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MG MGB Technical - Oil consumption

A thread in the general section raises the issue of oil consumption.

How many miles per pint do you get from your engine?
Chris Betson

About 300 miles per pint. Which is a shame because the engine is running really well, smooth and powerful. I'm pretty sure it is the rings as the head was renewed not long ago by Mr Burgess himself. I'm just putting up with it for now.
Mike
Mike Howlett

On the 77, I go 3000 miles to each oil change without adding any. I rebuilt the engine very carefully 2 years ago with special attention paid to oil sealing surfaces, it has about 22,000 miles on it since. The 71 GT, uses about a pint every 500 miles. I've only had the car a little more than a year, and don't have a complete history on it. The odometer is showing 160K miles, but the engine is still pretty strong, so it has probably been rebuilt once.
Paul Konkle

The engine I took out took about a litre to every 400-500 miles... the one I have in there now get about 600-700... goth are original higher mileage engines... actually the newer one(actually it's onlder, but newer to mea anyway) has 88,000 miles... the old one takes up space in the garage and will continue to do so until i get enough cash to rebuild it
Dave

My 71 roadster uses no oil between annual changes on a mileage of about 2-3000pa. The car has done about 135,000 miles, of which the current unmodified Gold Seal engine has dome maybe 40,000
agbridgewater

Chris

I fear the response may not be very scientific as probably only those of us with extreme oil consumption (whether high or low) will respond.

For what it’s worth my last standard 3 bearing MGB, sold many years ago , used no oil between changes every 3k miles, except during the running in period when I seem to remember that it used a little.

My RV8 and my GT V8 with a John Eales engine also use no oil between 3k changes.

My MGA 1600 depends on how it is driven. On normal road work it uses virtually no oil. When driven hard on a rally in the hills though it probably uses half a litre every 300 miles or so.

The RV8 uses semi-synthetic oil, and the BGT V8 & MGA good old Duckhams 20/50.

Nigel
Nigel Steward

My 71 B uses a pint every 250 miles, so every time I fill up with petrol I bung a pint of 20/50 in. I changed my oil and filter after 4000 miles but wont bother again for 6000 as its changing its own. Odometer is showing 4000 miles now but who knows how many times its been round or if its been clocked. It runs well, starts well and only blows smoke under hard acceletation. It is the original engine but I dont know if any work has been done on it.Plugs are blackened except for electrode. Exhaust is also a little black. Oil pressure is a little low when hot - just less than 20 psi at idle and on the motorway starts at 70 psi but drops to around 55 by the end of the run. Its also chewing up tappets. I changed four last year and one is pitted again in 3000 miles. I suspect camshaft might be a bit knackered. Do you think lower viscosity oils are a factor. I use GTX on changing (10W/40) but top up with good old Duckhams Q20/50. I've bugun to think about a recon engine but this thread has given me heart to carry on with the original. Its not let me down yet.
Paul Hollingworth

I'm not sure if my engine should be considered as part of a representative sample as it's highly modified and carefully broken in. I religously change the oil and the K&N oil filter every 3,000 miles. During that period it might consume between a cup and a pint of Mobil 1 synthetic oil, apparantly dependent on how hard I drive it. I'm sure that the valve stem seals from APT have a lot to do with it.
Steve S.

Thanks for the responses so far - I never expected a scientific analysis!

There are so many things that affect oil consumption - or should I say "apparent oil consumption".

I worry about people who say "my car uses no oil" - if they are driving short distances then their oil loss may be balanced by water and fuel!

I reckon that you SHOULD burn oil - otherwise how do the rings get lubricated? Oil SHOULD go down the valve guides - otherwise how do they get lubricated?

I'd much rather pour oil into an engine than rebuild it more often! (Whoops - p'haps I am doing myself out of business here!)

I have always considered 600 - 750 miles per pint to be about right for an engine in good condition, assuming there are no oil leaks and the PCV etc. is working OK.

I recently had what appeared to be a newly rebuilt engine burning oil excessively at motorway speeds - it turned out to be an ignition timing issue! Discussing this with Peter B, he said that often engines will burn excessive oil if they are pinking.

