Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Oil filler Cap

Maybe it has been already on this BBS but,.....

On my oil filler cap there was a message saying renew every 20.000 miles or 12 months, so I did.

My MGB is a 1976 model (European)
The other day I was searching on the internet and I found out that there are two types of filler caps.
Vented ones and non vented ones.
The vented caps are for the years 1962-1970, and the non vented caps are for the years 1970-1980.

If the right cap was fitted on my car why do i have to renew the cap every 12 months because it should be a non vented one, and I do not understand why you should renew this every 12 months.

So I think I have a vented one on my car, is this the right? What can happen if the wrong one is fitted?


Jacob Halma

Jacob. My cars are all US specification (68, 77 and two 79s). None of them have such a warning. Neither did either of my 61 MGAs. I can only assume that there is some form of filter in the European specification Bs of that era which needs to be replaced on an annual basis. Was it a factory cap or aftermarket? Les
Les Bengtson

In the case of the earlier vented cap, It is an important part of your crankcase ventilation. Fresh air is filtered by the cap and drawn thru the crankcase carrying mosture and gases to be burnt thru the crank vent valve. The earliest cars including the MGA vented the air via a venture under the car. Also instead of a vented cap they got there fresh air from a hose to the air filter canister. The later sealed system got it's fresh air via a hose to the charcoal canister in the USA. (can't speak for non USA) It got it's suction from two drillings into the constant depression area of the SU carbs. Any year (after venture cars) car can be used with the filtered cap but one should seal off any other vents in the valve cover. There is no reason to change the unvented cap unless it destortes from heat or does not seal. Bob Thompson/International Auto
Bob Thompson

In the start off this thread I mentioned 20.000 miles this must be 20.000 km (12.000 miles).
Les, I can not tell if the old cap is an factory or an after market cap.
The new one is a Rover Unipart GFE6003 (vented) and looks exactly the same as the original one. (no message for renewal on it.
My supplier told me that the non vented caps are for the American market???

Jacob Halma

Vented caps were used on UK and other RHD MGBs for the life of production, or at least from Feb 64. American spec cars from 1970 had a charcoal canister and used a non-vented cap to the end of production. From the 77 model year onwards *all* LHD cars were to American spec, no matter for what market, and so had the canister and non-vented cap. So I'd expect a 76 LHD to have no canister and need a vented cap.
Paul Hunt

If you look in the 1962-1970 Driver's Handbook (at least as reprinted in the Bentley Book), it says to renew the engine oil filter cap and clean the crankcase breather valve every 12,000 mi (20,000 km) or 12 months. In the 1971-1974 Handbook, it says to renew the charcoal cannister every 24,000 mi or 24 months. No mention of the filler cap as from 1971 on it would be non-vented.

Rob Edwards

This thread was discussed between 12/02/2005 and 13/02/2005

MG MGB Technical index

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