Chevy Silverado and GMC Sierra Radiator and Cooling Questions

bbydolly13bbydolly13 Member Posts: 2
edited August 2015 in GMC
Can anyone tell me why the temperature gauge in my 94 GMC Sierra pickup would shoot way up to the red for a few seconds then go back down really low? I have already had my radiator flushed and filled and thermostat replaced and it had not helped. It doesn't seem to matter if the engine is cold or hot when this happens. Also, since this problem has started my heater doesn't work as well either.

See Also
Why a Temperature Gauge Fluctuates



  • bhixsonbhixson Member Posts: 3
    Hi, I have the same problem with my 94 Suburban. I have also flushed everything out and replaced the water pump, thermostat, and even the radiator cap. Most mechanics I talk to susspect that there is not enough coolant flow through the engine but nobody can figure out how to fix it.
  • vawardvaward Member Posts: 1
    My 94 silverado did the same thing with a message of "check gauges" on the dash. I kinda figured with 215K on it the tmp sensor was going bad, so I unplugged it, checked the voltage to it and got a reading from the sensor. plugged it back up and have had no other occurance for about a month now. wiring connection maybe?? the sensor is cheap and easy to replace. i had no trouble codes in the OBD before testing the sensor and had 1 "low coolant temp" afterwards.
  • 1989c25001989c2500 Member Posts: 3
  • 1989c25001989c2500 Member Posts: 3
    Can anyone tell me the proper rotation of the water pump. I replaced the water pump and the thermostat with a failsafe and the temperature worked fine for about a week. Now it stay cool
    I know the water pump comes in two styles a clockwise and counter clockwise rotation. I purchased the clockwise rotation, I believe this is wrong. Can anyone help me.
  • fastballbakerfastballbaker Member Posts: 2
    I have a 1998 Chevy Z71 and I am having an odd problem with the temperature. I need help if anyone can figure this one out. I start and run my truck just as normal, but when the temperature gauge reaches 190 degrees the problem occurs. At 190 degrees the gauge will drop all the way back down to 100 or below, and also at this time the anti-freeze in the radiator will bubble up or overflow and run out into the reservoir tank. The temperature gauge will never rest or stay at one temperature. It will always rise up and then overflow anti-freeze into the reservoir tank and then cool down. Why is my truck not holding a steddy temperature? Why the overflow? Can anyone help with this? I have replaced the thermostat and that did not work. I have replaced the radiator cap and that did not work. I have checked pressure in all 8 cylinder and they read..
    125, 110, 110, 100, 100, 100, 90 and 90.Does any of this help. Thanks for your help..
  • fastballbakerfastballbaker Member Posts: 2
  • arkz71arkz71 Member Posts: 10
    I have 95,000 miles and I am losing coolant I have not seen any on the ground nor leaks on the composite intake manifold. Is there any known problems with the 5.3 have head gasket problems or any other coolant loss problems. I have not had any engine problems out of it or coolant in the oil. Any help would be greatly appreciated.
  • iowahunteriowahunter Member Posts: 3
    Have had the same issue for the last couple of months, I would have to put in about a pint or less every month and couldn't see it on the garage floor or find it on the truck anywhere, could smell it once in a while. Took the truck in for a 4x4 problem and they discovered the water pump had a small leak, sounds as if you would see that but I never did. Had it replaced and all is good now. Do not let it go too far and get stranded if this is what it is. Hope this helps and good luck!!!
  • arkz71arkz71 Member Posts: 10
    Water pump has been replaced already, I hope it is not the Intake Manifold gaskets I have read on the internet that they leak. The Intake is composite plastic and since the whole system is under pressure with NO radiator cap (dumb) it is just a pain. I guess the EPA mandated this stupid setup, I have not seen any coolant on the ground and just trying to figure out where it is going.

