5.7L overheats. not a newb. any ideas? - Third Generation F-Body Message Boards

thebigblue · 08-11-2009, 11:09 PM

1999 gmc 2500 5.7L, 60k miles chassis. Reman engine 2k miles ago. Was running fine but got 10-12.5mpg with slight hesitation off idle. Ran 170F indicated. Had read faulty temp sensors can run rich w/o CEL so replaced temp sending unit and coolant temp switch with complete tune up. Shop cleared old stored codes and it ran alot better. But instead of always 170F I got ~185-195 idle with heat on, ~210+ idle no heat, ~220+ idle with a/c on, ~210-220 driving A/C. I put in another new 195F tstat, sender and switch. No change. Burped system 4 times w/ heaters cranked. Radiator tested fine at shop. No noise or leaks from pump. Oil is clean/clear, coolant is green/clear.Vacuum and fuel press test fine. Shroud on. Heater works. Installed heavy duty fan clutch. Now 200F no a/c and 210 w a/c. Laser readings after 30min idle and 10 min drive at 55mph. HEAT ON - tstat house 175-180, up hose 165, top right rad 160, mid left rad 135, low hose 125-130, pass head near 6 and 8 195-205, pass head rear 195-200, drive head rear 185-190, temp send unit 185-195, dash reads 210. A/C ON - tstat housing 199-202, up hose 186, top right rad 185, mid left rad 165-170, low hose 165, pass head near 6 and 8 210-213, pass head rear 206, driver head rear 193, driver head near 5 and 7 207, temp send unit 215-218, dash reads 220-225. then 55mph for 10 min at 215-220 w heat on. no boil over. any ideas?

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camaronewbie · 08-12-2009, 12:48 AM

Already posted this in the cooling board (where it should be IF it was 3rd gen related, which it's not) - please don't double-post - especially when it's a non-3rd gen related subject! It makes folks around here

thebigblue · 08-12-2009, 01:57 PM

right. thanks for the help.