Truck Overheating - Chevrolet Forum - Chevy Enthusiasts Forums
Join Date: Feb 2009
Posts: 42
DFW, Texas

July 3rd, 2009, 10:01 AM   #1  
CF Junior Member
Truck Overheating

I have a 2000 Silverado Z71 with ~160K miles on it and it has been overheating on me for awhile. It started out only doing it when I was in stop and go traffic. Now it does it even when I'm driving 70 when it's 100 degrees outside. Whenever it goes over 210 degrees, I shutoff the AC and it does fine, but the people inside the truck suffer a little obviously. I drained out the old coolant and then let the truck run for about half an hour with the water hose sticking in the overflow reservoir. I put a jug of Prestone Super Cleaner in it and filled the rest of the way with water. It says to run it for 3-4 hours and then drain, fill with water, turn heater on high and run till reaches normal temp, then drain and fill with 50/50 coolant/water mixture.

I have a couple of questions. Does anyone know the exact fitting and contraption I would need to hook up to my drain on my radiator so that when I drain it I could collect all the old coolant? Right now it goes everywhere. I put 3 pans under there and only caught about 1/3 of it. Hopefully doesn't matter since it was diluted, old Dextron anyway. Also, is there any reason I can't replace the old Dextron with the yellow stuff that seems to not gunk up the engine so bad? By the way, I bought a new thermostat that I'm going to replace along with all new radiator hoses when I drain the Super Clean out. Anyone have any ideas on why my Haynes manual says my thermostat should be 195 degrees, but the one I bought from Auto Zone it a 185 degrees? Does it matter? Thanks.

Join Date: Jun 2009
Posts: 14

July 3rd, 2009, 2:38 PM   #2  
CF Beginner
Well, I have never found a contraption to hook on to the petcock. I have, however, taken a few coolant baths! You could make millions! lol. As far as the thermostat temp, ALWAYS go with the factory specs. I have mine at 195 (and the old one was 180).

Join Date: Apr 2009
Posts: 139

July 3rd, 2009, 3:38 PM   #3  
CF Active Member
The temp specs arent "that" important. the temperature on the box is when the thermostat will tell your obd that it needs additional help cooling the engine. (In other words, it'll turn on the ventilators, sucking in cold air). Just make sure it says degrees fahrenheit.

It might just be that your thermostat is the problem al along. Your radiator is a continuus loop of water. In that loop, your thermostat is the thinnest part. So it might be that some dirt or coolant residus is clogging the thermostat.

Instead of using the drain, just disconnect the lower hose. Water will come out fluently that way. Last time i used a drain, I ended up with the thing in my hands and was forced to reinstall an entire new radiator...

Dextron is the absolute must for your radiator. But then again... your warranty is already long overdue, so there is no harm in using another kind of coolant. Just make sure its good quality and always read the directions! (even if you dont follow them).

Join Date: Apr 2007
Posts: 236

July 3rd, 2009, 5:29 PM   #4  
CF Active Member
Koffietje  The temp specs arent "that" important. the temperature on the box is when the thermostat will tell your obd that it needs additional help cooling the engine. (In other words, it'll turn on the ventilators, sucking in cold air). Just make sure it says degrees fahrenheit.
that is definately wrong, the therostat is all a mechanical mechanism that opens at the temp specified to allow the flow through the radiator. it doesnt not make a difference when the fans come on, on that year it most likely has a belt driven fan anyway.
185* should be just fine, if its overheating like that you might end up having to replace the radiator, usually by that amount of miles they just get clogged up and alot of times you wont get them flushed out, but i would start by taking it out of the truck and trying to shake it around as your hosing it out to get as much crap as possible out of it.

