# 98 chevy 1500 overheating



## southpaw (Feb 25, 2009)

Hey guys, I'm new to this forum on 2cool. Seems like there's a lot of knowledge on here so I'd like to thank yall in advance for any advice. 

I've got a 1998 Chevy 1500 Z71 with a 5.7L V8. Now I still believe that this may be the greatest truck ever made, but in her old age she's been having a few problems. Lately it's been with the temperature. Usually when operating, my temp holds pretty steadily around 130-150. Awhile back though it began bouncing around. It'll heat up to over 200 then go back down, then after awhile it does the same thing over an over again. My truck hasn't over heated any but I'm sure this is not good for my engine. So far I've replaced the thermostat, even boiled the new thermostat to make sure it's opening at the right temp, flushed my radiator twice and am now kind of out of ideas. My next option would be to replace my heater core but that's kind of a pain in the butt and i don't want to do that if it could be something else. Has anybody had this problem before? If so what else do you think it could be? Thanks again in advance for any advice guys and for the great info on this board.


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## southpaw (Feb 25, 2009)

I forgot to add: If I turn on my heater it's warm but not nearly as hot as it used to be and I can smell coolant. Heater core?


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## seaark (May 23, 2010)

heater core for sure if temp gauge bounces and you have already changed thermostat . its not really that bad changing , just the back screw against firewall is a pain to get to . after i changed mine just did not replace that screw ,boxed sealed fine . went through the exact same thing about a year ago. if ya have any problems pm me i will try to help been turning wrenches for about 20 years


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## southpaw (Feb 25, 2009)

seaark said:


> heater core for sure if temp gauge bounces and you have already changed thermostat . its not really that bad changing , just the back screw against firewall is a pain to get to . after i changed mine just did not replace that screw ,boxed sealed fine . went through the exact same thing about a year ago. if ya have any problems pm me i will try to help been turning wrenches for about 20 years


Thanks for the help seaark. I'm gonna go ahead and buy a new heater core after work then get after it this weekend. Hopefully I won't have too much trouble changing it out, I'll let you know how it goes. Thanks again


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## BIG PAPPA (Apr 1, 2008)

*Here you go*

Heater Core Replacement 
*Removal Procedure*

1. Drain the coolant. Refer to Cooling System Draining and Filling 
2. Remove the instrument panel storage compartment. Refer to Instrument Panel Carrier Replacement in Instrument Panel, Gauges and Console.
3. Disconnect the electrical connectors, as necessary.
4. Remove the center floor air distribution duct.
5. Remove the hinge pillar trim panels. Refer to Instrument Panel Carrier Replacement in Instrument Panel, Gauges and Console.
6. Remove the blower motor cover.
7. Remove the blower motor. Refer to Blower Motor and Fan Replacement .
8. Remove the steering column. Refer to the applicable procedure:

9. Roll back the instrument panel. Refer to Instrument Panel Carrier Replacement in Instrument Panel, Gauges and Console.
10. Remove the coolant recovery reservoir. Refer to Coolant Recovery Reservoir Replacement in Engine Cooling.
11. Remove the heater hoses. Refer to Heater Hoses Replacement .​










12. While holding the heater case to the cowl, remove the screw on the interior side of the cowl, near the evaporator pipe, if equipped.​










13. On the engine side of the cowl, remove the 4 screws that hold the heater case to the cowl.
14. On the engine side of the cowl, remove the 2 nuts that hold the heater case to the cowl.
15. Remove the heater case.
Ask an assistant for help, if necessary.
16. Remove the 7 screws that hold the heater cover to the heater case.
17. Remove the heater cover.
18. Remove the heater core from the retainer.​*Installation Procedure
*

1. Install the heater core into the retainer.
2. Install the 7 screws that hold the heater cover to the heater case. Replace the seals.
3. Install the heater cover.
Verify that the heater cover is properly sealed.
4. Install the heater case.
If necessary, ask an assistant for help.​










5. On the engine side of the cowl, install the nuts that hold the heater case to the cowl.
6. On the engine side of the cowl, install the 4 screws that hold the heater case to the cowl.​










7. On the interior side of the cowl, install the screw.​ *Notice: *Refer to *Fastener Notice *in Cautions and Notices. 
8. Tighten the following fasteners:​
*Tighten* 
• Tighten the screws on the engine side of the cowl to 1.9 N​​


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## BIG PAPPA (Apr 1, 2008)

*Look at step #9*

Basically, to do this job RIGHT, you almost remove the entire Dash Carrier Assembly to the point of being able to ROLL it Back.
Pretty big Job.


