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LQQKatJon

Member
Just had a great weekend in the gmc. Was so looking forward to a week without worries, but the GMC decided to test my patience again.
8-9000+ miles on my new engine. Probably 5000-6000 since i did efi.

flawless drive about 200
Miles west friday. And 200 miles back home today. Got gas before heading home and i noticed between gas station and home engine was hot.
246 degrees on the efi computer. Stock guage creeping up past 1/2 way.
i have had a solid 198-202 temps since new engine was in.

i checked with IR gun. Engine hot. Radiator seemed plenty cool.


i went and pulled out the 195 robert shaw. And i stalled 195 of napa’s best thermostat.

fires it up and drove home. (Not far). It was creeping up temp again. Around 220 when I shut it off.

Belts are spinning. No noise. No leaks.
has to be a water pump??? What else. How should i test??

waterpump is I think the last roller bearing a-1 cardone rebuild summit had back in 2019.

IR gun says tank of radiator is 130. Confirms 220-240 at sender. And thermostat housing bolts. So sensors seem to be reading correctly.

hose does not seem to be pinched or collapsed. (Hoses all new with engine)
 

6cuda6

Active member
Oct 3, 2019
477
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Ontario, Canada
Hows your exhaust?

The other thing is did you check in coming and out going temps at the rad? (Not at motor) to make sure rad isnt plugged.

Hows the rad cap? When was the last time it was tested?

Did your efi go lean possibly?

Just a few things to check thst may weed out more diagnostic info.
 

LQQKatJon

Member
Hows your exhaust?

The other thing is did you check in coming and out going temps at the rad? (Not at motor) to make sure rad isnt plugged.

Hows the rad cap? When was the last time it was tested?

Did your efi go lean possibly?

Just a few things to check thst may weed out more diagnostic info.
Thought I did a good job ruling out radiator with IR gun.

but now I see the fan clutch is junk. Wobble wobble That should be an easy thing to swap tomorrow. I had alot of practice with that process the first couple years of gmc ownership.
 
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LARRYT

Member
Feb 9, 2020
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My 78/ 455 seems to run at about 220.. had some things checked out rad seem clean it side and out fan clutch seems ok.. this is why i attached a home made air scoop for testing see new post Larry xpb 78/455
 

LQQKatJon

Member
I took the coach around the block and coach still was getting hot.

Still seemed like my radiator was cooler, but I found when i grabbed the fan, i could rock it. Also had what looked to be an odd pattern on back of fan, so oil must be out. It also spun a little too easy.

so i installed a new fan clutch last night and it is staying cool now. Back locked in near 200 degrees. Actually a little cooler in the high 190’s then it used to.

seems the numbers move more on the ebl screen then they did with old thermostat. Up and down a few degrees as you accellerate hard and then let off.
Prior it rarely temp.

old one was a flowcooler. New one is a standard one, from napa.

time will tell. Should put on another 300-400
Miles this weekend