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MG MGB GT V8 Factory Originals Technical - oil consumption

I now have a 3.5 V8 roadster and it seems a bit heavy on oil consumption. However, I do not know what is normal for these engines? I would think that consumption is about 1 pint per 250 miles, how does that sound?
On my standard 1800cc B, the engine breathing is critical to oil consumption. Is this the same for the V8? The only breathing I can see with a quick look is a pipe from the RH rocker cover into the air filter. IS there any other, possibly with a filter that can get blocked?
T Green

My engine did not need a refill in 5000 km. But oil seals have been replaced. I think V8's are not really oil consumers, but simply leak it out someway.
V8 has two small grey "filters" that connect to the two carbs. These filters could need replacement.

Frank de Groot

i have a V8 conversion (engine from a Rover SD1). It has a minor oil leak from the Valley, but I have not yet had to top up and have covered over 250 miles since last change. it still reads just below the high level.

sounds like you are loosing oil from somewhere.
j w mcglynn

definitely something wrong, I drove 2000 miles at speed in France during the last 2 weeks, and didn't use any oil, I don't think I've ever topped up between oil changes. They can leak in the valley, but I used a composite gasket instead of the tin one at the last overhaul, and that cured it.

Michael barnfather

The two small grey "filters" that Frank describes sound more like the flame traps. The SD1 engine has one filter, to allow air into the engine, at the back of the rocker cover.

Geoff King

You're right Geoff. The breather is as you say at the back. But I discovered/have the impression that changing the flametraps helped improve oil consuption.

Frank de Groot

I currently own a "factory" B GT V8 now fitted with a John Eales engine, and an R V8.

In the past I have also owned two V8 Range Rovers, and a V8 SD1, and in all have driven over 500,000 miles in Rover V8 engined cars in the last 30 years.

I have always run-in new engines very carefully, and used a straight forward oil, usually Duckham's 20/50. I have rarely had to top-up between oil & filter changes which I have done religiously every 3,000 miles, even with engines which have done over 180,000 miles.

Every case of “oil consumption” has always turned out to be a leak rather than burning oil.

Off topic - but my experience is that the critical issue with these engines in corrosion. It is essential to adhere to the recommended water/anti-freeze mix if you are to avoid catastrophic problems.

Safety Fast

Nigel Steward

Many thanks for you notes
Well there are a few drips from the engine but nothing that could dispose of a pint in 250 miles. The engine sounds fine and does not appear to produce clouds of blue smoke.
But I do not have any "flame stoppers" in the breather system. There is a copper pipe inserted into the top of the RH Rocker cover (looks to have been a DIY job) and this connects with a 1/2 inch rubber tube to the bottom of the air filter. The tube has a U-bend in that could get full of oil and block off???
I wonder who I could ask?
T. Green

Try Terry Brown at Freckleton Rovers, he specialises in SD1's and has been very good with mine..
He's on the net at or you could ring him at 01772-635728

Michael barnfather

In principle the internal combustion engine will always burn oil - it will also replace oil burnt with waste products. Consumption varies but 1% of the fuel used is within tolerance.

The advice about the flame traps is correct - but the breathers also have a tendancy to block where the rubber hose vents into the carbs. The crank breather also needs to be clear.

The spark plugs usually give the game away.

Safety fast.

I tried to e;mail Mr Brown but got no response
I see that Roger mentions flame traps and a crank breather.
I cannot find a crankcase breather on my engine, but I do think this must be some of the problem. Where should the crank breather be?
I tried removing the rocker cover breather and oil pushed out of the dip-stick tube.
Please advise.
T Green

If you have a Rover SD1 engine there should be a flame trap from one rocker cover venting to downstream of the air filter, (MGB GT V8’s have two flame traps). The trap has a mesh inside where oil vapour condenses and returns to the crankcase; if you don’t have this mesh oil vapour will simply be sucked into the inlet manifold and will be burnt. But your problem appears to be that crankcase pressure cannot escape and it seems to me that the ‘U’ bend that you have in the hose may be blocked.

Air enters the engine at the back of the other rocker cover through a small filter connected upstream of the air filter or it may simply be a small filter on top of the rocker cover. This, I believe, is what Roger means by the crank breather, they are so cheap you may as well renew it.

What do you mean by “I tried removing the rocker cover breather”? Did you remove the hose and block the breather or leave the rocker cover open? What happens if you remove the oil filler cap, do you get oil fumes out of the rocker cover?