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## TheGoose (Jan 22, 2006)

It's been awhile since I had one of those trucks, but shouldn't the operating temp be closer to 190? 130-150 seems like the thermostat was stuck open.



southpaw said:


> Hey guys, I'm new to this forum on 2cool. Seems like there's a lot of knowledge on here so I'd like to thank yall in advance for any advice.
> 
> I've got a 1998 Chevy 1500 Z71 with a 5.7L V8. Now I still believe that this may be the greatest truck ever made, but in her old age she's been having a few problems. Lately it's been with the temperature. Usually when operating, my temp holds pretty steadily around 130-150. Awhile back though it began bouncing around. It'll heat up to over 200 then go back down, then after awhile it does the same thing over an over again. My truck hasn't over heated any but I'm sure this is not good for my engine. So far I've replaced the thermostat, even boiled the new thermostat to make sure it's opening at the right temp, flushed my radiator twice and am now kind of out of ideas. My next option would be to replace my heater core but that's kind of a pain in the butt and i don't want to do that if it could be something else. Has anybody had this problem before? If so what else do you think it could be? Thanks again in advance for any advice guys and for the great info on this board.


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## 6.5 shooter dude (Jan 8, 2008)

TheGoose said:


> It's been awhile since I had one of those trucks, but shouldn't the operating temp be closer to 190? 130-150 seems like the thermostat was stuck open.


Yup, It should have a 195 degree thermostat and will normally run about 210


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## southpaw (Feb 25, 2009)

Thanks for all of the helpful info guys. I really appreciate it.

I've owned the truck for almost 9 years now and have been through 3 thermostats. I've never had the operating temp above 150. Maybe my gauge is off? But even when I boiled the thermostat recently it still opened around 150.


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## CaptPb (Jan 26, 2005)

Unless your running a programmer or chip, 195 is a must on a vortec W-31. Even with a chip the new stat will be a 180. Your to cold and probably gobbling gas because it stays in open loop. The fluctuating temp gauge is classic symptom of low coolant. Is the carpet/floor all wet under the heater core? If so, don't wait to replace it. Seen a couple that went from slight leak to all of it on the passenger side floor while sitting at a red light.
Has the water pump ever been replaced? Those will quite pushing very good. Usually right before they start leaking. I've got a 99', last of the 350's. If it spins or pops I've replaced it. PM if you have any questions.


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## southpaw (Feb 25, 2009)

Thanks CaptPb. I actually replaced the water pump last year so it should be fine. I do all the work on my truck myself. Parts are so cheap and the engine is so simple so it saves me a lot of money. I have plenty of coolant so I don't think that's the problem. I've talked to a few other people about this before but if I have my AC button pushed in the compressor with flip on even when my AC isn't running. This also depletes my gas mileage. But I'll also look further into my thermostat as well

What's yall's opinion on dexcool? I still run it now, but I've had a few mechanics and other Chevy owners tell me I should switch to standard coolant bc of the organics in dexcool? What do yall run in yall's older trucks?


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## CaptPb (Jan 26, 2005)

Use the green stuff. Dexcool is supposed to last a long time. Then it turns to acid.


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## theman123 (Oct 21, 2011)

iv got a 97 c1500 had the same problem, but i found my radiator leaking, go figure, but i upgraded to a 2 pass, its helped alot. also 150 is a little cold, 190 is where you need to be


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## Bayman (Oct 18, 2004)

I had a 94 that was doing the same thing. I put a chip in it and the chip came with a 125 deg. thermostat. I changed the water pump, thermostat, removed the fan clutch and had an oversized fan on it, but it still didn't solve the problem. I didn't have a problem with the heater core. I was about to change the radiator, but the rear main started leaking at 185K so I traded it in.


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## Bassassassin (Nov 22, 2011)

*So....*

I didnt see where you mentioned a coolant loss. Check your fan clutch. It should be stiff, while the vehicle is off.


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## iridered2003 (Dec 12, 2005)

try a new rad cap


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## saltbranch (Apr 6, 2012)

I did not see anything about checking the temp sending unit? If you have coolant smell in the cab then yes heater core, if not I would look else where. Age of truck and electric guages, check sensors.Cant beat manual guages and good ole water, antifreaze/coolant helps in the long run


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## rowdyone (Aug 29, 2009)

iridered2003 said:


> try a new rad cap


This


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