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Discussion Starter #1
I'm hoping someone can help me with a problem I've discovered on my truck's AC system. It's been about 15 years since I've owned a vehicle with working AC, so when I learned this new truck had a good compressor, I was ecstatic. It gets to be about 742 million degrees (Celsius) here during the summer in Atlanta. After charging the system I found that it held pressure and would blow plenty of cold air. Everything was fine until about 20 miles into my trip today, when I looked down and saw the temp gauge had shot up to 230.

I just spent a week driving this thing with no AC in the most grueling commute you can imagine. 80 mile round trip, bumper to bumper traffic both ways, with a record heat wave. The truck never ran hot once. The gauge stayed pinned at 210 like it always has. It wasn't until I started mucking about with charging the AC that this problem occurred. I'm inclined to think it's related, because once I turned the AC off I could see the needle on the temp gauge begin to drop again. I also noticed the transmission clunking a bit, I'm guessing because the cooler wasn't getting cold enough to cool down the fluid.

This truck has a new(ish) radiator, water pump, thermostat, CTS and fan clutch. I might check the thermostat first since it was taken from my old truck. I don't see any visible signs of blow out on the radiator hose couplings. Does anyone know why the AC would be acting like this? Does the cooling system have any more parts that could go bad?
 

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Check for debris between the radiator and ac condenser...also behind the grill.
Good advice. Didn't seem to be anything back there, but it was a bit low on coolant. Maybe this radiator is crap after all. But it doesn't appear to be leaking, or blowing anything out the tailpipe.


Is the fan shroud all there?
The bottom part isn't. Is that a problem? My motor mounts have sagged so much that the fan chopped my lower shroud to pieces.
 

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Good advice. Didn't seem to be anything back there, but it was a bit low on coolant. Maybe this radiator is crap after all. But it doesn't appear to be leaking, or blowing anything out the tailpipe.




The bottom part isn't. Is that a problem? My motor mounts have sagged so much that the fan chopped my lower shroud to pieces.
That's a problem. Get new mounts and the bottom of the shroud. It needs to be there to pull the air thru the core. Make sure the radiator is sealed up around the core support...air needs to go thru...not around.

I think JTR has some 4.3 poly mounts that are a good replacement for the factory junk. You'll need to modify the heat shields so that the mounts won't cook. I think it was Bandit that had a thread on it.
 

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Discussion Starter #6
I got a new lower shroud installed. Turns out it wasn't the engine sagging, but rather the old shroud not making connection to the core, which caused it to jump up into the fan. I put some zip ties on it and it seems to be snug now. Doesn't seem to have made much difference though. The truck still chugs with the AC running, and it eventually stops blowing cold if you idle long enough.

I installed a different AC pressure sensor, but that seems to have done little good. The pressure was down considerably from yesterday's fill up, and the gauge on the filler went down from 50 to 40. I filled it again and looked for the leak. There's some kind of odd plastic tape wrapped around the connector coming out the back of the AC canister. Apparently it's holding in a bad leak, because I can feel cool air coming from around it. I guess undoing it will depressurize the system again. I imagine there's probably a little o ring or something in there that's cracked, allowing gas to escape the connector. I put some gasket sealer on it for now. Maybe that will hold for the time being.
 

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I'm having the same issue with mine. Atlanta doesn't get quite as warm as it is here! The past two weeks it's been around 96 degrees here. I take the Interstate part of the way home, and while I'm moving, the temp is normal. Once I'm off and have to sit at a light for 3 or 4 light changes, my temp gauge moves up towards the middle. It's not hot enough to worry about yet. But, when I think of my wife's Equinox where the temp needle doesn't move much at all once it's warmed up, I figure my truck should do the same.


I've got a rebuilt 4.3, all new AC, new heater core, thermostat, and all hoses. The only thing I haven't replaced is the radiator. That's my next move. I had the shroud issue also, but it was my mounts that caused it. I ordered the lower shroud and got sent 5 of them. The ebay seller didn't want them back, so they're still sitting in my garage. I'd send you one, but I see you already got a new one.


One other thing my truck does that I haven't seen before on another vehicle - in the morning when it starts to warm up, the needle moves up towards the center (210 mark?), then the thermostat opens and it drops down and stays there.
 

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I'm having the same issue with mine. Atlanta doesn't get quite as warm as it is here! The past two weeks it's been around 96 degrees here. I take the Interstate part of the way home, and while I'm moving, the temp is normal. Once I'm off and have to sit at a light for 3 or 4 light changes, my temp gauge moves up towards the middle. It's not hot enough to worry about yet. But, when I think of my wife's Equinox where the temp needle doesn't move much at all once it's warmed up, I figure my truck should do the same.


I've got a rebuilt 4.3, all new AC, new heater core, thermostat, and all hoses. The only thing I haven't replaced is the radiator. That's my next move. I had the shroud issue also, but it was my mounts that caused it. I ordered the lower shroud and got sent 5 of them. The ebay seller didn't want them back, so they're still sitting in my garage. I'd send you one, but I see you already got a new one.


One other thing my truck does that I haven't seen before on another vehicle - in the morning when it starts to warm up, the needle moves up towards the center (210 mark?), then the thermostat opens and it drops down and stays there.

Three things stick out that you didn't do...waterpump, radiator, and fan clutch. I was a non-believer about the pump and fan clutch. A drive up to Mt Rainier convinced me to finish the job. Temp is steady at 192-197.
 

