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MG MGB Technical - Oil consumption

Just wondering about this.

My '71 BGT is showing 95,000 miles (believed genuine by docs with the car)it runs well and has just covered a 1000 mile trip with no problems, it even returned an average of 32mpg.

My only concern is its thirst for oil. On the first leg of my journey (300ish miles) it used just under a liter of oil. Then I did 400 miles of short journeys at holiday destination and it used a quarter of a litre, On the way home, it used just under a litre again.

There weren't any big clouds of oil smoke, even when I tried to provoke them by having a long period on over run, then booting it, (which showed up worn rings/bores on my last midget)

There is a very slight misfire, which I imagine is a valve on way out from using unleaded and lrp petrol, could this lead to oil being used?

It doesn't leak any either.

any ideas gratefully received
John
John Collins

John,

Check your ignition timing - over advanced timing will cause pinking at speed which increases oil consumption.
Chris at Octarine Services

Oil smoke is sometimes hard to see from the driver's seat. Ask someone to follow you and give you their observations.
R. L Carleen

Hello John,

Your oil consumption isn't bad-----if it ain't broken don't fix it!

Regards, Bumpkin
Bumpkin

A liter or quart of oil used in less than 500 miles has to be considered high oil consumption. As suggested earlier, have someone follow and look for times when there is oil smoke.
William

The oil consumption doesn't sound too bad for an older engine. I'd suspect from your description of the amounts used and the type of driving that the valve seals are starting to leak a bit. Higher oil usage during sustained highway driving when the intake vacuum levels are highest. If you have good compression then you might consider having the valve seals repalced as this can be done with the head still on the engine if you are concerned about the usage.
Bill Young

As the engine wears oil consumption will get heavier and can be lost through leaks, valve stems but mostly past the pistons and rings. Leyland engines nearly always used some oil and this was particularly noticeable in the 1800 versions perhaps due to the minimum amount of metal between the bores and distortion as the engine heats up.

An engine in good condition could be expected to achieve 1000 miles per litre of oil and by the time that diminishes to say 3/400 miles that is unacceptable. My 1800s are both very different. One is bored to +.020" and uses about 1/2 litre per 1000 miles, the other is std size but is linered and uses virtually no oil between 3000 mile changes.

In view of your 95kmiles there is a fair chance that the problem lies in the pistons/cylinders and a blow down test would perhaps show this up quickly.
Iain MacKintosh

On a 100K engine, there will be wear in the valve guides and the piston rings / cylinder bores. Both will lose you oil. The harder you drive, the more you will lose. If I use mine hard, (mine has done at least 160,000 miles, but has had a new cylinder head along the way) I can get down to 300 miles per pint (half litre) but there is no sign of smoke, even when travelling behind. Mind you 300 miles per litre is a lot of oil consumed.

My advice, if the car is running well, is use a cheap oil (I use Homebase 20/50) top it up frequently and change the oil at 3000 miles. Wait for it to get worse before taking it to pieces.

For what it's worth,

Mike

ps. How come it doesn't leak oil? Don't you realise they did that from new? Yours is a non-standard car sir, by God!
Mike Howlett

NO Leaks? You sure you have an MG?
Bruce Cunha

Come on Bruce the MG has the same number of possible leak points as any other engine. Maybe less because of its simplicity. If the engine was built correctly and in good condition there is no reason for any leaks.
Iain MacKintosh

Sorry Iain. You are of course correct. I should not reinforce that myth. Both my BGT and my TD are nearly dripless. (well the B is, it is inherant in the TD although I have got it down to just a occasional drip)
Bruce Cunha

Thanks Bruce. Funnily enough I was at a show yesterday and a couple of TD owners were talking about oil leaks and apparently they ARE fairly common on that model. At that point a Swede came along and moaned about the very same point on a car that he had at home.
Iain MacKintosh

I was taught that MGs don't leak. They were intentionaly designed with a "flow through lubrication system." ;)
Cris DeYoung

Both mine would take about 3k to get from max to min if I let it get that low. However the roadster (unlike the V8) does noticeably use more on a long stint (100 miles or more) at motorway speeds than cruising at 50/60, but I don't often do that. If your 300 miles of to-ing and fro-ing were at high constant speeds and the 400 not then it sounds much the same as mine, for what ever that is worth. But 150 miles to the pint is getting a bit close to the old rule of thumb of 100 miles to the pint and something needs to be done. Leaks are optional.
Paul Hunt

Yes, I forgot about that one 100 miles to the pint was definitely rebore time. That was in the days when our engines needed a decoke every 10k miles and were worn out at anything between 17 & 25k. An engine still on the go at 40k was a miracle.
Iain MacKintosh

This thread was discussed between 12/08/2004 and 18/08/2004

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