MG TA (MPJG) Oil in the radiator problem

For a number of years, I, like many other TA owners with original type MPJG engines, suffered the problem of oil accumulating in the radiator header tank. Every now and again I would get a bent spoon and scoop out the oil floating on top of the water and wipe the internal neck of the radiator to get rid of any ‘mayonnaise’! It never affected the performance of the car, or made it overheat – it was just an annoyance!

I initially thought it was due to a cracked cylinder head, so I had the head off and had it crack tested. Sure enough, there was a crack on the top surface of the head between valves 4 and 5, the siamesed exhaust valves.

I got another head and had it crack tested; all was OK, so I built it up with new valves and guides and fitted it to the TA. I flushed out the radiator several times and filled it with water/antifreeze mix and thought my problems were over.

Sadly, after a short while, oil started to appear in the radiator header tank again; surely my new head couldn’t have cracked so soon! I magnafluxed it and it appeared OK.

Another TA owner I spoke to, told me he had a similar problem and he had cured it by fitting a modified rear rocker pillar. The oil to the rockers is fed directly off the main oil gallery via a copper pipe to the cylinder head, then via a hole in the centre of the base of the rear rocker pillar up to the rocker shaft. This oil can be up to a pressure of 60 to 70 psi and the back of the head oil gallery is very, very close to the internal water jacket in the head. It is possible that the head casting there is very thin and oil in very small quantities is forced through the porous casting into the water jacket, then via the water pump to the radiator, where it accumulates in large blobs! The cooling system is not pressurized, so no water flows the other way into the oil and the sump.

So, I purchased one of these modified rear rocker pillars and fitted it to the engine. It appears to have cured the problem as in the past year I have had no oil in the radiator. Following this early sign of success, I have had a small batch of these modified rocker pillars made and slightly improved on the one I purchased. This modification moves the oil feed to the rockers to being outbound of the back of the head where coolant is present.

Detailed below, is the procedure for fitting such a modified rear rocker pillar. This modification can be done without the need to strip the cylinder head down, and should not be beyond the scope of a competent home mechanic. You will need a couple of BSF spanners, a scriber, electric drill and a small Allen key. You will be replacing the rear rocker pillar.

  1. Remove the rocker cover and the rocker shaft, making sure that no pushrods drop down into the sump! Then disconnect the oil feed pipe to the cylinder head, and remove the male/male oil union in the head.

  2. Clean the area around the base of the rear rocker pillar, then put a clean rag into the head oil drain cavities where the push rods protrude. Cover the valves/springs with another rag to ensure no swarf gets into the engine. Place some gaffer tape around the edge of the rear rocker pillar mounting area.

  3. Scribe a centre line through the two 8mm tapped holes and current oil feed hole to the edge of the head, then mark a spot along this line 13mm from the rear edge of the outer M8 tapped hole for the rocker pillar mounting bolt. This will be the position for the new oil supply hole. Centre pop the mark and carefully drill a 1/8 inch hole down vertically through the head into the oil feed gallery. If possible, have a vacuum cleaner handy to suck away all the swarf! Then take a ¼ inch drill and enlarge the hole that you have just drilled. Clean away all the swarf from around and within the oil feed gallery.
  1. Now you will need to take the ¼ inch BSF tap supplied with the kit, apply a little drop of cutting oil (or 3 in1 oil) to the end of the tap, and carefully tap a ¼ BSF thread into the oil feed gallery. Be careful and watch the tap go through the first rear rocker pillar mounting bolt hole. It is not necessary to cut the thread all the way along the gallery. Once again, clean all swarf out of the gallery using a vacuum cleaner, and blowing down the hole.

  2. Now take the ¼ inch BSF grub screw that came with the kit, apply a drop of Loctite or thread sealant to the grub screw and using a small Allen key, screw the grub screw into the newly tapped hole in the oil gallery. You will only need to screw it in until it just goes past the rear of the new oil feed hole drilled in step 3. Finally, blow down the newly drilled oil feed hole using a short piece of tube, a cycle pump, or air-line if you have one – cleanliness is very important. Carefully remove the gaffer tape and rags from around the valves/springs and oil drain cavities.

  3. Take the rocker shaft assembly, remove the rear circlip, spring and spacer, plus No.8 rocker and the old rear rocker pillar. Fit the new rocker pillar with the oil hole outer-most and replace No. 8 rocker, spring, spacer and circlip.
  4. Refit the rocker shaft assembly, ensuring that the pushrods are correctly located. I usually put a bit of Loctite (or thread sealant) on all 8 bolts as I don’t have any lock-tabs. Do not over tighten these M8 x 1 bolts, certainly no more than 15lb/ft if you use a torque wrench. Then screw the male/male union back into the head complete with its copper washer and reconnect the oil feed pipe to the cylinder head. Quickly check the tappet clearances using the rule of 9 (adjust 3 with 6 open etc.,), 15 thou exhaust and 10 thou inlets. Start the engine and just visually check that oil is flowing around the rockers. If all OK, replace the rocker cover and run the engine until it is hot. Then remove the rocker cover and set the tappets correctly with the engine hot, replace with a new rocker cover gasket (if necessary) and then replace rocker cover.
  5. Drain the radiator and cylinder block, refill with water and a flushing agent, such as Holts Speedflush (or a dishwasher tablet) etc., then run the engine until the thermostat opens and the engine is hot. Drain the cooling system again and this time fill it with 50% clear water (preferably de-ionised water) and 50% blue antifreeze. The job is now complete.
  6. Hopefully, you will, like me, no longer see oil floating on top of the coolant in the radiator header tank.

    You can buy a kit for this modification from the MG Octagon Car Club under part number SCH051A – it comes complete with ¼ BSF tap and grub screw, plus instructions.


    Other brands are available

    Ed’s note:

    In accordance with their mutual status, you need to be a member of the MG Octagon Car Club to purchase their spares.

    To join the Club, please go to

    To view the Club spares list, please go to

One thought on “MG TA (MPJG) Oil in the radiator problem

  1. Mr Tim Parrott says:

    I tie my push rods with string to stop them dropping in the sump.

    Also a magnet will pick up the swarf if you have one. Chop up a fridge magnet to get into the smaller crevices.

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