Geoff King

I have a Rover 3.5 with the original rocker covers. Am I reading this thread right? Are my rockers reversed?
My flame trap (breather) is installed on the drivers side at the front of the rocker cover which is letting air into the engine. The PCV valve (breathing the crankcase) is located at the rear of the rocker cover on the passengers side. Is this backwards?



On Rover SD1 (RV8 and MGB GT V8) engines the flame trap is where air laden with oil vapour vents from, not to, the crankcase. The SD1 and RV8 engines have the flame trap on the front of the driver’s side (RHD) rocker cover, the MGB GT V8 has two, one on each cover. Clean air enters the crankcase through a small filter, which is either piped to upstream of the engine air filter housing or is simply an open filter. I believe the earlier P6 Rover engines and possibly the MGB GT V8 had this filter connected to the crankcase at the rear of the engine, on the SD1 it is on top of the rocker cover diagonally opposite to the flame trap.

The rocker covers are symmetrical and may be reversed.

Geoff King

I think I will have to do more research on this. My rocker covers are black ally castings with the MG logo on the top with ally coloured ribs on the top. It looks as though there are no breather holes intended in the castings, but a previous owner has drilled a 1/2 inch hole and inserted a bit of copper pipe which is connected directly to the air filter. No mesh fileters or flame traps. Where could I go to see the correct set-up? The B & G website doesn't show anything.
T Green

I have sent you a mail with a digital photograph of my engine, it is fuel injected but you can see the route for the vent pipes and the flame trap.


Do you have a photograph of your engine that you could send to Mr, Mrs or Miss Green? It sounds like the rocker covers are the same as yours and it might help identify the position of the vents.

Geoff King

I have a 69 P6 and it as you described, a flame trap on the front drivers rocker cover and I have installed a PCV Valve on the rear passengers side. I was under the impression that the flame trap was sucking air into the engine and then it was being sucked out the PCV valve. I do have a small pipe at the rear of the engine (about 5/16), which goes into the lifer gallery. This is all that allows air into the crankcase? Wow. I do have a small rocker oil leak and was considering flipping the rocker covers to the opposite sides. The only difference would be that to add oil, the cap would then be at the drivers rear instead of the drivers front. I don’t suppose there is right or wrong location for the oil filler is there?



No, Bruce, you're correct, the crankcase area is all connected together internally, so it doesn't matter which side you put the oil in. If there's some other consideration on a Rover engine that I'm not aware of, someone will bring it up.
I have the GM alloy engine, and don't know why Rover changed the method of inlet venting; must be some good reason. Joe
Joe Ullman

It does all sound a bit confusing but there is provision in the 3.5 and 3.9 Rover for what the manual describes as 'the engine breather'. This is a small .75cm diam hole (blanked or otherwise) at the rear of the engine. It can be reached (with difficulty) from the starboard side by tracing inwards under the patent bracket securing the metal gasket in the valley (ie above the hydraulic tappets). This lets filtered air into the pushrod/tappet/cam/crank area.

If anyone wants a diagram of this or of the rocker breather system for the GTV8 or RV8 send me an e-mail

Best wishes

Filtered air?? Right now I just have mine laying there. Is it suppose to be filtered through the air filter? In my case a 14” x 2” round drop down filter, or is there a line filter available for this application?

Bruce, The Rover system draws air through a filtered inlet at the back and out the flame traps then into the carburetors. The Buick system used a filtered oil filler cap as an inlet and a PCV to cut flow at idle or flow to the carburetor at speed. The impression you had about air in your car’s crankcase entering the flame trap and exiting the PCV is correct except that on your motor you have the unfiltered Rover inlet at the back that most certainly allows more air to enter than the flame trap. There should be nothing wrong with simply capping the back opening so dirt partials don’t get pulled in there and your system will work as in the Buick systems. Your 14-inch drop base filter should have a provision for attaching a hose that’s for supplying air to the crankcase that you could use in lieu of the flame trap. The only advantage I see to tapping off the air filter would be if the air to the air filter is ducted so the crankcase vapors exiting the PCV is a bit cooler and that probably isn’t the case in your application.
George Champion

Filtered Air
The GTV8 engine breather system provides air to the tappet area through a tee-piece, a length of rubber tube and an in-line petrol filter which is secured to the air supply trunking behind the SU carbs.

The rocker covers vent from the centre through a moulder rubber pipe to a mini flametrap and thence through another moulded pipe to the SU carb. There is one (back to back) for each cover.

The rocker cover vents tend to block with emulsified oil and water in the flame trap and are easily cleaned. Its easy to overlook the carb attachment which tends to block at the same time and increase oil burning

This thread was discussed between 26/06/2002 and 10/07/2002

MG MGB GT V8 Factory Originals Technical index

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