Chris Betson

My 79 uses less than a pint every 3000 miles (between
changes.) This is after a rebuild. The machine
shop sourced its own piston rings for me (they
weren't satisfied with the rings supplied with
County pistons.) I also had the shop gap and fit
the rings, as I was a first-time rebuilder.
I think the good oil consumption results are due
to the above points regarding rings, and the fact
that I had a nearly new head/valve guides.
Ronald

I drive my 74 about 3,000 mile per year and usually change oil
two times per year. I have never had to add oil but it goes down
a little between changes. I bought the car four years ago and
have no history so I don't know if it has been rebuilt. The oil
pressure is good and no major leaks. I have checked the valve
lift and one or two cam lobes are worn but in general the car runs
very well. My 68 has just been rebuilt so I have no idea yet about
it's oil consumption. Clifton
Clifton Gordon

I've just been browsing the pages of the Haynes manual and there is no mention of valve stem seals. I have done several head jobs on A series where there are those little caps that go over the top of the guides, but apparently nothing on B. I suspect that this is why I am burning so much oil. I am going to borrow a compression tester this week. I had shyed away from it so far as I was frightened what the result might be. I'll let you know.
Paul Hollingworth

Paul H,
My oil consumption and engine performance is almost identical to yours. I some how use a lot of oil, however there is no sign of smoke except under hard acceleration/between shifts if I'm driving hard (no doubt the rings). Other than that no leaks or smoke. My head is new so I doubt its the valve seals. I could be blowing it out the breather. But the motor runs good and strong, and the oil stays pretty clean.
I'll have to take out the compression tester as well. I also wonder about my timing. I've never been able to get it spot on, although there is no pinking.
Bill
69 B-GT
Bill Mertz

I was fortunate enough to own a new MGB, a 79 model. It would use less than a pint between oil changes up until I had to get rid of it when the second kid came along. On the current crop of cars, the 68GT has begun to use about a quart since I started racing it. Daughter's 77, with a rebuild 2K miles ago, is not using any oil now. My 79 LE is using about a pint between oil changes. All cars have their oil changed about 3K miles. (In other words, I do not pull over on the side of the interstate to do an oil change, but change it when I get back. No car goes much over 3k between changes.) Leaks are the biggest source of oil loss I have noticed. Second source is oil being blown out as the rings get older and do not seal quite as well. This oil is vented through the PVC system. Almost no loss has been noted from the rear of the engine (excellent rear oil seal) and little from the front. Tappet covers and rocker arm cover seem to be the areas of most common leaks. In good condition, these engines are as leak free as any I have found. However, my MGA used to use a quart every 150 miles with its old, worn engine. Les
Les Bengtson

My oil consumption is rather more puzzling (but I'm sure someone on here will explain it!!).

I try to change my oil every six months or 6000 miles (I'm a daily MGB driver and I do about 200 miles a week).

For a week or two after changing the oil, I need to keep topping it up. I'm not just talking about needing a bit of oil because I drained out more than I put in, I see the oil level drop from the top mark to off the bottom of the dip-stick. Then just when I'm starting to worry about the loss, it stops. Then I find that I only need to top it up about once a month or less.

I've also got one general question for all on the thread: If you have low or high oil consumption, does it tie in with how much the car is used?

Chris
Chris Byham

Paul H,
FWIW, Peter Burgess puts the seals on the inlets but not the exhaust valves. When the inlet is open, the piston is drawing a vacuum, and you could imagine some oil getting sucked down the valve stem. When the exhaust valve is open, the piston is pressurising the cylinder head and so oil should not be able to get into the chamber down the valve stem.
Well that's my theory!
Mike
Mike Howlett

Chris. I used a 68GT as a daily driver and my daughter uses a 77B. Neither uses much oil, with the 77 using almost none now that the engine has been rebuilt and run in. You will see the level of the oil drop the first time you run the car after an oil change because the filter is empty when the engine is first turned over and must be filled before you get oil pressure. That takes about one pint. After that, little or no change. If oil is leaking under pressure, the more the car is used, the more it will leak. If it is a non-pressurized leak, it depends on where the leak is coming from. Tappet covers and rocker arm cover are not a problem when the car is not running, even if the system is not under pressure there. Oil is also not there unless the system is operating. Leaks from the drain plug are constant regardless of use. So, basically, the more a car is used, the greater the opportunity for it to leak if it already does. But, regular use also helps to keep the rear crankshaft seal and front timing cover seals in good condition and an often used engine seems to have less leakage from these areas than one that is seldom used. Les
Les Bengtson

This thread was discussed between 16/01/2002 and 21/01/2002

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.