  • iowahunteriowahunter Member Posts: 3
    Man if you are not seeing it in the oil and you are not seeing it burning, I'm not sure. How often are you putting coolant in? I have a buddy that has a 02' and he said he loses it in the winter but not in the summer, he took it in and they could find nothing on it either. gotta be going somewhere??? I'll ask a buddy of mine that lives up north, he see's it all in his job, should talk to him tomorrow evening, he's kind of our mister fix it when we cannnot figure it out.
  • ahoronahoron Member Posts: 30
    Thr intake on your engine does not have coolant running thru it. The throttle body has 2 small coolant lines.
  • arkz71arkz71 Member Posts: 10
    Thanks a bunch, I added about a 1/4 of a gallon to the coolant tank but the dash will display low coolant, it has 95,000 miles on it. I have an extended warranty and they replaced the water pump about 60,000 because it was leaking around the base of the pump itself. It did not start losing coolant till around 90,000 or so. Plus the coolant was changed, when the other work was done, I would have done the work myself but the warranty deductible was only $100 and it was cheaper than buying the stuff myself.

    It has been a very good truck and I like it just wish I knew if it was the intake or something else.
  • gray01gray01 Member Posts: 2
    I have a 2001 silverado with the 4.8 in it. Once in a while I can smell anti-freeze but cannot see it. The other day my wife had it and the low coolant light came on. It had not shown any leaks or puddles on the ground until recently. I've read some of the forums here and it suggests the water pump might be bad or leaking. Also the front axle drips a little bit of oil on the ground right where the drive axle comes out of the front differential. Could the seals be bad? What could I expect to pay to have these changed. :lemon:
  • geo9geo9 Member Posts: 735
    You could possibly have a cracked or leaking heater
    core. Usually thats when you can smell it.
    Do you notice any fogging of the windows?
  • gray01gray01 Member Posts: 2
    no window fogging, I laid cardboard under it and it leaves small puddles right under the engine in the middle ofthe front wheels as well.
  • arkz71arkz71 Member Posts: 10
  • chososchosos Member Posts: 2
  • chososchosos Member Posts: 2
    I own an 89 K1500 Pickup. Originally, the radiator was leaking, so we replaced it. In the process, the seal for the waterpump went bad, so we replaced that too.

    Unfortunately, now most of the cooling system has been replaced, but my truck still overheats. I have replaced the thermostat 5 times, thinking it was bad as it was opening late.

    I do know that there were two types of radiator stop leak poured into the system prior to replacing the radiator.

    On my way to work in the morning, it is ~32 degrees F. My truck ussually overhearts quickly if I am driving at ~50-60 mph. However, if I take sideroads, I can do 40 mph and the truck will start to climb up to ~210 degrees and if I pull off and let it idle, the thermostat will eventually open and the system will be fine after that.

    This typically does not happen on my way home from work no matter how fast I drive. The temps going home are warmer ~40-50.

    I just replaced my Radiator cap yesterday, thinking that might be the problem - it wasnt. Then I flushed the radiator - that didn't help either.

    If I let the car idle until the thermostat opens every morning, it drives without a problem.

    I just can't figure this one out. Is my coolant system clogged or gummed up? Is the coolant mixture bad? I know I used 50/50 premix to fill my radiator last night after I drained it and flushed it.

    I have done everything just shy of having my whole system flushed... that was going to be my next step.
  • ricschricsch Member Posts: 540
  • ricschricsch Member Posts: 540
    I have a 2006 Silverado with a 5.3 and at 800 miles, the water pump had to be replaced because coolant was seaping from where the metal tube is inserted into the top of the water pump for attaching the upper radiator hose.

    Well, after 2,000 miles, it is leaking once again!!

    If I recall when looking at the new-style '07 Silverado, I believe they did away with the poor design. Wondering if it the new designed water pump will work on my truck.

    Sure don't feel like making a it a habit to have this repaired/replaced at the dealer, especially after the warranty is done!

    Anyone else experience the coolant leak as I described? What was done to correct it?

  • arkz71arkz71 Member Posts: 10
    I had gradual coolant loss over time, it was not from the water pump (replaced), intake manifolds because they are dry. I had paid $900 for an ext warranty when I bought my Z71 back in 2003 with a 5.3 reg cab. I have to say it has paid for itself, both of the heads were replaced due to a porosity crack in the head. After the rocker covers were off, there was plenty of dexcool that had gelled in the covers. The warranty paid for all of it for a total of around $2800 labor & heads, plus a electrical part.

