LT4 Overheating.....
Thread Starter
Race Director
Joined: Apr 2002
Posts: 17,723
Likes: 1
From: Santa Ana, Costa Rica
LT4 Overheating.....
Ok...There was just a post about overheating, but no follow up....Here's my problem
96 LT4, less than 18,000 miles on it......Heating up to 230-240+ and no fans....I put a new 180 degree t-Stat in it today, and still overheating....heater works fine, A/C works fine, in fact, the only time the fans come on is when I turn on the A/C.
The radiator is perfectly clean, the anit-freeze is fine, I checked all the fuses, and everything looks ok........Fan relay?
How can I check this out?
Any ideas would be appreciated!!
:cheers: :cheers:
:seeya
96 LT4, less than 18,000 miles on it......Heating up to 230-240+ and no fans....I put a new 180 degree t-Stat in it today, and still overheating....heater works fine, A/C works fine, in fact, the only time the fans come on is when I turn on the A/C.
The radiator is perfectly clean, the anit-freeze is fine, I checked all the fuses, and everything looks ok........Fan relay?
How can I check this out?
Any ideas would be appreciated!!
:cheers: :cheers:
:seeya
Burning Brakes
Joined: Apr 2001
Posts: 994
Likes: 0
From: Jamison PA
Re: LT4 Overheating..... (DCTC)
I looked at my GM Service manual and a cooling fan functional check has to be performed with a scan tool. However all signs point to either the cooling fan relays or the PCM. I know this isn't much help but it'll give you somewhere to start. Cooling fan relays are in line with the wiring for the fans in the engine compartment close to where the headlights would be if hood was down, on the drivers side.
[Modified by Tony.96LT4, 9:24 PM 11/23/2002]
[Modified by Tony.96LT4, 9:24 PM 11/23/2002]
Cruising
Joined: Aug 2002
Posts: 12
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From: Rockwall Tx
Re: LT4 Overheating..... (DCTC)
My 96 LT4 does the same thing if I am in traffic with the AC off. When I turn on the AC it cools right back down. Of course, in the winter, this procedure is tough to take. Please post with any solutions you may uncover.
Rick :cheers:
Rick :cheers:
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,008
From: Texas
Re: LT4 Overheating..... (DCTC)
Make sure you're verifying the temp based on the digital temp readout, and not the analog gauge.
Stock fan turn-on temps are 219* (1st fan) and 227* for the 2nd fan.
Also be sure to check for crude plastered against the a/c condensor and the radiator. All it takes is one plastic bag to be sucked up while driving to mess up cooling.
Jim Mason
'96 Grand Sport #007
LT4 HOT Cam, HD Meziere, Flowmasters, LT1 Edit, etc, etc
Stock fan turn-on temps are 219* (1st fan) and 227* for the 2nd fan.
Also be sure to check for crude plastered against the a/c condensor and the radiator. All it takes is one plastic bag to be sucked up while driving to mess up cooling.
Jim Mason
'96 Grand Sport #007
LT4 HOT Cam, HD Meziere, Flowmasters, LT1 Edit, etc, etc
Drifting
Joined: Jun 2000
Posts: 1,955
Likes: 2
Re: LT4 Overheating..... (96GS#007)
Make sure you're verifying the temp based on the digital temp readout, and not the analog gauge.
Jeff
Melting Slicks
Joined: May 2001
Posts: 2,143
Likes: 7
From: San Diego CA
Re: LT4 Overheating..... (DCTC)
If the fans come on with the A/C then the fan relays are most likely OK.
If the idle is high (>850rpm) when the car is warm I would suspect the sensor on the front of the water pump. Plug could be loose, contacts gummed up or just a bad sensor. This is the one the PCM uses to sense coolant temps.
If the idle is high (>850rpm) when the car is warm I would suspect the sensor on the front of the water pump. Plug could be loose, contacts gummed up or just a bad sensor. This is the one the PCM uses to sense coolant temps.
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Cruising
Joined: Aug 2002
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From: Rockwall Tx
Re: LT4 Overheating..... (John Row)
Good point on the crap in the radiator. I need to check mine. If the second fan comes on at 227 then I most likely am fine as mine never goes over 225 before stabilizing and then goes back down after I get some air rolling through it at speed.
Thread Starter
Race Director
Joined: Apr 2002
Posts: 17,723
Likes: 1
From: Santa Ana, Costa Rica
Re: LT4 Overheating..... (96GS#007)
Make sure you're verifying the temp based on the digital temp readout, and not the analog gauge.
Stock fan turn-on temps are 219* (1st fan) and 227* for the 2nd fan.
Also be sure to check for crude plastered against the a/c condensor and the radiator. All it takes is one plastic bag to be sucked up while driving to mess up cooling.
