NC 1.8 Oil consumption

Technical Area Engine, Transmission, Exhaust etc
2

Hi, My 1.8 early NC with 67K on clock, has started to burn some oil, approx. 1/2 litre every 1000 miles.  It has always had regular oil changes with the Mazda Ultra 5W-30 fully syn. being used. I assume the problem is clogged oil control rings, I have tried Forte engine flushes for the last couple of years with no success. 

First question, has anyone been successful of clearing rings on the Duratec engine without rebuilding? 

Also I have heard that using different oils may help (different manufacturers, semi-synthetic) anybody had experiences?  

Another comment has been, now the engine has some wear, using 10W-40 may help (when new apparently using this oil grade caused problems with hydraulic tappets, but this engine has adjustable shims) has anyone tried this?

Any recommendations would be appreciated, thanks.

3

"The chief difference between the 1.8 and 2.0 is that the latter has variable valve timing; otherwise, capacity aside, they’re essentially the same. Both, according to specialist Paul Roddison (mx5-racing.co.uk), are ‘bombproof’ so long as the oil is checked regularly and changed on time; Paul advises every year or 10,000 miles for oil changes.

‘They can use oil, up to half a litre every 1000 miles,’ he says. ‘The only problems we’ve ever seen are when the oil has run low. Our race car bounces off the rev limiter all day and we’ve never had a problem.’"

 

Copied from Evo.

4

My old Astra 1.4SE was doing that from new, but after 205,000 miles it was down to 1/2 litre every 3,000 miles… 

Fortunately the MX5 engine should be much cleaner than that was, my 2.0 NC has not used any oil at all in the last 4000 miles - same slightly over-full point on the dipstick.

Things to think about.

  1. Inlet valve stem seals leaking?

  2. If one or two plugs are more oily than the rest (sooty clag deep in the recess around the OK coloured insulator), suspect a ring or a valve seal or a head gasket.  But for only 1/2litre per 1000 I’d not expect to see this, unless you are doing mostly very short journeys where the engine doesn’t have time to get properly hot.

  3. If a ring has stuck, the cylinder walls will show this with uneven wear or staining.  Have a look at the cylinder walls with a borecam.

  4. Assuming the valve seats and head gasket are OK (important assumptions), a good way to find out what is going on is to do a compression check. All pots should be the same as each other, on two different sets of readings - first set without extra engine oil squirt on top and second set with.  Expect the second set to be only a very slightly higher value, a big difference means the rings are shot.

Use logic to work out where the problem might lie, try to find where the oil is coming in at the various possible points in the path through the engine; breathers, valves, rings, valves.

 

Hmm.  Don’t do this at home…  Think of the neighbours.

One of the bodge fixes for stuck (but unbroken) rings we used to do back when I bought old bangers was to squirt some Redex into each pot via the plug hole and then turn the engine by hand a few times to work it past the compression rings and leave it overnight, or even a couple of days with maybe an occasional few more turns of the engine on the starter but no plugs.  Sometimes we would just run the engine and steadily drip Redex into the carburettor air intake.

The problem with Redex is that it can mess up a Cat especially if you still have some of the old original stuff that was best for fixing stuck rings.  It can also strip the carbon that has built up on the bores so the engine almost needs to be run-in all over again.  On our old motorbikes for this ‘instant decoke’ we would run the engine briefly without the exhaust pipes, so all the clag would just shoot out and not block the silencers - very, very antisocial, but a great hoot especially on one occasion when the newspaper protecting the forks and front wheel caught fire.

Be prepared for the vast clouds of blue smoke it produces when first fired up after doing this bodge!  And yes it is definitely an outright bodge, but sometimes it really does work if none of the rings have broken.

 

5

Let’s get this into perspective and stop worrying about it, you say it has happened for the past couple of years re Forte flushing.

Go into Halfords and by two 4 litre tubs of oil for £12 a tub and that is the problem covered for over a years for £24

So take the car to 100k miles for an extra cost of say £100.

Cost of an engine rebuild my guess at least £1,000.

Now let’s talk about modern oil.

In a modern petrol engines post 2002 that has been regularly serviced with modern oils, the ones I have examined due to rusty external sump corrossion have been as clean as a whistle inside. So as you have found out the flushing oil was a waste of time. Diesel engines and badly serviced older engines are another case.

There are energy saving oil like the Total supplied oil you have been using, rebadged Mazda and that grade of oil is thinner and has a tendency to burn oil, my Mk3 if I do only motorway miles will use say half a litre in 2,000 miles but in mixed driving nearer half a litre in 5,000 miles. A lot of over 3,500 rpm driving uses oil in my Mk3 and the 1.8 is lower geared than the 2 litre that I have so it will rev a bit higher.

They have an HTHS viscosity of under 3.5 and give better fuel consumption look for ACEA A1/B1 or the more modern and more stringent A5/B5 on the tub that is what is termed a 5W/30 for Ford their latest spec calls for the A5/B5.

Still within the 5W/30 thickness range but at the top of it are the ACEA A3/B4 used in Diesels and long drain interval petrols they have an HTHS of above 3.5.

If we call those oil 5W/30 for Vauxhal GM with they use a touch more fuel but are a bit more stable with their higher HTHS and burn less oil, they also should shear slower thus lasting say 18,000 miles between changes.

There is now a large range of 5W/40 oils A3/B3 so good for winter starts, higher HTHS so a bit more fuel used. The ones I have checked are at the lower end of the 40 range but I have only checked a few.

The 10W/40 A3/B3 oils tend to be nearer the higher end of the 40 range.

As an experiment if I were you I would go into Halfords and buy one of the tubs of £12 for 4 litres 5W/30 for Vauxhal and one tub of the £12 for 4 litres 5W/40 and check out if they make any difference to fuel and oil consumption.

Quite a few of the Scobby Turbo guys use a 10W/50 in their engines with no problems.

6

Thanks all, lots of information there. I will try different oils as you suggest Drumtochty. Cheers.

7

Hi all, I know this is a very old thread, but I have the same problem with my 2006 NC, L8 1800, 84K miles.

The oil cons has always been bad in the 13 years we’ve had it, approx. 1 Lt per 1000 miles. Emissions have always been good at MOT time … until this year! Now failed on high CO and had to have 2 new cats and oxy sensors fitted (yowch!)

The garage made the comment that the second cat was very black and coked up, could this be caused by the long term oil cons? I’m wondering how long will the new cats and sensors last as it was a very expensive repair?

Has anyone else had to replace cats? whether both or one? was that due to oil cons?

Do I need to think of an engine repair. Is it always oil control rings on the 1800 or could it be valve oil seals? The engine has always been very clean, no leaks, but I do notice a blue puff of blue smoke on start up some times.

Any comments, advice or help would be appreciated. Thanks in advance.

8

Definitely the rings.
I did mine about 3 years ago, it’s a big job but do-able if you know what you are doing.
I did rings and big end shells plus 1 x piston which had picked up around the crown.
Mine is a NC 1.8 2006 with 60k mikes on the clock. Hasn’t used a drip of oil since being done

As for the 2nd cat, mine crumbled and fell apart so I took the Inners out. Probably gained an extra 0.005hp :grin:

9

Thanks Rich, that’s interesting. Were you able to replace rings etc. keeping the block in situ, or was it engine out and strip?

10

I left the block insitu.
Jack the front end up high, head off, timing chain off, I found that jacking the block about 1 inch off the front mounts and packing with bits of wood helps lowering the sump from underneath.
Haynes manual helps with the head and chain but useless for pistons out as it says it’s not possible.
There are some instructions online but it’s not that hard, just be prepared for oil dripping on your face while working underneath!