    So if anyone has slow coolant loss be-aware of the symptoms and you can find out by pulling a rocker cover off. If you got coolant then you have to have new heads. I have 99,300 miles on the truck and the warranty runs out at 100,000 I will most likely purchase an extension since it has more than paid for itself.

    Good info to know.
  • jandk4211jandk4211 Member Posts: 2
  • jandk4211jandk4211 Member Posts: 2
    I have a 2002 Chevrolet 2500HD crew cab. My low coolant light keeps coming on , I put coolant in each time but I have no idea why it is doing this. I just added coolant on Sept 1st and here it is 19 days later and the light is on again. What should I look into doing first? What can be causing this? My temp gauge is fine it never goes up when the light comes on. Any suggestions? Thanks!
  • garnoldgarnold Member Posts: 1
    Hope you've found the solution by now. I've got the same problem in the same model with 6.0 liter engine. Went and checked with a trusted mechanic this morning expecting to spend BUCKS. He said, "GM is aware of this problem. Go by the Chevrolet dealership, and pick up a package of 5 tablets. Put them into your cooling system and drive it. The tablets will seal the tiny cracks in your heads and gaskets." He claims it works! The dealership charged me $5.95 for the parts in a GM package, and seemed very aware of the problem. So if you haven't gotten a solution by now, don't be too scared....hope this works for both of us. My truck will see HEAVY usage from now until the end of february.
  • bhixsonbhixson Member Posts: 3
    I don't know if this will help at all but I have two chev trucks that would not keep a consistent water temp. It would fluxuate up and down all the time I was driving it and when idling my heater went cold. I did much of the same repair with no result and then before a trip to Fla I replaced my serpentine belt and the temp has been steady since. The pulley that drives the water pump and fan is on the flat side of the belt and not the ribbed side so it seems that all these years the belt has been slipping over that pulley causing the water pump to run slower than it should. If you don't want to replace the belt you can also try a belt dressing that can be sprayed on for extra traction
  • bhixsonbhixson Member Posts: 3
    I don't know if this will help at all but I have two chev trucks that would not keep a consistent water temp. It would fluctuate up and down all the time I was driving it and when idling my heater went cold. I did much of the same repair with no result and then before a trip to Fla I replaced my serpentine belt and the temp has been steady since. The pulley that drives the water pump and fan is on the flat side of the belt and not the ribbed side so it seems that all these years the belt has been slipping over that pulley causing the water pump to run slower than it should. If you don't want to replace the belt you can also try a belt dressing that can be sprayed on for extra traction
  • david1670david1670 Member Posts: 2
    I have a 2004 silverado. 5.3 engine with about 87000 miles. I noticed a coolant leak on the right side of the engine that appears to be a head gasket. Has there been any recalls for this? How much should I expect this to cost?
  • david1670david1670 Member Posts: 2
    Thanks for the tip!!! I was planning on taking my truck to the dealer in the morning. It does seems like a patch instead of a fix....but I guess if they are having trouble with crazing of the casting or porosity it should work. Too bad the warranty is expired!

