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My Pajero 2000 was overheating so I called AA. It would get hot going up hills and cooler going down. AA couldn't find anything wrong. I went from Waihi to Wellington with the heating on - which brought the temp down to just over half. I took it into Mitsi service. They couldn't find anything. I took it back a week later. They replaced the thermostat - which didn't work (even I knew that this fix didn't match the symptoms). They finally found out that the radiator was cooler on the bottom half. I googled this and found information about different coolants gelling together. Apparently a known problem with Pajeros.
See http://www.exploroz.com/Forum/Topic/23843/Pajero_overheating.aspx.

Mitsi Service sent the radiator away to a specialist. It has now been flushed.

I am beginning to loose faith in Mitsi service. I suspect that all these problems are due to poor service practices. Thank goodness I didn't blow the head gasket. What do you think? What should I pay for when I pick it up tomorrow? What shouldn't I pay for?

I get my Pajero serviced at Ngaio Motor Doctors and I use Mitsi Service in Wellington for anything complicated. Recently Mitsi replaced the timing belt, all other belts and the water pump (this means they must have drained the radiator - right?) The overheating problem started to occur after this major work.

I use Mitsi service for their "specialist" knowledge - but based on this experience, they have none. I should just use Motor Doctors for everything. do you agree?

Thanks for your help.

Yes, the coolant would have been changed when the cambelt was done, but whether or not this caused the problem is hard to determine, and on the balance of probability, I think it's unlikely that a Mitsubishi dealer would have used the wrong coolant. Also I'm not sure how you could have concluded that the thermostat would definitely not be the problem, as it is one of many potential cooling system components that could have caused the problem.
You don't say what mileage the vehicle has travelled, but on a 15 year old vehicle it is possible that the radiator could need a flush - especially if the service history from new may be unknown and whether or not all recommended coolant changes have been completed on time.
If it can be determined that the incorrect coolant was used and this caused the problem, then the dealer would be culpable for all costs. However, if this is not the case, then all costs would be your responsibility.

Thanks for the reply. The car has done about 110k.

I checked my invoice and the cam belt was changed 6 months ago. How time flies. If this was a cause, it would have been evident sooner. So I agree. Unlikely to have been the cause. (They also replaced the Radiator cap at this time).

They replaced the Thermostat. I was confused about the difference between "sender" and "radiator". I now understand. It did not help. Problem still existed.

They then sent the radiator away, and apparently 1/2 to 1/3 of the radiator was blocked at the bottom. I have not seen a report from the radiator specialist. This still did not solve the problem. Temperature gauge still going vertical.

After further testing, they found a faulty sender. Apparent it has two senders. They replaced the faulty sender.

They have bled the system several times. Apparently, they have a special radiator cap which bleeds the system automatically (if I understood correctly). Problem still exists. The gauge goes vertical.

They have tested the cooling system for head gasket problem. Apparently its OK. I am not sure what test they used. Don't they test for gas in the coolant?

They then said that diagnostic tests indicated that the engine temp is 80 degrees which is exactly where it should be. But the needle still goes vertical.

They now suspect the dashboard gauge. They want to send the dashboard component away to an electrical specialist. I guess this makes sense - sort of.

However it seams like a perfect storm of "coincidences": radiator, thermostat, sender and now gauge? They reassure me that it is not air in the system. They say they have bled it so many times.

Am I right to be suspicious? Four problems at the same time? That is like dealing yourself a Straight Flush. I have never had straight flush.

As far as the head gasket test is concerned, you are correct - a TeeKay test is carried out which checks for hydrocarbons in the coolant. It is a good test but not infallible, however it should always be done on any vehicle exhibiting overheating problems.
If the radiator had varying temperatures from top to bottom, flushing it out would be the appropriate course of action too.
Once the mechanic is satisfied that the cooling system is operating as it should, the next step would be to check the gauge. When you say the needle goes vertical, I believe the gauge layout on the Pajero is such that the vertical position is High. If I've correctly understood, your needle should be pointing horizontally (ie; about half way up the gauge).
If the cooling system and operating temperature are all good and the sender has been replaced, this would point to either the instrument cluster or a wiring fault - so it seems reasonable that the mechanic is suggesting sending the cluster to an instrument specialist for testing. However, it would also indicate that perhaps the sender wasn't faulty, as it's unlikely that the sender and the gauge are both defective.
I can understand your suspicion and although certain processes need to be taken and problems eliminated, like you, I doubt that all these things were necessary.
Good luck with that straight flush:)