The oil burning question

[AliK]

Dear Z brain trust, I need your expert advice please!

I have a 260z with 100k on clock. I was wondering if these engines burned oil even when new and how you decide what is a healthy amount of oil burning on a 100k miles engine?

Accelerating under full load and after 4k RPM I can see a small amount of blue smoke. Nothing that would be a bother to the driver behind, but none-the-less it's there. For perspective, my diesel Audi chucks out twice as much haze under load.

My neighbour who used to tine and rally cars is convinced the car has a fast road cam, apparently it sounds "cammy"!

I estimate she's burnt half a litre or so in the last 1000 miles of spirited revvy driving. Is this normal for these cars and especially with the age of mine?

I'm still on points and firing 10deg BTDC on the dot at idle, going to about 30ish at 3k RPM.

Carbs balanced & topped up by Fourways, but not too sure if mixture is perfect. Though no smelly tail pipe.

Thanks,
Ali

 

[Rob Gaskin]

From personal experience:

In good nick these cars don't burn oil - my track car was thrashed for 10 years and I was amazed how little oil it burned.

Before I turned it into a track car and rebuilt the engine it drank oil - I thought it was valve guides but it was VERY worn pistons and rings!

My low mileage (less than 30k mls) standard car does not use oil.

 

[AliK]

Thanks Rob that's good to know and v interesting re. worn pistons/rings!

As a matter of interest did you pay someone to rebuild or do it yourself?

I'm guessing a professional rebuild is c. £2k!?

 

[nospark]

ali,
I assume you know about the useful book "How to rebuild your nissan and datsun OHC engine". A helpful read in identifying engine issues and a good background reference even if you don't plan to do engine work yourself

 

[AliK]

Hey Nospark,

Thank you very much I didn't know about it and as i have a birthday coming up it would make a great present from my wife!

Cheers,
Ali

 

[nospark]

You could be greedy and ask her to also get you the companion book "How to modify your Nissan and Datsun OHC engine". I havn't got that one so don't know how useful it is or if that's the way you want to go with your car.

 

[andrew muir]

My 260z burns a bit, about 1L per 2000, miles.
I have a slight weep of oil from sump gasket, but not enough to drip.
It never smokes though no matter how hard I rev it, mileage is 60,000 genuine!
I do about 5000 mile a year in the zed.
All of my vehicles burn a bit even modern engines, in fact my Mazda 6 burns more than my Zed.

 

[jonbills]

My L24 was built 15k ago and doesn't use any oil that I notice.
I only do a couple of thousand miles a year, but I do habitually take it past 7k rpm at the drag strip and track days.
however, if it did use a bit of oil, I'd probably do nothing about it until I started losing power.

 

[Rob Gaskin]

Mine, mentioned earlier used so much I went on a trip to Scotland and it used a gallon of 20/50. On the over-run it left a cloud of smoke behind.

When I bought it I noticed some smoke on the test drive, I said to the seller 'does it use much oil' and he replied 'no negligible' . I wanted the car so much I let myself ignore my gut feeling. All the rings were broken - it still went reasonably well too.

 

[andrew muir]

It wasn't a one off 2 stroke special was it Rob!

Mine, mentioned earlier used so much I went on a trip to Scotland and it used a gallon of 20/50. On the over-run it left a cloud of smoke behind.

When I bought it I noticed some smoke on the test drive, I said to the seller 'does it use much oil' and he replied 'no negligible' . I wanted the car so much I let myself ignore my gut feeling. All the rings were broken - it still went reasonably well too.

 

[supermik]

My old 280zx turbo used to get through a load of oil but it always ran ok. I found out after it was gone that it may have been the oil seals on the turbo. (Janspeed). I never used to go that quick in it as the James Bond smokescreen that it left behind it at speed was never a good advert for an, at the time, quite cool looking car.

 

[AliK]

Thanks guys, appreciate all the input!

Rob, I pretty much did the same when I bought Z! Was embarrassingly child like excitement over logic!

The 280zx turbo I always used to think was way cool in the 80's especially as a cool school teacher had one!

 

[andrew muir]

I ve been reading quite a bit about this on other forums etc.
I know this has probably been discussed before, but the topic of correct oils in an L6 engine are too important to be ignored.

I was using Millers 20w50 semi synthetic oil until recently, when I got some ValvoleneVR1 10w60 synthetic blend racing oil.
After putting this in I noticed straight away that the engine felt stronger and now was willing to rev higher (300revs).
I have also noticed that the car was using no more oil than before although it does use some.
I think the use of modern synthetic oils is ok in older cars if the viscosity is thick enough?
I know a lot of people have had really bad oil consumption after switching to a synthetic oil this is due to a thinner film thickness getting blown past clearences which are larger than modern cars?
Although the film is thinner the strength is greater, so ensuring reduced wear?

