Overheating - new guy
That gauge is acting just like my Silverado did when it blew its head gasket. Air would build up and then when you reved it up it would push the air back out of the system because the water pressure rose. It to passed the head gasket test but you could clearly see air bubbles in the expansion tank
Thread Starter
Teching In
Joined: Oct 2019
Posts: 28
Likes: 1
It’s fixed. It was a bad thermostat.
I mentioned earlier I was going to replace the thermostat and radiator cap just to eliminate the easy stuff. I found AC Delco parts, not the Autozone no name type replacements.
When I had the old thermostat out I put it next to the new Delco unit. It didn’t pass the eye test. I put my ruler next to them. You can see in this photo that the old one on the right seems to be about 1/8 inch taller than the new unit.
http://www.arkansaspontiacs.org/25th/tstat.jpg
Next I did the boiling water test. You’ll remember I asked how wide these thermostats should open. Well I got that question answered. It’s a hell of a lot more than that old one.
I put the new thermostat in and drove it this afternoon. All good. It barely got to 180 idling in the driveway after an extended drive and it immediately dropped when I heard the first fan come on.
This is in the win column.
I mentioned earlier I was going to replace the thermostat and radiator cap just to eliminate the easy stuff. I found AC Delco parts, not the Autozone no name type replacements.
When I had the old thermostat out I put it next to the new Delco unit. It didn’t pass the eye test. I put my ruler next to them. You can see in this photo that the old one on the right seems to be about 1/8 inch taller than the new unit.
http://www.arkansaspontiacs.org/25th/tstat.jpg
Next I did the boiling water test. You’ll remember I asked how wide these thermostats should open. Well I got that question answered. It’s a hell of a lot more than that old one.
I put the new thermostat in and drove it this afternoon. All good. It barely got to 180 idling in the driveway after an extended drive and it immediately dropped when I heard the first fan come on.
This is in the win column.
Teching In
Joined: Nov 2019
Posts: 27
Likes: 1
From: Arizona
Hello. My first post. To explain, I recently purchased a 1994 25th anniversary Trans Am. It has 70K on the clock. It has some problems and I'm trying to work them out. Mechanically, I'm fairly adept since I've restored some 2nd generation Trans Ams and have owned a few Fieros in my day. I'm in uncharted waters with this LT1 however and I need your help please.
The problem is that the car runs very well as long as your cruising. But if you're at stop light for very long the temperature shoots up quickly.
What I've done so far:
I brought the car up to temp and opened both bleeder screws and verified a steady stream of coolant from both. Verified coolant levels in the radiator and in the overflow tank.
Removed the air intake box and verified that the coolant temperature sensor is installed in the water pump.
Verified that the temperature sensor for the gauge is plugged into the passenger head (and must be working since the gauge works).
What I've been told and know as fact:
I was told by the previous owner that they had recently replaced the water pump and the opti.
I know as a fact that the fans are all running as soon as you fire it up.
Today I data logged it using the Scan94/95 software with my ALDL cable. Here's where it gets weird. The real time display showed the coolant temperature at roughly 75 degrees, comparable to the outside air temp. I let it run for a minute or so while I checked for codes, electrical faults. I saved the data log. I shut it all down before it even came up to operating temp since I was mostly looking for codes even though there was no CEL. I did notice while it was running that both fan relays showed to be active and I could hear the fans running.
Then I came inside and played the data log back. When I did, from cold start, it showed the coolant temperature at 169 F. and went up from there. So I guess that explains why the fans are on.
So what the heck is going on here? Has someone screwed with the program to keep the fans on always? And why? To disguise or delay the overheating? And since the fans are running all the time this has nothing to do with the root problem of overheating, does it?
Thanks in advance for all responses. Much appreciated.
The problem is that the car runs very well as long as your cruising. But if you're at stop light for very long the temperature shoots up quickly.
What I've done so far:
I brought the car up to temp and opened both bleeder screws and verified a steady stream of coolant from both. Verified coolant levels in the radiator and in the overflow tank.
Removed the air intake box and verified that the coolant temperature sensor is installed in the water pump.
Verified that the temperature sensor for the gauge is plugged into the passenger head (and must be working since the gauge works).
What I've been told and know as fact:
I was told by the previous owner that they had recently replaced the water pump and the opti.
I know as a fact that the fans are all running as soon as you fire it up.
Today I data logged it using the Scan94/95 software with my ALDL cable. Here's where it gets weird. The real time display showed the coolant temperature at roughly 75 degrees, comparable to the outside air temp. I let it run for a minute or so while I checked for codes, electrical faults. I saved the data log. I shut it all down before it even came up to operating temp since I was mostly looking for codes even though there was no CEL. I did notice while it was running that both fan relays showed to be active and I could hear the fans running.
Then I came inside and played the data log back. When I did, from cold start, it showed the coolant temperature at 169 F. and went up from there. So I guess that explains why the fans are on.
So what the heck is going on here? Has someone screwed with the program to keep the fans on always? And why? To disguise or delay the overheating? And since the fans are running all the time this has nothing to do with the root problem of overheating, does it?
Thanks in advance for all responses. Much appreciated.
More unlikely/difficult suggestions would be maybe proper fan rotation direction, a weak low/high fan, improper voltage.
Start by flushing and bleeding the system. Are you losing any coolant? Check for a blow head gasket.
The line going under the battery tray is an often overlooked trouble spot, though. 
