though it and my new car have around 110k.

Mr.Diagnostic, I was also thinking the same, but it was more like 1&1/2 litres it took so this would have been too much to be accounted by a mis-read dipstick, wouldn't it?

So it was more like 1&1/2 litres over 1500 miles.

Henry Ford III

Darragh29 wrote:

If your car has an oil consumption/loss problem, it is usually one of, or a combination of, three different problems, none of which need the use of diagnostics equipment to diagnose:

(1) You either have a problem with your piston seals, causing excess oil to pass the seals and enter the combustion chamber, where the oil is burnt. Consider the job of (and the cost of) rectifying this problem to be akin to open heart surgery for your car, probably costing well over 1k, depending on make, model, etc.

(2) Alternatively you have a problem with your valve stem oil seals and the oil is passing these seals down from the top of the engine and entering the combustion chamber and is being burnt off this way. Cost of resolving this problem if probably not much less than option (1) above.

(3) The third option is that you might have an engine oil leak, in which case you will most likely have a puddle of oil in your driveway. Will cost you less to fix but you didn't mention any obvious oil leaks in your op so I guess this isn't a runner.

The only diagnostic equipment you could to point to either (1) or (2) being the problem would be to put the vehicle on a gas analyser and if you detect excess HC and CO, you "may" have the problems outlined above, however you also "may" have other problems, for example a problem with your cat.

Is there any sign of excess blue smoke from the exhaust? You need to get someone to do a dry & wet compression test on the engine to confirm or eliminate option (1) above. After getting this done, you should know whether you are dealing with problem (1) or else looking at problem (2), in the absence of problem (3) being a runner, unless you have a visable oil leak.

Lastly, does your engine have a turbo? If it does, there could be an option (4)!

I replaced valve stem oil seals on a 2.0 pinto. Seals cost STG£8 in total. It took 2 hours.

gyppo

Henry Ford III wrote:

I replaced valve stem oil seals on a 2.0 pinto. Seals cost STG£8 in total. It took 2 hours.

Did the same on a 1l starlet. Cost buttons and about 2 hours of my time.

cantdecide

I removed the engine cover today and found a substancial amount of dried up oil probably as result of a leaky rocker cover gasket in the passenger side cylinders. totally invisible under the cover. You can see some of it below the oil filler cap.

The pipe running alongside the manifold on the same side, with the oily white sleeve is also split and covered in oil. Any idea what this is for? It looks like it isn't so straight forward to repair.

Sorry for being such an autocondriac but I can't really afford to get a mechaniac to look at it for now so any help appreciated