96 Isuzu Rodeo - Overheating and Tappets issue

Hi, My 96 Isuzu Rodeo (V6 3.2L) tends to overheat when I am stopped in traffic. It cools down when I start to move again. I just had the water pump replaced a couple of months ago (when I noticed the
coolent level dropping consistently). But I still see it overheating though not quite as often as it used to before the water pump replacement. I am not sure if it's a thermostat issue or a fan clutch issue. Any ideas on how I can troubleshoot/fix this?
The second issue is related to the valve tappets as I have been told. The engine makes a fluttering noise and sometime sounds like a diesel engine. If I take the car out on a long road trip the noise goes away for a few days but comes back. Is there a way to fix this without having to replace the tappets (for $1500 which I've been quoted)? I've tried using heavier 10w40 motor oil although it only seems to be a temporary fix.
Thanks in advance for your suggestions. B.
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beeker01 wrote:

overheating at idel , sound like a cloged rafiator to me lifter noise on isuzu engine is quite normal specilly when they het older You may want to try flushing the engine a couple of time with either sea foam or a good other brand of flush
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