by Mike Owen of Owen Automotive

Our British cars have a well-deserved reputation for oil leaks.  This is particularly true of our MGs. Remember that these cars were not exactly precision built and often had leaks when new.

Excessive oil consumption can be a result of worn piston rings or valve guides.  The telltales will be a blue haze to the exhaust and a wet, oily exhaust pipe.  Sparking plugs will be wet as well.

Oil leaks from the engine can be from a variety of sources:

  • Valve cover gasket: Be careful to not to over-tighten the cover nuts as this will crush the cork gasket.  Use contact cement to fasten the gasket to the cover to keep it from slipping inside the rim.  You can apply white grease to the side that faces the head to prevent damage when removing.
  • Oil pressure hose: While original equipment was very reliable after market hoses have blown out occasionally.  The rubber in old hoses will get hard, have little flex and leak at the fittings.  A failure can be very serious as all the engine oil can pump out in a few minutes.  A smart idea is to have Coast Industrial build a new hose using original fittings.
  • Oil cooler hoses: These hoses are generally no problem but can sweat at the fittings.
  • Oil filters: The rubber seal in the housing can harden and fail.  Use a fish hook or like instrument to remove the old seal from the housing.  Also, be sure that there is only one seal fitted.  The advantage of the original bowl canister is that it stays full of oil.  Some new spin-on filters do not have a check valve to retain oil resulting in a three-second delay in oil pressure.  This means dry main bearings on startup.
  • Timing chain cover seal: MGAs had a felt seal that frequently leaked.  The solution is to install an MGB cover with a neoprene seal.
  • Side tappet covers: These have a cork or neoprene gasket that often leaks.  Again affix the gasket to the cover with contact cement and apply a silicone sealer to the surface facing the block.  Subaru seal washers, #812764110, can prevent leakage at the cover bolts.
  • Sump gaskets: These are not a problem.  Care should be taken to ensure a flat surface on the sump by filing any uneven spots or ball peening any raised bolt holes.
  • Drain plugs: These are not a problem although copper washers work better than nylon that can crush.
  • Rear engine seals: MGAs used a threaded mechanism to throw oil away from the rear seal.  Leaks were common.  If there is any vibration from a worn bearing, there will be leakage via the giggly pin in the bell housing.  MGBs have a neoprene seal.  A serious leak here means a large pool of oil on the floor.
  • Motor oil: A light mineral oil or a synthetic oil is not good for our engines.  A 5/30 or 10/30 oil will leak faster and be bad for the bearings.  Pennzoil has a 25/50 “Racing Motor Oil” that includes ZDDP that is excellent.  You should add ZDDP to your motor oil.

Oil leaks in the rear axle and differential are:

  • Breather cap: Ensure the breather cap atop the rear axle is clear.  Otherwise, pressure will build up and blow oil out of the seals.
  • Pinion oil seal: The neoprene seal will harden with time and not give a tight seal.
  • Rear hub oil seals and gaskets: These are generally reliable and should be replaced during a rebuild.  Ensure that the paper gasket is .10 thou thickness as thicker ones will not clamp the bearing in the hub properly.  Check to ensure the drain hole in the wheel back plate is clear.  Use a blast of brake cleaner to clear any blockage. 

That’s it on oil leaks…