Absolutely stumped on this I’ve replaced almost everything and she still slowly overheats honestly lost for words
Took heat gun to it & is accurate enough to gauge
Fan shroud is good
Stuck glove over rad cap hole didn’t blow up the glove
Have tried 50/50 & 70/30 coolant
New rad
New water pump
New coolant temp sensor
New rad cap
New overflow tank thought possibly cause there was a crack in it it could mess up the pressure
Have tried 3 195f thermostats and have tested them every time before putting them in, 1 thermostat I drilled two 1/8 holes in because I thought there could be a possibility it was airlocked, this fixed the overheating issue but engine wouldn’t get up to temp even after 2 hours of driving
Last things I can think of is head gaskets (highly doubt), fan clutch seemed fine when I replaced water pump, maybe when I put new rad in I installed hoses differently???, water pump isn’t reversed
Should mention it’s always overheated since I got her but the rad was in ROUGH shape so that’s where this rabbit hole started
I just fixed another GM with the same problem.
The owner did everything just like you which makes it very hard to diagnose when they start installing parts like a monkey with its hair on fire and once everything is done, the problem still exists.
Go back to basics .... assuming the thermostat is working
WNL ... the holes you drilled into it won't make much difference.
Here are a few observations that are critical to a good diagnosis --->
1. If you get into an overheating condition at less than 20 MPH or idling in traffic, you should suspect the thermal fan clutch.
2. If you get a slow rise in temperature at speeds greater than 45 MPH, suspect the radiator for heavy restrictions, as the thermal fan can't move more air than driving at a speed higher than the fan can achieve.
3. Bubbles or air in a GM cooling system (the exception is a Pontiac Fiero) - cannot exist once the thermostat opens, at least partially.
♠There are no zones where air can collect - this assumes the heater coolant flow is intact and operating with a flow restriction in it - somewhere.
♦ Many - not most - GM heater circuits MUST have a flow restrictor in it to slow the flow through the heater core!
4. A 195°F thermostat is a very good idea; I use the same in all my GMs.
Try this to help with a deeper diagnosis ---
Take an old-used radiator cap --- and remove the lower-smaller diameter rubber seal.
♦ Rip it completely off.
♦ This has now become a tool for testing your cooling system.
Install this modified cap on the radiator itself, start the engine - getting it up to at least 1/2 of the thermostat temperature allowed.
Stop the engine and watch to see if the coolant is sucked from the reservoir, back into the radiator.
♦ This may take a few minutes to happen.
DO this start-up - get some heat - shut down --- a few more times, watching the reservoir so that it doesn't get too low.
♦ You must keep a sufficient amount of coolant in the reservoir at all times!
There may be SOME air bubbles at first, but it will cease after a short while.
FUN FACT: you can "help" to purge the air from the system by FIRMLY squeezing the upper hose and letting go to help pump any air out of the system.
WHAT WE EXPECT TO SEE: We need to get to where there is no more air in the system.
♦ The lower seal, missing from the old cap, is what will allow free travel between the radiator and the tank.
♦ Report back with your findings so we can decide on the next step.
You
HAVE TO climb the limbs of the
LOGIC TREE correctly and in sequence - to arrive at a good diagnosis, and we need to get the basics out of the way first. .
REMEMBER --->
OVERHEATING and
RUNNING HOT are two different things.
Overheating means coolant is actually hitting the ground!
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