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Doug, Australia Car Mechanic
Category: Australia Car
Satisfied Customers: 8606
Experience:  ASE Certified Factory trained technician
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Mitsubishi Pajero: Mark,We have a teenager from overseas

Customer Question

Hi Mark,
We have a teenager from overseas staying with us and made the mistake of letting her drive our older 1994 Mitsubishi Pajero (NJ) 3.0L auto when we knew we had a slow radiator leak. She drove it with NO water/coolant in the engine. When she pulled into our driveway it stopped and would not go further she said. We could hear the steam whistling even after she turned off the vehicle. We allowed it to cool and added water. We drove it just a few feet out of the way of the other vehicles. When we turned it on it had a loud knocking noise. How much and what kind of damage do you think has been done. PS She will not be driving any of our other vehicles, since she does not understand how to read a heat gauge!
Submitted: 2 years ago.
Category: Australia Car
Expert:  Doug replied 2 years ago.
Unfortunately with it having been run dry to this level of over heating, it would be fair to expect a major over haul is in order now.
Whenever the vehicle is run out of coolant like that you will end up with head gasket failures usually within a mile or two of reaching full hot/over heat condition. If it is driven beyond that is when you risk more internal, as the dissimilar metals in the heads and bottom end are going to cause havoc and bottom end bearings will begin taking a beating, cam to head clearances, lash adjusters etc.
What needs to be done at this point is try to verify that the knock is bottom end related (And not just coincidental timing for some other issue). Running the engine while listening at the bottom end with a stethoscope to see if the noise is most obvious there, or up at the valve covers or somewhere else (accessory drive etc).
Once you have a good idea of the noise location, I would then pull the intake and perform a compression test to see how bad a hit the heads took, OR if you want to use a less scientific approach, run the engine up to operating temperature and see if it begins running hot even though it is full still, or burning coolant etc. Both indications the head gaskets took a hit.
There is always the slight chance that there was no permanent damage... but it is very unlikely from the way you describe it. I think your best case scenario here would have been that they cruised in to the driveway just as it was at its worst, no damage was done to the head gaskets/heads, and the knocking noise was the lash adjusters cooking and losing pressure. At that point you might get away with a fresh oil change an a*****to quiet it down or worst a new set of lash adjusters.
Again from your description, I don't think this is going to be the case though... it sounds more like it was driven to excess in an over heat condition, and at that I would anticipate the worst. Have the noise inspected to try to isolate its location (if it is bottom end, of course you know you're going all-in at that point), and check the compression for head failure (or again run to temperature for comparison, or use a chemical leak detection test etc).

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