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Put a new water pump on with the new engine. Replaced the fan clutch a little over a year ago (maybe a little longer - I don't remember). Like I said, the ONLY thing I haven't done is replace the radiator. Of course, my fan clutch came from Advance Auto, and isn't an AC Delco, like I know you're a stickler for. Wouldn't surprise me if it's the clutch...
 

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Mew Nember
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IF you drive in really dusty areas, like on a long gravel road, dirt roads, etc., the actual fins can start caking up with dirt. I used to have an issue with a semi I drove and despite having a radiator the size of a car hood and a mechanical fan the size of a beach ball, it started running hot.



Can remove the front grill, then carefully take a garden hose w/o the nozzle, just let it flow out the open hose end. Run the water through the fins, being careful to not touch the fins or they'll bend. Watch the flow of water out the other side (fan shroud side). If it's dark/dirty water, or flow is weak, there's a build up of dirt. Hold hose there until clear water is seen coming out. I suggest starting at one end and slowing moving across to the other, then go down 1 row of fins, and start over.



It takes 5-10 minutes and is easy enough to rule out if it's getting dirty and losing efficiency. If you drive through occasional rain and rarely dusty areas, it typically stays clean w/o intervention. But if no rain over a long period, dirt can build up.


If the internal rows (remove the cap when cold, look into the opening; squeeze the upper radiator hose if needed as it'll force some coolant out the radiator cap opening allowing you to see more rows) are showing white calcium build up on the row ends, then chances are tap water is in the system, and the radiator has been slowly choked to death as deposits have accumulated, and it's now bad enough that the radiator can't cool at idle under AC load. Just replace it if that's the case and use distilled water ONLY. Can buy gallon jugs for a $1 something at most grocery stores. You can use 50/50 pre-dilluted, but they are charging you for the water in the pre-diluted mix. Even though it costs a little more, it's smarter to mix it yourself. Two 50/50 jugs are ONE non-diluted coolant jug split with water.


You stated your fan made contact with the shroud? It might have bent a blade or numerous blades. If a blade is bent (even the tip of the blade), the fan will lose a ton of efficiency and have a bad imbalance that'll probably kill the water pump prematurely. If the fan was damaged, replace it ASAP.
 

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Been there, fixed that. 95 S10 4.3Z, wouldnt pull up the Cascade mountains with AC on, wouldnt accelarate with or without it. I always run 170 thermostats in all my vehicles, it would go up to 200+ although it didnt "overheat" (didnt boil over, but was close) but also wouldnt go over 35 mph without beating on it.

Otherwise, on flat land, it runs perfectly, 23 hwy mileage.

Driving thru Cherokee Natl Forest in NC, no power up hills. Was low on fuel, stopped at a station.

On a lark, I put about 1/2 tank of 95 octane fuel in with the cheapo 86 that I always use.

Problem disappeared instantly. It made more than enough power to accelrate up hills even with AC on. No more overheating

Low octane fuel was the problem. It didnt show up on flat land as the engine wasnt working hard. This is a computerized emissions vehicle with two knock sensors. It can sense detonation on low octane fuel and change the timing.

Before doing anything else, make sure the spark plugs are burning nice clean nearly white. Misfire can cause severe cylinder heating.
 

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Mew Nember
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Why do you use a 17u0 degree thermostat when factory calls for 195?



Keep in mind, factory specs cover the entire weather spectrum. 195 might be their all-around all-year all-weather compromise. On pre computer cars at least (w/o fiddling with tune) running a lower temp can help the engine a bit (speaking in general). I used to run lower temp t-stats in SBF carb'd engines. It does make a difference.
 

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One other thing my truck does that I haven't seen before on another vehicle - in the morning when it starts to warm up, the needle moves up towards the center (210 mark?), then the thermostat opens and it drops down and stays there.
That's a cheap thermostat or a failing thermostat. It will get worse and overheat, or it will start sticking open too, after it opens, and drop well below the target temp.

I strongly recommend the Stant Supertstat 45119 (stock temperature). I use those in all the 4.3L V6's I work on, an all of them run at about 200°F +/- 2°F on the OBD-II "Engine Coolant Temperature" PID, no matter the weather, the load, AC on or off, running empty or a Blazer/Bravada hauling 4,800 lbs of boat and trailer on hilly roads. The most stable temps I've ever seen in any engine are in these 4.3s with that particular thermostat.

<snip>
I always run 170 thermostats in all my vehicles, it would go up to 200+ although it didnt "overheat" (didnt boil over, but was close) but also wouldnt go over 35 mph without beating on it.
Why do you use a 17u0 degree thermostat when factory calls for 195?
Because he knows way more than all those engineers at GM. He also owns stock in an oil company and a catalytic converter manufacturer, so he profits when he buys more fuel and replaces the clogged up, burned out cats from his "improved" thermostat choice.
 

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Keep in mind, factory specs cover the entire weather spectrum. 195 might be their all-around all-year all-weather compromise. On pre computer cars at least (w/o fiddling with tune) running a lower temp can help the engine a bit (speaking in general). I used to run lower temp t-stats in SBF carb'd engines. It does make a difference.
Somehow..I don't think the engineers use those parameters.
 

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I always run 170 thermostats in all my vehicles, it would go up to 200+ although it didnt "overheat" (didnt boil over, but was close)

You do realize that a 50/50 mixture of antifreeze and water raises your boiling point, right?


You don't want the engine running much less than 200 degrees.
 
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