1990 gmc safari mini van

Maintenance/Repairs
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1

i have a 1990 gmc safari van when i frist start it up it sounds fine after awile of runninr it like driving 3 miles to wal-mart it starts making a knocking sound could it be the oil cooler clog i have replaced the oil pump oil pan frount mian seal on the timing cover or could it be the oil pan to small and not geting enoff oil i live in arizone and it get to 120 dergrees here please help

2

i forgot to tell you my oil presure is at 70 psi and when it starts geting hot lowers to 50 psi