Join Date: May 2009
Posts: 289
Munden Kansas

July 3rd, 2009, 7:28 PM   #5  
CF Active Member
the thermostat could be stuck open as well, when stuck open the coolant does not have time to cool in the radiator therefor would only get worse when the a/c is on, replace the thermostat and make sure it cycles properly, if your driving around in 100 degree heat alot i would recomend the 185, draing the antifreeze is something the engineers don't have to do so they are not going to make it easy

Join Date: Apr 2007
Posts: 236

July 3rd, 2009, 8:52 PM   #6  
CF Active Member
what helped on my older chevy, since the coolant ran all over the lower core support and made a mess was jacking one side way up so that it at least runs off one side of it...
agree with the T stat being stuck part way also, or it could be only opening part way. replace that first and see where it gets you. you might like the 195* better in winter.
ive seen people leave cardboard in front of the radiator after winter then not remember it untill replacing the radiator lol.... just a thought.

Join Date: Mar 2008
Posts: 435

July 4th, 2009, 10:54 PM   #7  
CF Senior Member
lukemoore646  the thermostat could be stuck open as well, when stuck open the coolant does not have time to cool in the radiator
REALLY? obviously, you never drove w-out thermostat, and i did on quite a few cars. gods, people have ideas....

anyhow, under these conditions: fans start, viscous fan works fine, thermostat functions (both radiator hoses are same temp on hot), radiator is not plugged with dirt and bugs, ALLL BELTS ARE IN GOOD SHAPE AND TENSION, and water pump is functional, you have exhaust leak into coolant.
no way to see it as you do not have radiator cap, but you might see some beer foam looking stuff coming into expansion canister with cap removed.

Join Date: Feb 2009
Posts: 42
DFW, Texas

July 12th, 2009, 2:12 PM   #8  
CF Junior Member
Truck Overheating.....Still!!

Well, I drained my radiator, then ran a hose into the overflow reservoir while it drained out the bottom, did this for about 30 minutes with heater on high although since putting in cool water, the thermostat probably never opened so I never would have drained the block this way. I put a bottle of Prestone Super Cleaner in there and filled radiator rest of way with water. Drove it for a week for a total of ~150 miles, then drained radiator, removed thermostat from t-stat housing with brute force and reinstalled housing and new upper/lower rad hoses. Did my super flush with hose going in top and draining out on ground for ~30 minutes again with heater on high. Got about 6 gallons of tomato juice looking Dex Cool between the two flushes I did that I'll have to figure out what to do with. Installed new t-stat and filled with 50/50 Auto Zone Extended Life (5 yrs/150K miles). On the way back from church, truck temperature zoomed past 210 degrees while I was sitting at a red light for only about 3 minutes with the A/C running at about 60% capacity since it was 102 degrees today.

Any ideas on next move? My guess is take out the radiator and take it to a radiator shop and have them do a clean on it. Then if that does not fix it, I'll probably look into replacing the fan as it is one of those temperature reacting clutch type fans rather than belt driven. Thanks.

Join Date: Jul 2008
Posts: 18

July 12th, 2009, 4:21 PM   #9  
CF Beginner
just a couple of questions: First, is the truck actually overheating...coolant overflow? Could it be a bad sending unit or guage? Second, have you checked the temp of the radiator in several places while it is hot? If you use a non-contact thermometer (infrared) you can detect cool spots in the radiator that would indicate clogged areas where the coolant is not flowing. You mentioned the temp "soared past 210" but my 95 cutlass supreme with the 3.4 routinely runs in the 220 to 230 range and it is normal. I guess GM found out that running hotter helps with the efficiency of the motor. You could also backflush the radiator without removing and try that. Harbor Freight has a non contact therm for like $20 so it is not too expensive.

Join Date: Apr 2007
Posts: 236

July 12th, 2009, 4:43 PM   #10  
CF Active Member
Honestly with it being 102* outside and the AC on i would expect it to get hot sitting idle.
Have you cleaned the AC condensor out and checked for stuff stuck in between it and the radiator? Being a dexcool system i am gonna say the rad is getting plugged. dexcool always has been and still is garbage.
Can you hear the fan pick up speed when the engine is hot? if its gets to a certain temp the fan clutch should start to tighten up and the fan should make alot more noise. if it doesnt, or you have a sticky syrup like stuff on the underside of the hood the fan clutch could have retired itself. if it cools down right away as soon as you are moving again id lean towards the fan clutch first, especially if it has 160k miles on it.

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