Oil consumption and popping

[CXW]

The good news is that Jasper managed a steady 55-60mph for 2 hours down the M5 today to Bristol.

The bad news is how much oil has been used - a good litre and a half over about 100 miles. There's a smallish leak from the back of the engine (pending), but I'm wondering if the engine is burning oil as well and there always seems to be oil around the filler cap and on the head. I've got a metal oil filler cap on, the engine's a 948cc (1957 4 door saloon).

The engine is "coughing" a little when I stop accelerating and when cold there's been a couple of very loud "pops" from the exhaust.

Any ideas? I'm supposed to be driving on to St Agnes tomorrow and would prefer to get there as smoothly as possible and without inflicting too much damage on the engine. I've got all the basic spares and tools with me.

Thanks, Claire

[Orkney]

Would certainly think about replacing the filler cap. If theres 'some' getting out there it shouldnt be so, and until you stop that happening you cant really tell what you are truly losing if any.
The coughing & cold pops could be as simple as the timing out - as a good a place any to start looking.

[CXW]

This is already a replacement filler cap - was originally a plastic one, this is the metal one (MMC Bath part number 8M221).

Am wondering whether the breathers in the crankcase need clearing - the Haynes manual isn't providing much info about how to do this though, can anyone point me in the right direction?

[MoggyTech]

Any ideas?

Remove oil filler cap at fast idle, any blue smoke from filler neck?
Do a warm compression test and look for 160psi from each cylinder.

The coughing combined with high oil consumption suggests worn bores and piston rings.

Crankcase ventilation varies across engine types and year, but a connection from the rocker cover or tappet chest to inlet manifold side of vacuum is the best method.

[bmcecosse]

Yes - you must have some ventilation on the crankcase - and if the rings are past their best then good vacuum on the crankcase can make a very big difference ! To clear the top breather just wiggle the rubber pipe off and poke it through, and clear the little pipe going into the rocker cover - and the connection to the air filter. If it's been breathing heavy fume into the air filter it will be choked solid with nasty oily gunge. To clear the lower pipe properly involves taking it off the engine - not something you should get into when not at home base. Just use cheap oil from ASDA/Morrissons - and make sure you don't overfill the sump.

[CXW]

Breather was quite gunky, though not blocked completely.

There isn't any smoke coming out when the oil filler cap is removed, which is positive, and even when revved hard the fumes from the exhaust turn mid/lightish-grey.

Will stock up on oil and head on - fingers crossed - and then move sorting the engine out up the list of priorities for January. Any other advice still welcome - am on a steep learning curve as a new Moggie owner.

[bmcecosse]

Be sure to use 20W 50 oil. 10W40 is too thin.