Jim Mason
'96 Grand Sport #007
LT4 HOT Cam, HD Meziere, Flowmasters, LT1 Edit, etc, etc
Stock fan turn-on temps are 219* (1st fan) and 227* for the 2nd fan.
Also be sure to check for crude plastered against the a/c condensor and the radiator. All it takes is one plastic bag to be sucked up while driving to mess up cooling.
Jim Mason
'96 Grand Sport #007
LT4 HOT Cam, HD Meziere, Flowmasters, LT1 Edit, etc, etc
I'm suspecting the temp sensor, because the fans HSOULD come on at the intervals you mentioned......But DON'T...
Thanks for the help so far...keep em coming, ok?
:cheers: :seeya
Thread Starter
Race Director
Joined: Apr 2002
Posts: 17,723
Likes: 1
From: Santa Ana, Costa Rica
Re: LT4 Overheating..... (vette40509)
You might also check the fuze box for a 5 amp fuze that can blow. I had this on mine last week and even the dealer didi not catch it.
:cheers:
:seeya
Racer
Joined: Jan 2001
Posts: 425
Likes: 0
From: Frederick MD
Re: LT4 Overheating..... (DCTC)
Primary fan kicks on at 228 then turns off when the temperature drops to about 215 (might be a little lower. The secondary kicks on at 238. But the oil temp is usually about 20-25 degrees warmer than coolant, so sitting in traffic with the coolant cycling from 228 down to 215, add 20 degrees and the oil temp will get up to about 235. If you get the computer reprogrammed the fans will come on sooner.
Might want to check the wiring connector to the fan make sure it hasn't been disconnected or a bad fan motor.
[Modified by tdock, 2:12 PM 11/25/2002]
Might want to check the wiring connector to the fan make sure it hasn't been disconnected or a bad fan motor.
[Modified by tdock, 2:12 PM 11/25/2002]
Racer
Joined: Aug 2002
Posts: 432
Likes: 0
From: Ashford CT
Re: LT4 Overheating..... (tdock)
I'm not sure about the LT4 but when I was doing heads on my ex-gf's L98 I noticed that the coolant temp sensor was unplugged/broken. It's located on the passenger side of the engine in the head. It has a round plug. You might want to check that also. The center piece of the plug was broken on hers and the sensor itself was also broken. It's about $7-10 at NAPA
Melting Slicks
Joined: May 2001
Posts: 2,143
Likes: 7
From: San Diego CA
Re: LT4 Overheating..... (DCTC)
A shot in the dark, but maybe the fans are set too high in the PCM. I don't recall the procedure, but you can review the settings in diagnostic mode in the odometer window ( or a scan tool ).
When did this start happening?
[Modified by John Row, 2:40 PM 11/25/2002]
When did this start happening?
[Modified by John Row, 2:40 PM 11/25/2002]
Le Mans Master
Joined: Feb 1999
Posts: 5,381
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From: Pineville, Louisiana
Re: LT4 Overheating..... (John Row)
Ok let me see if I am correct here, the fans come on when you have the a/c running so that rules out either bad fans or blown fuses. What temp does you car run if you have the a/c on or runing with the temp control set at auto?
Racer
Joined: Aug 2002
Posts: 432
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From: Ashford CT
Re: LT4 Overheating..... (Hamert)
I might add that the reason I was doing the heads on my ex-gf's car was because she drove the car while it was overheating and thus blew a head gasket and warped the heads. I am pretty sure the reason it overheated was the fact that the coolant temp switch I spoke of earlier was bad. $700 and a week and a half downtime for a $7 switch. Not to mention the time in labor. I would definitely check that. Even if you put a new one it's going to cost you less than $10 and you'll if that was the problem. Just my .02
Safety Car
Joined: Feb 2002
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From: financial-freedom-for-all.com
Cruise-In V Veteran
Cruise-In VI Veteran
Re: LT4 Overheating..... (DCTC)
You still might want to flush the system also. I mean the car is almost 7 years old and with that few miles I'm sure it is the original stuff! :yesnod: Does the temp. go down when the a/c is on? If this is the case you live in Florida and you always need the a/c on! :jester I know a good shop you can take it to also. You may need the "Vette doctors", or Giavanneti and sons. :D Drive that thing...will ya! :rolleyes:
Thread Starter
Race Director
Joined: Apr 2002
Posts: 17,723
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From: Santa Ana, Costa Rica
Re: LT4 Overheating..... (9vette3)
You still might want to flush the system also. I mean the car is almost 7 years old and with that few miles I'm sure it is the original stuff! :yesnod: Does the temp. go down when the a/c is on? If this is the case you live in Florida and you always need the a/c on! :jester I know a good shop you can take it to also. You may need the "Vette doctors", or Giavanneti and sons. :D Drive that thing...will ya! :rolleyes:
Giovannetti's gets it Wednesday....... Hope it's simple.
Call me Will Ya?
Let me know about the airport.....
:cheers: :seeya
