Heading for Trouble

June 5th, 2011

The other day I was talking to a guy about Tilly – Tilly, in case you didn’t know, is our 2.8 Mk2 LWB Pajero tow truck – we were talking about the usual things as one does around cars and trucks – you know the comfort, top speed, miles per gallon (or should that be metres per gallon?) anyway his last question was the usual “so going alright then?”  “Yes” says I “brilliant – no problems at all” then I made a joke of “Wood, wood where’s the wood” we both laughed as I drove off and I thought no more about it…

Until 2 days later that is, that was the next time I used Tilly, and it wasn’t long before I wished I had found that wood to touch. It took less than 2 miles for Tilly’s temperature gauge to hit the red, fortunately by a layby. Up went the bonnet and a quick squeeze of the top hose told me most of what I needed to know – it was hard, un-giving, not squeezable as it should be – a sure indication of a pressurised coolant system, so that was the end of that trip, and Tilly ended up back in her garage, but not before I did a block test on her, but she didn’t turn the block tester green as would normally happen with head or head gasket problems.

Now she was definitely pressurising the cooling system, and, as far as I know, there are only 3 causes for that to happen

  1. Faulty water pump impeller (if the impeller doesn’t turn and circulate the coolant then the coolant overheats and builds up enough pressure to blow the top of the radiator off)
  2. Faulty thermostat (this also can cause overheating and pressure build up in the cooling system)
  3. Cracked head or damaged head gasket

Now it was time to find out which of the above 3 was Tilly’s problem. First the water pump was ruled out as it was only replaced at the beginning of the year when the impeller came loose on the old one (due to lack of anti-freeze) and caused the top of the radiator to blow off! As we had tested for head problems and she’d passed that we went for the thermostat, so we took it out and tested it to find that it opened and closed quite well around about the temperature it was supposed to.

The thermostat went back in and we ran up the engine again and once more the cooling system pressurised. So we did another test with the block tester but it still stayed in the blue. So now it was back to basics, before we got the block tester, head problems were diagnosed by the following symptoms:

  1. Engine overheating
  2. Cooling system pressurising
  3. After taking the radiator cap off – revving the engine causes the coolant to flow up out of the radiator
  4. On tick over with a topped up radiator bubbles will come to the top of the filler

Tilly managed 4 out of 4 of those, so she had head problems. Now came the strip down.

As with all strip downs there are things you need to take off and others you don’t. With a 2.8 we are looking at the following:

  1. Remove the intercooler
  2. Remove the air hoses and air filter (I find the empty air box to be a handy storage place for nuts and bolts removed from the engine)
  3. Drain coolant system
  4. Remove top radiator hose
  5. Remove the bolts holding the pipework to the engine, the vacuum pipe can be removed from the vacuum pump and the small pressure hose removed from the fuel pump but the PAS pipework can be left connected
  6. We removed the bolts from the thermostat housing to facilitate easier removal of the solid cooling pipe between it and the head
  7. The manifolds stay on the head there are 2 studs and a bolt that connects the exhaust manifold to the turbo, these are undone
  8. The oil feed pipe to the turbo is connected to the engine block, not the head on the 2.8, removal is not needed
  9. Remove the wiring to the fuel pump, oil pressure switch and glo plugs (most sane people will have isolated the batteries before step 1)
  10. Remove the small coolant hose between fuel pump and top hose union
  11. Undo injector pipework and pull back from injectors
  12. Remove hose from injector fuel spill line
  13. Remove the oil pressure switch
  14. Remove the oil feeder pipe between the vacuum pump and the head, be careful you do not lose the copper washer from the head end down behind the fuel pump
  15. Remove heater matrix hoses
  16. Remove the 2 bolts holding the rocker cover and remove rocker cover (be careful – there is a small pot on the cover that contains oil which will spill all over the engine compartment if you don’t drain it)
  17. Remove the half moon gaskets at the rear and the front of the head
  18. Remove the chain tensioner from the side of the head
  19. Remove the bolt holding the chain sprocket to the camshaft WARNING – this bolt has a left hand thread
  20. Remove the sprocket from the camshaft, putting a cable tie through the chain will hold the sprocket safely in position (it is important not to remove the sprocket from the chain)
  21. Undo and remove the two front bolts on the head – these have a 12mm hex head and bolt into the timing chain cover
  22. Crack off the 18 head bolts in reverse order (the bolts are tightened from the centre outwards so undo them from the ends to the center) You may find that one or two of these bolts seem not so tight as the rest – make a note of where these are as they could point to the position of your trouble
  23. Completely remove the head bolts
  24. A soft headed mallet can now be used to loosen the head or a lever used to pry it up DO NOT PRY BETWEEN HEAD AND BLOCK you will damage the aluminium head
  25. Now the head is free you should be able to lift it off

There will be oil in the head still so make sure you have something on the bench or floor to soak up the oil – cardboard or newspaper is best – don’t use sand or sawdust until after you put the engine back together (both sand and sawdust are excellent for destroying engines). With the head upside down you can now check the face for hairline cracks – No cracks can mean a 85% chance (possibly more) of the head being ok, at the same time some cracking may not mean that the head is shot, to be 100% sure you’ll need to have it pressure tested – have a look for engine rebuilding engineers for that service. Many may advise a head skim as well, be careful here because the 2.8 head has ceramic inserts and they can’t be skimmed ask advice of the person that will skim it.

