Lt1 running hot - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
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post #1 of 11 (permalink) Old 05-02-2018, 10:00 AM Thread Starter
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Lt1 running hot

Hi guys I’m sean I own a 1996 firebird formula it has the lt1 engine and for some reason the car will run hot on my wile I’m in traffic or a drive threw pretty much if the car idles for longer then 10 minutes it starts running hot any help with this issue would be greatly appreciated
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post #2 of 11 (permalink) Old 05-02-2018, 11:47 PM
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First, how hot is hot? Second, have you checked if the fans are working?

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post #3 of 11 (permalink) Old 05-03-2018, 06:34 AM
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After making sure fans work, know that fan factory turn on temps are 226 degrees for low speed & 236 degrees for high speed. Use an obd 2 scan tool with real time sensor data to check fan turn on temps.

This is because pcm sees coolant temp from different sensor than gauge does. Pcm water temp sensor is on water pump. You can make fans come on eariler than 226 degrees several ways. You can change turn on temps in pcm. Or you can wire in a manual fan switch as per Shoebox's instructions on his site.

#7 in electrical section. And you don't need a double switch to give 2 speeds. I just wired in a switch on my 95 for high speed fan operation. THe good part of the manual fan switch, the way shoebox has it wired is, when switch is in off position, pcm can still command fans on.

If you check out fans and they don't work, shoebox has the 3 relay fan wiring diagram on his site. #4 in electrical section.

Also you can go to the following link and download the 96 service manual.

Last edited by cocobolo95; 05-03-2018 at 06:41 AM.
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post #4 of 11 (permalink) Old 05-03-2018, 07:02 AM Thread Starter
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Yes the fans come on but they won’t kick on until about 255 degrees or until the needle goes into the red driving on the highway it’s fine but any kind of drive threw or traffic it gets hot quick 10 minutes or less I’ve changed water pump thermostat bleed the coolent system several times the car has no a/c I’ve read how the a/c tells the fans when to kick on or something similar I was wondering if a performance radiator would work also when I’m accelerating 3500 rms and higher it feels like the engine runs a little rough it has about 150,000 miles on it but other then some slight vibration and the over heating the car runs great. Thanks much for the reply’s men.
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post #5 of 11 (permalink) Old 05-04-2018, 07:13 AM
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I would still put car on obd 2 scanner to compare guage temp to what pcm is seeing.

Did you bleed air out of system when you changed the temp sensor at water pump? Air in cooling system will cause coolant to heat up quickly, especially while idling & slow driving.

Yes, if you have working ac, fans should kick on when you turn ac on.

Running a fan switchto control high speed fan is easy to do. Per pic on shoebox site, you splice a wire into the blue wire at cavity D of connector C100. The connector is on passenger side inner fender near computer.

Run the wire you spliced into blue wire into passenger compartment. Connect this wire to 1 side of an on off switch. To the other side of the switch, attach a wire and run this wire to a good ground in passenger compartment.

You now have a switch so you can turn on your fans anytime you want them on. And when switch is in off position pcm can command fans on.

Last edited by cocobolo95; 05-04-2018 at 07:21 AM.
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post #6 of 11 (permalink) Old 05-14-2018, 02:37 PM
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I had the same issue with my '96 Z28 6-speed. I first dug into the shop manual and designed a 3 position switch to manually control the fans either at high or lower speed, with the third position at the factory automatic mode. Although it worked just as planned, the ECM didn't like it and lit the dreaded "check engine light". I could not stand to drive with that on all the time , plus I wouldn't know if it was indicating another issue. I purchased a kit from Caspers Electronics that plugs into one of the wiring harnesses to the ECM. It works great, and the computer is satisfied. When city driving, I will manually turn on the fan(s) to get more air through the radiator. I also installed a 180 degree thermostat.
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post #7 of 11 (permalink) Old 08-14-2018, 06:14 PM
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I Have an LT1 with 121K Miles on. Found out Fans were Not Running. Wired the Up together. Both Burned Out?? Bummer. Ground was to Small. Bigger Fan Still Gets to the Red Mark. Checked Stat. Was Completely Closed. #$&%?? New 200 Degree Stat. Still Will Peg 260 If I Let it. Now Trying No Stat. Got to 220 & I Went Back Home?? Water Pump & Head Gaskets. When I Take Cap off Like a Volcano. Pressured Cap. No Leaks Unless I Open the Factory Cap.. ??????? PUZZLED in Minnesota..

Pop's Body & Kustoms @ 74 Years Old. Used 2 Work 4

House Of Kolor in Mpls. Mn.
Jon Kosmoski....

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post #8 of 11 (permalink) Old 12-23-2018, 01:53 PM
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I just replaced blown head gaskets on a 95 Z28. The guy I got it from said it overheated and finally started leaking out the back of the motor. He let it get so hot the heads warped, then the water jacket blew out the back of the head gasket. Compression rings were still intact.

After I got it all together, I could just tell standing next to it that the reason the water jackets blew was because of a bad radiator cap. It wasn't opening at 18psi to allow excess pressure to go into the overflow. I replaced the cap and now it's running perfect.

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post #9 of 11 (permalink) Old 12-31-2018, 02:01 PM
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My 97 runs very hot, it will stay at 225-235 while moving, but as soon as I stop and let it idle it starts creeping up to 250+. Its always done that though, despite coolant flushes, radiator change, cleaning leaves out of the grill area, etc. Mine has 155k miles now and still runs strong. It even does this when its relatively cold outside, like just last week it did it at 50 deg F.

Since its not my only car, I tend to avoid driving it in traffic, mainly to avoid overheating and to spare the clutch that torture. I think its pretty normal. The only way to make it run cooler while idling is to somehow get more air to the radiator (which isn't easy with the retarded way the front end is designed) or add higher flow rate fans, which I have never seen done.

You could try adding that coolant additive they sell at autozone, I dont think it does much, but even just a few less degrees will help. A performance radiator may be doable as well, but then again, that wont change how much air is getting to your radiator to begin with. So idk. It hasnt seemed to hurt mine though after 100k+ miles of it doing that.
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post #10 of 11 (permalink) Old 02-21-2019, 01:20 AM
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My experience with overheating...mine was the aftermarket radiator cap...and not bleeding the system properly...After installing a OEM radiator cap new hoses and bleeding properly....the temps stayed at a cool 225f.....and I definitely get nervous if my car is sitting in traffic too long...
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post #11 of 11 (permalink) Old 02-25-2019, 07:04 AM
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Somethings no one has mentioned in this thread are; the steam pipe system. Is it intact and not clogged up. It is vital to the proper cooling of the reverse cooled lt1.

Next, are all the hoses & tubes attached to the right place. Not doing this correctly can cause all sorts of overheating problems. There are diagrams of proper hose & tube connections @

Don't forget proper bleeding of air from system. Because radiator is lower than engine , like on a mid engine car, bleeding the air out is essential to proper cooling.

If fans are not coming on, repair them. Also make sure fan is not wired in reverse. The proper direction of air travel is in, with air flowing into engine compartment. If fans are wired so they push air out of engine compartment, the airflow through the radiator is substantially less than with fans pulling air in.

Don't forget the proper radiator cap, and try a thermostat with a lower opening temp. And lt1 engines use a special thermostat made especially for the lt1. A sbc thermostat will fit the opening, but will not work correctly with the lt1 reverse cooling system.
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