    Thanks again
  • dust_man21dust_man21 Member Posts: 1
    my radiator cracked and i found one at a junk yard but it has a small hose right below the cap that my truck doesn't have can i cap it off? it has all the other hoses and hardlines that my truck has
  • 57bob57bob Member Posts: 2
    The coolant temperature gauge over the last two months has slowly stopped working. The truck has a new radiator, hoses, thermostat and I replaced the coolant temperature sending unit that is in the front engine manifold near the thermostat housing. It is a v6 4.3. Is there something else that I should check or is it the gauge.
  • bowanabowana Member Posts: 9
    I don't know if the 4.3 is the same as the 5.7 but I have a 99 350 and I have just been chasing a problem with the guage fluctuating as well. I did change the sending unit on the water thermostat housing but have found out that particular sensor runs to the computer (2 wires). Look at the side of the engine heads between the plugs for another sending unit. It will be the unit with 1 wire and it will send the information to the guage. Hope this helps.
  • edw6edw6 Member Posts: 2
    Hi, I have recently purchased a 1993 Chev truck with a 6.2L diesel motor and I am fixing a few problems on it, the current fix I am addressing is a coolant leak between the timing gear cover and the engine block. I have removed the water pump and mounting plate and I see that the water pump pumps water through two passages in the timing gear cover into the block and it is at the joint between the back of the timing gear cover and the block where I have some leakage, I don't see a lot of leakage there but there will always be some coolant on the steering parts underneath. I will replace the water pump and install new gaskets and hope that retorquing will fix the problem because to remove the timing gear cover requires considerable work beyond what I would care to do.I am wondering if anyone else dealt with sort of a problem and how they resolved it. Would a stop leak product be a successfull resolve? Thanks for any feedback in this matter.
  • beavermanbeaverman Member Posts: 3
    Hey folks, new here, with an issue. I've owned my 1998 Silverado since Thanksgiving, 2007. It has a Vortec 4.3L, 5-speed. For about a month I have been smelling antifreeze, but haven't seen any signs of a leak anywhere. Interior heat is good, temp gauge is good. Today while out and about I noticed when getting back in the truck, leaking from the back of the engine. It's dripping down from above the oil filter on the driver's side. I would think it's a freeze plug issue; possible? Is it something I can do in the backyard myself, how many freeze plugs are there, where are they, does the motor need to come out, can a freeze plug corrode and develop a small hole that could be fixed with Barr's leaks? Any comments would be appreciated! It's a 2-wheel drive. Thanks.
  • beavermanbeaverman Member Posts: 3
    3 hours after my last post, I started my truck, turned the heat on. It's still leaking somewhere, dripping down from above the oil filter. I noticed a little coolant on the intake manifold next to the valve cover on the driver's side. After idling for 15 min., still warm in the interior, but now it smells faintly of coolant. Water pump, rad, hoses, heater core all look dry, no milky foamy stuff in oil/dipstick. With rad cap removed, coolant wasn't visibly moving. Temp reading about 125-130. Ideas?
  • srtttusrtttu Member Posts: 1
    I have a 97 Sierra 1500 with 126,000 miles. I have a somewhat loud sound of water running through the passenger side of my dash. This is nothing new. It's done this for over 2 years. There has never been a problem until now...maybe? Now, the truck will randomly overheat until the sound of the water rushes through the dash and then the temp will drop to normal operating temp. Also, I would like to add that when the truck overheats and there is no water sound, the heater does not work. Then as if some type of magic, you'll hear the sound of water, the truck drops in temp and the heater works. The mechanic changed the thermostat and flushed the radiator and this clearly did nothing. The theory I have developed is that when I hear the water, things are normal and all is good, when there is no water, all is not good. Help.
  • 1offroader1offroader Member Posts: 208
    I had a similar problem in my 2002 Altima. The sound of swishing water was quite loud. It turns out there was a very small leak in the radiator. The leak was so small the radiator fluid would evaporate before dripping onto the ground, so there was never a puddle underneath to tip me off to the problem. Apparently, when there is a leak, the cooling system wouldn't hold pressure and an air bubble would form in the system. The bubble wants to rise to the top of the system, which is the heater core inside the pasenger cabin. The bubble would create a condition like vapor lock that can occur in a fuel system. Anyway, long story short, once the radiator was replaced no more swishing sound and all is well.

    I'd have a pressure test run on the cooling system.