You also need to check the condition of the old head gasket, examine it carefully look at the condition around the waterways – some of the pockmarks in it will be caused by bits of the gasket having stuck to either the block or head. Look for track marks between cylinder and waterways, check the metal ring that runs around the hole for the cylinders – this was the problem on Tilly, one of them, Head Gasket Problem #1 cylinder, had split and it was this causing the problem the pressure was escaping through this split and then through the gasket material and pressurising the waterways, the gasket material acting as a filter to filter out the gasses that would have turned the block tester green


Head Gasket Problem 2Another giveaway was the bolts around the #1 cylinder on the right side felt looser than the rest when cracking them off and one had a trace of contaminated oil on the thread on removal.

Now let’s build the new parts list, although the head was showing cracks we were not too concerned with them, they were small surface cracks and not in places where they would be pressurising the waterways so our list was as follows:

  1. Head gasket
  2. Head bolts – Mitsubishi tell us that the head bolts can be reused up to 3 times and should be marked with a center punch each time it is reused – our head bolts had only been used once but were of unknown origin so we decided to replace them again
  3. Rocker cover gasket
  4. Front and rear half moon gasket
  5. Gasket cones for under the rocker cover bolts

Those last 3 items are very important if you want to keep the oil on the inside, Tilly’s half moons were hard and un-giving, like metal but brittle and both Tilly’s engine and engine bay have a coating of black oil on them – perhaps this is something that should be done every other oil change…

A few days later…

The spares duly arrived and with the head and block scraped clean of old gasket it was time to reassemble – we have the Mitsubishi workshop manual to follow, the Haynes head tightening sequence is a straight copy of this, however, had the head gasket come with it’s own tightening sequence we would have followed those (if a gasket company goes to the trouble to supply instructions then those instructions match the gasket)

Two things I hate with the instructions – one is to tighten a head bolt by bolt to 100Nm – I’ll always take it to 50Nm first then 100Nm, I see no point in attempting to warp the head by putting such uneven pressure on it the other is the two quarter turns – we spend years developing a tool that will measure torque accurately and what do the big boys do  – they tell us to give the bolt two extra quarter turns – they’ll be telling us to turn the truck on it’s side and jump up and down on a spanner next…

For the rest reassembly is the reverse of disassembly but remember that you have to reset the chain tensioner, do this by pushing on the end of the tensioner while prying the pawl away from the teeth with a small screwdriver then setting the hook to keep the piston in it’s closed position. Once you have the sprocket back on the cam shaft you can replace the tensioner and then with a longish screwdriver push down on the hook to release the piston allowing the tensioner to tension the chain – Standard warning: do not turn the engine backwards once you have done this or the tensioner will over tension.

Assembly is no real problem except the seals I obtained for the rocker cover did anything but seal, whether it was because they were too hard I don’t know, but sealant was needed as well and then extra sealant a day later when the seal still leaked. I shall be looking to buy genuine Mitsubishi ones the next time I take off the rocker cover!

Some afterthoughts:

We discussed some reasons as to why the gasket had gone:

  1. Faulty gasket – possible going to see how the replacement holds out
  2. Incorrect tightening of the head bolts – ruled out because the last gasket was fitted by us and we use a professional and certificated torque wrench
  3. Overheating – contrary to popular belief overheating in the first instance is usually caused by a component other than the head or head gasket giving way…

When we originally fitted a replacement head with a new gasket to Tilly it was getting into summer last year and antifreeze was the last thing thought of, in fact it was forgotten about until she overheated and blew off the top of the radiator. The cause was a loose impeller on the water pump (the coolant had frozen the impeller and when the engine had started it forced the pump shaft to revolve in the impeller hole) Then less than a fortnight later the alternator or drive belts (what was once called fan belts) broke causing yet another overheat. Both of these overheats may have possibly contributed to weakening of the head gasket causing it to fail about 5 months later…

Leave a Reply

What is 2 + 5 ?
Please leave these two fields as-is:
IMPORTANT! To be able to proceed, you need to solve the following simple math (so we know that you are a human) :-)