I believe the most important factor is the amount of Zinc and phosphor added to the oil. This is Important for the Lseries to reduce the wear in the valve train.
The ZDDP has been getting reduced steadily over the years, but a way round this is for oil manufacturers to state oil is for classic or racing,motorcycle etc.
Millers classic, Mobile 1 (racing) and Valvolene VR1 oils all seem to have added ZDDP or enhanced levels.
Also Millers has just released a Classic Hiperformance 20w50 fully synthetic oil for older classic car and racing, which might be ideal for our old cars?
here is a link
https://www.merlinmotorsport.co.uk/...currency=GBP&gclid=CLq54ufPir0CFagBwwod-5oA1Q

Just want to get some feedback about oils for the Lseries!

 

[AliK]

Fellas (and ladies of course!)

I'm concerned! I took the plugs out yesterday and cyls 6-3 have oil on the rims of their plugs as below and identically so ...

Cyls 1&2 though are perfect as below ...

I'm strongly leaning towards a rebuild as I see smoke on blipping throttle when stationary and under load. I may post a video if Make it home in the daylight one eve.

Spoke to Fourways who normally do stuff I can't do myself (and excellently so!). The ball park is about £3k.

Interested in thoughts on keeping same engine (which I like for originality) or other options?

I love the car and can spend that money but is it worth it?

Thanks,
Ali

 

[morbias]

Are you sure it's not the rear carb running too rich? Carbon deposits soaked in fuel can look like oil.

[EDIT] oops misread your post, thought you wrote cyl 4-6

 

[Rob Gaskin]

If you are not sufficiently mechanically-minded to investigate yourself then you have no option but to involve other's however £3k does seem a lot. Have they broken the costs down for you?

Are you capable of a compression test? That might highlight issues but it also might reassure you if it's only the smoke that is bothering you.

Is the engine the original one, if not then your car is not a 'matching numbers' car so originality is not so important (IMO). A 2.8 from a 280Zx might be worth looking for and MIGHT be a cheaper alternative to a full rebuild.

You might also want to consider having yours over-bored (during a rebuild) to give 2.8 but that's not without consideration to block condition and perhaps a 280 head. Just a thought.

 

[AliK]

Thanks Rob. I used to rebuild gearboxes for fun as a teenager so I'm pretty confident with mech stuff but time poor in the extreme (esp with another baby due in 4 wks) + don't have enough garage space either, hence outsourcing options.

It was a ball park figure so no breakdown except taking engine out, balancing, bores, rings, head/valve conditioning and rebuild + refit.

Good idea re compression test. Is there an easy way of knowing if it's valve guides v rings? (Without taking head off?) The car picks up lovely from 1500 rpm and not noticeably down on power. The idle is creamy but if left for 5 mins gets lumpy until blipped.

On the boring out point: what are the benefits of going to 2.8l beyond the additional ponies!? Would the transmission / clutch need any mods to cope?

Thanks
A

 

[Rob Gaskin]

..It was a ball park figure so no breakdown except taking engine out, balancing, bores, rings, head/valve conditioning and rebuild + refit.

Good idea re compression test. Is there an easy way of knowing if it's valve guides v rings? (Without taking head off?) The car picks up lovely from 1500 rpm and not noticeably down on power. The idle is creamy but if left for 5 mins gets lumpy until blipped.

On the boring out point: what are the benefits of going to 2.8l beyond the additional ponies!? Would the transmission / clutch need any mods to cope?

Thanks
A

Ali, the usual diagnostic trick is to test the compression normally and then do it again but squirt oil into the plug hole first. If the compression rises significantly then the rings/bore are worn. If not and the readings across cylinders vary a lot then you have valve or gasket issues.

My gut feeling is that your rings/bore are worn but you need to dismantle the engine to be sure. If the car is driving ok then fit a rebuild into your calendar or look for another engine. Be careful what you buy though - PM me if you find something.

2.8 is good Over-boring (3mm) can fail due to thin cylinder walls but my old 240 block is still going strong. However an L2.8 is a better bet. Transmission should be ok but you may need a stronger clutch. That will depend on torque increase and what clutch you have now.

My advice would be to take your time and perhaps fit a hotter running plug.

 

[Alphabettispaghetti]

who have quoted you 3k?

 

[AliK]

Thanks Rob, I'll try that at weekend if time allows and will post results.

Franky, that was Fourways Engineering - have used them twice and while not the cheapest, I rate their work highly! Not to mention the automotive porn on display at their workshop!

FYI the z farm quoted £500 less. But it'll cost me that in fuel to go there and back