  • 57bob57bob Member Posts: 2
    Thanks for the information on the other sending unit on the engine head. I finally got it replaced and fixed the problem. I had a hard time finding it at the auto parts places and even the dealer parts department because they call it a temperature switch for some reason but it looks like a sending unit.
    Thanks again
  • chainlinkchainlink Member Posts: 3
    whats involved with the replacement of thermostat on 2000 gmc z\71 5.3 litter: maybe someone can help me with this.on regular days with outside temps 70 are above,I get average mileage,as average as you can get with a 4x4,but on the way to the lease with temps in the 30's and below,I pass everything but the gas station,I use twice the fuel there and back,but gauge is in the normal range,if i make a stop for any amount of time the gauge drops below normal range,,way below.thats while it has been idling ,I have 275 thousand on her and have never changed the stat,could that be the problem.THANKS
  • chainlinkchainlink Member Posts: 3
    my friend had the simular problem,is the smell more apparent inside or outside the vehical, his was outside,turned out it was the intake manifold,
  • kegabearkegabear Member Posts: 5
    hi again,
    been awhile since i last posted..silverado 1500
    5.3, 4wd just ovrheated..pulled over to check things out and added some water and it seems to be pouring out the backside of the engine..not dripping put a gallon in and its out in less then 30 seconds.....both sides,passenger and drivers side..tough to see but either its on the heads or just below on the block....havent done a freeze plug in 15 they still have them on the back of the block ,,2 at once tho???
    even if its a head gasket..both at once??
    and my big question here is do blown head gaskets always leak into the oil to show that white filmy telltale sign...engine runs skips or stalls..was only 2 miles from home so i filled it and drove away and the temp gauge went up then down and then blew warm heat then back to cold..
    i'm an old timer and just like tinkering with 70's and pre 70's engines,would there be any other coolant lines on the backside of the engine that might cause the leak?
    thanks for any help!!
  • obyoneobyone Member Posts: 7,841
    Heater hose.
  • kegabearkegabear Member Posts: 5
    doesnt seem to be leaking by the heater hoses that goes to the heater core if thats what you a better look today..seem to be coming in and all around the tranny bell housing..another post told me the block heater near the oil filter housing..dont have a block heater..are the freeze plugs on the block behind the bell housing? meaning the tranny has to come out?
  • obyoneobyone Member Posts: 7,841
    There are two block drain plugs toward the left and right rear of the block that you could check. These are the plugs used when draining coolant from the block or to back flush.
  • PatrickMD70PatrickMD70 Member Posts: 1
    I have a 1999 Yukon 2WD with the 5.7 lt engine. There is cooloant leaking out of the intake manifold just behind the alternator. It is coming out of the gasket where the manifold mounts to the engine block. How hard of a project am I getting myself into? I am fairly competant and have worked on a lot of engines in the past when I used to buy/sell used cars. That was 15 years ago and now it looks very complicated. Could I be biting off more than i can chew? Are there any big "pit falls" I need to be aware of? I will not do it myslef if I have to disconnect A/C lines.
    Thank you!
  • whantonwhanton Member Posts: 1
    I have no pressure at the expasion tank lid after driving till temp gauge reaches normal reading. I had to add about 3 quarts of Dex Coolant the other day. The level is still the same. I can't find any trace of a leak except slight smell at exhaust pipe. What are the pills someone mentioned sold by GM to stop leak? I don't want to pull intake gasket then both heads.
  • hotrudderedbumhotrudderedbum Member Posts: 4
    The truck is a 5.7L 2WD with only 137K on it and I hope to keep it forever.

    I recently disconnected and bypassed the oil cooler hoses from the radiator while troubleshooting a curious high oil pressure indication. When I went to reconnect the hoses I found the lower fitting on the radiator stripped (the radiator was replaced several years ago, too late to raise a warranty/installation issue).

    The nut that threads into the radiator is fine.

    My question the female thread in the radiator an insert, sort of like a helicoil, or is the thread milled into the radiator body?

    I'd really prefer to not have to put in another new radiator.

    Any ideas?

  • drainman881999drainman881999 Member Posts: 1
    I have a 1999 Sierra,small block v-8.
    For several months,I have been smelling antifreeze,ever now and then seeing a small amount on the driveway.
    Just the other day saw a leak from the heater core area by the hoses.
    Not the hoses;but a small 90 ell shaped rubber hose.I think maybe a drain to release coolant mix if the heater core was leaking.
    Has anyone seen this?Is there a way to stop a small leak?
    Maybe some type of stop leak?
  • pwryanpwryan Member Posts: 1
    I have an '04 Silverado 5.3L with the same coolant leak mentioned in the forums. Pressure testing, both at cool and hot, revealed nothing. No visible leaks. Not a huge loss. The thought was a seeping head gasket. Coolant would just burn before showing up on the ground. Was going to try the GM pills referenced in the forums but cannot find anyplace to add them to the radiator. Any suggestions?
  • obyoneobyone Member Posts: 7,841
    Add them to the recovery tank. Not while the engine is hot though as it's under pressure.
  • mpcarpentrympcarpentry Member Posts: 1
    I have the same problem with the '04 Chevy Silverado 5.3L. Where is the recovery tank located? and you add them when the truck is turned off? Thanks.
Sign In or Register to comment.