operating temp range of LSX??
operating temp range of LSX?? OK folks, I just took my ride out for a shake down run for the first time today, & have a question about proper temp readings. The set up is this. 51 GMC with 5.3 LSX (2004) stock, with Speartech harness & reworked computer. Cooling system is a custom "Wizard Cooling" aluminum radiator 2 core, 1.75" tubes, 25" X21" down flow, 7 LB cap. Factory mechanical fan, no shroud. Runs great, but I am concerned about the temp readings. After 20 miles on the hiway with A/C on and 93 degrees ambiant temp. my gage reads. 220 on the (rebuilt) factory gage. After I got home, left the truck running & I used a infra temp gun & am getting readings of 230 at the location of gage conection, rear of R/H head. I get the same reading at the water pump, next to the block. Its not boiling or making any noise, but the temp readings are bothering me. Is this normal??
IMO.. that is a bit hot and even with the A/C on and at freeway speed, it should drop some. How are the plugs looking.. (running lean) ?
Since you elected not to use Electrical fans that are controlled by the PCM.. you will have to make sure your mechanical fan working correctly and drawing enough air flow and I would suggest that you install a shroud.
It is possible that you have a air pocket in the system, see if you can bleed any air out of the sytem, did you fill the block from the upper radiator hose 1st before you fill the rest of the radiator ? What mixture of Coolant are you using ?
How about running a cooler t-stat ?
Since you elected not to use Electrical fans that are controlled by the PCM.. you will have to make sure your mechanical fan working correctly and drawing enough air flow and I would suggest that you install a shroud.
It is possible that you have a air pocket in the system, see if you can bleed any air out of the sytem, did you fill the block from the upper radiator hose 1st before you fill the rest of the radiator ? What mixture of Coolant are you using ?
How about running a cooler t-stat ?
thanks for the input guys, I have not looked at the plugs yet, I did fill the block with the upper hose, & I also provided a fitting in the upper tank to connect the "vent" hose to. My coolant mix is approx. 50 percent (good to -4). When running it in the shop, never got above 200. I will check the plugs tomorrow.
What t-stat you running?? Aint a 7lbs pound radiator cap to low? I thought it should be a 15 to 18 lbs cap. A shroud would help a lot and I guess it would be better to run electric fans. Thats definitely a bit hot.
yeah.. forgot to question that 7lb cap.. try switching over to a 16lb one. Are you running a recovery tank. I would recommend a 180 deg stat at lease... What temp did John program your running temp to be and with with temp stat?..
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I have the stock T-stat, with a recovery tank, I am not sure replacing the cap with a higher pressure cap would make a diff., I am not loosing any coolant now with the 7 LB. cap, but heck I'll try it. This higher temp. is only on the hiway, It will sit in the shop running for 40 minutes & not get above 210.. got me baffled?? Thanks for the inputs guys
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With the 5.3L are you running an automatic trans? If so, does the radiator have sufficient cooling capacity for the transmission? The trans will get pretty hot on the highway if it doesn't have sufficient cooling, and it will raise the coolant temp. If it isn't overheating when in park/nuetral, but is on the highway, you want to make sure that the trans isn't overheating. A fan shroud will help as well. The higher PSI in the tank will raise the boiling point of your coolant. Even if the coolant isn't boiling currently, as it nears that point it does not work as efficiently.
With the 5.3L are you running an automatic trans? If so, does the radiator have sufficient cooling capacity for the transmission? The trans will get pretty hot on the highway if it doesn't have sufficient cooling, and it will raise the coolant temp. If it isn't overheating when in park/nuetral, but is on the highway, you want to make sure that the trans isn't overheating. A fan shroud will help as well. The higher PSI in the tank will raise the boiling point of your coolant. Even if the coolant isn't boiling currently, as it nears that point it does not work as efficiently.
67rsss, thanks for your help, I am running the factory auto (4L60E). I'm running the trans lines from the trany to the radiator, then thru a B&M cooler mounted in front of radiator. B&M cooler is approx. 8 X 11". I think I'll install a trans temp gage & start figuring out how to get a shroud installed also. This new tech (LSX) is a challage & expensive!!
There is a reason that that the late model engine need a higher rating cap.. a higher pressure cap also increases the operating temp of the coolant, making it able to operate at a higher temp before boil over. At lease give it a shot.
Joined: Sep 2004
Posts: 3,148
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From: Downers Grove, IL
Are you running a heater core? The last time I drained my coolant I filled the engine through the upper hose, filled the radiator and started it. Everything appeared to be full of coolant but the temp stayed around 220-230. It never ran that hot before. I checked everything again and it was still full.
I then pulled the cap off of the flush T that I installed next to the heater core and it looked dry in there. I dumped almost a gallon of coolant in through the T, fired the engine and the temp went right down to 190-200 and stayed there like it always had. Moral of the story check for cheap easy stuff first
. I still don`t understand why I had to fill it through the flush T, I didn`t change any of the hose routing and never had that problem any of the other times I filled the engine with coolant.
I then pulled the cap off of the flush T that I installed next to the heater core and it looked dry in there. I dumped almost a gallon of coolant in through the T, fired the engine and the temp went right down to 190-200 and stayed there like it always had. Moral of the story check for cheap easy stuff first
. I still don`t understand why I had to fill it through the flush T, I didn`t change any of the hose routing and never had that problem any of the other times I filled the engine with coolant. 
LS motors relly need to be purged of any air that is stuck in the motor. with the cap off the rad you need to run the rpm up and look at the coolent bypass tube to make sure you see coolent comming out of it. I do have a electric fan and a big AL rad. I don't care if it is the middle of summer at the woodward cruse and it takes all day to go 5 miles. or I have been driving it hard. it never goes over 190 degrees F
