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I have done this (ran just below the red) several times and three times out of about five I have regreted doing so cause I ended up with cracked heads.
As far as I know the 74 99 head and engine are no more suceptable to cooling problems than other years.
Having owned/owning several 99s and driving in Australian summers (100+ degrees F, 38 degrees C) I know that 99s do not need to overheat. 99s can and do have problems (especially the 99t with A/C) with heat but it definatley can be managed. I have always run my 99s with thermostats and they never have been the cause of overheating. Also I doubt your prob is the water pump as it usually works or it doesn't, and when it fails you will usually know about it through instant overheating or oil in the water or vice versa.
From the sounds of it you have already identified the problem with your 99. If it running ok without the thermostat but runs hot with....replace it. Even if it tests ok it may be sticking and besides Thermostats are relatively cheap and you can buy cooler (82 C?) versions....much cheaper than an new head/engine.
You also NEED to have your radiator rodded, especially if it has been getting hot as this often loosens scale from the block which become lodged in the radiator. 99 cooling systems (in the tubo at least) operate at near capacity and only need to by 10% blocked to cause overheating. Running a good quality radiator flush and flushing the engine throughly may help and should be done regardless.
As for corrosion in 99 heads...99 heads like any alloy other head will corrode badly and quickly if you use tap water and or no corrosion inhibitor. Always use a brand name pre mixed radiator fluid or (as I do) distilled water and corrosion inhibitor.
Does that help?
Justin
ex 78 99t
ex 72 99
curent 77 99 EMS
posted by 203.59.11...
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