MGB Oil Consumption

[Jonnyc]

Hi, this is my first post in this forum, and I hope someone can help me. I own a 71 MGB, and this year I've been doing some upgrades to improve the appearance and performance. In doing so, I replaced the Valve cover with an Alunimum cover without a breather vent. It came with what they claim was a breather cap instead. I also removed the emission pump (bad anyway), gulp valve and all additional emission related hoses. Again, I've done a few things to this car, so I'm not sure what is causing my problem.

Heres my problem. This year I'm losing about 1 quart of oil per 200 miles! This car NEVER used that much oil in the past, and I very nervous what is causing it.

Could the breather cap be the culprit?? I've read that this can be a problem because of increased pressure in the system.

Any other advice would be helpful. Thanks in advance.

[Moppie]

1st rule of British cars: If its not leaking or useing oil then there is something wrong with it.



If its losing oil out of the new breather cap then you will be able to see it, literaly flowing over the rocker cover.

First you need to work out where its losing the oil from, being old and MG it could be anywhere, but get in as close and personal as you can with the engine and try and find the source.

There are three main possiblities:
1, most likly considering the cars age; Its simply burning it, as the valve guides and pistons bores wear it allows the oil to enter the compustion chamber where its burned off. You will see it as a blue smoke in the exhaust. Of course you can rule this out of the engine has been recently rebuilt, but if its oringal then you could lose as much as 1/4 of a liter every fill up.

2. An oil leak somewhere. Most likely a gasket that is old and worn out. You should be able to see where the oil is flowing over the engine.
I would start with your new rocker cover, the cork gaskets used compress over time, and you might simply need to tighten it down a little more.
Also check time cover on the frount, the sump, and around the mechanical fuel pump. Once you find it you simply need to replace the relevant gasket, which is an easy afternoon job on all but the sump.
Its also possible, infact given the age of the engine quite likly that the frount or back main seals will be worn and also leaking. There is little you can do to fix with out spending a lot of money, and your better off leaving them for a complete engine rebuild.
A leaking rear main will show as oil dripping out of the bellhousing.
You could be losing as much .5L every tank of gas.

3. A combination of the above 2, which considering how much your losing is the most likely.


If the new breather cap is unable to relieve the pressure in the system to the same extent the orginal did then it would most deffinitly increase the rate of oil loss from any of the above, but the only real way to tell would be to refit your old rocker cover, and since your removed all the emissions garbage simply run the vent pipe into a small plastic bottle (600ml coke bottle is perfect).



And of course the best advice I can give is to find and join the nearest branck of the MG club. Its one of the worlds largest car clubs, and by far and away the best source of information and parts.

[Jonnyc]

Moppie, Thanks for the fast reply!

This car never lost any oil per Summer let alone every 200 miles. I did most of my recent work on this car about 1000 miles ago (nothing internal), and last week I noticed my oil was down about 2.5 quarts! Very alarming indeed! I first suspected internal engine wear, but I couldn't figure out why all of a sudden the engine would just fall apart so fast. I'm hoping it's just something simple like the breather cap. What do you think.

Heres a little more info. Yes, I believe the rear seal is leaking, has been for years. A drop here and there, nothing big as far as I can tell. Does not smoke at all. But it does spit out some black soot from the exhaust (leaves it on the pavement) when I start it cold.

[Moppie]

The soot out the back is just un-burnt fuel as it will run a little rich on the choke and when cold. Nothing to worry about, and quite normal.
(it will have been doing it since new)


Its possible the breather cap has upped the pressure in the open part of the oil system (sump, rocker cover, and return channels in block and head) causing more oil to leak out, and more oil to enter the compustion chamber via the valve guides.
But like I said you need to visualy inspect the engine to try and find any major leaks first.

If there are none, then providing it keeps doing it you can put it down to internal wear and start badgeting for a new engine (easily avliable for the B, and a must do if you want it to ever go fast).


Engines are funny things, especialy when thier 32 years old and British, even a small change in what has become a very well worn system can lead to the complete failure or one part or another, or reviel previously masked wear. For example the increased pressure in under rocker cover might have forced more oil than normal into the valve guides which had a sealing effect, increasing the compresion ratio, which increased the temp in the combustion chamber which caused a layer of carbon around the piston top to be burned off which then allowed oil to enter past the rings.
I doubt that's what actualy happened, but its an example of how an apprently small cosmetic change can radicaly alter the engines performance.
Number of things than cause a change is limitless, but it might have been something as simple as going over a bump in the road at a certian RPM.


I assume the engine has never been opened before in its life?
If so then its pretty much a given that its due for a rebuild.

[Jonnyc]

Moppie, just wanted to stop by and thank you for trying to help me a couple of weeks ago.

I've been busy!! Reinstalled my old valve cover which had the breather tube to the canister - ran it for 200 miles - still lost a quart. Finally I cleaned the entire engine, including the underside. Started looking for leaks. Found one on the flex hose going to the oil pressure sending unit. Wanted to replace it, but of course that won't happen on Labor Day weekend! So I simply tightened it down - kinda cranked it down! - and now after over 50 miles it's dry. In fact the entire engine seems very dry of any oil at this point.

So, I will drive it for another 200 miles to give it a true test. I'll report back and let you know. Right now I'm feeling pretty good!!

[Moppie]

Cool, and well done!

Its always satisfying to find and cure and oil leak, consider it a small battle won against a never ending war.

You'll be able to put the new rocker cover back on now, and dont forget to replace that hose, now thats it been tightened down its life span will be limited.

[Corgitoysaver]

Don't forget the gaskets of the inspection lids, behind the exhaust manifold. Cork ones wich can be replaced by newer versions.

Raymond.